ABSTRACT: 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: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: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-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.
Project description:Modulating signaling pathways including Wnt and Hippo can induce cardiomyocyte proliferation in vivo. Applying these signaling modulators to human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) in vitro can expand CMs only to modest extent (< 5-fold). Here, we demonstrate massive expansion of hiPSC-CMs in vitro (i.e. 100-250-fold) by glycogen synthase kinase-3β (GSK-3β) inhibition using CHIR99021 and concurrent removal of cell-cell contact. We show GSK-3β inhibition suppresses CM maturation while contact removal prevents CMs from cell cycle exit. Remarkably, contact removal enabled 10-to-25-times greater expansion beyond GSK-3β inhibition alone. Mechanistically, cell cycle re-activation required both LEF/TCF activity and AKT phosphorylation, but it was independent from Yes associated protein (YAP) activity. Engineered heart tissues from expanded hiPSC-CMs showed the comparable contractility to those from unexpanded hiPSC-CMs, demonstrating uncompromised cellular functionality after expansion. In sum, we uncovered a molecular interplay that enables massive expansion hiPSC-CMs for large-scale drug screening and tissue engineering.
Project description:We developed a novel somite-based step-wise strategy for the efficient derivation of functional human myocytes, suggesting that past failures were due to incomplete specification. Treatment with two small molecules inhibiting glycogen synthase kinase 3β (GSK-3β) and the Notch signaling pathway in undifferentiated hPSCs results in the formation of somite-like cells by Day 4 and, subsequently contractile myotubes in vitro around Day 25 with the ability to engraft and actively participate in muscle repair in vivo. Antibody-based purification can enrich homogenous myocyte populations exhibiting genuine myogenic molecular and cellular characteristics, including extraocular muscle-like features. Furthermore, hPSCs derived from patients with multiple neuromuscular diseases successfully give rise to patient-specific skeletal muscle cells bearing signature phenotypes.
Project description:Recurrent Glycogen synthase kinase-3 (GSK-3) phosphorylates multiple splicing factors, including SRSF2, 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 and not in cells with wild-type splicing factors. To characterize how GSK-3 inhibition alters the cellular proteome in SRSF2-P95H/+ cells, we have performed quantitative mass spectrometry (qMS) on K562 cells with SRSF2P95H/+ knocked into the endogenous locus (PMID 30799057) and parental K562 cells, treated with the GSK-3 inhibitor CHIR99021. We focused on the mitochondrial proteome using human proteome (UniprotKB) and mitochondrial (MitoCarta 3.0) databases for protein identification, identifying 163 mitochondrial proteins whose levels are affected by SRSF2 mutation.
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: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:To analyze the roles of GSK-3β in podocytes, GSK-3β knockdown lentivirus by Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein (Cas)9 was applied to establish stable cell lines. Phosphoproteome and proteome evaluation was conducted using TMT labeled LC-MS/MS technologies.