The phosphorylation defective RARα mutant inhibits EGFR expression, ERK1 activation, and AP-1 protein levels. (A) Cultures of G418 resistant (neo) and S77A RARα mutant (RAR1-4) SCC25 clones were harvested for western blot as described in Methods. Blots were incubated with anti-human primary antibodies to AP-1 proteins Fra-1, c-jun, or JunB. These experiments were performed three times using different lysates with similar results. Representative blots are shown.