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

Abstract

Membrane and cytosol fractions from hepatocytes of both normal and streptozotocin-induced diabetic animals were probed with a panel of polyclonal anti-peptide antisera in order to identify protein kinase C (PKC) isoforms. Immunoreactive species were noted with antisera specific for ~ (-81 kDa), fl-ll (-82 kDA), E (--95 kDa) and ~" (~ 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-c~. 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 fl-I, 7, ~ and 1/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 fl-I1 isoform and the ~ 90 kDa (upper) form of PKC-~, with no apparent/little change in the levels of the -81 kDa (lower) form of PKC-cc and those of PKC-~'. Diabetes induction also appeared to have elicited the translocation of PKC-fl-II and the -81 kDa (lower) form of PKC-c~ to the membrane fraction where immunoreactivity for these species was now apparent. The level of PKC-e, 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.

Free fatty acid-induced muscle insulin resistance and glucose uptake dysfunction: Evidence for PKC activation and oxidative stress-activated signaling pathways

“…Additional supportive evidence is the amelioration of the glucose uptake in cells treated with both oleate and the Bis-I, but not in cells treated with palmitate. PKC activation has been implicated in several studies of insulin resistance and diabetes and even in the absence of lipid oversupply [11,25,26]. The inhibitory effects of PKC on insulin signaling may at least in part be explained by the more recently identified role of the serine/ threonine phosphorylation of IRS-1, which has been implicated in the inhibition of its tyrosine phosphorylation [26,27].…”

Proteomic Profiling of Hepatic Endoplasmic Reticulum-associated Proteins in an Animal Model of Insulin Resistance and Metabolic Dyslipidemia

“…The abundant hepatic proteins identified in our analysis included PDI, ER60, peroxiredoxin 4, aldolase B, glutathione S-transferase, retinol-binding protein, cytochrome b 5 , nonmuscle actin, 40 S ribosomal protein SA, ATPase, BiP, and calreticulin (49 -62). RACK1, which was shown not to be expressed differentially in the hepatic ER, is associated with the hepatic ER through its interaction with protein kinase C-␤ (63)(64)(65)(66)(67)(68)(69).…”

Specific protein kinase C isoforms as transducers and modulators of insulin signaling

“…In an early study on hepatocytes of both normal and streptozotocin-induced diabetic animals [142], it was reported that streptozotocin increased levels of the PKCβII and α, with no change in the level of PKCς. Diabetes induction also appeared to have elicited the translocation of PKCβII and PKCα to the membrane fraction.…”