OKADAIC ACID-ELICITED TRANSCRIPTIONAL ACTIVATION OF COLLAGENASE GENE-EXPRESSION IN HT-1080 FIBROSARCOMA CELLS IS MEDIATED BY JUNB

Okadaic acid (OA) is a novel, non-phorbol ester-type tumor promoter, w hich is a specific inhibitor of protein phosphatases 1 and 2A. Treatme nt of human fibrosarcoma HT-1080 cells with OA resulted in induction o f collagenase and stromelysin-1 mRNA levels, while mRNA levels for tis sue inhibitor of metalloproteinases-1 were enhanced to a lesser extent . Induction of collagenase and stromelysin-1 mRNA levels was dependent on protein synthesis. Exposure of HT-1080 cells to OA resulted in mar ked and persistent induction of junB, junD, and c-fos mRNA levels up t o 24 h, white c-jun mRNA levels were only slightly elevated. In transi ently transfected HT-1080 cells, OA-elicited activation of a 3.8-kilob ase collagenase promoter/reporter gene construct was entirely dependen t on junB expression, as determined by cotransfection with a junB anti sense expression construct. Overexpression of JunB in HT-1080 cells en hanced collagenase promoter activity by 10-fold, and OA augmented tran s-activation of collagenase promoter by c-Jun and JunB. The results in dicate that induction of collagenase gene expression by OA is mediated by enhanced JunB expression, as well as enhanced trans-activating cap acity of AP-1 complexes containing c-Jun and JunB. These results also suggest that selective overexpression of junB may enhance invasive and metastatic potential of neoplastic cells.