A COMMON RESPONSE ELEMENT MEDIATES DIFFERENTIAL-EFFECTS OF PHORBOL ESTERS AND FORSKOLIN ON TYPE-1 PLASMINOGEN-ACTIVATOR INHIBITOR GENE-EXPRESSION IN HUMAN BREAST-CARCINOMA CELLS

We have characterized regulation of type-1 plasminogen activator inhib itor (PAT-1) gene expression by phorbol 12-myristate 13-acetate (PMA) and the cAMP-inducing agent forskolin in the human breast carcinoma ce ll line MCF-7. PMA caused a strong induction of PAI-1, while forskolin suppressed the PMA response. Transfection experiments with fusion gen es showed that sequences mediating PMA induction as well as forskolin suppression were present between base pairs -100 and -30 of the 5'-fla nking region of the PAI-1 gene. The region was found to contain two Sp 1 binding sites. A proximal sequence in the region, TGAGTTCA (P box), with sequence similarity to phorbol ester response elements (TRE) as w ell as to cAMP response elements (CRE), bound a low-abundance, as yet unidentified nuclear protein in MCF-7 cells. This sequence had a highe r affinity to purified c-jun homodimer than to c-jun/c-fos heterodimer in MCF-7 nuclear extracts; it had no affinity to the proteins binding to CRE consensus sequences in these extracts. A distal TRE-like seque nce, TGAGTGG (D box), had a weak affinity to c-jun/c-fos heterodimer a nd c-jun homodimer; binding of proteins to this sequence was facilitat ed by binding of proteins to the P box. Both the P box and the D box w ere necessary for PMA responsiveness, suggesting a cooperativity betwe en the two binding sites. A mutation of the P box removing the CRE sim ilarity abolished the forskolin suppression of the PMA response. We pr opose that the protein kinase C and the protein kinase A signal-transd uction pathways, with opposite effects on PAI-1 gene expression, conve rge by modulating differently P-box-binding proteins.