Yoshimi Takai

Possible involvement of protein kinase C in platelet-derived growth factor-stimulated DNA synthesis in vascular smooth muscle cells☆

In cultured rabbit aortic vascular smooth muscle cells (VSMC), protein kinase C-activating phorbol esters such as 12-O-tetradecanoylphorbol-13-acetate (TPA) and phorbol-12,13-dibutyrate (PDBu) stimulated DNA synthesis in the presence of 10% cell-free plasma-derived serum. This stimulation was half that shown by PDGF. 4 alpha-Phorbol-12,13-didecanoate, known to be inactive for protein kinase C, was without effect in stimulating DNA synthesis. Prolonged treatment of the cells with PDBu led to a marked decrease in protein kinase C. In the pDBu-treated cells, the TPA-stimulated DNA synthesis was completely abolished whereas the PDGF-stimulated DNA synthesis was decreased to about half that in the control cells. These results suggest that protein kinase C is involved in PDGF-stimulated proliferation of VSMC.

Involvement of three intracellular messenger systems, protein kinase C, calcium ion and cyclic AMP, in the regulation of c-fos gene expression in Swiss 3T3 cells

In quiescent cultures of Swiss 3T3 cells, platelet‐derived growth factor or fibroblast growth factor known to induce both protein kinase C activation and Ca2+ mobilization raised c‐fos mRNA. This action of the growth factors was mimicked by the specific activators for protein kinase C, such as phorbol esters and a membrane‐permeable synthetic diacylglycerol, and also by the Ca2+ ionophores, such as A23187 and ionomycin. Prostaglandin E1 known to elevate cyclic AMP also raised c‐fos mRNA, and this action was mimicked by 8‐bromo‐cyclic AMP, dibutyryl cyclic AMP and forskolin. These results suggest that expression of the c‐fos gene is regulated by three different intracellular messenger systems, protein kinase C, Ca2+ and cyclic AMP, in Swiss 3T3 cells.

Enhancement of fibroblast growth factor-induced diacylglycerol formation and protein kinase C activation by colon tumor-promoting bile acid in Swiss 3T3 cells: Different modes of action between bile acid and phorbol ester

A small amount (50–200 μM) of deoxycholate (DOC), a colon tumor‐promoting bile acid, did not show a direct effect on protein kinase C activity in a cell‐free system, but enhanced fibroblast growth factor (FGF)‐induced diacylglycerol formation and protein kinase C activation in Swiss 3T3 cells. DOC potentiated both reactions induced by submaximal doses of FGF but showed little effect on the maximal levels of the reactions. DOC alone was inactive in eliciting both reactions in the absence of FGF. DOC did not affect the binding of FGF to the cells. Since it has been described that diacylglycerol serves as a messenger for the activation of protein kinase C in the action of FGF in Swiss 3T3 cells [(1985) FEBS Lett. 191, 205‐210], these results suggest that a small amount of DOC increases the sensitivity to FGF of diacylglycerol formation and thereby potentiates protein kinase C activation in this cell line. This action of DOC was in marked contrast to that of 12‐O‐tetradecanoylphorbol‐13‐acetate, a potent tumor‐promoting phorbol ester, which directly activated protein kinase C in cell‐free and intact cell systems.

Enhancement of secretagogue-induced phosphoinositide turnover and amylase secretion by bile acids in isolated rat pancreatic acini.

Small amounts (0.1-0.5 mM) of deoxycholate enhanced amylase secretion, which had been induced by submaximal doses of carbachol or cholecystokinin octapeptide, without affecting the maximal levels of these reactions from isolated rat pancreatic acini. Deoxycholate alone did not induce these reactions. The other bile acids such as cholate, chenodeoxycholate, ursodeoxycholate, and taurocholate were also active. Under the similar conditions, deoxycholate enhanced the secretagogue-induced diacylglycerol formation that was derived mainly from the phospholipase C-mediated hydrolysis of phosphatidylinositol and phosphatidylinositol-4-monophosphate. Deoxycholate did not enhance the secretagogue-induced hydrolysis of phosphatidylinositol-4,5-bisphosphate or Ca2+ mobilization. Deoxycholate did not affect amylase secretion, which was induced by the simultaneous addition of protein kinase C-activating 12-O-tetradecanoylphorbol-13-acetate and Ca2+ ionophore ionomycin. Since diacylglycerol and Ca2+ may be responsible for the secretagogue-induced amylase secretion, our results indicate that small amounts of bile acids increase the sensitivity to the secretagogue of diacylglycerol formation and subsequent activation of protein kinase C, and thereby enhance amylase secretion from pancreatic acini.

Possible involvement of protein kinase C in interleukin-1 production by mouse peritoneal macrophages

Both lipopolysaccharide (LPS) and phorbol-12,13-dibutyrate (PDBu), a protein kinase C-activating phorbol ester, induced interleukin-1 (IL-1) production in mouse peritoneal macrophages. Prolonged treatment of the cells with PDBu led to the down-regulation and complete disappearance of protein kinase C. In these cells, PDBu did not increase IL-1 production, but LPS still stimulated IL-1 production although the maximum level was slightly reduced. These results suggest that protein kinase C and another unknown signal pathway are involved in LPS-induced IL-1 production.

Enhancement of growth factor-induced DNA synthesis by colon tumor-promoting bile acids in Swiss 3T3 cells: Their different mode of action from that of phorbol esters

In Swiss 3T3 cells, colon tumor‐promoting deoxycholate (DOC) enhanced DNA synthesis which was induced by fibroblast growth factor (FGF) in the presence of insulin. This effect was observed only when DOC was added within 10 h after the addition of FGF. DOC by itself did not induce DNA synthesis irrespective of the presence or absence of insulin. Similar results were obtained with other colon tumor‐promoting bile acids such as cholate, chenodeoxycholate and taurocholate. In contrast to these bile acids, 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) induced DNA synthesis fully without FGF in the presence of insulin. DOC did not affect TPA‐induced DNA synthesis. Prolonged treatment of the cells with phorbol‐12, 13‐dibutyrate caused the down‐regulation of the phorbol ester receptor and rendered the cells unresponsive to TPA. In these cells, FGF still induced DNA synthesis in the presence of insulin, but the maximal level was reduced to about one third of that in the control cells. DOC did not enhance this DNA synthesis any more. DOC did not alter the binding of FGF to the cells. These results indicate that colon tumor‐promoting bile acids enhance the mitogenic action of FGF and thereby stimulate DNA synthesis, although the phorbol ester substitutes for the mitogenic action of FGF.