Protein kinase C expression and translocation in dispersed chief cells from guinea-pig stomach

Association of protein kinase A with AKAP150 facilitates pepsinogen secretion from gastric chief cells

Cross talk between signal transduction pathways augments pepsinogen secretion from gastric chief cells. A-kinase anchoring proteins (AKAPs) associate with regulatory subunits of protein kinase A (PKA), protein kinase C (PKC), and protein phosphatase 2B (PP2B) and localize this protein complex to specific cell compartments. We determined whether an AKAP-signaling protein complex exists in chief cells and whether this modulates secretion. In Western blots, we identified AKAP150, a rodent homologue of human AKAP79 that coimmunoprecipitates with PKA, PKC, and actin. The association of PKA and PP2B was demonstrated by affinity chromatography. Confocal microscopy revealed colocalized staining at the cell periphery for AKAP150 and PKC. Ht31, a peptide that competitively displaces PKA from the AKAP complex, but not Ht31P, a control peptide, inhibited 8-Br-cAMP-induced pepsinogen secretion. Ht31 did not inhibit secretion that was stimulated by agents whose actions are mediated by PKC and/or calcium. However, Ht31, but not Ht31P, inhibited carbachol- and A23187-stimulated augmentation of secretion from cells preincubated with cholera toxin. These data suggest the existence in chief cells of a protein complex that includes AKAP150, PKA, PKC, and PP2B. Disruption of the AKAP-PKA linkage impairs cAMP-mediated pepsinogen secretion and cross talk between signaling pathways.

Protein kinase C isoform expression and function in transformed and non-transformed pancreatic acinar cell lines

Members of the protein kinase C (PKC) family of multifunctional serine/threonine phosphorylating enzymes are believed to play a role in regulating cellular differentiation and proliferation in many cell types. In the present study, we examined the expression of PKC isoforms in non-transformed (BMRPA.430) and transformed (TUC3) rat pancreatic acinar cell lines and compared this to PKC expression in freshly dispersed acini from rat pancreas. BMRPA.430 cells maintain characteristics of normal acini and are not tumorigenic, whereas TUC3 cells do not express tight junctions or polygonal morphology and are tumorigenic. As reported previously, PKC alpha, delta, epsilon, and zeta are expressed in freshly prepared acini. Likewise, these isoforms were detected in both the BMRPA.430 and TUC3 cell lines. In addition, PKC theta, a novel isoform, was detected in all three cell types at low levels. We used two PKC inhibitors to examine the role of PKC in acinar cell proliferation. CGP 41 251, a selective PKC inhibitor, and Go 6976, an agent which specifically inhibits calcium-dependent PKC isoforms, inhibited cell proliferation of both cell lines. Translocation of PKC alpha to the membrane was not observed in either cell line. Hence, our data indicate that ras-induced transformation does not alter PKC isoform expression in pancreatic acinar cells and that activation of PKC alpha is involved with acinar cell growth.

sn-1,2-diacylglycerol and choline increase after fertilization in Xenopus laevis

sn-1,2-Diacylglycerol (DAG) mass and translocation of protein kinase C alpha and beta to a membrane fraction increased approximately 7 min after insemination of Xenopus laevis eggs. The DAG mass increase of 48 pmol (from 62 to 110 pmol/cell) was greater than that for inositol 1,4,5-trisphosphate (IP3; an increase of approximately 170 fmol or approximately 280-fold smaller than the DAG increase), and DAG peaks approximately 5 min after IP3. Choline mass (a measure of phosphatidyl choline-specific phospholipase D) also peaked before DAG and the choline increase (134 pmol/cell) was greater than that of DAG. There was no detectable change in phosphocholine mass (a measure of phosphatidylcholine-specific phospholipase C). During first cleavage, DAG decreased, PKC translocation was low, and choline increased and peaked (whereas published work shows an increase in IP3 mass). Artificial elevation of intracellular calcium ([Ca2+]i) increased DAG levels but prevention of the [Ca2+]i increase after fertilization did not block DAG production. Thus, sperm stimulate production of DAG and choline through [Ca2+]i-independent and [Ca2+]i-dependent paths.