Protein Kinase C-activating Phorbol Ester Research Articles

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. 4α-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.

Selective effects of cholera toxin on the activation of mouse B cells by different polyclonal activators.

Murine B cells were stimulated in vitro with anti-immunoglobulin (Ig) antibodies, lipopolysaccharide, or with various combinations of phorbol dibutyrate and ionomycin. Very low concentrations (ca. 10(-14) M) of cholera toxin inhibited anti-Ig-stimulated DNA synthesis, while the response to LPS was only abrogated by 2 X 10(4)-10(5)-fold greater concentrations of the toxin. Earlier responses in anti-Ig-stimulated B cells, such as increases in Ia antigen levels, were not affected by the toxin. Protein kinase C-activating phorbol esters, together with Ca2+ ionophores, are believed to stimulate DNA synthesis in lymphocytes by mimicking the two second messengers resulting from ligation of the antigen receptors. However, concentrations of cholera toxin which totally abolish anti-Ig-induced B cell proliferation significantly enhanced DNA and RNA synthesis induced by phorbol dibutyrate plus ionomycin. The results are discussed in terms of possible effects of cholera toxin on guanine nucleotide-binding (G) proteins controlling receptor coupling to second messenger-generating systems in B cells.

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.

Possible involvement of protein kinase C and calcium ion in growth factor-induced expression of c-myc oncogene in Swiss 3T3 fibroblasts.

The addition of platelet-derived growth factor and fibroblast growth factor to quiescent cultures of Swiss 3T3 fibroblasts rapidly induced protein kinase C activation and Ca2+ mobilization and afterwards markedly increased c-myc mRNA levels. 1-Oleoyl-2-acetylglycerol, a membrane-permeable synthetic diacylglycerol, and 12-O-tetradecanoylphorbol 13-acetate, a tumor-promoting phorbol ester, stimulated protein kinase C activation without Ca2+ mobilization. Inversely, Ca2+ ionophores, A23187 and ionomycin, elicited Ca2+ mobilization without protein kinase C activation. Both protein kinase C-activating and Ca2+-mobilizing agents were able to increase c-myc mRNA levels in an additive manner. Prolonged treatment of the cells with phorbol 12,13-dibutyrate, another protein kinase C-activating phorbol ester, led to the down-regulation and complete disappearance of protein kinase C. In these cells, 1-oleoyl-2-acetylglycerol and 12-O-tetradecanoylphorbol 13-acetate did not increase c-myc mRNA levels, but platelet-derived growth factor, fibroblast growth factor, and the Ca2+ ionophores, all of which still induced Ca2+ mobilization, stimulated the increase of c-myc mRNA levels. These results strongly suggest that both protein kinase C and Ca2+ may be involved in platelet-derived growth factor- as well as fibroblast growth factor-induced expression of the c-myc oncogene in Swiss 3T3 cells.