Connection between integrins and cell activation in rat adrenal glomerulosa cells: A role for Arg-Gly-Asp peptide in the activation of the p42/p44mapk pathway and intracellular calcium

Abstract

Integrins are responsible for adhesion and activation of several intracellular cascades. The present study was aimed at determining whether the interaction between fibronectin and integrins could generate pathways involved in physiological functions of rat adrenal glomerulosa cells. Immunofluorescence studies and adhesion assays showed that fibronectin was the best matrix in promoting the formation of focal adhesion. Binding of glomerulosa cells to fibronectin, but not to collagen I or poly-L-lysine, involved the integrin-binding sequence Arg-Gly-Asp (RGD). Activation of glomerulosa cells with Arg-Gly-Asp-Ser (RGDS) induced an increase in [Ca2+]i, whereas fibronectin triggered a release of Ca2+ from InsP3-sensitive Ca2+ stores. Aldosterone secretion induced by ACTH, angiotensin II, and RGDS and proliferation were improved on fibronectin, compared with poly-L-lysine. The RGDS peptide induced a transient increase in the activity of the p42/p44mapk, independent of phosphatidylinositol-3 kinase and protein kinase C. Integrins α5 and αv as well as their fibronectin receptor partners β1 and β3, were identified. These results suggest that in rat adrenal glomerulosa cells, binding of the α5β1, αvβ1, αvβ3 integrins to fibronectin is involved in the generation of two important signaling events, increase in intracellular calcium, and activation of the p42/p44mapk cascade, leading to cell proliferation and aldosterone secretion.