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GSK-3 inactivation or depletion promotes ?-cell replication via down regulation of the CDK inhibitor, p27 (Kip1).

ABSTRACT: Diabetes (T1DM and T2DM) is characterized by a deficit in ?-cell mass. A broader understanding of human ?-cell replication mechanism is thus important to increase ?-cell proliferation for future therapeutic interventions. Here, we show that p27 (Kip1), a CDK inhibitor, is expressed abundantly in isolated adult human islets and interacts with various positive cell cycle regulatory proteins including D-type cyclins (D1, D2 and D3) and their kinase partners, CDK4 and CDK6. Also, we see interaction of cyclin E and its kinase partner, CDK2, with p27 suggesting a critical role of p27 as a negative cell cycle regulator in human islets. Our data demonstrate interaction of p27 with GSK-3 in ?-cells and show, employing rodent ?-cells (INS-1), isolated human islets and purified ?-cells derived from human islets, that siRNA-mediated depletion of GSK-3 or p27 or 1-AKP / BIO - mediated GSK-3 inhibition results in increased ?-cell proliferation. We also see reduction of p27 levels following GSK-3 inactivation or depletion. Our data show that serum induction of quiescent INS-1 cells leads to sequential phosphorylation of p27 on its S10 and T187 residues with faster kinetics for S10 corresponding with the decreased levels of p27. Altogether our findings indicate that p27 levels in ?-cells are stabilized by GSK-3 and thus p27 down regulation following GSK-3 depletion / inactivation plays a critical role in promoting ?-cell replication.

SUBMITTER: Stein J

PROVIDER: S-EPMC3060436 | biostudies-literature | 2011 Jan-Feb

REPOSITORIES: biostudies-literature

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GSK-3 inactivation or depletion promotes β-cell replication via down regulation of the CDK inhibitor, p27 (Kip1).

Stein Jeffrey J Milewski Wieslawa M WM Hara Manami M Steiner Donald F DF Dey Arunangsu A

Islets 20110101 1

Diabetes (T1DM and T2DM) is characterized by a deficit in β-cell mass. A broader understanding of human β-cell replication mechanism is thus important to increase β-cell proliferation for future therapeutic interventions. Here, we show that p27 (Kip1), a CDK inhibitor, is expressed abundantly in isolated adult human islets and interacts with various positive cell cycle regulatory proteins including D-type cyclins (D1, D2 and D3) and their kinase partners, CDK4 and CDK6. Also, we see interaction ...[more]

PMID: 21278490

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Project description:BackgroundPoly C Binding Protein 1 (PCBP1) is an RNA-binding protein that binds and regulates translational activity of subsets of cellular mRNAs. Depletion of PCBP1 is implicated in various carcinomas, but the underlying mechanism in tumorigenesis remains elusive.MethodsWe performed a transcriptome-wide screen to identify novel bounding mRNA of PCBP1. The bind regions between PCBP1 with target mRNA were investigated by using point mutation and luciferase assay. Cell proliferation, cell cycle, tumorigenesis and cell apoptosis were also evaluated in ovary and colon cancer cell lines. The mechanism that PCBP1 affects p27 was analyzed by mRNA stability and ribosome profiling assays. We analyzed PCBP1 and p27 expression in ovary, colon and renal tumor samples and adjacent non-tumor tissues using RT-PCR, Western Blotting and immunohistochemistry. The prognostic significance of PCBP1 and p27 also analyzed using online databases.ResultsWe identified cell cycle inhibitor p27Kip1 (p27) as a novel PCBP1-bound transcript. We then demonstrated that binding of PCBP1 to p27 3'UTR via its KH1 domain mainly stabilizes p27 mRNA, while enhances its translation to fuel p27 expression, prior to p27 protein degradation. The upregulated p27 consequently inhibits cell proliferation, cell cycle progression and tumorigenesis, whereas promotes cell apoptosis under paclitaxel treatment. Conversely, knockdown of PCBP1 in turn compromises p27 mRNA stability, leading to lower p27 level and tumorigenesis in vivo. Moreover, forced depletion of p27 counteracts the tumor suppressive ability of PCBP1 in the same PCBP1 over-expressing cells. Physiologically, we showed that decreases of both p27 mRNA and its protein expressions are well correlated to PCBP1 depletion in ovary, colon and renal tumor samples, independent of the p27 ubiquitin ligase Skp2 level. Correlation of PCBP1 with p27 is also found in the tamoxifen, doxorubincin and lapatinib resistant breast cancer cells of GEO database.ConclusionOur results thereby indicate that loss of PCBP1 expression firstly attenuates p27 expression at post-transcriptional level, and subsequently promotes carcinogenesis. PCBP1 could be used as a diagnostic marker to cancer patients.

Dataset Information

GSK-3 inactivation or depletion promotes ?-cell replication via down regulation of the CDK inhibitor, p27 (Kip1).

Publications

GSK-3 inactivation or depletion promotes β-cell replication via down regulation of the CDK inhibitor, p27 (Kip1).

Similar Datasets

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