AP-1 activation and altered AP-1 composition in association with increased phosphorylation and expression of specific Jun and Fos family proteins induced by vinblastine in KB-3 cells.
Vinblastine and other microtubule inhibitors are important antitumor agents that cause mitotic arrest, and induce apoptosis through poorly understood mechanisms, in a wide variety of cell lines. The activating protein 1 (AP-1) transcription factor is a major target of the c-Jun NH2-terminal kinase (JNK) signaling pathway, which is activated by microtubule inhibitors. Therefore, we examined the effect of vinblastine on AP-1 composition and activity in human KB-3 carcinoma cells. Vinblastine caused highly selective effects on AP-1 proteins in a concentration- and time-dependent manner. Specifically, c-Jun, expressed at a low level in control cells, was greatly increased and phosphorylated, Jun D was phosphorylated, Jun B underwent phosphorylation and subsequently became undetectable, and Fra 1 expression was also greatly increased. In contrast. Fra 2, c-Fos, and Fos B were relatively unchanged by vinblastine. Changes in AP-1 preceded caspase 3 activation and, therefore, occurred prior to the commitment phase of apoptosis. With the exception of c-Jun, which was not affected by paclitaxel, the same alterations in AP-1 proteins occurred after exposure to vincristine, paclitaxel, and colchicine, demonstrating that these are general responses to microtubule inhibition. Supershift assays demonstrated that in control cells, AP-1 binding activity was mediated by Jun D/Fra 2 heterodimers, whereas after vinblastine treatment, AP-1 complexes also containing c-Jun and Fra 1 were present, suggesting that induction of these latter proteins by vinblastine is functionally significant. Consistent with these observations, vinblastine stimulated AP-1-dependent luciferase reporter gene transcription. These findings suggest that alterations in AP-1 composition and activity may be key events in the early response of KB-3 cells to microtubule inhibitors.
Berry
A
A
Deportment of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock 72205-7199, USA.
Goodwin
M
M
Moran
C L
CL
Chambers
T C
TC
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D001665:Binding Sites; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D004247:DNA / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D008868:Microtubule Proteins / Q000037:antagonists & inhibitors; D010766:Phosphorylation / Q000187:drug effects; D016760:Proto-Oncogene Proteins c-fos / Q000187:drug effects / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000187:drug effects / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured; D014747:Vinblastine / Q000494:pharmacology*
D000972:Antineoplastic Agents, Phytogenic; D008868:Microtubule Proteins; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D018808:Transcription Factor AP-1; D014747:Vinblastine; D004247:DNA; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases