Activation of PKC isoforms by ATP/UTP and PMA in murine astrocytes

Abnormal myelin formation appears to be one defect contributing to the neuropathology associated with the fetal alcohol syndrome, the major cause of noncongenital mental retardation. Using the CG-4 cell line we previously showed that 25–75 m m ethanol (EtOH) down-regulates myelin basic protein (MBP) expression in differentiating oligodendrocytes (OLGs) without affecting the 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) expression or morphological development (Bichenkov and Ellingson 2001). Here we observed that a relatively low concentration of 12-phorbol-13-myristate acetate (PMA) mimicked the EtOH-caused inhibition of MBP expression without affecting CNP expression or morphology. The inhibition of MBP expression by 100 m m EtOH or 1 n m PMA was completely counteracted by three inhibitors of protein kinase C (PKC); bisinodoylmaleimide I, chelerythrine chloride, and calphostin C, indicating that EtOH down-regulated MBP expression by activating PKC. We investigated whether the EtOH-caused activation resulted in part from up-regulation of the expression of PKC isozymes. Of 11 PKC isozymes examined, CG-4 OLGs expressed nine; PKC α, β1, β2, δ, ε, λ, μ, nu and zeta; while PKC isozymes γ and theta were not detected. Only five PKC isozymes, α, β1, β2, μ, and nu, displayed developmental changes in expression. However, EtOH did not up-regulate the early expression of any PKC isozyme during the first two days of differentiation, the developmental stage when it down-regulates the MBP expression in CG-4 cells. The results indicate that EtOH delays MBP expression by activating at least one phorbol ester-sensitive PKC isozyme in differentiating oligodendrocytes without up-regulating its expression.
Acknowledgements:   Support: NIAAA Grant AA072185.