EXTRACELLULAR-MATRIX STIMULATES PRODUCTION AND BREAKDOWN OF INOSITOL PHOSPHOLIPIDS

Adhesion of rat glomerular epithelial cells (GEC) to collagen stimulat es production of D-myo-inositol 1,4,5-trisphosphate (IP3) and 1,2-diac ylglycerol. This process is mediated via beta(1)-integrins, and it mod ulates GEC proliferation. In this study, we address the changes in ino sitol-lipid turnover induced by GEC adhesion to extracellular matrix ( ECM). The masses of both phosphatidylinositol 4,5-bisphosphate (PIP2) and IP3, as well as [H-3]inositol phosphates, were increased in GEC ad herent to collagen, compared with plastic substratum. Phosphatidylinos itol-4-phosphate (PIP) 5-kinase activity was predominantly membrane as sociated and was enhanced in GEC on collagen. Phospholipase C (PLC) ac tivity and PLC-gamma 1 protein were increased in membrane fractions of GEC adherent to collagen, compared with plastic. Stable overexpressio n of PLC-gamma 1 in GEC amplified the effect of ECM on the production of [H-3]inositol phosphates. In addition, the PLC-gamma 1 that was mem brane associated in collagen-adherent GEC was tyrosine phosphorylated. Thus production of IP3 in GEC adherent to ECM is associated with incr eased production of PIP2. Moreover, adhesion to ECM increases tyrosine phosphorylation and membrane association of PLC-gamma 1, which may fa cilitate PIP2 hydrolysis by increasing the catalytic activity of PLC-g amma 1 and the proximity of PLC-gamma 1 and its substrate. Understandi ng the process of ECM-induced inositol Lipid production and breakdown in GEC may provide insights into the regulation of GEC proliferation a nd differentiated functions in normal conditions and during glomerular injury.