G-Protein-Coupled Receptor Signaling in Cilia

Home , GPR161, GPR88, Neuropeptide Y receptor, Somatostatin receptor, Somatostatin receptor 3

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Kirk Mykytyn1,2 and Candice Askwith2,3

1Department of Biological Chemistry and Pharmacology, The Ohio State University, Ohio 43210 2Neuroscience Research Institute, The Ohio State University, Ohio 43210 3Department of Neuroscience, The Ohio State University, Ohio 43210 Correspondence: [email protected]

G-protein-coupled receptors (GPCRs) are the largest and most versatile family of signaling receptors in humans. They respond to diverse external signals, such as photons, proteins, peptides, chemicals, hormones, lipids, and sugars, and mediate a myriad of functions in the human body. Signaling through GPCRs can be optimized by enriching receptors and downstream effectors in discrete cellular domains. Many GPCRs have been found to be selectively targeted to cilia on numerous mammalian cell types. Moreover, investigations into the path- ophysiology of human ciliopathies have implicated GPCR ciliary signaling in a number of developmental and cellular pathways. Thus, cilia are now appreciated as an increasingly important nexus for GPCR signaling. Yet, we are just beginning to understand the precise signaling pathways mediated by most ciliary GPCRs and how they impact cellular function and mammalian physiology.

t is estimated that the human genome encodes In canonical GPCR signaling at the plas- Iapproximately 950 G-protein-coupled recep- ma membrane, agonist binding to a receptor tors (GPCRs), of which 500 correspond to causes a change in receptor conformation and odorant or taste receptors (Takeda et al. 2002). results in activation of heterotrimeric GTP- Approximately 150 of the remaining 450 binding proteins (G proteins) (Fig. 1A) (She- GPCRs have no known natural ligand and so noy and Lefkowitz 2011). G proteins consist are referred to as orphan GPCRs (Tang et al. of three associated protein subunits: a, b, and 2012). GPCRs represent the largest group of g. G proteins are classiﬁed based on the na- therapeutic drug targets, with more than a third ture of their a-subunits and there are 16 of all drugs acting on GPCRs (Rask-Andersen known a-subunits that are functionally cate- et al. 2011). Because of the functional diversity gorized into four subfamilies: Gas,Gai,Gaq, of GPCRs, there is little conservation of amino and Ga12. When inactive, the a-subunit is acid sequence across the GPCR superfamily. bound to GDP and a bg-complex to form a Yet, all GPCRs share a common structure: an trimeric protein complex (Fig. 1A). On ago- extracellular amino terminus, seven transmem- nist binding, the receptor facilitates GDP re- brane domains, and an intracellular carboxyl lease, GTP binding to the a-subunit, and dis- terminus. sociation of the a-subunit from the bg-

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K. Mykytyn and C. Askwith

A Ligand

N N GPCR

C GTP C GDP

Gγ Gα Gβ α G Gγ

Gβ

i/o S 12/13 T q Ion channels Numerous other effectors Adenylyl RHO/GEFs cyclase Phospholipases (inhibition) Phosphodiesterase Adenylyl cyclase (stimulation) B N Activated GPCR

GRK β-Arrestin

G-protein-independent signaling ERK, MAPK, Src, JNK, REF, many others

Internalization, desensitization, and/or endosomal signaling

Figure 1. Overview of G-protein-coupled receptor (GPCR) signaling at the plasma membrane. (A) Ligand binding to a GPCR facilitates GDP release from the G-protein a-subunit and stimulates GTP binding to the a-subunit, which leads to dissociation of the a-subunit from the bg-complex. Both the a-subunit and bg- complex can then regulate various intracellular effectors. (B) Activated GPCRs are phosphorylated at speciﬁc sites on their intracellular domains predominantly by G-protein-coupled receptor kinases (GRKs). Phosphor- ylated receptors are targets for the recruitment of b-arrestins, which prevent further G-protein activation and mediate internalization of receptors by promoting clathrin-mediated endocytosis. b-Arrestins bind to numerous intracellular signaling proteins and can act as signal transducers independently of G-protein coupling. In some cases, GPCR signaling can be sustained or enhanced on endocytosis.

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Ciliary GPCR Signaling

complex (Fig. 1A). Both the a-subunit and OLFACTORY RECEPTOR SIGNALING bg-complex can then regulate various intracellular effectors (e.g., adenylyl cyclases by the Ciliopathies can be associated with deﬁcits in a-subunit and potassium channels by the bg- olfaction (Kulaga et al. 2004; Iannaccone et al. complex). 2005; McEwen et al. 2007). Mammalian olfac- Activated GPCRs are then phosphorylated tion is mediated by olfactory sensory neurons at speciﬁc sites on their intracellular domains (OSNs) that project from the olfactory bulb in predominantly by G-protein-coupled receptor the brain to the olfactory epithelium located in kinases (GRKs) (Fig. 1B) (Marchese et al. 2008), the nasal cavity (Fig. 3A). OSNs are bipolar but also other kinases such as protein kinase A neurons with a single axon that projects distally (PKA) or protein kinase C (PKC) (Kelly et al. to the olfactory bulb and a single dendrite that 2008). Once phosphorylated, the receptors be- projects apically to the olfactory epithelium. At come targets for the recruitment and binding the apical end of the OSN, the dendritic tip is of scaffolding proteins, termed b-arrestins, enlarged to form a dendritic knob from which which prevent further G-protein activation and 10 to 30 nonmotile 9þ2 cilia project (Menco mediate internalization of receptors by pro- 1980, 1997). These olfactory cilia range from 50 moting clathrin-mediated endocytosis (Fig. to 60 mm in length and extend into the olfactory 1B) (Shenoy and Lefkowitz 2011). This pro- mucus where they are directly exposed to odor- cess is known as homologous desensitization. ants (Jenkins et al. 2009). There are two impor- Although internalization of GPCRs is gener- tant consequences of the ciliary structure. First, ally associated with a decrease in signaling, the presence of numerous cilia increases the in some cases receptor signaling can be sus- surface area that is exposed to the external en- tained or enhanced on endocytosis (Sorkin vironment by about 40 times and enhances our and von Zastrow 2009; McMahon and Boucrot ability to detect odorants (Menco 1992). Sec- 2011). In addition, b-arrestins bind to numer- ond, the small diameter of the distal ends of ous intracellular signaling proteins, includ- these cilia (0.1 mm) leads to a large ratio of ing Src, ERK1/2, p38, and PI3K, and can act membrane surface area to cytoplasmic volume as signal transducers independent of G-protein (Menco 1980), allowing a small signal to gener- coupling (DeFea 2011; Shukla et al. 2011). ate a large effect. There are two b-arrestin isoforms (1 and 2) that The molecular elements required for olfac- are expressed ubiquitously and regulate most tory transduction are concentrated within the GPCRs. ciliary compartment (Fig. 3B). Olfaction be- There is an ever-expanding list of GPCRs gins with binding of an odorant to an olfactory that are enriched in cilia on a variety of cell types receptor (OR) on the ciliary membrane. In ro- (Table 1; Fig. 2). Numerous GPCR effector mol- dents, each OSN predominantly expresses one ecules have also been localized to cilia (Fig. 2) of approximately 1000 ORs (Ressler et al. 1993; (Hilgendorf et al. 2016), suggesting that cilia Vassar et al. 1993), which triggers the activation mediate signaling of a diverse set of GPCRs. of the heterotrimeric stimulatory G protein Importantly, ciliopathies are associated with al- comprising Gaolf, b1, and g13 (Jones and terations in GPCR signaling. In this review, we Reed 1989; Kerr et al. 2008; Li et al. 2013). will focus on mammalian cilia-mediated GPCR Gaolf then activates type 3 adenylyl cyclase signaling transduction pathways. We will begin (AC3), which increases cAMP levels within with a brief account of the well-described sig- the cilium (Bakalyar and Reed 1990). The naling pathways mediated by the prototypical cAMP then binds to and activates cyclic-nucle- ciliary GPCRs, odorant receptors, and opsins. otide-gated (CNG) channels on the ciliary Then we will discuss more recently described membrane, allowing the entry of calcium ions examples of GPCR ciliary signaling with a focus and depolarizing the membrane potential. In- on the potential functional impacts of cilia on creased ciliary Ca2þ levels leads to activation GPCR signaling. and opening of Ca2þ-gated chloride channels,

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Table 1. Nonodorant/nonvisual G-protein-coupled receptors (GPCRs) with confirmed ciliary localization GPCR Cell type References b2-adrenergic receptor (b2AR) Neurons Yao et al. 2015 Bile acid receptor (TGR5) Cholangiocytes Keitel et al. 2010; Masyuk et al. 2013 Bitter taste receptors (T2R) Airway epithelial cells Shah et al. 2009 Dopamine receptor 1 (D1) Neurons Domire et al. 2011 Dopamine receptor 5 (D5) Vascular endothelial cells, Abdul-Majeed and Nauli 2011; renal epithelial cells Jin et al. 2014b Galanin receptor 3 (GALR3) Neurons Loktev and Jackson 2013 GPR83 Neurons Loktev and Jackson 2013 GPR161 Neurons, mouse embryonic Mukhopadhyay et al. 2013 fibroblasts GPR175 Mouse embryonic Singh et al. 2015 fibroblasts Kisspeptin receptor 1 (KISS1R) Neurons Koemeter-Cox et al. 2014 Melanin-concentrating hormone Neurons Berbari et al. 2008 receptor 1 (MCHR1) Muscarinic acetylcholine receptor 3 Olfactory sensory neurons Jiang et al. 2015 (M3R) Neuropeptide Y receptor 2 (NPY2R) Neurons Loktev and Jackson 2013 Neuropeptide Y receptor 5 (NPY5R) Neurons Loktev and Jackson 2013 Prolactin-releasing hormone Glial cells Omori et al. 2015 receptor (PRLHR) Prostaglandin E receptor 4 (EP4) Human retinal pigment Jin et al. 2014a epithelial cells Pyroglutamylated RFamide peptide Neurons Loktev and Jackson 2013 receptor (QRFPR) Serotonin receptor 6 (HTR6) Neurons Brailov et al. 2000 Smoothened (SMO) Fibroblasts, nodal cells Somatostatin receptor 3 (SSTR3) Neurons Handel et al. 1999 Trace amine-associated receptor 1 Thyroid epithelial cells Szumska et al. 2015 (TAAR1) Vasopressin receptor 2 (V2R) Renal epithelial cells Raychowdhury et al. 2009

causing an efﬂux of Cl2 ions that augments arrestin 2 to ORs, thereby potentiating odor- depolarization of the neuron (Kleene 1993; induced signaling (Fig. 3C) (Jiang et al. 2015). Lowe and Gold 1993; Stephan et al. 2009), The olfactory epithelium is innervated by nerve which eventually initiates an action potential endings that release acetylcholine (Baraniuk that propagates along the axon to the olfactory and Merck 2009). Thus, acetylcholine release bulb. may enhance the sensitivity of OR signaling b-Arrestin 2 is recruited to activated ORs to via M3-Rs. mediate desensitization and receptor internali- In summary, olfactory cilia possess several zation at the dendritic knob (Dawson et al. critical attributes that optimize OR signaling: 1993; Mashukova et al. 2006). Interestingly, a (1) They extend into the olfactory epithelium nonodorant GPCR has been found to localize where ORs are exposed to odorants; (2) they to olfactory cilia and modulate OR signaling in allow for enrichment and concentration of the mice. Speciﬁcally, activation of type 3 musca- molecular components of the olfactory trans- rinic acetylcholine receptor (M3-R) on the cil- duction cascade, thereby optimizing signaling; iary membrane inhibits the recruitment of b- and (3) they are present in large numbers and

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Ciliary GPCR Signaling

Figure 2. Examples of G-protein-coupled receptors (GPCRs) and effectors that are enriched in primary cilia. (A) Image of a day 7 mouse hippocampal neuron immunolabeled with an antibody to somatostatin receptor subtype 3 (SSTR3) showing an SSTR3-positive cilium projecting from the cell body. (B) Adult mouse brain section corresponding to the medial hypothalamus immunolabeled with an antibody to kisspeptin receptor 1 (KISS1R). Note the presence of multiple KISS1R-positive cilia. (C) Image of a day 7 mouse hippocampal neuron treated with somatostatin and immunolabeled with an antibody to b-arrestin. Arrow indicates b- arrestin ciliary localization. (D) Image of a day 7 mouse hippocampal neuron immunolabeled with an antibody to type 3 adenylyl cyclase (AC3) showing an AC3-positive cilium projecting from the cell body. Scale bars, 5 mm.

have a large surface-to-volume ratio, which in- intracellular cGMP levels and causes cGMP- creases sensitivity to odorants. gated channels to close, thereby hyperpolariz- ing the cell and generating a transient photo- response within milliseconds. Rhodopsin OPSIN SIGNALING kinase then phosphorylates rhodopsin, which Vision is initiated when photons are absorbed leads to visual arrestin binding and a block by the rod and cone photoreceptors in the in transducin activation, thereby terminating retina (Arshavsky and Burns 2012). Photore- the signal. In response to sustained bright ceptors are highly polarized neurons with a light, there is a massive redistribution of pho- distal end that is comprised of the light-sens- totransduction proteins that involves transdu- ing outer segment and a proximal end that cin exiting the rod outer segment and visual synapses on downstream neurons. The outer arrestin accumulating in the outer segment. segment is a highly modiﬁed primary cilium This adaptive mechanism plays a role in setting packed with membrane disks containing light- photoreceptor sensitivity and may protect rods sensitive GPCRs and downstream signaling ef- from the adverse effects of persistent light ex- fectors. Upon light activation in rods, rhodop- posure (Arshavsky and Burns 2012). Thus, the sin activates the G protein transducin, which ciliary outer segment facilitates signaling in then stimulates its effector, cGMP phospho- response to light and provides a protective diesterase. This leads to a reduction in mechanism by allowing the physical separation

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BC CNG Chloride Mucus layer Olfactory cilia Odorant channel channel Odorant Adenylyl receptor + 2+ cyclase Na Ca Cl–

Dendritic knob Microvilli Gβ α GTP Gγ G olf ATP Ca2+ Cl– cAMP

Activated M3 Acetylcholine D odorant acetylcholine receptor receptor

Olfactory sensory neuron

β-Arrestin

Desensitization

Figure 3. Overview of odorant receptor signaling in olfactorysensory neurons. (A) Scanning electron microscopy image of the surface of the mouse olfactoryepithelium. Scale bar, 1 mm (courtesy of Jeff Martens). (B) Schematic of a single olfactory sensory neuron with cilia projecting into the olfactory epithelium. (C) Odorant activation of olfactory G-protein-coupled receptors (GPCRs) triggers the activation of the stimulatory G protein Gaolf, which then activates type 3 adenylyl cyclase (AC3) and increases cAMP levels within the cilium. The cAMP binds to and activates cyclic-nucleotide-gated (CNG) channels on the ciliary membrane, leading to an increase in Ca2þ levels, subsequentactivation of Ca2þ-gated chloridechannels, anddepolarizationof the neuron. (D)b-Arrestin binding to activated odorant receptors mediates desensitization. The type 3 muscarinic (M3) acetylcholine receptor can inhibit the recruitment of b-arrestin to odorant receptors, thereby potentiating odor-induced signaling.

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Ciliary GPCR Signaling

of components of the phototransduction Gpr161 knockout mice, Gpr175 knockout cascade. mice are viable and do not have any developmental defects (Singh et al. 2015). The effect of Gpr175 on Hh signaling is dependent on Smo GPCR MODULATION OF HEDGEHOG activity, suggesting it acts on Gai downstream SIGNALING from Smo to modulate PKA activity. Although Hedgehog (Hh) signaling, which plays an essen- it does not play an essential role in Hh signaling, tial role in mammalian development, requires it may enhance signaling in certain contexts the presence of primary cilia (Huangfu et al. (Singh et al. 2015). 2003). Briefly, in the absence of Hh ligand, the 12-transmembrane Hh receptor patched CILIARY GPCR SIGNALING IN THE RENAL (Ptch1) is enriched on the ciliary membrane SYSTEM and the GPCR Smoothened (Smo) is excluded from the cilium (Rohatgi et al. 2007). In this A link between renal cilia dysfunction and “OFF” state, cAMP-dependent PKA functions cystic disease is well established (Cramer and at the base of the cilium to phosphorylate mem- Guay-Woodford 2015). Primary cilia on renal bers of the Gli family of transcription factors, epithelial cells are generally regarded as mecha- which promotes the formation of truncated Gli nosensors that illicit Ca2þ signals in response to repressors and inhibits transcription of Hh tar- fluid flow (Fig. 4A). However, there is increasing get genes (Sasaki et al. 1999; Pan et al. 2006; evidence that renal cilia also mediate GPCR Tempeet al. 2006; Tusonet al. 2011). Repression signaling. For example, the type 2 vasopressin of Hh signaling is further enforced by the ciliary receptor (V2R), which regulates Naþ and water GPCR Gpr161. Gpr161 has constitutive activity reabsorption in the mammalian nephron, local- and couples to Gas to increase cellular cAMP izes to cilia on renal epithelial cells (Raychowd- levels, thereby increasing activation of PKA hury et al. 2009). In response to vasopressin, (Mukhopadhyay et al. 2013). It is hypothesized ciliary V2R functionally couples with adenylyl that Gpr161 establishes a basal cAMP gradient cyclase to increase local cAMP concentrations within the cilium that is important for proper and activate a cation-selective channel (Fig. 4B) regulation of Hh signaling. Indeed, disruption (Raychowdhury et al. 2009). These data suggest of Gpr161 in mouse is embryonic lethal and the presence of a GPCR-mediated cAMP-de- causes increased Hh signaling in the neural pendent second-messenger signaling mecha- tube (Mukhopadhyay et al. 2013). nism in renal cilia that regulates intraciliary In the presence of Hh ligand, Ptch1 and Ca2þ signals. This signaling, in turn, may mod- Gpr161 leave the cilium, allowing Smo to enter ulate different cellular processes, including the cilium, activate Gli transcription factors, cell proliferation, ciliary microtubule stability, and initiate signaling (Corbit et al. 2005; and/or the ciliary membrane resting potential. Rohatgi et al. 2007; Mukhopadhyay et al. 2013). Interestingly, renal cAMP levels are increased Recently, another orphan GPCR, Gpr175, has in numerous animal models of polycystic kid- been shown to localize to cilia in response to ney disease (PKD) (Torres and Harris 2014) Hh treatment and enhances Hh signaling in and treatment with V2R antagonists in- several mammalian cell lines (Singh et al. hibits cyst formation (Gattone et al. 2003; 2015). Specifically, Gpr175 interacts with ciliary Torres et al. 2004). Yet, it is unclear how much Gai, which leads to a lowering of cAMP levels V2R signaling within the cilium contributes to and an inhibition of PKA activity and Gli re- these effects. pressor formation (Singh et al. 2015). Depletion Dopaminergic signaling in the kidney plays of Gpr175 in cell lines has a relatively modest an important role in controlling renal sodium effect on signaling (50%), suggesting that it excretion and blood pressure (Carey 2013). Re- plays a regulatory role rather than an essential cently, dopamine receptor type 5 (D5) has been role in Hh signaling. Indeed, as opposed to localized to cilia on renal epithelial cells (Jin

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A Renal tubule B Cation-selective Vasopressin Adenylyl channel(s) receptor 2 cyclase + 2+ Vasopressin Na Ca

ATP cAMP Ca2+ Protein Na+ Ca2+ kinase A Dopamine Flow Cilia C L-type calcium channel Dopamine receptor 5 Ca2+ Ca2+ Ca2+

Gα Gβ Ca2+ GTP Gγ Renal epithelial cell

Figure 4. Overview of ciliary signaling in renal cilia. (A) Cross section of a renal tubule showing primary cilia projecting into the lumen of the tubule (top). Schematic of ﬂow-induced Ca2þ signaling (bottom). (B) Vaso- pressin binding to vasopressin receptor 2 (V2R) on the ciliary membrane activates adenylyl cyclase. The increase in local cAMP concentrations activates a cation-selective channel, possibly through protein kinase A, thereby regulating intraciliary Ca2þ signals. (C) Agonist binding to dopamine receptor 5 on the ciliary membrane results 2þ in CaV1.2 channel activation, possibly through the action of dissociated Gbg, which increases intraciliary Ca levels.

et al. 2014b; Upadhyay et al. 2014). Evidence for 2015). This increased Ca2þ concentration sub- D5-mediated signaling on cilia comes from sequently leads to cilia elongation and confers studies looking at calcium signaling in the cili- greater sensitivity to fluid-shear stress. Interest- ary compartment. Specifically, Jin et al. (2014b) ingly, the most frequent target found in a chem- used a ciliary-targeted calcium sensor to show ical screen of pathways involved in flagellar that treatment of renal epithelial cells with the length control in the unicellular green alga D5 agonist fenoldopam causes an increase in Chlamydomonas was the family of dopamine calcium levels in the cilium that precedes an binding GPCRs (Avasthi et al. 2012). Thus, cil- increase in calcium levels in the cytosol of the iary dopaminergic signaling may be an evolu- cell. This calcium signal is dependent on the tionarily conserved mechanism for regulating CaV1.2 L-type calcium channel, which is local- ciliary length, which may then impact sensitiv- ized in the cilium (Jin et al. 2014b). With regard ity to signals. to a functional consequence, fenoldopam treatment also causes an actin-mediated increase in GPCR SIGNALING IN CHOLANGIOCYTE cilia length and increased calcium signaling in CILIA response to fluid flow (Upadhyay et al. 2014). Taken together, these results suggest that agonist Cholangiocytes are ciliated epithelial cells that binding to D5 on the ciliary membrane results line bile ducts and are responsible for bile acid in CaV1.2 channel activation, possibly through transport and bicarbonate secretion (Tabibian the action of dissociated Gbg, which increases et al. 2013). Cholangiocyte primary cilia have intraciliary Ca2þ levels (Fig. 4C) (Atkinson et al. been determined to be mechano-, chemo-, and

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Ciliary GPCR Signaling

osmosensory organelles that regulate cholan- CILIARY GPCR SIGNALING ON CENTRAL giocyte proliferation (Masyuk et al. 2006, NEURONS 2008a,b; Gradilone et al. 2007). The importance of these cilia is highlighted by the fact that Most, if not all, adult neurons in the mamma- polycystic liver disease, which is characterized lian brain possess a primary cilium (Handel by the development of fluid-filled hepatic cysts et al. 1999; Fuchs and Schwark 2004; Bishop arising from cholangiocytes, is associated with et al. 2007). Numerous GPCRs are selectively ciliopathies (Masyuk et al. 2015). In cholangio- enriched in neuronal cilia (Table 1). Seminal cytes, bile acid signaling is transmitted through studies using mouse knockout models have pro- TGR5, a GPCR that is localized to the apical vided compelling evidence for cilia-dependent plasma membrane, subapical compartment, GPCR signaling in the brain. For example, mice and cilium (Keitel et al. 2009, 2010; Keitel and lacking cilia on specific neuronal subpopula- Haussinger 2011; Keitel and Haussinger 2012; tions in the brain manifest prominent pheno- Masyuk et al. 2013). TGR5 is coupled to Gas types, such as obesity and learning and memory and activation of TGR5 by bile acids causes deficits (Davenport et al. 2007; Berbari et al. an increase in intracellular cAMP levels 2013, 2014). Moreover, mice lacking ciliary (Maruyama et al. 2002; Kawamata et al. 2003). GPCRs or ciliary-enriched downstream effec- Downstream effectors of GPCR signaling, in- tors of GPCR signaling display similar pheno- cluding adenylyl cyclase, PKA, and the exchange types (Wang et al. 2009, 2011; Einstein et al. protein directly activated by cAMP 2 (EPAC-2), 2010). Together, these results suggest that neu- have also been localized to cholangiocyte cilia ronal cilia provide a unique platform for GPCRs (Masyuk et al. 2006, 2008b). In addition, Gai to signal in response to factors in the extracel- localizes to the base of cilia on ciliated cholan- lular milieu. Recent studies have begun to elu- giocytes. Taken together, these data suggest that cidate these signaling pathways and how they cholangiocyte cilia mediate bile acid signaling impact neuronal function. through TGR5. Neuropeptide Y (NPY) is one of the most Intriguingly, the presence or absence of cilia abundant neuropeptides in the mammalian on cultured cholangiocytes determines the im- brain and plays an important role in regulating pact of TGR5 agonists (Masyuk et al. 2013). food intake and energy expenditure (Herzog Specifically, agonist treatment of nonciliated 2003). Recently, two of the NPY receptor sub- cholangiocytes increases colocalization of TGR5 types, NPY2R and NPY5R, were found to be with Gas and results in increased cAMP signal- enriched in neuronal cilia in mice (Loktev and ing, inhibition of ERK signaling, and increased Jackson 2013). Interestingly, genetically modi- cellular proliferation. Agonist treatment of cil- fied mice that are unable to transport NPY2R iated cells, on the other hand, results in in- into neuronal cilia are obese and do not respond creased colocalization of TGR5 with Gai and to administration of the anorexigenic ligand decreased cAMP signaling, activation of ERK PYY3-36 (Loktev and Jackson 2013), suggesting signaling, and decreased cellular proliferation. that NPY2R ciliary localization is important for Together, these results suggest that TGR5 is ligand-dependent signaling in vivo. In support functionally coupled to Gas on the plasma of this model, quantification of cAMP signaling membrane and stimulates cellular proliferation on RPE cells expressing NPY2R revealed that in response to bile acid signaling, but is func- ligand treatment produced a more pronounced tionally coupled to Gai in the cilium to prevent inhibition of cAMP signaling in cells with a cellular proliferation in response to bile acid cilium (Fig. 5A) (Loktev and Jackson 2013). signaling. Thus, cholangiocyte cilia provide a Thus, cilia localization seemingly enhances compartment for TGR5 to functionally couple NPY2R signaling and may provide a more ro- with different effectors and provide an alterna- bust signal to control food intake. tive signal to TGR5 signaling on the plasma Somatostatin is a widely distributed neuro- membrane. transmitter and modulator of neural activity

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Adenylyl [cAMP] cyclase Adenylyl cyclase β-Arrestin

Neuropeptide Y Activated Somatostatin NPY2R α G i Activated SSTR3 NPY2R SSTR3

β-Arrestin recruitment

Exits the cilium Exits the cilium

Figure 5. Overview of G-protein-coupled receptor (GPCR) signaling on neuronal cilia. (A) Ligand binding to neuropeptide Y receptor 2 (NPY2R) on the ciliary membrane may activate Gai and inhibit adenylyl cyclase, thereby leading to a reduction in cAMP levels. Ligand treatment also leads to a reduction in NPY2R ciliary localization, suggesting that activated receptor exits the cilium. (B) Somatostatin treatment stimulates endogenous b-arrestin recruitment into somatostatin receptor subtype 3 (SSTR3)-positive cilia. Somatostatin treatment also causes a b-arrestin-dependent decrease in SSTR3 ciliary localization, suggesting that b-arrestin mediates SSTR3 ciliary export.

that can affect many physiological processes, gest that agonist binds to SSTR3 on the ciliary including motor activity and cognitive function membrane and leads to phosphorylation of the (Patel 1999; Barnett 2003; Olias et al. 2004; receptor, which facilitates b-arrestin ciliary lo- Viollet et al. 2008). Somatostatin receptor sub- calization (Fig. 5B). type 3 (SSTR3) colocalizes with AC3 in cilia Another finding from this study was throughout the mouse brain (Handel et al. that somatostatin treatment causes a rapid b- 1999). Interestingly, mice lacking SSTR3, AC3, arrestin-dependent decrease in the ciliary local- or cilia in the hippocampus show similar defi- ization of endogenous SSTR3 (Green et al. cits in learning and memory (Wang et al. 2009; 2016). These findings suggest a model whereby Einstein et al. 2010; Berbari et al. 2014). To- activation of SSTR3 on the ciliary membrane gether, these results suggest that SSTR3 signals stimulates b-arrestin recruitment, which binds on cilia and this signaling is required for to the receptor and mediates export of SSTR3 proper learning and memory. In support of from the cilium (Fig. 5B). There are several po- this model, it was recently shown that somato- tential functional consequences of b-arrestin statin treatment stimulates endogenous b-ar- ciliary recruitment, including (1) SSTR3 desen- restin recruitment into SSTR3-positive cilia sitization, (2) potentiation of SSTR3 signaling on hippocampal neurons (Green et al. 2016). through internalization, and/or (3) b-arrestin- This recruitment is reminiscent of b-arrestin mediated ciliary signaling. Yet, additional stud- translocation to activated GPCRs on the ies are required to determine the functional plasma membrane. Furthermore, expressing consequences of b-arrestin recruitment into SSTR3-containing mutations that prevent ago- cilia and whether this is a ubiquitous mecha- nist binding or phosphorylation blocks b-ar- nism for modulating ciliary GPCR signaling on restin recruitment into cilia. These results sug- neurons.

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Ciliary GPCR Signaling

The kisspeptin receptor (KISS1R), which way epithelial cells, a-gustducin localizes to cilia regulates the onset of puberty and adult repro- and PLC-b2 localizes to the apical portion ductive function, has recently been found to be of the cell below the cilia (Shah et al. 2009). enriched in cilia on mouse gonadotropin-re- Application of bitter compounds causes an in- leasing hormone (GnRH) neurons (Koemeter- crease in intracellular calcium concentra- Cox et al. 2014). Intriguingly, GnRH neurons in tions only in ciliated cells, which further results adult animals possess multiple KISS1R cilia and in a 25% increase in ciliary beat frequency the percentage of multiciliated GnRH neurons (Shah et al. 2009). Thus, T2R ciliary localiza- increases during postnatal development and tion may facilitate sensing of noxious com- correlates with sexual maturation. Disruption of pounds and generation of a signal that leads GnRH cilia leads to a significant reduction in to an increase in ciliary activity to eliminate kisspeptin-mediated GnRH neuronal activity the substance. (Koemeter-Cox et al. 2014), suggesting that cilia enhance KISS1R signaling. More recently, the POTENTIAL FUNCTIONAL CONSEQUENCES b2-adrenergic receptor (b2AR) has been shown OF CILIA ON GPCR SIGNALING to be localized to neuronal cilia in the mouse hippocampus (Yao et al. 2015). b2AR is acti- A key question is how ciliary localization im- vated by noradrenalin and plays a role in hip- pacts GPCR signaling. The examples of ciliary pocampal synaptic plasticity (Hagena et al. GPCR signaling discussed above highlight sev- 2016). Interestingly, b2AR colocalizes in neuro- eral general functional consequences cilia can nal cilia with the nonselective cation channel confer on GPCR signaling. First, ciliary locali- polycystic kidney disease 2-like 1 (Pkd2l1). zation can enhance GPCR signaling. This may However, b2AR ciliary localization is disrupted be due to several reasons. Cilia may extend to- in mice lacking Pkd2l1, suggesting that Pkd2l1 ward the origin of a signal, thereby increasing is required for b2AR ciliary localization (Yao sensitivity. The cilium may enhance signaling by et al. 2015). Pkd2l1 mice have decreased cAMP allowing more efficient coupling of the receptor levels in the brain and increased susceptibility to and its effectors. Note that these two functions pentylenetetrazol-induced seizures (Yao et al. are not mutually exclusive. Another possibility 2015). As b2AR is coupled to Gas, a potential is GPCRs generate a unique signal when they are model is that ciliary localization of b2AR and activated on the ciliary membrane versus the Pkd2l1 form a ciliary complex that enhances plasma membrane. This may be the result of cAMP production, which inhibits neuronal coupling to distinct effectors in the cilium, as excitability. Further studies are required to di- in cholangiocyte cilia. As b-arrestins can func- rectly test whether KISS1R and b2AR signal tion as signal transducers, the finding that en- within cilia. dogenous b-arrestin is recruited into cilia on somatostatin treatment is particularly provoca- tive. This could be analogous to biased agonism, GPCR SIGNALING IN MOTILE CILIA whereby a ligand preferentially triggers G-pro- The primary function of motile cilia on human tein- or b-arrestin-mediated signaling pathways airway epithelia is to move mucus out of the (Rajagopal et al. 2010). Perhaps activation of lung and their disruption results in airway dis- a receptor on the ciliary membrane activates ease (Fliegauf et al. 2007). Interestingly, several b-arrestin-mediated signaling but not G-pro- members of the bitter taste receptor (T2R) fam- tein signaling, or vice versa. Another potential ily have been localized to cilia on human airway mechanism for generating a unique signal is epithelia (Shah et al. 2009; Lee et al. 2012). by facilitating heteromerization of different Downstream effectors of the T2R signal trans- GPCRs, which can alter ligand binding, G- duction pathway include the G-protein a-gust- protein coupling, and/or desensitization and ducin and the enzyme phospholipase C-b2 internalization. There is evidence that SSTR3 (PLC-b2) (Devillier et al. 2015). In ciliated air- and melanin-concentrating hormone receptor

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K. Mykytyn and C. Askwith

1 heteromerize in cilia in multiple mouse brain screen identifies class a G-protein coupled receptors as regions (Green et al. 2012). Alternatively, ciliary regulators of cilia. ACS Chem Biol 7: 911–919. Bakalyar HA, Reed RR. 1990. Identification of a specialized localization may act as an insulator to prevent adenylyl cyclase that may mediate odorant detection. Sci- GPCR cross regulation (Marley et al. 2013). It is ence 250: 1403–1406. possible that some or all of these mechanisms Baraniuk JN, Merck SJ. 2009. New concepts of neural regu- are used in ciliary GPCR signaling and the lation in human nasal mucosa. Acta Clin Croat 48: precise effects vary between cell types or even 65–73. Barnett P. 2003. Somatostatin and somatostatin receptor between different cells in the same tissue. physiology. Endocrine 20: 255–264. Berbari NF,Johnson AD, Lewis JS, Askwith CC, Mykytyn K. CONCLUDING REMARKS 2008. Identification of ciliary localization sequences within the third intracellular loop of G protein-coupled Given the prevalence of GPCRs as drug targets, receptors. Mol Biol Cell 19: 1540–1547. Berbari NF, Pasek RC, Malarkey EB, Yazdi SM, McNair AD, understanding ciliary GPCR signaling will likely Lewis WR, Nagy TR, Kesterson RA, YoderBK. 2013. Lep- have important ramifications for therapeutic tin resistance is a secondary consequence of the obesity in development. The remaining overarching chal- ciliopathy mutant mice. Proc Natl Acad Sci 110: 7796– lenges in the ciliary GPCR field are to identify 7801. Berbari NF, Malarkey EB, Yazdi SM, McNair AD, Kippe JM, the complete complement of ciliary GPCRs, Croyle MJ, Kraft TW, Yoder BK. 2014. Hippocampal and define the signaling pathways mediated by cili- cortical primary cilia are required for aversive memory in ary GPCRs and determine how these signal- mice. PLoS ONE 9: e106576. ing pathways impact cellular function. Meeting Bishop GA, Berbari NF,Lewis JS, Mykytyn K. 2007. Type III these challenges will require the development adenylyl cyclase localizes to primary cilia throughout the adult mouse brain. J Comp Neurol 505: 562–571. of new tools to visualize and/or modulate cili- Brailov I, Bancila M, Brisorgueil MJ, Miquel MC, Hamon ary GPCR signaling as well as assays to deter- M, Verge D. 2000. Localization of 5-HT(6) receptors at mine how these signals impact cellular function. the plasma membrane of neuronal cilia in the rat brain. A better understanding of GPCR signaling will Brain Res 872: 271–275. Carey RM. 2013. The intrarenal renin-angiotensin and dop- likely yield new therapeutic strategies to target- aminergic systems: Control of renal sodium excretion specific aspects of GPCR function and lend im- and blood pressure. Hypertension 61: 673–680. portant insight into the consequences of cilia Corbit KC, Aanstad P, Singla V, Norman AR, Stainier DY, loss and disruption for human health. Reiter JF. 2005. Vertebrate Smoothened functions at the primary cilium. Nature 437: 1018–1021. Cramer MT, Guay-Woodford LM. 2015. Cystic kidney disease: A primer. Adv Chronic Kidney Dis 22: 297–305. ACKNOWLEDGMENTS Davenport JR, Watts AJ, Roper VC, Croyle MJ, van Groen T, This work is supported by research project Wyss JM, Nagy TR, Kesterson RA, Yoder BK. 2007. Dis- ruption of intraflagellar transport in adult mice leads to Grant R21 MH107021 from the National Insti- obesity and slow-onset cystic kidney disease. Curr Biol 17: tutes of Health/National Institute of Mental 1586–1594. Health (NIH/NIMH) to K.M. Dawson TM, Arriza JL, Jaworsky DE, Borisy FF, Attramadal H, Lefkowitz RJ, Ronnett GV. 1993. b-Adrenergic receptor kinase-2 and b-arrestin-2 as mediators of odorant- REFERENCES induced desensitization. Science 259: 825–829. DeFea KA. 2011. b-Arrestins as regulators of signal termi- Abdul-Majeed S, Nauli SM. 2011. Dopamine receptor type 5 nation and transduction: How do they determine what to in the primary cilia has dual chemo- and mechano-sen- scaffold? Cell Signal 23: 621–629. sory roles. Hypertension 58: 325–331. Devillier P, Naline E, Grassin-Delyle S. 2015. The pharma- Arshavsky VY, Burns ME. 2012. Photoreceptor signaling: cology of bitter taste receptors and their role in human Supporting vision across a wide range of light intensities. airways. Pharmacol Ther 155: 11–21. J Biol Chem 287: 1620–1626. Domire JS, Green JA, Lee KG, Johnson AD, Askwith CC, Atkinson KF, Kathem SH, Jin X, Muntean BS, Abou-Alaiwi Mykytyn K. 2011. Dopamine receptor 1 localizes to neu- WA,Nauli AM, Nauli SM. 2015. Dopaminergic signaling ronal cilia in a dynamic process that requires the Bardet- within the primary cilia in the renovascular system. Front Biedl syndrome proteins. Cell Mol Life Sci 68: 2951–2960. Physiol 6: 103. Einstein EB, Patterson CA, Hon BJ, Regan KA, Reddi J, Avasthi P, Marley A, Lin H, Gregori-Puigjane E, Shoichet Melnikoff DE, Mateer MJ, Schulz S, Johnson BN, Tallent BK, von Zastrow M, Marshall WF. 2012. A chemical MK. 2010. Somatostatin signaling in neuronal cilia is

12 Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a028183 Downloaded from http://cshperspectives.cshlp.org/ on October 4, 2021 - Published by Cold Spring Harbor Laboratory Press

Ciliary GPCR Signaling

critical for object recognition memory. J Neurosci 30: mechanical and chemical stimuli. Cell Mol Life Sci 71: 4306–4314. 2165–2178. Fliegauf M, Benzing T, Omran H. 2007. When cilia go bad: Jones DT, Reed RR. 1989. Golf: An olfactory neuron specif- Cilia defects and ciliopathies. Nat Rev Mol Cell Biol 8: ic–G protein involved in odorant signal transduction. 880–893. Science 244: 790–795. Fuchs JL, Schwark HD. 2004. Neuronal primary cilia: A Kawamata Y, Fujii R, Hosoya M, Harada M, Yoshida H, review. Cell Biol Int 28: 111–118. Miwa M, Fukusumi S, Habata Y, Itoh T, Shintani Y, et Gattone VH II, Wang X, Harris PC, Torres VE. 2003. Inhi- al. 2003. A G protein-coupled receptor responsive to bile bition of renal cystic disease development and progres- acids. J Biol Chem 278: 9435–9440. sion by a vasopressin V2 receptor antagonist. Nat Med 9: Keitel V, Haussinger D. 2011. TGR5 in the biliary tree. Dig 1323–1326. Dis 29: 45–47. Gradilone SA, Masyuk AI, Splinter PL, Banales JM, Huang Keitel V, Haussinger D. 2012. Perspective: TGR5 (Gpbar-1) BQ, Tietz PS, Masyuk TV, Larusso NF. 2007. Cholangio- in liver physiology and disease. Clin Res Hepatol Gastro- cyte cilia express TRPV4 and detect changes in luminal enterol 36: 412–419. tonicity inducing bicarbonate secretion. Proc Natl Acad Keitel V, Cupisti K, Ullmer C, Knoefel WT, Kubitz R, Haus- Sci 104: 19138–19143. singer D. 2009. The membrane-bound bile acid receptor Green JA, Gu C, Mykytyn K. 2012. Heteromerization of TGR5 is localized in the epithelium of human gallblad- ciliary G protein-coupled receptors in the mouse brain. ders. Hepatology 50: 861–870. PLoS ONE 7: e46304. Keitel V, Ullmer C, Haussinger D. 2010. The membrane- Green JA, Schmid CL, Bley E, Monsma PC, Brown A, Bohn bound bile acid receptor TGR5 (Gpbar-1) is localized LM, Mykytyn K. 2016. Recruitment of b-arrestin into in the primary cilium of cholangiocytes. Biol Chem neuronal cilia modulates somatostatin receptor subtype 391: 785–789. 3 ciliary localization. Mol Cell Biol 36: 223–235. Kelly E, Bailey CP, Henderson G. 2008. Agonist-selective Hagena H, Hansen N, Manahan-Vaughan D. 2016. b-Ad- mechanisms of GPCR desensitization. Br J Pharmacol renergic control of hippocampal function: Subserving 153: S379–388. the choreography of synaptic information storage and Kerr DS, Von Dannecker LE, Davalos M, Michaloski JS, memory. Cereb Cortex 26: 1349–1364. Malnic B. 2008. Ric-8B interacts with Gaolf and Gg13 Handel M, Schulz S, Stanarius A, Schreff M, Erdtmann- and co-localizes with Gaolf, Gb1 and Gg13 in the cilia of VourliotisM, Schmidt H, WolfG, Hollt V.1999. Selective olfactory sensory neurons. Mol Cell Neurosci 38: 341– targeting of somatostatin receptor 3 to neuronal cilia. 348. Neuroscience 89: 909–926. Kleene SJ. 1993. Origin of the chloride current in olfactory Herzog H. 2003. Neuropeptide Y and energy homeostasis: transduction. Neuron 11: 123–132. Insights from Y receptor knockout models. Eur J Phar- Koemeter-Cox AI, Sherwood TW, Green JA, Steiner RA, macol 480: 21–29. Berbari NF,YoderBK, Kauffman AS, Monsma PC, Brown Hilgendorf KI, Johnson CT, Jackson PK. 2016. The primary A, Askwith CC, et al. 2014. Primary cilia enhance kiss- cilium as a cellular receiver: Organizing ciliary GPCR peptin receptor signaling on gonadotropin-releasing signaling. Curr Opin Cell Biol 39: 84–92. hormone neurons. Proc Natl Acad Sci 111: 10335–10340. Huangfu D, Liu A, Rakeman AS, Murcia NS, Niswander L, Kulaga HM, Leitch CC, Eichers ER, Badano JL, Lesemann A, Anderson KV. 2003. Hedgehog signalling in the mouse Hoskins BE, Lupski JR, Beales PL, Reed RR, Katsanis N. requires intraflagellar transport proteins. Nature 426: 2004. Loss of BBS proteins causes anosmia in humans 83–87. and defects in olfactory cilia structure and function in the Iannaccone A, Mykytyn K, Persico AM, Searby CC, Baldi A, mouse. Nat Genet 36: 994–998. Jablonski MM, Sheffield VC. 2005. Clinical evidence of Lee RJ, Xiong G, Kofonow JM, Chen B, Lysenko A, Jiang P, decreased olfaction in Bardet–Biedl syndrome caused Abraham V, Doghramji L, Adappa ND, Palmer JN, et al. by a deletion in the BBS4 Gene. Am J Med Genet A 2012. T2R38 taste receptor polymorphisms underlie sus- 132A: 343–346. ceptibility to upper respiratory infection. J Clin Invest Jenkins PM, McEwen DP,Martens JR. 2009. Olfactory cilia: 122: 4145–4159. Linking sensory cilia function and human disease. Chem Li F, Ponissery-Saidu S, Yee KK, Wang H, Chen ML, Iguchi Senses 34: 451–464. N, Zhang G, Jiang P, Reisert J, Huang L. 2013. Hetero- Jiang Y, Li YR, Tian H, Ma M, Matsunami H. 2015. Musca- trimeric G protein subunit Gg13 is critical to olfaction. rinic acetylcholine receptor M3 modulates odorant re- J Neurosci 33: 7975–7984. ceptor activity via inhibition of b-arrestin-2 recruitment. Loktev AV, Jackson PK. 2013. Neuropeptide Y family recep- Nat Commun 6: 6448. tors traffic via the Bardet-Biedl syndrome pathway to Jin D, Ni TT, Sun J, Wan H, Amack JD, Yu G, Fleming J, signal in neuronal primary cilia. Cell Rep 5: 1316–1329. Chiang C, Li W,Papierniak A, et al. 2014a. Prostaglandin Lowe G, Gold GH. 1993. Nonlinear amplification by calci- signalling regulates ciliogenesis by modulating intrafla- um-dependent chloride channels in olfactory receptor gellar transport. Nat Cell Biol 16: 841–851. cells. Nature 366: 283–286. Jin X, Mohieldin AM, Muntean BS, Green JA, Shah JV, Marchese A, Paing MM, TempleBR, Trejo J. 2008. G protein- Mykytyn K, Nauli SM. 2014b. Cilioplasm is a cellular coupled receptor sorting to endosomes and lysosomes. compartment for calcium signaling in response to Ann Rev Pharmacol Toxicol 48: 601–629.

Advanced Online Article. Cite this article as Cold Spring Harb Perspect Biol doi: 10.1101/cshperspect.a028183 13 Downloaded from http://cshperspectives.cshlp.org/ on October 4, 2021 - Published by Cold Spring Harbor Laboratory Press

K. Mykytyn and C. Askwith

Marley A, Choy RW, von Zastrow M. 2013. GPR88 reveals a Pan Y, Bai CB, Joyner AL, Wang B. 2006. Sonic Hedgehog discrete function of primary cilia as selective insulators of signaling regulates Gli2 transcriptional activity by sup- GPCR cross-talk. PLoS ONE 8: e70857. pressing its processing and degradation. Mol Cell Biol 26: Maruyama T, Miyamoto Y,Nakamura T, Tamai Y,Okada H, 3365–3377. Sugiyama E, Itadani H, Tanaka K. 2002. Identification of Patel YC. 1999. Somatostatin and its receptor family. Front membrane-type receptor for bile acids (M-BAR). Bio- Neuroendocrinol 20: 157–198. chem Biophys Res Commun 298: 714–719. Rajagopal S, Rajagopal K, Lefkowitz RJ. 2010. Teaching old Mashukova A, Spehr M, Hatt H, Neuhaus EM. 2006. b- receptors new tricks: Biasing seven-transmembrane re- Arrestin2-mediated internalization of mammalian odor- ceptors. Nat Rev Drug Discov 9: 373–386. ant receptors. J Neurosci 26: 9902–9912. Rask-Andersen M, Almen MS, Schioth HB. 2011. Trends in Masyuk AI, Masyuk TV,Splinter PL, Huang BQ, Stroope AJ, the exploitation of novel drug targets. Nat Rev Drug Dis- LaRusso NF. 2006. Cholangiocyte cilia detect changes in cov 10: 579–590. luminal fluid flow and transmit them into intracellular Raychowdhury MK, Ramos AJ, Zhang P,McLaughin M, Dai Ca2þ and cAMP signaling. Gastroenterology 131: 911– XQ, Chen XZ, Montalbetti N, Del Rocio Cantero M, 920. Ausiello DA, Cantiello HF. 2009. Vasopressin receptor- Masyuk AI, Gradilone SA, Banales JM, Huang BQ, Masyuk mediated functional signaling pathway in primary cilia TV, Lee SO, Splinter PL, Stroope AJ, Larusso NF. 2008a. of renal epithelial cells. Am J Physiol Renal Physiol 296: Cholangiocyte primary cilia are chemosensory organelles F87–97. that detect biliary nucleotides via P2Y12 purinergic re- Ressler KJ, Sullivan SL, Buck LB. 1993. A zonal organization ceptors. Am J Physiol Gastrointest Liver Physiol 295: of odorant receptor gene expression in the olfactory ep- G725–G734. ithelium. Cell 73: 597–609. Masyuk AI, Masyuk TV,LaRusso NF. 2008b. Cholangiocyte primary cilia in liver health and disease. Dev Dyn 237: Rohatgi R, Milenkovic L, Scott MP.2007. Patched1 regulates 2007–2012. hedgehog signaling at the primary cilium. Science 317: 372–376. Masyuk AI, Huang BQ, Radtke BN, Gajdos GB, Splinter PL, Masyuk TV, Gradilone SA, LaRusso NF. 2013. Ciliary Sasaki H, Nishizaki Y,Hui C, Nakafuku M, Kondoh H. 1999. subcellular localization of TGR5 determines the cholan- Regulation of Gli2 and Gli3 activities by an amino-ter- giocyte functional response to bile acid signaling. Am J minal repression domain: Implication of Gli2 and Gli3 as Physiol Gastrointest Liver Physiol 304: G1013–G1024. primary mediators of Shh signaling. Development 126: 3915–3924. Masyuk TV, Masyuk AI, LaRusso NF. 2015. TGR5 in the cholangiociliopathies. Dig Dis 33: 420–425. Shah AS, Ben-Shahar Y, Moninger TO, Kline JN, Welsh MJ. 2009. Motile cilia of human airway epithelia are chemo- McEwen DP,Koenekoop RK, Khanna H, Jenkins PM, Lopez sensory. Science 325: 1131–1134. I, Swaroop A, Martens JR. 2007. Hypomorphic CEP290/ NPHP6 mutations result in anosmia caused by the selec- Shenoy SK, Lefkowitz RJ. 2011. b-Arrestin-mediated recep- tive loss of G proteins in cilia of olfactory sensory neu- tor trafficking and signal transduction. Trends Pharmacol rons. Proc Natl Acad Sci 104: 15917–15922. Sci 32: 521–533. McMahon HT, Boucrot E. 2011. Molecular mechanism and Shukla AK, Xiao K, Lefkowitz RJ. 2011. Emerging physiological functions of clathrin-mediated endocyto- paradigms of b-arrestin-dependent seven transmem- sis. Nat Rev Mol Cell Biol 12: 517–533. brane receptor signaling. Trends Biochem Sci 36: 457– Menco BP.1980. Qualitative and quantitative freeze-fracture 469. studies on olfactory and nasal respiratory epithelial sur- Singh J, Wen X, Scales SJ. 2015. The orphan G protein- faces of frog, ox, rat, and dog. III: Tight-junctions. Cell coupled receptor Gpr175 (Tpra40) enhances Hedgehog Tissue Res 211: 361–373. signaling by modulating cAMP levels. J Biol Chem 290: Menco B. 1992. Ultrastructural studies on membrane, cyto- 29663–29675. skeletal, mucous, and protective compartments in olfac- Sorkin A, von Zastrow M. 2009. Endocytosis and signalling: tion. Microsc Res Tech 22: 215–224. Intertwining molecular networks. Nat Rev Mol Cell Biol Menco BP.1997. Ultrastructural aspects of olfactory signal- 10: 609–622. ing. Chem Senses 22: 295–311. Stephan AB, Shum EY, Hirsh S, Cygnar KD, Reisert J, Zhao Mukhopadhyay S, Wen X, Ratti N, Loktev A, Rangell L, H. 2009. ANO2 is the cilial calcium-activated chloride Scales SJ, Jackson PK. 2013. The ciliary G-protein- channel that may mediate olfactory amplification. Proc coupled receptor Gpr161 negatively regulates the Sonic Natl Acad Sci 106: 11776–11781. Hedgehog pathway via cAMP signaling. Cell 152: 210– Szumska J, Qatato M, Rehders M, Fuhrer D, Bie- 223. bermann H, Grandy DK, Kohrle J, Brix K. 2015. Olias G, Viollet C, Kusserow H, Epelbaum J, Meyerhof W. Trace amine-associated receptor 1 localization at the 2004. Regulation and function of somatostatin receptors. apical plasma membrane domain of fisher rat thyroid J Neurochem 89: 1057–1091. epithelial cells is confined to cilia. Eur Thyroid J 4: Omori Y, Chaya T, Yoshida S, Irie S, Tsujii T, Furukawa T. 30–41. 2015. Identification of G protein-coupled receptors Tabibian JH, Masyuk AI, Masyuk TV, O’Hara SP, LaRusso (GPCRs) in primary cilia and their possible involvement NF. 2013. Physiology of cholangiocytes. Compr Physiol 3: in body weight control. PLoS ONE 10: e0128422. 541–565.

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Ciliary GPCR Signaling

Takeda S, Kadowaki S, Haga T, Takaesu H, Mitaku S. 2002. Upadhyay VS, Muntean BS, Kathem SH, Hwang JJ, Identiﬁcation of G protein-coupled receptor genes from Aboualaiwi WA, Nauli SM. 2014. Roles of dopa- the human genome sequence. FEBS Lett 520: 97–101. mine receptor on chemosensory and mechanosensory Tang XL, Wang Y, Li DL, Luo J, Liu MY. 2012. Orphan G primary cilia in renal epithelial cells. Front Physiol protein-coupled receptors (GPCRs): Biological func- 5: 72. tions and potential drug targets. Acta Pharmacol Sin 33: VassarR, Ngai J, Axel R. 1993. Spatial segregation of odorant 363–371. receptor expression in the mammalian olfactory epithe- Tempe D, Casas M, Karaz S, Blanchet-Tournier MF, lium. Cell 74: 309–318. Concordet JP. 2006. Multisite protein kinase A and Viollet C, Lepousez G, Loudes C, Videau C, Simon A, glycogen synthase kinase 3b phosphorylation leads to Epelbaum J. 2008. Somatostatinergic systems in brain: Gli3 ubiquitination by SCFbTrCP. Mol Cell Biol 26: Networks and functions. Mol Cell Endocrinol 286: 4316–4326. 75–87. Torres VE, Harris PC. 2014. Strategies targeting cAMP sig- WangZ, Li V,Chan GC, Phan T,Nudelman AS, Xia Z, Storm naling in the treatment of polycystic kidney disease. JAm DR. 2009. Adult type 3 adenylyl cyclase-deﬁcient mice Soc Nephrol 25: 18–32. are obese. PLoS ONE 4: e6979. Torres VE, Wang X, Qian Q, Somlo S, Harris PC, Gattone Wang Z, Phan T, Storm DR. 2011. The type 3 adenylyl cy- VH II. 2004. Effective treatment of an orthologous model clase is required for novel object learning and extinction of autosomal dominant polycystic kidney disease. Nat of contextual memory: Role of cAMP signaling in prima- Med 10: 363–364. ry cilia. J Neurosci 31: 5557–5561. TusonM, He M, Anderson KV.2011. Protein kinase A acts at YaoG, Luo C, Harvey M, Wu M, Schreiber TH, Du Y,Basora the basal body of the primary cilium to prevent Gli2 N, Su X, Contreras D, Zhou J. 2015. Disruption of poly- activation and ventralization of the mouse neural tube. cystin-L causes hippocampal and thalamocortical hyper- Development 138: 4921–4930. excitability. Hum Mol Genet 25: 448–458.

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G-Protein-Coupled Receptor Signaling in Cilia

Kirk Mykytyn and Candice Askwith

Cold Spring Harb Perspect Biol published online February 3, 2017

Subject Collection Cilia

Ciliary Mechanisms of Cyst Formation in Cilia in Left−Right Symmetry Breaking Polycystic Kidney Disease Kyosuke Shinohara and Hiroshi Hamada Ming Ma, Anna-Rachel Gallagher and Stefan Somlo Photoreceptor Cilia and Retinal Ciliopathies Discovery, Diagnosis, and Etiology of Craniofacial Kinga M. Bujakowska, Qin Liu and Eric A. Pierce Ciliopathies Elizabeth N. Schock and Samantha A. Brugmann G-Protein-Coupled Receptor Signaling in Cilia Axoneme Structure from Motile Cilia Kirk Mykytyn and Candice Askwith Takashi Ishikawa Evolution of Cilia Cilia and Ciliopathies in Congenital Heart Disease David R. Mitchell Nikolai T. Klena, Brian C. Gibbs and Cecilia W. Lo Transition Zone Migration: A Mechanism for Sperm Sensory Signaling Cytoplasmic Ciliogenesis and Postaxonemal Dagmar Wachten, Jan F. Jikeli and U. Benjamin Centriole Elongation Kaupp Tomer Avidor-Reiss, Andrew Ha and Marcus L. Basiri Cilia and Obesity Primary Cilia and Coordination of Receptor Christian Vaisse, Jeremy F. Reiter and Nicolas F. Tyrosine Kinase (RTK) and Transforming Growth Berbari Factor β (TGF-β) Signaling Søren T. Christensen, Stine K. Morthorst, Johanne B. Mogensen, et al. Posttranslational Modifications of Tubulin and Primary Cilia and Mammalian Hedgehog Signaling Cilia Fiona Bangs and Kathryn V. Anderson Dorota Wloga, Ewa Joachimiak, Panagiota Louka, et al. Radial Spokes−−A Snapshot of the Motility Cilia and Mucociliary Clearance Regulation, Assembly, and Evolution of Cilia and Ximena M. Bustamante-Marin and Lawrence E. Flagella Ostrowski Xiaoyan Zhu, Yi Liu and Pinfen Yang For additional articles in this collection, see http://cshperspectives.cshlp.org/cgi/collection/

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