Project description:Estrogen receptor alpha (ERα) phosphorylation modulates receptor activity and downstream signaling. Previous studies identified human phosphorylation sites, serine-167 (S167) and serine-212 (S212) as critical regulators of ERα-mediated gene expression. Serine(S) to alanine(A) phospho knock-in mouse models of the corresponding murine sites, S171 and S216, were generated to assess physiological impact. Compared to WT mice, ERα protein levels in tissues were altered in a sex- and phosphorylation site-dependent manner. S216A males exhibited reduced adipose and increased lean mass. S216A females exhibited decreased femur bone density whereas S171A females exhibited increased bone density. S216A females were subfertile with fewer pups/litter. Single-cell and spatial transcriptomics revealed markedly altered E2-regulated uterine gene expression in both models. S216A mice exhibited reduced plasma metabolites in several key metabolic pathways. This study identifies critical roles for site-specific ERα phosphorylation in modulating receptor level/activity and gene expression that has profound impact on murine body composition, fertility, and metabolism.
Project description:The Positive Transcription Elongation Factor b (P-TEFb) phosphorylates Ser2 residues of RNA polymerase II’s C-terminal domain (CTD) and is essential for the transition from transcription initiation to elongation in vivo. Surprisingly, P-TEFb exhibits Ser5 phosphorylation activity in vitro. The mechanism garnering Ser2 specificity to P-TEFb remains elusive and hinders understanding the transition from transcription initiation to elongation. Through in vitro reconstruction of CTD phosphorylation, mass spectrometry analysis, and chromatin immunoprecipitation-seq analysis we uncover a mechanism by which Tyr1 phosphorylation directs the kinase activity of P-TEFb and alters its specificity from Ser5 to Ser2. The loss of Tyr1 phosphorylation causes the reduction of Ser2 and accumulation of RNA polymerase II in the promoter region as detected by ChIP-seq. We demonstrate the ability of Tyr1 phosphorylation to generate a heterogeneous CTD modification landscape that expands the CTD’s coding potential. These findings provide direct experimental evidence for a combinatorial CTD phosphorylation code wherein previously installed modifications direct the identity and abundance of subsequent coding events by influencing the behavior of downstream enzymes.
Project description:We re-introduced Flag-mTRADD into Tradd-/- MEFs, and identified the phosphorylation sites of TRADD which were induced by TNF and inhibited by TAK1 inhibitor 5Z7 using mass spectrometry. We found that TAK1 could mediate the phosphorylation of multiple sites in TRADD upon TNF stimulation. We next performed in vitro kinase assay using recombinant human TAK1 and human TRADD, followed by mass spectrometry to identify the sites directly phosphorylated by TAK1.
Project description:The present study reports an unbiased analysis of the cytotoxic T cell serine-threonine phosphoproteome using high resolution mass spectrometry. Approximately 2,000 phosphorylations were identified in CTLs of which approximately 450 were controlled by TCR signaling. A significantly overrepresented group of molecules identified in the phosphoproteomic screen were transcription activators, co-repressors and chromatin regulators. A focus on the chromatin regulators revealed that CTLs have high expression of the histone deacetylase HDAC7 but continually phosphorylate and export this transcriptional repressor from the nucleus. HDAC7 dephosphorylation results in its nuclear accumulation and suppressed expression of genes encoding key cytokines, cytokine receptors and adhesion molecules that determine CTL function. The screening of the CTL phosphoproteome thus reveals intrinsic pathways of serine-threonine phosphorylation that target chromatin regulators in CTLs and determine the CTL functional program. We used Affymetrix microarray analysis to explore the molecular basis for the role of HDAC7 in CTLs and the impact of GFP-HDAC7 phosphorylation deficient mutant expression on the CTL transcriptional profile. In vitro generated P14 TCR cytotoxic T cells were retrovirally infected with a construct encoding GFP-HDAC7 phosphorylation deficient mutant, sorted in base of GFP expression (GFP positive and GFP negative) and processed for microarray analysis in three biological replicas.
Project description:The effects of specific modification types and sites on protein lifetime have not been illustrated in large scale. We describe a proteomic method, DeltaSILAC, to quantify the impact of site-specific phosphorylation on the turnover of thousands of proteins in live cells. Being configured on the accurate and reproducible mass spectrometry, the pulse labeling approach using stable isotope-labeled amino acids in cells (pSILAC), phosphoproteomics, as well as a novel peptide-level matching strategy, our DeltaSILAC profiling revealed a global, unexpected delaying effect of many phosphosites on protein turnover. We further found that phosphorylated sites accelerating protein turnover are functionally selected for cell fitness, enriched in Cyclin-dependent kinase substrates, and evolutionarily conserved, whereas the Glutamic acids surrounding phosphosites significantly delay protein turnover. Our investigation provides a generalizable approach and a rich resource for prioritizing the effects of phosphorylation sites on protein lifetime in the context of cell signaling and disease biology.
Project description:The zinc finger CCCTC-binding protein (CTCF) carries out many, at times contradictory, functions in the cell. Although previous studies have sought to explain CTCF multivalency based on sequence composition of binding sites, few have examined how CTCF post-translational modification (PTM) could contribute to the its many functions. Here, we performed CTCF mass spectrometry, identified a novel phosphorylation site at Serine 224 (Ser224-P), and demonstrate that phosphorylation is carried out by Polo kinase 1 (PLK1). CTCF Ser224-P is chromatin-associated, mapping to at least a subset of known CTCF sites. Interestingly, CTCF Ser224-P accumulates during the G2/M transition of the cell cycle and is enriched at pericentric regions. To test function, we mutated residue 224. The phospho-obviation mutant, S224A, appeared normal. However, the phospho-mimic mutant, S224E, is detrimental to mouse embryonic stem cell colonies. While ploidy and chromatin architecture appear unaffected, S224E mutants exhibit differential expression of hundreds of genes, including p53 and p21. We have thus identified a new CTCF PTM and provided evidence of function during cellular growth and gene regulation.
Project description:Signaling pathways that drive gene expression are typically depicted as having a dozen or so landmark phosphorylation and transcriptional events. In reality, thousands of dynamic post-translational modifications (PTMs) orchestrate nearly every cellular function, and we lack technologies to find causal links between these vast biochemical pathways and genetic circuits at scale. Here, we describe “signaling-to-transcription network” mapping through the development of PTM-centric base editing coupled to phenotypic screens, directed by temporally-resolved phosphoproteomics. Using T cell activation as a model, we observe hundreds of unstudied phosphorylation sites that modulate NFAT transcriptional activity. We identify the phosphorylation-mediated nuclear localization of PHLPP1 which promotes NFAT but inhibits NFκB activity. We also find that specific phosphosite mutants can alter gene expression in subtle yet distinct patterns, demonstrating the potential for fine-tuning transcriptional responses. Overall, base editor screening of PTM sites provides a powerful platform to dissect PTM function within signaling pathways.
Project description:Human lymphoid malignancies are often characterized by oncogenic translocations involving the antigen receptor gene loci. CtIP is a DNA end-resection factor that has been widely implicated in alternative end-joining (A-EJ) mediated chromosomal translocations in reporters. The ATM and ATR kinases phosphorylate CtIP at T859 (T855 in mouse) and other sites to promote DNA end-resection. Using two classical non-homologous end-joining (cNHEJ) and Tp53-double deficient mouse models, we identified a role of CtIP T855 phosphorylation in the neonatal development of Xrcc4-/-Tp53-/- mice and the IgH-Myc translocation driven lymphomagenesis in DNA-PKcs-/-Tp53-/- mice. Mechanistically, we found that CtIP T855 phosphorylation is important for the progression of DNA end-resection, while dispensable for hairpin opening and inter-sister DNA break ligation. Moreover, we found that CtIP-T855 phosphorylation supports the proliferation of Myc-driven lymphoma cells by promoting the transition from ATM-mediated to ATR-mediated G2/M cell cycle checkpoint. Correspondingly, the CtIP-T855A mutation delays splenomegaly in l-Myc mice. Collectively, our findings suggest that DNA damage-induced CtIP phosphorylation has a checkpoint function during lymphomagenesis independent of its role in A-EJ-mediated chromosomal translocation
Project description:The key lipid metabolism transcription factor sterol regulatory element-binding protein (SREBP)-1a integrates gene regulatory effects of hormones, cytokines, nutrition and metabolites as lipids, glucose or cholesterol via stimuli specific phosphorylation by different MAPK cascades. We have formerly reported the systemic impact of phosphorylation in transgenic mouse models with liver-specific overexpression of the N-terminal transcriptional active domain of SREBP-1a (alb-SREBP-1a) or a MAPK kinase phosphorylation sites deficient variant (alb-SREBP-1a∆P; (S63A, S117A, T426V)), respectively. Here we investigated the molecular basis of the systemic observation in holistic hepatic gene expression analyses and lipid degrading organelles involved in the pathogenesis of metabolic syndrome, i.e. peroxisomes, by 2D-DIGE and mass spectrometry analyses. Although alb-SREBP-1a mice develop a severe phenotype with visceral adipositas and hepatic lipid accumulation featuring a fatty liver, the hepatic differential gene expression and alterations in peroxisomal protein patterns compared to control mice were surprisingly relative low. In contrast, phosphorylation site deficient alb-SREBP-1a∆P mice, protected from hepatic lipid accumulation phenotype, showed gross alteration in hepatic gene expression and peroxisomal proteome. Further knowledge based analyzes revealed that overexpression of SREBP-1a favored mainly acceleration in lipid metabolism and indicated a regular insulin signaling, whereas disruption of SREBP-1a phosphorylation resulted in massive alteration of cellular processes including signs for loss of lipid metabolic targets. These results could be the link to a disturbed lipid metabolism that overall resembles a state of insulin resistance.