DIABETES INDUCES SELECTIVE ALTERATIONS IN THE EXPRESSION OF PROTEIN-KINASE-C ISOFORMS IN HEPATOCYTES

Membrane and cytosol fractions from hepatocytes of both normal and str eptozotocin-induced diabetic animals were probed with a panel of polyc lonal anti-peptide antisera in order to identify protein kinase C (PKC ) isoforms. Immunoreactive species were noted with antisera specific f or alpha (approximately 81 kDa), beta-II (approximately 82 kDA), epsil on (approximately 95 kDa) and zeta (approximately 79 kDa). In addition , a species migrating with an apparent size of approximately 94 kDa wa s also detected in cytosol fractions using an antiserum specific for P KC-alpha. Each of these species was specifically displaced when the PK C-isoform specific peptide was included in the immnodetection system. No immunoreactive species consistent with the presence of the beta-I, gamma, delta and eta isoforms of protein kinase C was observed. Induct ion of diabetes using streptozotocin invoked selective alterations in the expression of PKC isoforms which were reversed upon insulin therap y. In the cytosol fraction, marked increases of approximately 3-fold o ccurred in levels of the beta-II isoform and the approximately 90 kDa (upper) form of PKC-alpha, with no apparent/little change in the level s of the approximately 81 kDa (lower) form of PKC-alpha and those of P KC-zeta. Diabetes induction also appeared to have elicited the translo cation of PKC-beta-II and the approximately 81 kDa (lower) form of PKC -alpha to the membrane fraction where immunoreactivity for these speci es was now apparent. The level of PKC-epsilon, which was noted only in membrane fractions, was also increased upon induction of diabetes. It is suggested that the selective alterations in the expression of PKC isoforms occurring upon streptozotocin-induced diabetes may lead to al tered cellular functioning and underly defects in inhibitory G-protein functioning and insulin action which characterise this animal model o f diabetes.