Regulation of Rho Gtpases by Rhogdis in Human Cancers
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cells Review Regulation of Rho GTPases by RhoGDIs in Human Cancers 1, 1, 1 2, 1,3, Hee Jun Cho y, Jong-Tae Kim y, Kyoung Eun Baek , Bo-Yeon Kim * and Hee Gu Lee * 1 Immunotherapy Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon 34141, Korea; [email protected] (H.J.C.); [email protected] (J.-T.K.); [email protected] (K.E.B.) 2 Anticancer Cancer Research Center, Korea Research Institute of Bioscience and Biotechnology, Cheongju 28116, Korea 3 Department of Biomolecular Science, University of Science and Technology (UST), Daejeon 34141, Korea * Correspondence: [email protected] (B.-Y.K.); [email protected] (H.G.L.) These authors have contributed equally to this work. y Received: 23 July 2019; Accepted: 3 September 2019; Published: 5 September 2019 Abstract: Rho GDP dissociation inhibitors (RhoGDIs) play important roles in various cellular processes, including cell migration, adhesion, and proliferation, by regulating the functions of the Rho GTPase family. Dissociation of Rho GTPases from RhoGDIs is necessary for their spatiotemporal activation and is dynamically regulated by several mechanisms, such as phosphorylation, sumoylation, and protein interaction. The expression of RhoGDIs has changed in many human cancers and become associated with the malignant phenotype, including migration, invasion, metastasis, and resistance to anticancer agents. Here, we review how RhoGDIs control the function of Rho GTPases by regulating their spatiotemporal activity and describe the regulatory mechanisms of the dissociation of Rho GTPases from RhoGDIs. We also discuss the role of RhoGDIs in cancer progression and their potential uses for therapeutic intervention. Keywords: RhoGDI1; RhoGDI2; Rho GTPases; cancer; migration; metastasis 1. Introduction Rho GTPases regulate various cellular processes, including cell motility, cell adhesion, cytokinesis, cell polarity, cell cycle, and cell survival [1,2]. Anomalous signaling of Rho GTPases is commonly found in many human cancers and can be attributed to several mechanisms, such as overexpression of Rho GTPases with oncogenic activity or alterations of upstream regulators or downstream effectors [3,4]. As in the Ras superfamily, Rho GTPases cycle between an active guanosine triphosphate (GTP)-bound firm in the cell membrane and an inactive guanosine diphosphate (GDP)-bound in the cytoplasm [5]. This cycling is highly regulated by three classes of proteins. Rho guanine nucleotide exchange factors (RhoGEFs) promotes the exchange of GDP for GTP, thereby activating Rho GTPases [6]. Rho GTPase-activating proteins (RhoGAPs) catalyze intrinsic GTP hydrolysis, thereby inactivating Rho GTPases [7]. Rho-specific guanosine nucleotide dissociation inhibitors (RhoGDIs) bind to Rho GTPases and control their spatiotemporal activity [8,9]. There are a large number of Rho GEFs and Rho GAPs, whereas the RhoGDI family only has three members in mammals: RhoGDI1 is ubiquitously expressed in various cells [10]; RhoGDI2 is preferentially expressed in hematopoietic cells [11,12]; and RhoGDI3 is expressed in the brain, testes, and pancreas [13,14]. RhoGDI1 and RhoGDI2 are present exclusively in the cytoplasm and form complexes with most Rho GTPases. In contrast, RhoGDI3 is associated with the Golgi complex and exhibits specificity for interactions with RhoB and RhoG [15]. In addition, little is known about the association between RhoGDI3 and human cancer. Therefore, we will focus on RhoGDI1 and RhoGDI2, Cells 2019, 8, 1037; doi:10.3390/cells8091037 www.mdpi.com/journal/cells Cells 2019, 8, x FOR PEER REVIEW 2 of 12 Cells 2019, 8, 1037 2 of 12 association between RhoGDI3 and human cancer. Therefore, we will focus on RhoGDI1 and butRhoGDI2, not RhoGDI3. but not RhoGDIsRhoGDI3. interact RhoGDIs with interact most Rho with GTPases most Rho in the GTPases cytoplasm in the and cytoplasm prevent Rhoand GTPasesprevent fromRho bindingGTPases to from GEFs binding or their efftoector GEFs molecules. or their Thus, effector RhoGDIs molecules. have been Thus, considered RhoGDIs to behave negative been regulatorsconsidered ofto Rhobe negative GTPases regulators [16]. When of Rho GT GTPasesPases [16]. are dissociated When Rho fromGTPases RhoGDIs, are dissociated they can from bind toRhoGDIs, the plasma they membrane can bind to and the be plasma activated membrane by GEFs [and17]. be The activated interaction by betweenGEFs [17]. Rho The GTPases interaction and RhoGDIsbetween Rho is dynamically GTPases and regulated RhoGDIs by several is dynamically mechanisms, regulated including by interactions several mechanisms, with specific including proteins orinteractions lipids, phosphorylation, with specific proteins ubiquitination, or lipids, and phosphorylation, sumoylation [18 ubiquitination,]. Accumulating and evidence sumoylation has shown [18]. thatAccumulating RhoGDIs are evidence implicated has inshown cancer that cell RhoGDIs migration, are invasion, implicated metastasis, in cancer and cell chemoresistance migration, invasion, via the deregulationmetastasis, and of thechemoresistance Rho GTPase signaling via the deregulati pathway [on19, 20of ],the making Rho GTPase them an si attractivegnaling pathway target for [19,20], cancer treatment.making them Here, an weattractive review target how RhoGDIsfor cancer control treatment. the functionHere, we of review Rho GTPases how RhoGDIs by regulating control their the spatiotemporalfunction of Rho activity GTPases and by describe regulating the regulatorytheir spatiotemporal mechanisms activi of thety and dissociation describe of the Rho regulatory GTPases frommechanisms RhoGDIs. of the We dissociation also discuss theof Rho role GTPases of RhoGDIs from in RhoGDIs. cancer progression We also discuss and their the potential role of RhoGDIs uses for therapeuticin cancer progression intervention. and their potential uses for therapeutic intervention. 2. Regulation of Rho GTPases by RhoGDIs RhoGDIs contain contain a aflexible flexible N-terminalN-terminal domain domain and and a hydrophobic a hydrophobic C-terminal C-terminal domain. domain. The TheN-terminal N-terminal domain domain of RhoGDIs of RhoGDIs binds to binds switch to I switch and switch I and II switchdomains II of domains Rho GTPases, of Rho which GTPases, are whichthe binding are the region binding for regionGEFs and for GAPs. GEFs andThe GAPs.interaction The between interaction these between two domains these two inhibits domains the inhibitstransition the between transition the betweenGTP- and the GDP-bound GTP- and GDP-boundforms [21–23]. forms The [21C-terminal–23]. The domain C-terminal of RhoGDIs domain offorms RhoGDIs a hydrophobic forms a hydrophobic pocket and pocket interacts and with interacts the membrane with the membrane targeting targetingprenyl moiety prenyl of moiety Rho ofGTPases Rho GTPases [24,25]. [Most24,25 ].Rho Most GTPases Rho GTPases bind to RhoGDI bind to RhoGDIss in the cytoplasm in the cytoplasm and reside and in reside their inactive in their inactiveform. When form. Rho When GTPases Rho GTPases are disengaged are disengaged from from RhoGDIs, RhoGDIs, they they can can integrate integrate into into the the plasma membrane, where they are activatedactivated byby RhoGEFs.RhoGEFs. Re-association of Rho GTPases with RhoGDIs mediates the the extraction extraction of of Rho Rho GTPases GTPases from from the the me membranembrane and and recycles recycles them them to tothe the cytosol cytosol [26], [26 as], asshown shown in Figure in Figure 1. Therefore,1. Therefore, RhoGDIs RhoGDIs were were originally originally characterized characterized as inhibitory as inhibitory regulators regulators of Rho of RhoGTPases. GTPases. Recent Recent studies, studies, however, however, have have shown shown that that they they regulate regulate Rho Rho GTPases GTPases activity activity in in more complex manners. Figure 1.1. The regulation of Rho GTPases by GEPs,GEPs, GAPs,GAPs, andand GDIs.GDIs. GEFs bind to GDP-bound RhoGTPases and promotes the exchange of GDP forfor GTP,GTP, therebythereby activatingactivating RhoGTPases.RhoGTPases. GAPs bind to GTP-bound RhoGTPases and catalyze the exchange of GDP for GTP, thereby inactivating RhoGTPases. The The N-terminal N-terminal domain domain of of RhoGDIs RhoGDIs bi bindsnds to to switch switch I I and II domains of RhoGTPases. The C-terminalC-terminal region region of RhoGDIsof RhoGDIs forms forms a hydrophobic a hydrophobic pocket andpocket binds and to prenylated binds to RhoGTPases. prenylated Therefore, RhoGDIs can extract RhoGTPases from plasm membrane by binding the isoprenoid moiety and sequester them away in the cytoplasmic compartment. Cells 2019, 8, 1037 3 of 12 RhoGDIs can also act as chaperones for Rho GTPases. Active Rho GTPases are located on the plasma membrane, whereas most Rho GTPases are present in their inactive state in the cytosol [27,28]. The C-terminus of Rho GTPases is prenylated and thus highly hydrophobic. Although prenylation of Rho GTPases is required for their membrane targeting and signaling, free prenylated Rho GTPases in the cytosol are highly unstable. In fact, non-prenylated Rho GTPases fail to localize at the proper action site but they are more stable than prenylated Rho GTPases [29,30]. In addition, inactive Rho GTPases, which are not bound to RhoGDI1 in the cytosol, are degraded through proteasome-dependent mechanisms. RhoGDIs can bind to the prenyl moiety of Rho GTPases through a hydrophobic pocket at their C-terminus. This interaction stabilizes cytosolic Rho GTPases and protects them from proteasomal