Extracellular matrix stimulates production and breakdown of inositol phospholipids

Adhesion of rat glomerular epithelial cells (GEC) to collagen stimulates production of D-myo-inositol 1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol. This process is mediated via beta 1-integrins, and it modulates GEC proliferation. In this study, we address the changes in inositol-lipid turnover induced by GEC adhesion to extracellular matrix (ECM). The masses of both phosphatidylinositol 4,5-bisphosphate (PIP2) and IP3, as well as [3H]inositol phosphates, were increased in GEC adherent to collagen, compared with plastic substratum. Phosphatidylinositol-4-phosphate (PIP) 5-kinase activity was predominantly membrane associated and was enhanced in GEC on collagen. Phospholipase C (PLC) activity and PLC-gamma 1 protein were increased in membrane fractions of GEC adherent to collagen, compared with plastic. Stable overexpression of PLC-gamma 1 in GEC amplified the effect of ECM on the production of [3H]inositol phosphates. In addition, the PLC-gamma 1 that was membrane associated in collagen-adherent GEC was tyrosine phosphorylated. Thus production of IP3 in GEC adherent to ECM is associated with increased production of PIP2. Moreover, adhesion to ECM increases tyrosine phosphorylation and membrane association of PLC-gamma 1, which may facilitate PIP2 hydrolysis by increasing the catalytic activity of PLC-gamma 1 and the proximity of PLC-gamma 1 and its substrate. Understanding the process of ECM-induced inositol lipid production and breakdown in GEC may provide insights into the regulation of GEC proliferation and differentiated functions in normal conditions and during glomerular injury.