Induction of apoptosis by vinblastine via c-Jun autoamplification and p53-independent down-regulation of p21WAF1/CIP1.
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.
Kolomeichuk
Sergey N
SN
Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Mail Slot 516, 4301 W. Markham Street, Little Rock, AR 72205-7199, USA.
Bene
Anca
A
Upreti
Meenakshi
M
Dennis
Richard A
RA
Lyle
Christopher S
CS
Rajasekaran
Maheswari
M
Chambers
Timothy C
TC
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000502:physiology*; D015536:Down-Regulation / Q000187:drug effects*; D004789:Enzyme Activation; D006801:Humans; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*; D014747:Vinblastine / Q000494:pharmacology*
D000972:Antineoplastic Agents, Phytogenic; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D014747:Vinblastine; D053148:Caspase 3