GSK-3? Is a Novel Target of CREB and CREB-GSK-3? Signaling Participates in Cell Viability in Lung Cancer.
ABSTRACT: Overexpression or activation of cyclic AMP-response element-binding protein (CREB) has been known to be involved in several human malignancies, including lung cancer. Genes regulated by CREB have been reported to suppress apoptosis, induce cell proliferation, inflammation, and tumor metastasis. However, the critical target genes of CREB in lung cancer have not been well understood. Here, we identified GSK-3? as one of the CREB target genes which is critical for the viability of lung cancer cells. The CREB knockdown significantly reduced the expression of GSK-3? and the direct binding of CREB on the promoter of GSK3A was identified. Kaplan-Meier analysis with a public database showed a prognostic significance of aberrant GSK-3? expression in lung cancer. Inhibition of GSK-3? suppressed cell viability, colony formation, and tumor growth. For the first time, we demonstrated that GSK-3? is regulated by CREB in lung cancer and is required for the cell viability. These findings implicate CREB-GSK-3? axis as a novel therapeutic target for lung cancer treatment.
Project description:Here we examine the roles of two isoforms of glycogen synthase kinase-3 (GSK-3), GSK-3? and GSK-3?, in skeletal development. Both isoforms were unphosphorylated and active in chondrocyte differentiation stages during SOX9 and type II collagen (COL2A1) expression. Although knock-out of both alleles of Gsk3a (Gsk3a(-/-)) or a single allele of Gsk3b (Gsk3b(+/-)) in mice did not significantly affect skeletal development, compound knock-out (Gsk3a(-/-);Gsk3b(+/-)) caused dwarfism with impairment of chondrocyte differentiation. GSK-3? and GSK-3? induced differentiation of cultured chondrocytes with functional redundancy in a cell-autonomous fashion, independently of the Wnt/?-catenin signal. Computational predictions followed by SOX9 and COL2A1 transcriptional assays identified RelA (NF-?B p65) as a key phosphorylation target of GSK-3. Among several phosphorylation residues in RelA, Thr-254 was identified as the critical phosphorylation site for GSK-3 that modulated chondrocyte differentiation. In conclusion, redundant functions of GSK-3? and GSK-3? through phosphorylation of RelA at Thr-254 play a crucial role in early stages of chondrocyte differentiation.
Project description:Glycogen synthase kinase-3 (GSK-3) dysregulation has been implicated in nigral dopaminergic neurodegeneration, one of the main pathological features of Parkinson's disease (PD). The two isoforms, GSK-3? and GSK-3?, have both been suggested to play a detrimental role in neuronal death. To date, several studies have focused on the role of GSK-3? on PD pathogenesis, while the role of GSK-3? has been largely overlooked. Here, we report in situ observations that both GSK-3? and GSK-3? are dephosphorylated at a negatively acting regulatory serine, indicating kinase activation, selectively in nigral dopaminergic neurons following exposure of mice to 1-methyl-4-pheny-1,2,3,6-tetrahydropyridine (MPTP). To identify whether GSK-3? and GSK-3? display functional redundancy in regulating parkinsonian dopaminergic cell death, we analysed dopaminergic neuron-specific Gsk3a null (Gsk3a ?Dat ) and Gsk3b null (Gsk3b ?Dat ) mice, respectively. We found that Gsk3b ?Dat , but not Gsk3a ?Dat , showed significant resistance to MPTP insult, revealing non-redundancy of GSK-3? and GSK-3? in PD pathogenesis. In addition, we tested the neuroprotective effect of tideglusib, the most clinically advanced inhibitor of GSK-3, in the MPTP model of PD. Administration of higher doses (200 mg/kg and 500 mg/kg) of tideglusib exhibited significant neuroprotection, whereas 50 mg/kg tideglusib failed to prevent dopaminergic neurodegeneration from MPTP toxicity. Administration of 200 mg/kg tideglusib improved motor symptoms of MPTP-treated mice. Together, these data demonstrate GSK-3? and not GSK-3? is critical for parkinsonian neurodegeneration. Our data support the view that GSK-3? acts as a potential therapeutic target in PD and tideglusib would be a candidate drug for PD neuroprotective therapy.
Project description:Cerebellar development requires regulated proliferation of cerebellar granule neuron progenitors (CGNPs). Inadequate CGNP proliferation causes cerebellar hypoplasia whereas excessive CGNP proliferation can cause medulloblastoma, the most common malignant pediatric brain tumor. Although sonic hedgehog (SHH) signaling is known to activate CGNP proliferation, the mechanisms downregulating proliferation are less defined. We investigated CGNP regulation by GSK-3, which downregulates proliferation in the forebrain, gut and breast by suppressing mitogenic WNT signaling in mouse. In striking contrast to these systems, we found that co-deleting Gsk3a and Gsk3b blocked CGNP proliferation, causing severe cerebellar hypoplasia. The GSK-3 inhibitor CHIR-98014 similarly downregulated SHH-driven proliferation. Transcriptomic analysis showed activated WNT signaling and upregulated Cdkn1a in Gsk3a/b -deleted CGNPs. Ctnnb co-deletion increased CGNP proliferation and rescued cerebellar hypoproliferation in Gsk3a/b mutants, demonstrating physiological control of CGNPs by GSK-3, mediated through WNT. SHH-driven medulloblastomas similarly required GSK-3, as co-deleting Gsk3a/b blocked tumor growth in medulloblastoma-prone SmoM2 mice. These data show that a GSK-3/WNT axis modulates the developmental proliferation of CGNPs and the pathological growth of SHH-driven medulloblastoma. The requirement for GSK-3 in SHH-driven proliferation suggests that GSK-3 may be targeted for SHH-driven medulloblastoma therapy.
Project description:BACKGROUND: Chronic lung diseases such as asthma, COPD and pulmonary fibrosis are characterized by abnormal extracellular matrix (ECM) turnover. TGF-? is a key mediator stimulating ECM production by recruiting and activating lung fibroblasts and initiating their differentiation process into more active myofibroblasts. Glycogen synthase kinase-3 (GSK-3) regulates various intracellular signalling pathways; its role in TGF-??-induced myofibroblast differentiation is currently largely unknown. PURPOSE: To determine the contribution of GSK-3 signalling in TGF-??-induced myofibroblast differentiation. EXPERIMENTAL APPROACH: We used MRC5 human lung fibroblasts and primary pulmonary fibroblasts of individuals with and without COPD. Protein and mRNA expression were determined by immunoblotting and RT-PCR analysis respectively. RESULTS: Stimulation of MRC5 and primary human lung fibroblasts with TGF-?? resulted in time- and dose-dependent increases of ?-sm-actin and fibronectin expression, indicative of myofibroblast differentiation. Pharmacological inhibition of GSK-3 by SB216763 dose-dependently attenuated TGF-??-induced expression of these myofibroblasts markers. Moreover, silencing of GSK-3 by siRNA or pharmacological inhibition by CT/CHIR99021 fully inhibited the TGF-??-induced expression of ?-sm-actin and fibronectin. The effect of GSK-3 inhibition on ?-sm-actin expression was similar in fibroblasts from individuals with and without COPD. Neither smad, NF-?B nor ERK1/2 were involved in the inhibitory actions of GSK-3 inhibition by SB126763 on myofibroblast differentiation. Rather, SB216763 increased the phosphorylation of CREB, which in its phosphorylated form acts as a functional antagonist of TGF-?/smad signalling. CONCLUSION AND IMPLICATION: We demonstrate that GSK-3 signalling regulates TGF-??-induced myofibroblast differentiation by regulating CREB phosphorylation. GSK-3 may constitute a useful target for treatment of chronic lung diseases.
Project description:Acute leukemias induced by MLL chimeric oncoproteins are among the subset of cancers distinguished by a paradoxical dependence on GSK-3 kinase activity for sustained proliferation. We demonstrate here that GSK-3 maintains the MLL leukemia stem cell transcriptional program by promoting the conditional association of CREB and its coactivators TORC and CBP with homedomain protein MEIS1, a critical component of the MLL-subordinate program, which in turn facilitates HOX-mediated transcription and transformation. This mechanism also applies to hematopoietic cells transformed by other HOX genes, including CDX2, which is highly expressed in a majority of acute myeloid leukemias, thus providing a molecular approach based on GSK-3 inhibitory strategies to target HOX-associated transcription in a broad spectrum of leukemias.
Project description:Aging is regulated by conserved signaling pathways. The glycogen synthase kinase-3 (GSK-3) family of serine/threonine kinases regulates several of these pathways, but the role of GSK-3 in aging is unknown. Herein, we demonstrate premature death and acceleration of age-related pathologies in the Gsk3a global KO mouse. KO mice developed cardiac hypertrophy and contractile dysfunction as well as sarcomere disruption and striking sarcopenia in cardiac and skeletal muscle, a classical finding in aging. We also observed severe vacuolar degeneration of myofibers and large tubular aggregates in skeletal muscle, consistent with impaired clearance of insoluble cellular debris. Other organ systems, including gut, liver, and the skeletal system, also demonstrated age-related pathologies. Mechanistically, we found marked activation of mTORC1 and associated suppression of autophagy markers in KO mice. Loss of GSK-3?, either by pharmacologic inhibition or Gsk3a gene deletion, suppressed autophagy in fibroblasts. mTOR inhibition rescued this effect and reversed the established pathologies in the striated muscle of the KO mouse. Thus, GSK-3? is a critical regulator of mTORC1, autophagy, and aging. In its absence, aging/senescence is accelerated in multiple tissues. Strategies to maintain GSK-3? activity and/or inhibit mTOR in the elderly could retard the appearance of age-related pathologies.
Project description:CREB-H, an ER-anchored transcription factor, plays a key role in regulating secretion in metabolic pathways, particularly triglyceride homeostasis. It controls the production both of secretory pathway components and cargoes, including apolipoproteins ApoA-IV and ApoC-II, contributing to VLDL/HDL distribution and lipolysis. The key mechanism controlling CREB-H activity involves its ER retention and forward transport to the Golgi, where it is cleaved by Golgi-resident proteases, releasing the N-terminal product, which traffics to the nucleus to effect transcriptional responses. Here we show that a serine-rich motif termed the P-motif, located in the N-terminus between serines 73 and 90, controls release of the precursor transmembrane form from the ER and its forward transport to the Golgi. This motif is subject to GSK-3 phosphorylation, promoting ER retention, while mutation of target serines and drug inhibition of GSK-3 activity coordinately induce both forward transport of the precursor and cleavage, resulting in nuclear import. We previously showed that for the nuclear product, the P-motif is subject to multiple phosphorylations, which regulate stability by targeting the protein to the SCFFbw1a E3 ubiquitin ligase. Thus phosphorylation at the P-motif provides integrated control of CREB-H function, coupling intercompartmental transport in the cytoplasm with stabilization of the active form in the nucleus.
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. Overall design: 2 biological replicates of Gsk3a+/+;Gsk3b+/+ (Wild Type) and Gsk3a-/-;Gsk3b-/- (DKO) E15 mouse embryonic stem cells were analyzed by RNA-Seq
Project description:The protein kinase GSK-3 is constitutively active in quiescent cells in the absence of growth factor signaling. Previously, we identified a set of genes that required GSK-3 to maintain their repression during quiescence. Computational analysis of the upstream sequences of these genes predicted transcription factor binding sites for CREB, NF?B and AP-1. In our previous work, contributions of CREB and NF?B were examined. In the current study, the AP-1 component of the signaling network in quiescent cells was explored.Using chromatin immunoprecipitation analysis, two AP-1 family members, c-Jun and JunD, bound to predicted upstream regulatory sequences in 8 of the 12 GSK-3-regulated genes. c-Jun was phosphorylated on threonine 239 by GSK-3 in quiescent cells, consistent with previous studies demonstrating inhibition of c-Jun by GSK-3. Inhibition of GSK-3 attenuated this phosphorylation, resulting in the stabilization of c-Jun. The association of c-Jun with its target sequences was increased by growth factor stimulation as well as by direct GSK-3 inhibition. The physiological role for c-Jun was also confirmed by siRNA inhibition of gene induction.These results indicate that inhibition of c-Jun by GSK-3 contributes to the repression of growth factor-inducible genes in quiescent cells. Together, AP-1, CREB and NF?B form an integrated transcriptional network that is largely responsible for maintaining repression of target genes downstream of GSK-3 signaling.
Project description:Recently we demonstrated that IGF-1 expression is increased in the diabetic kidney and that it may involve in renal hypertrophy and extracellular matrix protein (ECM) accumulation in mesangial cells as seen in diabetic glomerulopathy. The present study investigates the molecular mechanism(s) of IGF-1 and Akt/glycogen synthase kinase-3beta (GSK-3beta) signaling pathway in the regulation of fibronectin and cyclin D1 expression and survival of renal mesangial cells. A proteomic approach is also employed to identify protein targets of IGF-1 signaling via GSK-3beta inhibition in mesangial cells. We show that IGF-1 (100 ng/ml) significantly increases the protein kinase Akt/PKB activity (1.5-2-fold, p<0.05) within 1-5 minutes, which is completely blocked by the presence of 100 nM Wortmannin (phosphatidyl-inositol 3-kinase inhibitor). Akt activation is coupled with Ser9 phosphorylation and inactivation of its down-stream target GSK-3beta. IGF-1 increases the cyclic AMP-responsive element (CRE) binding transcription factor CREB phosphorylation at Ser 133 and CRE-binding activity in mesangial cells, which parallels cyclin D1 and fibronectin expressions. Both proteins are known to have CRE-sequences in their promoter regions upstream of the transcription start site. Suppression of GSK-3beta by SB216763 (100 nM) increases CREB phosphorylation, cyclin D1 and fibronectin levels. Two dimensional gel electrophoresis followed by MALDI-TOF mass spectrometric analysis of mesangial proteins reveals that IGF-1 treatment or an inhibition of GSK-3beta increases the expression of the phosphorylated Ser/Thr binding signal adapter protein 14-3-3zeta. Immuno-precipitation of 14-3-3zeta followed by Western blotting validates the association of phosphorylated GSK-3beta with 14-3-3zeta in renal mesangial cells. Stable expression of a constitutively active GSK-3beta(Ser9Ala) induces cell death while overexpression of HA-tagged 14-3-3zeta increases cell viability as measured by MTT assays. These results indicate that the Akt/GSK-3beta pathway and the adapter protein 14-3-3zeta may play an important role in IGF-1 signaling and survival of mesangial cells in diabetic nephropathy.