RETINOIC ACID-INDUCED TRANSITION FROM PROTEIN-KINASE C-BETA TO PROTEIN-KINASE C-ALPHA IN DIFFERENTIATED F9 CELLS - CORRELATION WITH ALTEREDREGULATION OF PROTOONCOGENE EXPRESSION BY PHORBOL ESTERS

Retinoic acid (RA) induced differentiation of F9 embryonal carcinoma c ells is accompanied by changes in cellular responsiveness to extracell ular signals. These changes include an increase in the AP1 transcripti on factor that is associated with the expression of differentiation ma rkers (e.g., cytokeratin 18 and plasminogen activator). Since AP1 acti vity is a target for protein kinase C (PKC)-regulated changes in gene expression, we have examined the effects of RA on the expression and f unction of the PKC isozymes. F9 stem cells express PKC beta, delta, ep silon, and zeta. RA-induced differentiation to primitive endoderm led to a transition from PKC beta to PKC alpha expression. Additional trea tment with dibutyryl cyclic AMP (dbcAMP), required for terminal differ entiation into parietal endoderm, further increased PKC alpha expressi on and total PKC activity. RA and dbcAMP had negligible effects on the expression of PKC delta, epsilon, and zeta. The PKC beta to PKC alpha transition was specific for parietal endoderm; aggregation of RA-trea ted F9 cells induced visceral endoderm differentiation with elevated e xpression of PKC beta. The PKC activation with phorbol esters induced the expression of c-fos, c-jun, and junB proto-oncogenes in F9 stem ce lls. In the presence of either RA or RA and dbcAMP, phorbol ester trea tment enhanced the expression of type IV collagen, a parietal endoderm marker. It also increased the expression of c-jun gene but not c-fos. The specific involvement of PKC beta in c-fos induction and PKC alpha in type IV collagen induction was confirmed in each PKC isozyme-trans fected F9 cells. Together, our data demonstrate that the RA-induced (a nd dbcAMP-induced) changes in conventional PKC expression alters gene expression during parietal endoderm formation.