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

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Abstract
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.