PTH stimulates PLC beta and PLC gamma isoenzymes in rat enterocytes: influence of ageing

We previously reported that in rat duodenal cells (enterocytes), parathyroi d hormone (PTH [1-34]: PTH) stimulates the hydrolysis of polyphosphoinositi des by phospholipase C (PLC), generating the second messengers inositol tri sphosphate (IP3) and diacylglycerol (DAG) and that this mechanism is severe ly altered in old animals. In the present study, we show that PTH [1-34]-de pendent IP3 release in young rats was blocked to a great extent by an antib ody against guanine nucleotide binding protein G alphaq/11, indicating that the hormone activates a beta isoform of PLC coupled to the alpha subunit o f Gq/11. In addition, PTH rapidly (within 30 s, with maximal effects at 1 m in) stimulated tyrosine phosphorylation of PLC gamma in a dose-dependent fa shion (10(-10)-10(-7) M). The hormone response was specific as PTH [7-34] w as without effects. The tyrosine kinase inhibitors, genistein (100 muM) and herbimycin (2 muM), suppressed PTH-dependent PLC gamma tyrosine phosphoryl ation. Stimulation of PLC gamma tyrosine phosphorylation by PTH [1-34] grea tly decreased with ageing. PP1 (10 muM), a specific inhibitor of the Src fa mily of tyrosine kinases, completely abolished PLC gamma phosphorylation. T he hormone-induced Src tyrosine dephosphorylation, a major mechanism of Src activation, an effect that was blunted in old animals. These results indic ate that in rat enterocytes PTH generates IP3 mainly through G-protein-coup led PLC beta and stimulates PLC gamma phosphorylation via the nonreceptor t yrosine kinase Src. Impairment of PTH activation of both PLC isoforms upon ageing may result in abnormal hormone regulation of cell Ca2+ and prolifera tion in the duodenum. (C) 2001 Elsevier Science Inc. All rights reserved.