title: Regulation of p21WAF1/CIP1 expression by p53-independent pathways.
abstract: The CDK-inhibitor p21WAF1/CIP1 has been implicated as a growth arrest mediator in p53-tumour suppression, cellular senescence and terminal differentiation. Cell type specific differences in p53-independent p21 expression and cell cycle arrest were found following treatment of human tumour cell lines with serum, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), or okadaic acid (OA). TPA induced p21 in ML1, K562 and HL60 leukemia cells, whereas OA induced p21 in SW480 and GM4723 carcinoma cells as well as in leukemic cells. In addition, TPA- and serum- but not OA-induced cell cycle arrest was reversed upon return of p21 to basal levels. To further investigate the mechanisms underlying p53-independent regulation of p21, the transcription inhibitor, Actinomycin D (AMD), was used to block p21 expression. The results showed a complete inhibition of p21 mRNA and protein induction by TPA or adriamycin but little effect on p21 mRNA induced by OA in the presence of AMD. These results suggested that TPA-induced p21 expression requires transcription initiation, while a post-transcriptional mechanism may be involved in OA-induction as well. Transient transfection assays with p21 promoter-luciferase reporters and TPA or OA treatment further confirmed that TPA, and to a lesser extent, OA, initiated transcription of p21. Finally, the protein kinase C inhibitor, staurosporine, was found to interfere with p21 induction and prevent cell cycle arrest following treatment with TPA but not OA, suggesting a requirement for PKC in TPA activation of p21 expression.
authors.affiliation: Howard Hughes Medical Institute, Department of Medicine, Genetics, and Cancer Center, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Y X
authors.initials: YX
authors.lastname: Zeng
authors.forename: W S
authors.initials: WS
authors.lastname: el-Deiry
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D001769:Blood; D002453:Cell Cycle / Q000235:genetics; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics*; D004988:Ethers, Cyclic / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D016158:Genes, p53; D006801:Humans; D019319:Okadaic Acid; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D000470:Alkaloids; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004988:Ethers, Cyclic; D019319:Okadaic Acid; D011493:Protein Kinase C; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate