PROLACTIN STIMULATION OF PHOSPHOINOSITIDE METABOLISM IN CHO CELLS STABLY EXPRESSING THE PRL RECEPTOR

PRL receptor (PRL-R) activation by PRL triggers a cascade of intracell ular events including homodimerization of the receptor, activation of cytoplasmic receptor-associated tyrosine kinase and tyrosine-phosphory lation of various signal transducers. In CHO cells, transfected with t he long form of PRL-R, an increase in [Ca2+](i) was observed following PRL stimulation whereas Ca2+ is generally coupled with the phosphoino sitide metabolism. In this study, we investigated phosphoinositide inv olvement in the PRL transduction pathway. We report that PRL induces r apid increases in two novel inositol phospholipids, almost certainly P tdIns(4,5)P2 and PtdIns(3,4,5)P3. Pre-traitment of CHO cells with wort manin, a specific PtdIns3-kinase inhibitor, considerably reduces the P RL-induced increase in PtdInd(3,4,5)P3, thus suggesting an involvement of this enzyme in the cascade of activation of cytoplasmic kinase pro teins. A pathway beginning with the activation of PtdIns3-kinase, phos phorylation of PtdIns(4,5)P2 and rapid synthesis of PtdIns(3,4,5)P3 is proposed. PtdIns(3,4,5)P3 may acts as a lipid second messenger, direc tly or indirectly responsible for some of the multiple cell changes at tributed to PRL. (C) 1998 Academic Press.