title: Dexamethasone-mediated protection from drug cytotoxicity: association with p21WAF1/CIP1 protein accumulation?
abstract: Dexamethasone (DEX)-mediated inhibition of drug-induced, but not CD95 ligand-induced, apoptosis in malignant glioma cells correlates with wild-type p53 status. Here, we examined mechanisms underlying DEX-mediated protection from apoptosis. DEX did not induce p53 expression in two p53 wild-type cell lines (U87MG, LN-229) and did not alter drug-induced p53 accumulation. Forced expression of temperature-sensitive p53val135 in mutant conformation failed to prevent accumulation of endogenous wild-type p53 but acted in a transdominant negative manner to inhibit p53-mediated, camptothecin-induced p21WAF1/CIP1 expression. p53val135-transfected cells retained responsiveness to DEX at restrictive temperature, suggesting that p53 activity is not required for cytoprotection. Forced expression of wild-type p53val135 abrogated the protective effect of DEX, suggesting redundant cytoprotective effects of DEX and p53. Indeed, DEX induced moderate accumulation of p21WAF1/CIP1 in U87MG, LN-229 and p53 mutant LN-18 cells, but not in p53 mutant LN-308 or T98G cells. LN-18 is also the p53 mutant cell line with the best cytoprotective response to DEX. p21WAF1/CIP1 accumulation occurred in the absence of changes in p21WAF1/CIP1 mRNA expression. Wild-type p53 was not required for this DEX effect since DEX induced p21WAF1/CIP1 accumulation in p53val135-transfected LN-229 cells, too. DEX failed to induce p21WAF1/CIP1 expression or cytoprotection in untransformed rat astrocytes. The same lack of modulation of p21WAF1/CIP1 expression and drug toxicity was observed in p21(+/+), p21(+/-) and p21(-/-) human colon carcinoma cells. Paradoxically, while only p21(+/+) and p21(+/-) mouse embryonic fibroblasts showed enhance p21WAF1/CIP1 levels after exposure to DEX, only p21(-/-) fibroblasts were protected from drug toxicity by DEX. The present study links DEX-mediated protection from cancer chemotherapy to a p53-independent pathway of regulating p21WAF1/CIP1 expression in glioma cells but this effect appears to cell type-specific.
authors.affiliation: Department of Neurology, University of Tübingen, Medical School, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Naumann
authors.forename: S
authors.initials: S
authors.lastname: Durka
authors.forename: M
authors.initials: M
authors.lastname: Weller
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism*; D019610:Cytoprotection; D003907:Dexamethasone / Q000494:pharmacology*; D005910:Glioma / Q000188:drug therapy / Q000378:metabolism; D005938:Glucocorticoids / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D051379:Mice; D020011:Protective Agents / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D019014:fas Receptor / Q000502:physiology
chemical_list: D000970:Antineoplastic Agents; C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; C493958:Cdkn1a protein, rat; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D005938:Glucocorticoids; D020011:Protective Agents; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D019014:fas Receptor; D003907:Dexamethasone; D005978:Glutathione