D-MYO-INOSITOL 1,4,5,6-TETRAKISPHOSPHATE PRODUCED IN HUMAN INTESTINALEPITHELIAL-CELLS IN RESPONSE TO SALMONELLA INVASION INHIBITS PHOSPHOINOSITIDE 3-KINASE SIGNALING PATHWAYS

Several inositol-containing compounds play key roles in receptor-media ted cell signaling events. Were, we describe a function for a specific inositol polyphosphate, D-myo-inositol 1,4,5,6-tetrakisphosphate [Ins (1,4,5,6)P-4], that is produced acutely in response to a receptor-inde pendent process. Thus, infection of intestinal epithelial cells with t he enteric pathogen Salmonella, but not with other invasive bacteria, induced a multifold increase in Ins(1,4,5,6)P-4 levels. To define a sp ecific function of Ins(1,4,5,6)P-4, a membrane-permeant, hydrolyzable ester was used to deliver it to the intracellular compartment, where i t antagonized epidermal growth factor (EGF)-induced inhibition of calc ium-mediated chloride (Cl-) secretion (CaMCS) in intestinal epithelia. This EGF function is likely mediated through a phosphoinositide 3-kin ase (PtdIns3K)-dependent mechanism because the EGF effects are abolish ed by wortmannin, and three different membrane-permeant esters of the PtdIns3K product phosphatidylinositol 3,4,5-trisphosphate mimicked the EGF effect on CaMCS. We further demonstrate that Ins(1,4,5,6)P-4 anta gonized EGF signaling downstream of PtdIns3K because Ins(1,3,5,6)P-4 i nterfered with the PtdInsP(3) effect on CaMCS without affecting PtdIns 3K activity. Thus, elevation of Ins(1,4,5,6)P-4 in Salmonella-infected epithelia may promote CI-flux by antagonizing EGF inhibition mediated through PtdIns3K and PtdInsP(3).