HEPARIN DECREASES ACTIVATOR PROTEIN-1 BINDING TO DNA IN PART BY POSTTRANSLATIONAL MODIFICATION OF JUN-B

Heparin is a potent inhibitor of the proliferation and migration of va scular smooth muscle cells. This agent selectively inhibits the transc ription of tissue-type plasminogen activator and interstitial collagen ase, probably by decreasing the binding of activator protein-1 (AP-1) to phorbol ester-responsive elements in the promoters of these genes. Decreased AP-1 binding is not due to a direct inhibition by heparin, s ince heparinase digestion of nuclear extracts prepared from heparin-tr eated smooth muscle cells does not restore AP-1 binding activity. Trea tment of cells with heparin suppresses the expression of Jun B, one of the components of AP-1. The major effect of heparin is at the level o f posttranslational modification of Jun B. Results from pulse-chase la beling experiments show that the newly synthesized Jun B is rapidly co nverted to a higher-molecular-weight form and that conversion is suppr essed by heparin. Evidence is presented suggesting that the heparin-in hibited event is phosphorylation of Jun B.