d-myo-Inositol 1,4,5,6-tetrakisphosphate produced in human intestinal epithelial cells in response to Salmonella invasion inhibits phosphoinositide 3-kinase signaling pathways

d-myo-Inositol 1,4,5,6-tetrakisphosphate produced in human intestinal epithelial cells in response to Salmonella invasion inhibits phosphoinositide 3-kinase signaling pathways

Departments of ^*Medicine and ^‡Pediatrics and ^§Howard Hughes Medical Institute, University of California at San Diego, La Jolla, CA 92093; ^†Institute of Organic Chemistry, University of Bremen, 28359 Bremen, Germany; and ^¶Inositide Signaling Group, Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709

Edited by Philip W. Majerus, Washington University School of Medicine, St. Louis, MO, and approved October 30, 1997 (received for review September 8, 1997)

Abstract

Several inositol-containing compounds play key roles in receptor-mediated cell signaling events. Here, we describe a function for a specific inositol polyphosphate, d-myo-inositol 1,4,5,6-tetrakisphosphate [Ins(1,4,5,6)P₄], that is produced acutely in response to a receptor-independent process. Thus, infection of intestinal epithelial cells with the enteric pathogen Salmonella, but not with other invasive bacteria, induced a multifold increase in Ins(1,4,5,6)P₄ levels. To define a specific function of Ins(1,4,5,6)P₄, a membrane-permeant, hydrolyzable ester was used to deliver it to the intracellular compartment, where it antagonized epidermal growth factor (EGF)-induced inhibition of calcium-mediated chloride (Cl⁻) secretion (CaMCS) in intestinal epithelia. This EGF function is likely mediated through a phosphoinositide 3-kinase (PtdIns3K)-dependent mechanism because the EGF effects are abolished 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)P₄ antagonized EGF signaling downstream of PtdIns3K because Ins(1,4,5,6)P₄ interfered with the PtdInsP₃ effect on CaMCS without affecting PtdIns3K activity. Thus, elevation of Ins(1,4,5,6)P₄ in Salmonella-infected epithelia may promote Cl⁻ flux by antagonizing EGF inhibition mediated through PtdIns3K and PtdInsP₃.

Footnotes

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Abbreviations: PtdIns3K, phosphoinositide 3-kinase; PtdInsP₃, phosphatidylinositol 3,4,5-trisphosphate; CaMCS, calcium-mediated chloride secretion; EGF, epidermal growth factor; Ins(1,4,5,6)P₄, d-myo-inositol 1,4,5,6-tetrakisphosphate; ΔI_sc, short circuit current.