Induction of Apoptosis by Vinblastine via c-Jun Autoamplification and p53-Independent Down-Regulation of p21WAF1/CIP1

Abstract

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.

Apoptosis Induced by Cytoskeletal Disruption Requires Distinct Domains of MEKK1

“…In this paper and our previous study, MEKK1-dependent JNK activation correlates strongly with apoptosis, and previous reports have shown that absence or inhibition of JNK resulted in decreased levels of apoptosis with vinblastine treatment [28], [29]. We also show that the JNK substrate c-Jun upregulation after vinblastine treatment is partially dependent upon MEKK1, and upregulation of c-Jun has been shown to contribute to vinblastine-induced apoptosis [30]. The duration of JNK activation may also be important for inducing apoptosis.…”

Distinct signaling pathways of microtubule inhibitors – vinblastine and Taxol induce JNK‐dependent cell death but through AP‐1‐dependent and AP‐1‐independent mechanisms, respectively

“…For these studies we used mainly KB-3 cells, a HeLa subline, because they undergo a welldefined and predictable time course of mitotic arrest followed by apoptosis when treated with antimitotic drugs. We have previously shown, and confirmed in this study, that vinblastine activates the classical JNK ⁄ AP-1 pathway [6,7] and promotes high levels of c-Jun expression, which occurs through a JNK-mediated auto-regulatory pathway [15]. Despite these advances, it is still not clear how the JNK ⁄ c-Jun pathway is activated in response to mitotic arrest caused by microtubule inhibitors.…”

Caffeic Acid Phenethyl Ester Causes p21Cip1 Induction, Akt Signaling Reduction, and Growth Inhibition in PC-3 Human Prostate Cancer Cells

“…Mitoxantrone induces p21 Cip1 [63]. Vinblastine induces apoptosis via reduction of p21 Cip1 [64]. Paclitaxol induces an Akt-dependent phosphorylation on p21 Cip1 leading to an association of p21 Cip1 with 14-3-3 and thus accumulation of the phosphorylated form of p21 Cip1 in cytoplasm which prevents the inhibitory effect of p21 Cip1 [65].…”