Project description:Glycogen Synthase Kinase-3 (GSK-3) is a constitutively active, ubiquitously expressed protein kinase that regulates multiple signaling pathways. Over 100 putative GSK-3 substrates have been reported in diverse cell types based on in vitro kinase assays or genetic and pharmacological manipulation of GSK-3. Many more have been predicted based on a recurrent GSK-3 consensus motif, but this prediction has not been tested by analyzing the GSK-3 phosphoproteome. We used stable isotope labeling of amino acids in culture (SILAC) and mass spectrometry to analyze the repertoire of GSK-3 dependent substrates in mouse embryonic stem cells (ESCs). A comparison of wild-type and Gsk3a;Gsk3b knockout (DKO) ESCs revealed prominent GSK-3-dependent phosphorylation of multiple splicing factors and regulators of RNA biosynthesis, as well as proteins that regulate transcription, translation, and cell division. We demonstrate direct, GSK-3-dependent phosphorylation of the splicing factors RBM8A and PSF as well as the nucleolar protein NPM1. RNA sequencing to compare the transcriptomes of wild-type and Gsk3 DKO ESCs identified more than 210 genes that are alternatively spliced in a GSK-3-dependent manner, supporting a broad role for GSK-3 in regulating alternative splicing. Overall, this study provides the first unbiased analysis of the GSK-3 phosphoproteome and strong evidence for GSK-3 as a regulator of alternative splicing.
Project description:Recurrent mutations in the splicing factors SRSF2 and SF3B1 are common in myelodysplasia (MDS) and acute myeloid leukemia (AML). These mutations are invariably heterozygous, as cells with splicing factor mutations nevertheless depend on wild-type splicing activity. Disrupting splicing further is lethal, suggesting a therapeutic vulnerability for splicing factor mutant hematopoietic neoplasms. Glycogen synthase kinase-3 (GSK-3) phosphorylates multiple splicing factors, including SRSF2 and SF3B1, and regulates the splicing of a broad range of mRNAs in human cells. Inhibition of GSK-3 disrupts splicing and promotes cell death in hematopoietic cells with heterozygous mutations in SRSF2 or SF3B1 and not in cells with wild-type splicing factors. To characterize how GSK-3 inhibition alters splicing and leads to cell death in SRSF2P95H/+ and SF3B1K700E/+ cells, we have performed deep RNA sequencing on K562 cells with SRSF2P95H/+ or SF3B1K700E/+ knocked into the endogenous locus (provided by Omar Abdel-Wahab (Wang et al; PMID 30799057) and treated with the GSK-3 inhibitor CHIR99021. Parental cells with wild-type splicing factors were included as controls. RNA-Seq data were further analyzed through the rMATS pipeline to assess changes in mRNA splicing (Liu et al, 2023).
Project description:APC is a classical tumor suppressor in humans, and truncating mutations are early somatic events in most cases of sporadic colon cancer. APC directly enhances the activity of glycogen synthase kinase 3 (GSK-3) and therefore loss of full length APC reduces GSK-3 activity, leading to stabilization of b-catenin protein and activation of downstream Wnt/b-catenin signaling. GSK-3 also phosphorylates multiple core mRNA splicing factors and loss of Gsk3a/b in mouse ES cells and human lymphocytes alters mRNA splicing at a genome wide level. We therefore predict that loss of APC should similarly alter splicing by reducing GSK-3 activity. Here we use RNA-seq to assess differential gene expression and altered splicing in apc-mcr mutant zebrafish embryos at 48hpf. We find robust activation of known Wnt/b-catenin target genes, as expected. Surprisingly, we also find markedly increased expression of multiple genes related to inflammation and cytokine signaling. We also identify 340 mRNA splicing variations in apc mutant zebrafish. Many of these local splice variants (LSVs) occur in mRNAs the regulate cell adhesion, migration, and morphogenesis.
Project description:Nuclear myosin 1c (NM1) mediates RNA polymerase I (pol I) transcription activation and cell cycle progression by facilitating PCAF-mediated H3K9 acetylation, but the molecular mechanism by which NM1 is regulated remains unclear. Here, we report that at early G1 the glycogen synthase kinase (GSK) 3β phosphorylates and stabilizes NM1, allowing for NM1 association with the chromatin. Genomic analysis by ChIP-Seq showed that this mechanism occurs on the rDNA as active GSK3β selectively occupies the gene. ChIP assays and transmission electron microscopy in GSK3β-/- mouse embryonic fibroblasts indicated that at G1 rRNA synthesis is suppressed due to decreased H3K9 acetylation leading to a chromatin state incompatible with transcription. We found that GSK3β directly phosphorylates the endogenous NM1 on a single serine residue (Ser-1020) located within the NM1 C-terminus. In G1 this phosphorylation event stabilizes NM1 and prevents NM1 polyubiquitination by the E3 ligase UBR5 and proteasome-mediated degradation. We conclude that GSK3β-mediated phosphorylation of NM1 is required for pol I transcription activation. Examination of GSK3beta with the genome in mouse embryonic fibroblasts
Project description:Gene expression data from AML cell lines, MOLM-14, U937, THP-1 and HL-60, that were infected with a scrambled control hairpin (shControl), two shRNAs directed against GSK-3B (shGSK3B_1 and shGSK3B_2), or two shRNAs directed against GSK-3A (shGSK3A_5 and shGSK3A_6). Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults. Long-term survival of patients with AML has changed little over the past decade, necessitating the identification and validation of new AML targets. Integration of genomic approaches with small-molecule and genetic-based high-throughput screening holds the promise of improved discovery of candidate targets for cancer therapy. Here, we identified a role for glycogen synthase kinase 3A (GSK-3A) in AML by performing two independent small-molecule library screens and an shRNA screen for perturbations that induced a differentiation expression signature in AML cells. GSK-3 is a serine-threonine kinase involved in diverse cellular processes including differentiation, signal transduction, cell cycle regulation, and proliferation. We demonstrated that specific loss of GSK-3A induced differentiation in AML by multiple measurements, including induction of gene expression signatures, morphological changes, and cell surface markers consistent with myeloid maturation. GSK-3AM-bM-^@M-^Sspecific suppression also led to impaired growth and proliferation in vitro, induction of apoptosis, loss of colony formation in methylcellulose, and anti-AML activity in vivo. Although the role of GSK-3B has been well studied in cancer development, these studies support a role for GSK-3A in AML. The AML cell lines, MOLM-14, U937, THP-1 and HL-60, were infected with a scrambled control hairpin (shControl), two shRNAs directed against GSK-3B (shGSK3B_1 and shGSK3B_2), and two shRNAs directed against GSK-3A (shGSK3A_5 and shGSK3A_6).
Project description:Glycogen synthase kinase-3β (GSK-3β) has been recently identified as an important regulator of stem cell function. In vitro studies show that GSK-3β inhibition delays proliferation of human haematopoietic progenitor cells while increasing numbers of late dividing multipotent progenitors. Gene expression analysis revealed that GSK-3β inhibition modulates the expression of a subset of genes that are transcriptional targets for cytokines. GSK-3β inhibition antagonised down-regulation of genes encoding cyclin dependent kinase inhibitor p57 and a member of the growth arrest and DNA damage 45 family, GADD45B as well as up-regulation of cyclin D1 by cytokines, providing a possible mechanism for the BIO-induced delay in cell cycle progression. Surprisingly, inhibition of GSK-3β earlier shown to prevent β-catenin degradation and promote the nuclear accumulation of β-catenin was not sufficient to activate its transcriptional targets in haematopoietic stem cells. GSK-3β inhibition up-regulated the expression of a several positive regulators of stem cell function suppressed during cytokine-induced proliferation. The data supports a clinical role for GSK-3β inhibition to improve engraftment efficiency of ex vivo expanded stem cells. Total RNA was isolated from three groups following expansion of CD34+ cells in cytokikes and then treatment with BIO, as described below.
Project description:Nuclear myosin 1c (NM1) mediates RNA polymerase I (pol I) transcription activation and cell cycle progression by facilitating PCAF-mediated H3K9 acetylation, but the molecular mechanism by which NM1 is regulated remains unclear. Here, we report that at early G1 the glycogen synthase kinase (GSK) 3β phosphorylates and stabilizes NM1, allowing for NM1 association with the chromatin. Genomic analysis by ChIP-Seq showed that this mechanism occurs on the rDNA as active GSK3β selectively occupies the gene. ChIP assays and transmission electron microscopy in GSK3β-/- mouse embryonic fibroblasts indicated that at G1 rRNA synthesis is suppressed due to decreased H3K9 acetylation leading to a chromatin state incompatible with transcription. We found that GSK3β directly phosphorylates the endogenous NM1 on a single serine residue (Ser-1020) located within the NM1 C-terminus. In G1 this phosphorylation event stabilizes NM1 and prevents NM1 polyubiquitination by the E3 ligase UBR5 and proteasome-mediated degradation. We conclude that GSK3β-mediated phosphorylation of NM1 is required for pol I transcription activation.
Project description:Glycogen synthase kinase (GSK) 3β phosphorylates and protects nuclear myosin 1c from proteasome-mediated degradation to activate rDNA transcription in early G1 cells
Project description:Neural progenitor cells (NPCs) can be induced from somatic cells by defined factors. Here we report that NPCs can be generated from mouse embryonic fibroblasts by a chemical cocktail, namely VCR (V, VPA, an inhibitor of HDACs; C, CHIR99021, an inhibitor of GSK-3 kinases and R, Repsox, an inhibitor of TGF-β pathways), under a physiological hypoxic condition. These chemical-induced NPCs (ciNPCs) resemble mouse brain-derived NPCs regarding their proliferative and self-renewing abilities, gene expression profiles, and multipotency for different neuroectodermal lineages in vitro and in vivo. Further experiments reveal that alternative cocktails with inhibitors of histone deacetylation, glycogen synthase kinase, and TGF-β pathways show similar efficacies for ciNPC induction. Moreover, ciNPCs can also be induced from mouse tail-tip fibroblasts and human urinary cells with the same chemical cocktail VCR. Thus our study demonstrates that lineage-specific conversion of somatic cells to NPCs could be achieved by chemical cocktails without introducing exogenous factors. To access the exact identity of ciNPCs, we extracted mRNA from mouse brain-derived NPCs (as control NPCs), MEFs, ciNPCs at passage 5 and passage 13 and compared the global gene expression patterns of these cells by microarray analysis.