Regulatory Evolution Through Divergence of a Phosphoswitch in the Transcription Factor CEBPB

LETTER doi:10.1038/nature10595

Regulatory evolution through divergence of a phosphoswitch in the transcription factor CEBPB

Vincent J. Lynch1, Gemma May1 &Gu¨nter P. Wagner1

There is an emerging consensus that gene regulation evolves through Previous studies have characterized several functionally distinct changes in cis-regulatory elements1,2 and transcription factors3–6. regions in CEBPB including three activation domains (ADM1–3), Although it is clear how nucleotide substitutions in cis-regulatory two internal regulatory domains (RD1–2) and a DNA-binding domain elements affect gene expression, it is not clear how amino-acid sub- (DBD)22–24. To determine which domains and amino-acid substitu- stitutions in transcription factors influence gene regulation4–10.Here tions are responsible for the derived function of CEBPB, we made we show that amino-acid changes in the transcription factor CCAAT/ enhancer binding protein-b (CEBPB, also known as C/EBP-b)inthe a stem-lineage of placental mammals changed the way it responds to 40 cyclic AMP/protein kinase A (cAMP/PKA) signalling. By functionally Human AncEu analysing resurrected ancestral proteins, we identify three amino-acid 35 30 –332 –270 –32 substitutions in an internal regulatory domain of CEBPB that are Luc responsible for the novel function. These amino-acid substitutions 25 CEBPB/FOXO1A HoxA11/FOXO1A CRE reorganize the location of key phosphorylation sites, introducing a new site and removing two ancestral sites, reversing the response of 20 CEBPB to GSK-3b-mediated phosphorylation from repression to 15 AncTh activation. We conclude that changing the response of transcription Opossum Chicken factors to signalling pathways can be an important mechanism of 10 Relative luciferase expression gene regulatory evolution. 5

A major challenge in evolutionary and developmental biology is 0 discovering the molecular mechanisms of gene regulatory evolution. Both Both Both Both Both dPRL Although it is clear that changes in transcription factors have contributed CEBPB CEBPB CEBPB CEBPB CEBPB to the evolution of gene regulation7–11, most studies of gene regulatory FOXO1A FOXO1A FOXO1A FOXO1A FOXO1A evolution have focused on cis-regulatory elements1,2,12–15. Thus, how mutations in transcription factors generate new regulatory functions is not well understood. b The mammalian transcription factor CEBPB plays an essential role 16 16–18 Human during pregnancy , including physically and functionally interacting 14 AncEu c with FOXO1A to activate prolactin (PRL) expression in endometrial CEBPBFOXO1ACEBPBFOXO1ACEBPB IP stromal cells (ESCs)19–21 (Supplementary Fig. 1a). To test if this function 12 AncTh AncEu evolved coincident with the origin of pregnancy in placental mammals, 10 we assayed chicken, opossum and human CEBPB (LAP) and FOXO1A input co-IP for their ability to transactivate luciferase expression from the ESC PRL 8 enhancer. We found that each species’ CEBPB moderately trans- 6 activated luciferase expression in HeLa and ESC (Fig. 1a, b). Co- 4 Chicken expressed human FOXO1A and CEBPB cooperatively transactivated Opossum AncTh luciferase expression approximately 3.6-fold (Fig. 1a, b). In stark con- Relative luciferase expression 2 trast, co-expression of CEBPB and FOXO1A from opossum and chicken were unable to transactivate luciferase expression cooperatively 0 (Fig. 1a, b). Both Both Both Both Both dPRL CEBPB CEBPB CEBPB CEBPB CEBPB These results suggest that the cooperative CEBPB/FOXO1A inter- FOXO1A FOXO1A FOXO1A FOXO1A FOXO1A action evolved in placental mammals. To test this hypothesis we Figure 1 | CEBPB cooperatively regulates gene expression with FOXO1A in used maximum likelihood to reconstruct the sequence of the ancestral placental mammals. CEBPB and FOXO1A from human and the therian (AncTherian) and eutherian (AncEutherian) CEBPB and reconstructed ancestor of eutherian mammals (AncEu) cooperatively FOXO1A genes, synthesized them using human codon-usage and transactivate luciferase expression from the decidual prolactin promoter tested their function in the assay described above. We found that the (dPRL) when co-transfected into HeLa (a) or human ESCs (b). Inset, the AncEutherian CEBPB/FOXO1A complex strongly transactivated structure of the luciferase reporter vector and experimentally characterized luciferase expression whereas the AncTherian complex was unable transcription-factor binding sites. CEBPB and FOXO1A from non-mammals, including the reconstructed ancestor of therian mammals (AncTh), do not to do so (Fig. 1a, b). This derived cooperativity in placental mammals, show cooperative upregulation. Luciferase values are shown as fold changes however, does not result from a newly evolved physical interaction (mean 6 s.e.m., n 5 6) relative to the reporter control (dPRL). c, Both the between CEBPB and FOXO1A because both the AncEutherian ancestral therian and eutherian CEBPB proteins directly interact. CEBPB-V5/ and AncTherian CEBPB proteins are able to interact physically with His and FOXO1A–Flag were expressed in HeLa cells and immunoprecipitated ancestral FOXO1A proteins (Fig. 1c). with anti-Flag agarose beads followed by DNase treatment.

1Yale Systems Biology Institute and Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06511, USA.

15 DECEMBER 2011 | VOL 480 | NATURE | 383 ©2011 Macmillan Publishers Limited. All rights reserved RESEARCH LETTER amino (N)-terminal truncation mutants of the AncTherian and and identified several differences between non-placental and placental AncEutherian CEPBPB genes and tested their ability to transactivate mammals, including the loss of two ancestral serine phosphosites at luciferase expression when co-expressed with FOXO1A. Deletion of sites three (S3A) and four (S4A) and the gain of a serine phosphosite at ADM1 (D39) or ADM1–2 (D109) abrogated the transactivation ability site five (N5S) in placental mammals. These sites are generally of the AncEutherian protein whereas the ADM1–3 (D131) deletion conserved at state S-(S/T)-N outside placental mammals and at state restored transactivation. Deletion of RD1 (D175) and the region A-A-S within placental mammals, suggesting they are functionally between RD1 and RD2 (D200) had little effect on the enhanced activa- constrained (Fig. 2c). Remarkably, the eutherian-specific serine at site tion of D131. Deletion of RD2 (D236), however, reduced the trans- five has previously been shown to be phosphorylated by GSK-3b kinase activation ability of the AncEutherian protein to that observed for the in rat CEBPB27. We confirmed that this site was phosphorylated in the AncTherian protein (Fig. 2a), indicating that RD2 plays a critical role AncEutherian CEBPB using nano-LC-ESI-MS/MS on purified protein in PRL regulation. in vitro phosphorylated with MAPK and GSK-3b kinases. Automated To test if the five eutherian-specific amino-acid changes within this analysis of the tandem mass spectrometry (MS/MS) spectra indicated region are responsible for the derived function in placental mammals, we that the derived serine at site five is phosphorylated by GSK-3b kinases. reverted the derived amino acids in AncEutherian RD2 back to their To test if phosphorylation by GSK-3b plays a role in potentiating ancestral state in the AncTherian protein and tested their ability to transactivation by CEBPB, we repeated our luciferase reporter assays transactivate luciferase expression. We found that back mutation of with the ancestral CEBPB and FOXO1A proteins but blocked GSK-3b derived sites one and two had no effect on transactivation, whereas back phosphorylation with the kinase inhibitor 6-bromoindirubin 39-oxime mutation of sites three, four and five resulted in a pronounced loss of (BIO); if phosphorylation by GSK-3b is functionally important for trans- transactivation ability (Fig. 2b). Next, we tested whether forward muta- activation of reporter gene expression by CEBPB, then inhibiting this tion of sites three, four and five was sufficient to impart a transactivation kinase should block transactivation. Indeed, we found that inhibiting function to the AncTherian CEBPB. Unlike the progressive loss of func- GSK-3b blocked the ability of the AncEutherian CEBPB to transactivate tion observed for reverse mutations, forward mutation of sites three and luciferase expression from the dPRL enhancer (Fig. 2b). Unexpectedly, four, alone or in combination, had no effect on the ability of AncTherian however, inhibiting GSK-3b dramatically potentiated transactivation by CEBPB to transactivate luciferase expression (Fig. 2b). Forward mutation AncTherian CEBPB. These results indicate that the AncEutherian of site five only modestly enhanced transactivation; however, forward CEBPB is activated by GSK-3b, whereas the AncTherian CEBPB is mutation of sites three and four in combination with site five dramat- repressed by GSK-3b (Fig. 2b). ically enhanced transactivation by the AncTherian CEBPB (Fig. 2b). To determine which amino acids are responsible for interpreting GSK- Thus, although the amino-acid substitutions at sites three and four con- 3b-mediated phosphorylation as an inhibiting signal in AncTherian tribute to the derived regulatory ability of CEBPB in placental mammals, CEBPB and an activating signal in AncEutherian CEBPB, we com- they are dependent on the amino-acid substitution at site five. pared the ability of back and forward mutated proteins to cooperatively Previous studies have shown that CEBPB is phosphorylated in res- transactivate luciferase expression with FOXO1A in the presence of ponse to cell-signalling, differentiation25 and cAMP/PKA stimulation26. BIO. We found that back mutation of site three, four and three/four in We mapped known and predicted phosphorylation sites in CEBPB the AncEutherian CEBPB protein, which restores ancestral putative

Relative luciferase expression AncEu a ADM1 ADM2 ADM3RD1 RD2 DBD 0 50 100 150 200 250 d AAn AAS CDS Δ39 GSK-3β Δ60 sAn sAS Δ109 Δ131 Δ175 Δ200 Asn AsS Δ236 β Δ262 GSK-3

dPRL ssn ssS b AncTh

c S1 S2 S3 S4 S5

400 340 327 360 343 305 293 305 307 4 300 3 2 1 200 0 Placentals β β 100 111 100 84 81 75 72 52 55 67 βMAPK 32 38 323252 30 36 315452 51 4 GSK-3GSK-3GSK-3 29 26 30 29 18 15 3 0 2 – + – + – + – + – + – + – + – + – + – + – + – + – + – + – + – + – + 1 Relative luciferase expression AAS* sAS AsS AAn ssS sAn Asn ssn* dPRL Others 0 Figure 2 | CEBPB evolved a novel GSK-3B phosphorylation site in an letters indicate the state in the ancestral eutherian. c, Amino-acid substitutions internal regulatory domain. a, N-terminal deletion mutants of ancestral at sites three, four and five reposition the location of key phosphosites. RD2 eutherian (yellow) and ancestral therian (blue) CEBPB differentially logos are shown for placental mammals and other species with the location of transactivate the dPRL-luciferase reporter when co-transfected with FOXO1A. S/T phosphosites highlighted in yellow with the name of the phosphorylating Deletion of regulatory domain 2 (RD2; D236) in the ancestral eutherian CEBPB kinases; nano-liquid chromatography–electrospray ionization/tandem mass protein reduces its transactivating ability to that of the ancestral therian protein. spectrometry of in vitro phoshorylated ancestral eutherian CEBPB confirmed Luciferase values are shown as fold changes relative to the full-length (CDS) site five (S5) is phosphorylated by GSK-3b. d, Mutational pathway between the ancestral eutherian CEBPB protein (mean 6 s.e.m., n 5 6). Red lines indicate ancestral therian (AncTh, blue) and eutherian (AncEu, yellow) functions. Each the position of eutherian-specific amino-acid changes. b, Effect of forward and corner of the cube represents a possible intermediate state for amino acids at back mutation of sites three, four, and five in the ancestral therian (blue) and sites three, four and five; amino-acid identity at each state is shown as single eutherian (yellow) CEBPB on transactivation in the presence of BIO (1) or BIO letter amino code. Red edges show unlikely evolutionary paths through control (2) media. Luciferase values are shown relative to wild-type ancestral intermediate states that cannot transactivate reporter gene expression (red eutherian CEBPB (mean 6 s.e.m., n 5 6); *wild-type proteins; lower-case nodes), black edges show paths through functional intermediate states (green letters indicate amino-acid state in the ancestral therian whereas upper-case nodes).

384 | NATURE | VOL 480 | 15 DECEMBER 2011 ©2011 Macmillan Publishers Limited. All rights reserved LETTER RESEARCH phosphorylation sites that were lost in the stem lineage of placental structural models suggest the differential response of AncEutherian mammals, recapitulated the dramatic enhancement of transactivation and AncTherian proteins to GSK-3b stimulation results from the observed for AncTherian CEBPB in the presence of BIO (Fig. 2b). acquisition of different conformational states upon phosphorylation. Conversely, forward mutations of sites three, four and three/four in To test if GSK-3b-mediated phosphorylation induces a conforma- the AncTherian CEBPB protein, which abolish the ancestral tion change in CEBPB, we immunoprecipitated AncEutherian and phosphorylation sites but do not introduce the derived phosphosite AncTherian proteins from BIO-treated or control HeLa cells and at site five, blocked its ability to transactivate reporter gene expression incubated the purified protein with 20S proteasome, which degrades regardless of BIO treatment, leading to an essentially functionless proteins with extended unstructured regions30. We found that the protein in this assay (Fig. 2b). Incorporating a forward mutation at AncEutherian CEBPB isolated from BIO-treated cells was less effi- site five increased the transactivation ability of AncTherian CEBPB in ciently degraded than protein from untreated cells, suggesting that the absence of BIO while maintaining a strong enhancement of trans- inhibiting GSK-3b shifts the conformation of the AncEutherian activation with BIO treatment; however, transactivation with BIO was CEBPB to the inactive state, which prevents digestion by the 20S lost upon forward mutations of sites three and four (Fig. 2b). We proteasome (Fig. 3b). In contrast, AncTherian CEBPB isolated from conclude that the N5S substitution probably came before S3A and BIO-treated cells was more efficiently degraded than protein isolated S4A because these substitutions lead to non-functional proteins when from untreated cells, suggesting that inhibiting GSK-3b shifted the not paired with N5S and evolution is unlikely to pass through such conformation of the AncTherian CEBPB to the active state (Fig. 3b). non-functional intermediates (Fig. 2d). To test if GSK-3b-mediated phosphorylation of site five is Previous studies suggest that phosphorylation of RD2 induces a important for inducing a conformation change in AncEutherian conformation change in CEBPB that disrupts intramolecular contacts CEBPB, we immunopurified transiently expressed wild-type and site between RD1–2, ADM1-3 and the bZIP/DNA-binding domain, lead- five back-mutated AncEutherian CEBPB in HeLa cells, and either in ing to activation of the intrinsically repressed protein17,22–24,28. To infer vitro phosphorylated the protein with MAPK/GSK-3b kinases or the structural consequences of repositioning phosphorylation sites, we dephosphorylated it with calf intestinal alkaline phosphatase. We generated structural models of unphosphorylated and phosphorylated found that in vitro phosphorylated wild-type AncEutherian CEBPB proteins using Rosetta/Robetta29. The model of the unphosphorylated was nearly completely degraded by the 20S proteasome, but that back AncEutherian protein suggests that ADM1–3 and RD1–2 are mutation at site five and dephosphorylation protected the protein intrinsically unstructured and collapsed into a tight knot-like bundle from degradation (Fig. 3c). These results suggest that in the ancestral in close contact with the helical bZIP/DNA-binding domain (Fig. 3a) state (likely) phosphorylation of sites three and/or four flips the con- similar to previous molecular and biochemical models22–24.Incontrast, formation of CEBPB to the closed, transcriptionally repressed state. In ADM1–3 and RD1–2 associate with neither each other nor the bZIP/ contrast, in the derived-state phosphorylation at site five flips the DNA-binding domain in the model of the phosphorylated AncEutherian switch to the open, transcriptionally active conformation (Fig. 3d). CEBPB (Fig. 3a), freeing residues critical for nuclear localization These results uncover a potentially important mechanism of gene and DNA binding from an intramolecular masking. Unlike the regulatory evolution and suggest that evolution can affect transcription phosphorylated AncEutherian CEBPB, the model of the AncTherian factor functions in a cell-type-dependent way, probably avoiding CEBPB phosphorylated at ancestral sites three and four assumes the deleterious pleiotropic effects on functions in different cellular and repressed, transcriptionally inactive, conformation (Fig. 3a). These developmental contexts. Thus, modification of phosphorylation sites

GSK-3β

S3 S4

GSK-3β S5 ‘Active’ ‘Inactive’

bc1.0 1.0 1.0 0.90 0.91 0.8 0.59 0.6 0.51 pAncEupAncEu-S5dAncEu pHsadHsa 0.4 20s 0.2 Input 0.0

Undigested protein (%) Undigested protein AncTh AncTh AncTh+ AncEu AncEu AncEu+ input input Figure 3 | Phosphorylation induces a conformation change in CEBPB. (pHsa) and ancestral eutherian (pAncEu) CEBPB with purified 20S a, Structural models of unphosphorylated and phosphorylated ancestral proteasome leads to protein degradation whereas dephosphorylated proteins therian (blue) and eutherian (yellow) CEBPB proteins. The model of the (dHsa, dAncEu) are protected from degradation. Back mutation of site 5 phosphorylated ancestral eutherian CEBPB is in the ‘active’ conformation (pAncEu-S5) decreases susceptibility of the in vitro phosphorylated protein to whereas the model of the unphosphorylated ancestral therian CEBPB is in the degradation. Arrows indicate CEBPB bands in Coomassie-blue-stained gel. ‘active’ conformation. Sites three, four and five are shown as spheres. d, Models of the conformational phospho-switch in CEBPB. Phosphorylation b, Ancestral therian (AncTh) and ancestral eutherian (AncEu) CEBPB protein of the ancestral therian CEBPB (top) at sites three (S3) and four (S4) by GSK-3b grown in cells treated with the GSK-3b inhibitor BIO (1) or control (2) media flips the switch from the ‘active’ conformation (light blue) to the ‘inactive’ are differentially digested by the 20S proteasome. The percentage of undigested conformation (dark blue). In contrast, phosphorylation of the ancestral protein after a 30-min digestion with the 20S proteasome is shown relative to eutherian CEBPB (bottom) at site five (S5) by GSK-3b flips the switch from the input. c, Phosphorylation of site five induces a conformation change in the ‘inactive’ conformation (dark yellow) to the ‘active’ conformation (yellow). ancestral eutherian CEBPB. Incubation of in vitro phosphorylated human

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METHODS cells were co-transfected with either 200 ng empty pcDNA3.1(1)-V5/His, 100 ng Identification and cloning of CEBPB genes. CEBPB genes were identified from of the FOXO1A expression vector and 100 ng of one of the CEBPB expression BLAST/BLAT searches of whole-genome databases at the National Center for vector. Luciferase expression was assayed 48 h after transfection using the Dual Biotechnology Information, University of California, Santa Cruz, and Ensembl Luciferase Reporter System (Promega). Each experiment was repeated four times, including anole (Anolis carolinensis), chicken (Gallus gallus), zebra finch with eight replicates per experiment. GSK-3B was inhibited with 10 nM InSolution (Taeniopygia guttata), opossum (Monodelphis domestica), wallaby (Macropus GSK-3 Inhibitor IX BIO (EMD Chemicals); control media included 10 nM GSK-3 eugenii), armadillo (Dasypus novemcinctus), elephant (Loxodonta africana), Inhibitor IX, control, MeBIO (EMD Chemicals). We note that caution should be two-toed sloth (Choloepus hoffmanni), cow (Bos taurus), dolphin (Tursiops taken when applying luciferase assay results to the situation in vivo; we are currently truncates), Seba’s short-tailed bat (Carollia perspicillata), flying fox (Pteropus developing a knockdown/xeno-gene rescue system to test the applicability our vampyrus), horse (Equus caballus), dog (Canis familiaris), rat (Rattus norvegicus), results to in vivo systems. mouse (Mus musculus), rabbit (Oryctolagus cuniculus),guineapig (Cavia porcellus), Co-immunoprecipitations and proteomics. HeLa and hESC cells were cultured pika (Ochotona princeps), marmoset (Callithrix jacchus), macaque (Macaca as described above. Before transfection, cells were plated at a density of approxi- 6 mulatta), orang-utan (Pongo pygmaeus), gorilla (Gorilla gorilla), chimpanzee mately 4.4 3 10 cells per millilitre on 10-cm plates. The next day, CEBPB-V5/His (Pan troglodytes) and human (Homo sapiens). construct was transfected into HeLa cells with either empty pcDNA3.1(1)-V5/His We amplified CEBPB by PCR from the genomic DNA of two snakes (Lichanura vector, or Flag–FOXO1A pcDNA3.1 vector using Lipofectamine 2000 (Invitrogen) trivirgata and Eryx jayakari) and two lizards (Chalcides chalcides and Sceloporus according to the manufacturer’s protocol. A total of 12 mg of DNA was mixed with undulatus) using amniote-specific primers (forward: 59-CCTTTAAATCCA Lipofectamine (1:3) in 3 ml OptiMEM reduced serum media (Gibco) and incubated TGGAAGTGGC-39; reverse: 59-GACAAGCACAGCGACGAGTA-39). PCR for 4 h at 37 uC, before addition of 7 ml DMEM. After 16 h the transfection media products were cloned into the pGEM-T vector (Promega). Cloned PCR products were removed and replaced with fresh DMEM, and the cells were incubated an were sequenced in both directions by dideoxy chain termination using BigDye additional 24 h before collection. chemistry and an automated sequencer. Multiple colonies (at least four) were After removing DMEM and washing cells twice with PBS, 1 ml ice-cold lysis sequenced for each species. buffer (20 mM Tris, pH 8.0, 40 mM KCl, 10 mM MgCl2, 10% glycerol, 1% Triton Ancestral sequence reconstruction. To estimate the substitution rate of the 49 X-100, 13 Complete EDTA-free protease inhibitor cocktail (Roche), 13 amino acids within and outside placental mammals, we used CODEML in PhosSTOP (Roche)) was added to each plate and cells were collected by scraping PAML4.0, the tree shown in Supplementary Fig. 1, and f334 codon frequencies. with a rubber spatula; they were then incubated on ice for 30 min after the addition Ancestral sequences were inferred with PAML, which uses maximum likelihood of 5 M NaCl to a final concentration of 420 mM. Whole-cell lysate was cleared by and an empirical Bayes approach to estimate ancestral character states, and the centrifugation at 10,000g for 30 min at 4 uC, and supernatant was transferred to a phylogeny shown in Supplementary Fig. 1. The Bayesian posterior probability at clean microfuge tube. After equilibrating protein concentrations, 1 ml of sample each site of the reconstructed therian CEBPB ancestral sequence (AncTherian) was mixed with 40 ml of M2 anti-Flag agarose beads (Sigma) pre-washed with was 0.96 and the probability of the eutherian CEBPB (AncEutherian) ancestral TNT buffer (50 mM Tris-HCl, pH 7.5, 150 mM NaCl, 0.05% Triton X-100), and sequence was 1.0. Ancestral FOXO1A sequences were also inferred with rotated overnight at 4 uC. CODEML using the same species for the CEBPB reconstruction. The Bayesian The next day, samples were treated with 50 U DNase (Roche) and 2.5 mg RNase posterior probability of the reconstructed therian FOXO1A ancestral sequence (Roche) for 60 min at room temperature, as indicated. Samples were washed three was 0.96 and the probability of the eutherian FOXO1A ancestral sequence was times with 1 ml of Hepes Wash (10 mM Hepes, 150 mM NaCl, 0.5% Triton X-100). 0.98. Between each wash, agarose beads were collected by centrifugation at 1,000g for CEBPB expression vector construction. We amplified CEBPB by PCR from the 1 min at 4 uC and supernatant was removed. After the final wash, beads were cDNA of human (Homo sapiens), opossum (Monodelphis domesticus) and chicken re-suspended in elution buffer (500 mM Tris pH 7.5, 1 M NaCl) and incubated (Gallusgallus) using primers to designed specific to each species for LAP, theisoform for 1 h at 4 uC. For in vitro phosphorylation assays, immunoprecipitated proteins of CEBPB expressed in ESCs. PCR products were cloned into the mammalian were either incubated with MAPK/GSK-3b and ATP (New England Biolabs) or expression vector pcDNA3.1(1)-V5/His (Invitrogen) and verified by sequencing. calf intestinal phosphatase (New England Biolabs) according to the manufacturer’s Deletions were made by PCR and cloned into pcDNA3.1(1)-V5/His. Site-directed protocol. For 20S assays, in vitro phosphorylated and dephosphorylated protein mutagenesis was performed with the QuickChange Lightning Site Directed was incubated for 30 min at 37 uC with 1 mg purified human 20S proteosome (Enzo Mutagensis kit (Stratagene). Life Sciences) in 40 ml digestion buffer. The ancestral therian and ancestral eutherian genes were synthesized by Immunoprecipitated proteins were either excised from SDS–polyacrylamide gel GeneScript Corporation with human-optimized codon usage and ligated into electrophoresis gels and sent to the Keck Proteomics centre for further processing and pcDNA3.1(1)-V5/His. Proper expression and nuclear localization of all tagged nano-liquid chromatography–electrospray ionization/tandem mass spectrometry- CEBPB and FOXO1A genes was checked by western blotting using an anti-V5 based identification of post-translational modifications, or transferred to a PVDF antibody and nuclear lysate. membrane for western blotting. After transfer to PVDF, the membrane was Cell culture and luciferase reporter assays. HeLa cells were grown in DMEM blocked with TBS Tween20 1 BSA (25 mM Tris, 150 mM NaCl, 3% BSA), then supplemented with 10% FBS. Human ESCs were grown in DMEM supplemented incubated with anti-V5-HRP antibody (1:5,000; Invitrogen) for 2 h. Bands were with charcoal stripped 10% FBS and differentiated with the progesterone analogue visualized using the ECL SuperSignal West Pico Chemiluminescent Substrate MPA and cAMP. Cells were transiently transfected with transIT-LT1 (Mirus) (Thermo Scientific). Membranes were stripped with Restore Western Blot according to the manufacturer’s protocol with 2 ng of the Renilla control vector stripping buffer (Thermo Scientific) and re-probed with anti-Flag-HRP antibody (pGL4.71) and 50 ng of the dPRL luciferase reporter. Depending on treatment, (1:100,000; Sigma).