CHARACTERIZATION OF CONVENTIONAL PROTEIN-KINASE-C (PKC) ISOTYPE EXPRESSION DURING F9 TERATOCARCINOMA DIFFERENTIATION - OVEREXPRESSION OF PKC-ALPHA ALTERS THE EXPRESSION OF SOME DIFFERENTIATION-DEPENDENT GENES

F9 teratocarcinoma is a useful model for studying early embryogenesis since these cells can differentiate into primitive or parietal endoder m under the influence of retinoic acid or retinoic acid and cyclic AMP , respectively. We have found that three isoforms of protein kinase C (PKC alpha, -beta, and -gamma) were expressed in undifferentiated stem cells. When the cells were treated with retinoic acid either alone or in the presence of cAMP for 120 h, PKC alpha mRNA and protein levels increased, whereas those of PKC beta and PKC gamma became undetectable . These changes began within 24 h of drug treatment and were complete by 48-72 h. In order to determine the functional significance of the i nduction of PKC alpha during F9 differentiation, we established two st able transfectants that overexpressed PKC alpha protein between 4- and 5-fold compared to wild type cells. Characterization of these cell li nes revealed an altered pattern of expression of some of the markers o f F9 differentiation. The clone that had the highest amount of PKC alp ha protein constitutively expressed mRNA for type IV collagen and c-Ju n, which are not normally expressed until 24-48 h of treatment with di fferentiation agents. In the other overexpressing clone, these markers were induced much faster than in wild type cells. The growth rate of both overexpressing clones was less than wild type cells, while the ex pression of the PKC beta protein in these clones was similar to the le vels found in differentiated F9 cells. However, other markers of diffe rentiation, including the cellular morphology and levels of pST6-135 a nd c-myc RNA, responded to agents identically in both wild type and PK C-alpha-overexpressing clones. Therefore, overexpression of PKC alpha is not sufficient to induce full differentiation of F9 cells. However, our data suggest that certain pathways that lead to the expression of differentiation-dependent genes are regulated by PKC alpha protein le vels.