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In Adrenal Glomerulosa Cells, Angiotensin II Inhibits Proliferation by Interfering with Fibronectin-Integrin Signaling

Service of Endocrinology (M.O., N.G.-P.), Department of Medicine, and Department of Physiology and Biophysics (S.C., M.D.P.), Faculty of Medicine, Université de Sherbrooke, Sherbrooke, Quebec, Canada J1H 5N4

Address all correspondence and requests for reprints to: Dr. Nicole Gallo-Payet, Service of Endocrinology, Faculty of Medicine, Université de Sherbrooke, 3001, 12th Avenue North, Sherbrooke, Quebec, Canada J1H 5N4. E-mail: Nicole.Gallo-Payet{at}USherbrooke.ca.

Angiotensin II (Ang II), through the Ang II type 1 receptor subtype, inhibits basal proliferation of adrenal glomerulosa cells by inducing the disruption of actin stress fiber organization. This effect is observed in cells cultured on plastic or on fibronectin. The aim of the present study was to investigate how Ang II may interfere with extracellular matrix/integrin signaling. In cells treated for 3 d with echistatin (EC) (a snake-venom RGD-containing protein that abolishes fibronectin binding to ₅β₁ or _vβ₃ integrins), basal proliferation decreased by 38%, whereas Ang II was unable to abolish basal proliferation. In cells grown on fibronectin, Ang II decreased binding of paxillin to focal adhesions and, similarly to EC, induced a rapid dephosphorylation of paxillin (1 min), followed by an increase after 15 min. Fibronectin enhanced RhoA/B and Rac activation induced by Ang II, an effect abolished by EC. Under basal conditions, paxillin was more readily associated with RhoA/B than with Rac. Stimulation with Ang II induced a transient decrease in RhoA/B-associated paxillin (after 5 min), with a return to basal levels after 10 min, while increasing Rac-associated paxillin. Finally, results reveal that glomerulosa cells are able to synthesize and secrete fibronectin, a process by which cells can stimulate their own proliferative activity when cultured on plastic. Together, these results suggest that Ang II acts at the level of integrin-paxillin complexes to disrupt the well- developed microfilament network, a condition necessary for the inhibition of cell proliferation and initiation of steroidogenesis.