Role of protein kinase C in diacylglycerol-mediated induction of ornithine decarboxylase and reduction of epidermal growth factor binding.

Abstract

Tumor-promoting phorbol esters induce ornithine decarboxylase (ODCase) activity and reduce epidermal growth factor (EGF) binding in rat tracheal epithelial 2C5 cells. Phorbol esters activate protein kinase C by interacting at the same site as sn-1,2-diacylglycerols, the presumed physiological regulators. The effects of added sn-1,2-diacylglycerols and those generated by phospholipase C treatment of 2C5 cells on ODCase induction and EGF binding were investigated to establish a role for protein kinase C in these cellular responses. Treatment of 2C5 cells with phospholipase C induced ODCase activity and reduced EGF binding, whereas phospholipases A2 and D were inactive. When sn-1,2-diacylglycerols containing fatty acids 3-10 carbons in length were added to 2C5 cells, those diacylglycerols containing fatty acids 5-10 carbons in length caused ODCase induction and reduction in EGF binding. sn-1,2-Dioctanoylglycerol was one of the most active compounds tested. It induced ODCase in a dose-(50-500 FzM) and time-dependent manner. The reduction of binding of '2sI-labeled EGF by sn-1,2-dioctanoylglycerol was also time and dose dependent and appeared to result from a change in EGF affinity and not the number of receptor sites. This series of sn-1,2-diacylglycerols showed similar structure-function relationships in their ability to induce ODCase activity, to decrease EGF binding, to stimulate protein kinase C, and to inhibit[3H]phorbol dibutyrate binding to the phorbol ester receptor.These data demonstrate biological activities for a number of diacylglycerols and indicate that protein kinase C activation is implicated in ODCase induction and decreased EGF binding.Tumor promoters are compounds that are noncarcinogenic but induce tumors in animals treated with suboptimal doses of chemical carcinogens (1-4). Phorbol esters, the most extensively studied class of tumor promoters, cause profound biological and biochemical alterations in a variety of cells. Two of these alterations, the inhibition of epidermal growth factor (EGF) binding and the induction of ornithine decarboxylase (ODCase) activity, have been widely studied (5-12). A strong correlation exists between the induction of ODCase and the promotion of tumor formation (4,(12)(13)(14)(15)(16) results suggest that protein kinase C activation is implicated in the cellular responses to diacylglycerols and phorbol esters and demonstrate that diacylglycerols are biologically active. In view of the established correlation between ODCase activity and tumor promotion (10-16), a role for diacylglycerols and protein kinase C in tumor promotion is suggested.

The proximal tubule in the pathophysiology of the diabetic kidney

“…In particular, diabetes can enhance proximal tubular activity of the PKC␤1 isoform (107), and PKC␤ has been implicated in Akt activation in the renal cortex of diabetic rats (175). Activation of PI3K/ Akt (133) and PKC pathways (58,63) are both linked to ODC activation. In accordance with a role of PKC␤ in kidney growth, the early diabetes-induced increase in kidney weight was blunted in mice lacking this PKC isoform (90).…”

PKCα Mediates Maternal Touch Regulation of Growth-Related Gene Expression in Infant Rats

“…DiC8 is a synthetic, long-acting, cell permeable DAG analog that has been reported to enhance both PKC and ODC activity in cultured cells (Jetten et al, 1985). As shown in Figure 2a, ODC values in animals administered diC8 were markedly higher than those obtained in pups treated with vehicle (DMSO : saline; 2 : 1).…”

“…Although details of the molecular processes mediating ODC induction by trophic hormones are still unclear, strong evidence indicates a major role for the signaling enzyme PKC. Indeed, upregulation of ODC activity was one of the first cellular events to be associated with PKC function (Jetten et al, 1985). Specifically, PRL and GH appear to increase hepatic ODC activity by stimulating the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) to sn-1,2-diacylglycerol (DAG) (Jetten et al, 1985;Buckley and Buckley, 1991), a physiologic activator of PKC (Nishizuka, 1988).…”

“…Indeed, upregulation of ODC activity was one of the first cellular events to be associated with PKC function (Jetten et al, 1985). Specifically, PRL and GH appear to increase hepatic ODC activity by stimulating the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) to sn-1,2-diacylglycerol (DAG) (Jetten et al, 1985;Buckley and Buckley, 1991), a physiologic activator of PKC (Nishizuka, 1988). Furthermore, PKC activation via receptor-mediated phosphoinositide turnover heightens c-myc expression (Rozengurt and Sinnett-Smith, 1987), a protooncogene thought to act physiologically as a regulator of ODC gene transcription (Bello-Fernandez et al, 1993;Peña et al, 1993).…”

Mechanisms of differentiation in melanoma cells and melanocytes.

“…Lastly, the polyamines could play a part, presumably a negative one since inhibition of their synthesis promoted melanogenesis (75). Protein kinase C can also promote polyamine synthesis (76 …”