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A cyclin-dependent kinase inhibitor (p21(WAF1/CIP1)) affects thymidine incorporation in human liver cancer cells.

ABSTRACT: p21(WAF1/CIP1) is a universal cyclin-dependent kinase inhibitor. To investigate the role of p21(WAF1/CIP1) in proliferation of human liver cancer cells, we examined the expression of p53, p21(WAF1/CIP1), cdk2 and cdk4 expression in two human liver cancer cell lines (HepG2 and PLC/PRF/5 cells). The effects of p21(WAF1/CIP1) on [(3)H]thymidine incorporation and cdks were also examined in these cells. HepG2 cells expressed all these proteins with lower level of cdk4. PLC/PRF/5 cells expressed the other proteins except p21(WAF1/CIP1). Transfection of p21(WAF1/CIP1) gene inhibited [(3)H]thymidine incorporation of both cells with different extent. Although the transfection of p21(WAF1/CIP1) did not affect cdk2 and cdk4 expression, it did reduce cdk2 kinase activity by 20%. These results suggest that: (a) p21(WAF1/CIP1) involved in DNA synthesis of human liver cancer cells; (b) p21(WAF1/CIP1) could be a target gene for the treatment of human hepatocellular carcinoma.

SUBMITTER: Gong Y

PROVIDER: S-EPMC2375268 | biostudies-other | 2002 Feb

REPOSITORIES: biostudies-other

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Visualizing the dynamics of p21(Waf1/Cip1) cyclin-dependent kinase inhibitor expression in living animals.

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| S-EPMC1975854 | biostudies-literature

The cyclin dependent kinase inhibitor p21<sup>Cip1/Waf1</sup> is a therapeutic target in high-risk neuroblastoma.

Project description:Platinum-based chemotherapies such as cisplatin are used as first-line treatment for the paediatric tumour neuroblastoma. Although the majority of neuroblastoma tumours respond to therapy, there is a high fraction of high-risk neuroblastoma patients that eventually relapse with increased resistance. Here, we show that one key determinant of cisplatin sensitivity is phosphorylation of the cyclin-dependent kinase inhibitor p21Cip1/Waf1. A panel of eight neuroblastoma cell lines and a TH-MYCN mouse model were investigated for the expression of p21Cip1/Waf1 using RT-qPCR, Western blot, and immunofluorescence. This was followed by investigation of sensitivity towards cisplatin and the p21Cip1/Waf1 inhibitor UC2288. Whereas the cell lines and the mouse model showed low levels of un-phosphorylated p21Cip1/Waf1, the phosphorylated p21Cip1/Waf1 (Thr145) was highly expressed, which in the cell lines correlated to cisplatin resistance. Furthermore, the neuroblastoma cell lines showed high sensitivity to UC2288, and combination treatment with cisplatin resulted in considerably decreased cell viability and delay in regrowth in the two most resistant cell lines, SK-N-DZ and BE(2)-C. Thus, targeting p21Cip1/Waf1 can offer new treatment strategies and subsequently lead to the design of more efficient combination treatments for high-risk neuroblastoma.

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Phosphatidylinositol 3-Akt-kinase-dependent phosphorylation of p21(Waf1/Cip1) as a novel mechanism of neuroprotection by glucocorticoids.

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Stabilization of p21 (Cip1/WAF1) following Tip60-dependent acetylation is required for p21-mediated DNA damage response.

Project description:The molecular mechanisms controlling post-translational modifications of p21 have been pursued assiduously in recent years. Here, utilizing mass-spectrometry analysis and site-specific acetyl-p21 antibody, two lysine residues of p21, located at amino-acid sites 161 and 163, were identified as Tip60-mediated acetylation targets for the first time. Detection of adriamycin-induced p21 acetylation, which disappeared after Tip60 depletion with concomitant destabilization of p21 and disruption of G1 arrest, suggested that Tip60-mediated p21 acetylation is necessary for DNA damage-induced cell-cycle regulation. The ability of 2KQ, a mimetic of acetylated p21, to induce cell-cycle arrest and senescence was significantly enhanced in p21 null MEFs compared with those of cells expressing wild-type p21. Together, these observations demonstrate that Tip60-mediated p21 acetylation is a novel and essential regulatory process required for p21-dependent DNA damage-induced cell-cycle arrest.

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Loss of Notch1-dependent p21(Waf1/Cip1) expression influences the Notch1 outcome in tumorigenesis.

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TFEB Modulates p21/WAF1/CIP1 during the DNA Damage Response.

Project description:The MiT/TFE family of transcription factors (MITF, TFE3, and TFEB), which control transcriptional programs for autophagy and lysosome biogenesis have emerged as regulators of energy metabolism in cancer. Thus, their activation increases lysosomal catabolic function to sustain cancer cell growth and survival in stress conditions. Here, we found that TFEB depletion dramatically reduces basal expression levels of the cyclin-dependent kinase (CDK) inhibitor p21/WAF1 in various cell types. Conversely, TFEB overexpression increases p21 in a p53-dependent manner. Furthermore, induction of DNA damage using doxorubicin induces TFEB-mediated activation of p21, delays G2/M phase arrest, and promotes cell survival. Pharmacological inhibition of p21, instead, abrogates TFEB-mediated protection during the DNA damage response. Together, our findings uncover a novel and direct role of TFEB in the regulation of p21 expression in both steady-state conditions and during the induction of DNA-damage response (DDR). Our observations might open novel therapeutic strategies to promote cancer cell death by targeting the TFEB-p21 pathway in the presence of genotoxic agents.

| S-EPMC7290768 | biostudies-literature

Mist1 regulates pancreatic acinar cell proliferation through p21 CIP1/WAF1.

Project description:Background & aimsMist1 is a basic helix-loop-helix (bHLH) transcription factor that is important to the proper development of the exocrine pancreas. The aim of this study was to investigate the role of Mist1 in modulating acinar cell proliferation.MethodsDuctal and acinar pancreatic cell lines were engineered to express an inducible Mist1 complementary DNA or to express a short hairpin RNA that targeted endogenous Mist1. Alterations in RNA and protein levels were detected by real-time reverse-transcription polymerase chain reaction and immunoblots. Chromatin immunoprecipitation and reporter gene assays were performed to map Mist1-responsive elements on target genes; the overall proliferation index of acinar cells from Mist1 null pancreata was evaluated by immunohistochemistry.ResultsExpression of Mist1 resulted in a significant decrease in the proliferative potential of cells that was associated with induced expression of p21(CIP1/WAF1). Short hairpin RNA-directed knockdown of p21(CIP1/WAF1) generated cells that were refractory to Mist1 expression, whereas knockdown of Mist1 transcripts or deletion of Mist1 from the mouse genome led to increased cell proliferation and a concomitant decrease in p21(CIP1/WAF1) protein levels. Surprisingly, Mist1-dependent activation of the p21(CIP1/WAF1) promoter was independent of classic basic helix-loop-helix protein binding sites. Instead, Sp1 binding sites were essential for Mist1-dependent transcription, suggesting that Mist1 activates p21(CIP1/WAF1) expression through a unique Sp1 pathway. Indeed, coimmunoprecipitation studies demonstrated that Mist1 and Sp1 were found within the same transcription complex.ConclusionsOur results show that Mist1 has a dual role in the development of the exocrine pancreas: controlling cell proliferation and promoting terminal differentiation.

| S-EPMC2853247 | biostudies-literature

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