PT - JOURNAL ARTICLE AU - Sergey N. Kolomeichuk AU - Anca Bene AU - Meenakshi Upreti AU - Richard A. Dennis AU - Christopher S. Lyle AU - Maheswari Rajasekaran AU - Timothy C. Chambers TI - Induction of Apoptosis by Vinblastine via c-Jun Autoamplification and p53-Independent Down-Regulation of p21<em><sup>WAF1/CIP1</sup></em> AID - 10.1124/mol.107.039750 DP - 2008 Jan 01 TA - Molecular Pharmacology PG - 128--136 VI - 73 IP - 1 4099 - http://molpharm.aspetjournals.org/content/73/1/128.short 4100 - http://molpharm.aspetjournals.org/content/73/1/128.full SO - Mol Pharmacol2008 Jan 01; 73 AB - Vinblastine treatment in all cell lines examined causes a robust increase in c-Jun protein expression and phosphorylation and a corresponding increase in activator protein-1 (AP-1) transcriptional activity. We show in KB-3 carcinoma cells that this is due to a strong autoamplification loop involving the proximal AP-1 site in the c-Jun promoter, resulting in highly increased c-Jun mRNA and c-Jun protein. Inhibitors of RNA transcription and protein translation blocked both vinblastine-induced c-Jun expression and apoptotic cell death, suggesting that apoptosis is dependent, at least in part, on transcription/translation. Small interfering RNA (siRNA) to c-Jun was used to interrupt the amplification cycle and was found to be highly effective, reducing vinblastine-induced c-Jun expression at both the mRNA and protein levels by 90%. Apoptosis and caspase-3 activation were significantly inhibited in c-Jun siRNA-treated cells. To uncover potential mechanisms of c-Jun-mediated cell death and protection by c-Jun siRNA, candidate target genes were examined. Chromatin immunoprecipitation revealed preferential association of c-Jun with the p21 (cyclin-dependent kinase inhibitor) gene promoter after vinblastine treatment. In KB-3 cells, which have compromised p53 function, and in p53-null cells but not in p53 wild-type cells, vinblastine caused down-regulation of p21 expression concomitant with increased c-Jun expression, suggesting a role for c-Jun in negative regulation of the p21 promoter independent of p53. These results provide strong evidence that c-Jun induction in response to vinblastine plays a proapoptotic role in part via down-regulation of p21, promoting cycling and subsequent cell death of mitotically impaired cells. The American Society for Pharmacology and Experimental Therapeutics