Activation of intestinal arginine transport by protein kinase C is mediated by mitogen-activated protein kinases

Abstract

L-Arginine uptake by the small intestine can play a pivotal role in regulating nitric oxide synthesis and immune functions in catabolic states. We previously showed that protein kinase C (PKC) activation stimulates intestinal brush-border membrane arginine transport. However, the signaling pathways implicated in this activation have not been studied. The purpose of this study was to investigate the intracellular signal transduction pathways involved in the protein kinase C stimulation of arginine transport across the apical membrane of intestinal epithelial Caco-2 cells. [3H]-L-arginine transport activity, Northern blot analysis of mRNA levels of the intestinal arginine transporter CAT1, and Western blot analysis of the mitogen-activated protein (MAP) kinases phospho-p44/42 activity and phospho-MEK1/2 were measured in cultured Caco-2 cells treated with phorbol ester (phorbol 12-myristate 13-acetate, TPA; 0 to 0.5 micromol/L), and the MEK1 inhibitor PD 98059 (0 to 50 micromol/L). Phorbol ester stimulated intestinal arginine transport activity. Arginine transporter gene CAT1 mRNA, phospho-p44/42, and phospho-MEK1/2 levels were stimulated in phorbol ester-treated cells, compared with the control group. Phorbol ester stimulation of arginine transport activity and transporter CAT1 mRNA levels was blocked by PD 98059. These data suggest that phorbol ester stimulates arginine transport in Caco-2 cells via signaling pathways that lead to increased transcription and/or stabilization of CAT1 mRNA. Protein kinase C and MAP kinases MEK1/2 and p44/42 are key intracellular regulators involved in this signal transduction cascade.