FIG. 4.

CHOP cooperates with c-Jun or c-Fos to activate the human collagenase promoter containing a TRE. CHOP enhances the activation of the human collagenase transcriptional reporter, ColTRE-41TK-CAT, by c-Jun (A) or by c-Fos (B). The enhancement of transcription is attenuated when the leucine zipper of CHOP is deleted (CHOP-LZ⁻). Transcriptional reporter and transcription factor expression plasmids were transfected to NIH 3T3 cells. At 24 h after transfection, the cells were placed in medium containing only 0.5% serum for an additional 24 h to decrease the expression of endogenous AP1 proteins before harvesting.