JUN and breast carcinoma: We show that MMP-1 expression is regulated by an AP-1 element in its promoter in highly metastatic MDA-MB-231 mammary carcinoma cell derivatives.  Fra-1, an AP-1 family transcription factor, differentially binds this element in highly metastatic cells compared to low metastatic cells and is required for MMP-1 expression.  Overexpression of Fra-1 also caused increased MMP-1 expression.