A REQUIREMENT FOR EXTRACELLULAR SIGNAL-REGULATED KINASE (ERK) FUNCTION IN THE ACTIVATION OF AP-1 BY HA-RAS, PHORBOL 12-MYRISTATE 13-ACETATE, AND SERUM

The role of ERK-1 and ERK-2 in wild-type (wt) Ha-Ras, phorbol 12-myris tate 13-acetate (PMA), and serum-induced AP-1 activity was studied. Mi croinjection of ERK-specific substrate peptides inhibited the inductio n of AP-1 activity by all three stimuli, whereas a control peptide had no effect. By using eukaryotic expression constructs encoding wt ERK- 1 and kinase deficient mutants of ERKs 1 and 2, it was found that ERK- 1 and ERK-2 activities are required for AP-1 activation stimulated by either wt Ha-Ras, PMA, or serum. Overexpression of ERK-1 augmented wt Ha-Ras stimulation of AP-1, while having no effect upon PMA or serum s timulation. Overexpression of either kinase-deficient ERK-1 or kinase- deficient ERK-2 partially inhibited AP-1 activation by wt Ha-Ras but h ad no effect on PMA or serum-induced activation. Coexpression of both interfering mutants abolished AP-1 induction by wt Ha-Ras, PMA, or ser um. We conclude that ERKs are necessary components in the pathway lead ing to the activation of AP-1 stimulated by these agents.