DEVELOPMENTAL EXPRESSION OF PROTEIN-KINASE-C ISOZYMES IN OLIGODENDROCYTES AND THEIR DIFFERENTIAL MODULATION BY 4-BETA-PHORBOL-12,13-DIBUTYRATE

Myelin gene expression in normal oligodendrocytes (OLG) depends on developmentally regulated protein kinase C (PKC) enzyme activity (Asotra and Macklin: J Neurosci Res 34:571-588, 1993). We studied the developmental expression of the Ca++-dependent PKC-alpha, -beta(I) -beta(II) and -gamma isozymes, and the Ca++-independent PKC-delta, -epsilon, -zeta and -eta isozymes in enriched rat brain OLG cultures. In A2B5(+) O-2A progenitors, only PKC-delta, PKC-epsilon and PKC-zeta were detected immunocytochemically. In O4(+) proligondendrocytes, PKC-beta(I), -delta and -zeta were expressed moderately and low levels of PKC-alpha and -epsilon were detected. GD3(+) OLG, GC(+) OLG and MBP(+) OLG showed increased levels of PKC-alpha, -beta(I), -delta and -zeta isozymes. PKC-beta(II), -gamma and -eta were poorly expressed in OLG. On immunoblots, PKC-alpha was present early and increased continually up to 18 days but PKC-beta(I) increased until 12 days in cultured OLG. High levels of PKC-delta, PKC-epsilon and PKC-zeta, the most abundant PKC isozymes in OLG, were maintained up to 12 days and were then slightly reduced. Interestingly, relatively high levels of PKC-alpha, PKC-beta(I), PKC-beta(II), PKC-gamma and PKC-epsilon isozymes were detected in purified myelin membrane although greater levels of PKC-delta were found in OLG than in purified myelin. Thus, most of the PKC isozymes found in cultured OLG were also present in myelin, although at different levels. Treatment with 50 nM 4 beta-phorbol-12,13-dibutyrate (PDB) caused a delayed downregulation of PKC-delta levels after 8 hr without modulating the expression of other PKC isozymes in 1-day OLG; in the 3-day-old and 6-day-old OLG, PDB downmodulated PKC-beta(I), -delta and epsilon isozymes with only a minor effect on PKC-alpha and no reduction in PKC-zeta. Induction or downmodulation of individual PKC isozymes by phorbol esters appears to depend on the differentiation state of OLG. These data suggest that PKC-beta(I), -delta and -epsilon isozymes have an important function in different cellular events of OLG differentiation. We conclude that the PKC-dependent modulation of myelin gene expression in OLG results predominantly from the Ca++-dependent PKC-beta(I) isozyme activity and the Ca++-independent PKC-delta and PKC-epsilon activities in a cell differentiation state-dependent manner. Because of continuous presence of PKC-zeta isozyme in all the OLG phenotypes and its regulation by a mechanism unlike that for the regulation of other PKC isozymes, PKC-zeta may have a unique role in OLG function. (C) 1994 Wiley-Liss, Inc.