Lack of translocation of protein kinase C from the cytosol to the membranes in vasopressin-stimulated hepatocytes

Abstract

The ability of Ca2(+)-mobilizing hormones to promote changes in the subcellular distribution of protein kinase C (PKC) was studied in isolated hepatocytes. In recently isolated cells the distribution of PKC between the soluble and particulate fractions was 47 and 53% respectively. Exposure of the hepatocytes to 100 nM-vasopressin produced an increased phosphoinositide turnover, as reflected by the changes in the concentrations of inositol trisphosphate and Ca2+, and in glycogen phosphorylase a activity. However, the distribution of both PKC activity and [3H]phorbol dibutyrate binding between the cytosol and the membranes remained unchanged under these conditions. To determine the threshold values of the concentrations of Ca2+ and diacylglycerol required to produce a redistribution of PKC, the hepatocytes were treated with the Ca2+ ionophore ionomycin, and with permeant diacylglycerol derivatives. Hepatocytes incubated in the presence of 100 nM-vasopressin required concentrations of Ca2+ 2.5 times those produced physiologically by the hormone to produce translocation of PKC from the cytosol to the membranes. These studies suggest that, at least in hepatocytes, activation of PKC in response to Ca2(+)-mobilizing hormones involves only the pre-existent membrane-bound enzyme without affecting the soluble enzyme.

Modulation of basal nitric oxide-dependent cyclic-GMP production by ambient glucose, myo-inositol, and protein kinase C in SH-SY5Y human neuroblastoma cells.

“…For example, sciatic nerve from untreated streptozotocin-diabetic rats exhibits diminished total and arachidonyl-DAG (17,18), and increased activation (71) and phosphorylation (20) of (Na,K)-ATPase by exogenous PKC agonists, consistent with a diminished basal level of PKC-mediated phosphorylation of (Na,K)-ATPase. In separate studies, diminished activation of PKC (72) and decreased total and cytoplasmic intrinsic PKC activity have been noted in streptozotocin-diabetic rat sciatic nerve (16), perhaps reflecting the reported discordance between measures of cellular PKC activity and its translocation (73,74). In other tissues equally prone to diabetic complications, d-glucose appears to increase rather than decrease total DAG and PKC activation (36,38,41,62).…”

Hypoxia-induced accumulation of erythropoietin mRNA in isolated hepatocytes is inhibited by protein kinase C

“…However, the results obtained so far appear entirely compatible with an inhibitory effect of the activation of PKC alpha on EPO mRNA accumulation in hepatocytes. A low efficacy of synthetic diacylglyerol analogues in inducing PKC-mediated reactions in hepatocytes has previously been observed [11,27], possibly due to high rates of metabolism of these substances [14]. Thus the failure to lower EPO mRNA levels with DOG or OAG appears no compelling argument against PKC-mediated reduction of EPO gene expression.…”

Regulation of H2O2-induced necrosis by PKC and AMP-activated kinase signaling in primary cultured hepatocytes

“…It is possible that the different PKC isoforms very transiently translocated to membranes and were missed in our experiments. In addition, in some cases, PKC activation has been reported not to involve membrane translocation (12,19). Consequently, we next examined the time course of PKC activation following H 2 O 2 treatment in hepatocyte lysates using an antibody that recognizes proteins phosphorylated by PKC (PKC recognition motif: serine residues surrounded by arginine or lysine at the Ϫ2 and ϩ2 positions and a hydrophobic residue at the ϩ1 position) (37).…”