Diabetes induces selective alterations in the expression of protein kinase C isoforms in hepatocytes

Membrane and cytosol fractions from hepatocytes of both normal and streptozotocin-induced diabetic animals were probed with a panel of polyclonal anti-peptide antiscra in order to identify protein kinase C (PKC) isoforms. Immunoreactive species were noted with antisera specific for α (∼ 81 kDa), β-II (∼ 82 kDA), ε (∼ 95 kDa) and ξ (∼ 79 kDa). In addition, a species migrating with an apparent size of ∼ 94 kDa was also detected in cytosol fractions using an antiserum specific for PKC-α. Each of these species was specifically displaced when the PKC-isoform specific peptide was included in the immunodetection system. No immunoreactive species consistent with the presence of the β-I, λ, δ and η isoforms of protein kinase C was observed. Induction of diabetes using streptozotocin invoked selective alterations in the expression of PKC isoforms which were reversed upon insulin therapy. In the cytosol fraction, marked increases of ∼ 3-fold occurred in levels of the β-II isoform and the ∼ 90 kDa (upper) form of PKC-α, with no apparent/little change in the levels of the ∼ 81 kDa (lower) form of PKC-α and those of PKC-ξ. Diabetes induction also appeared to have elicited the translocation of PKC-β-II and the ∼ 81 kDa (lower) form of PKC-α to the membrane fraction where immunoreactivity for these species was now apparent. The level of PKC-ϵ, 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 altered cellular functioning and underly defects in inhibitory G-protein functioning and insulin action which characterise this animal model of diabetes.