Differential Involvement of Cytoskeleton and Rho-Guanosine 5′-Triphosphatases in Growth-Promoting Effects of Angiotensin II in Rat Adrenal Glomerulosa Cells

Glomerulosa cells readily proliferate in primary culture. However, 3-d treatment with angiotensin II (Ang II) promotes cellular hypertrophy with a concomitant decrease in proliferation. The aim of the present study was to investigate the manner by which cytoskeleton and Rho-GTPase proteins may be involved in Ang II-induced growth and MAPK activation. Preincubation with Y27632 (an inhibitor of Rho-associated kinase) decreased basal proliferation, as did Ang II, whereas toxin B, which inhibits Rho-GTPases, enhanced the inhibitory effect of Ang II. Conversely, toxin B inhibited protein synthesis induced by Ang II, whereas Y27632 had no effect. Ang II induced a rapid but transient activation of RhoA/B, an effect abolished in Y27632-preincubated cells. Activation of Rac appeared biphasic, with an early activation at 1 min, followed by a more sustained effect at 10 min. Toxin B abolished Rac activation. Immunofluorescence studies revealed that Y27632 and toxin B disrupted the F-actin network similarly to Ang II. Y27632 also abolished the cortical F-actin ring induced by Ang II. Preincubation of cells with toxin B abolished p38 MAPK phosphorylation and early activation of p42(mapk) (ERK2) and decreased p44(mapk) (ERK1) induced by Ang II. In contrast, Y27632, abolished p44(mapk) (ERK1) but had no effect on p42(mapk) (ERK2) or p38. Together these results indicate that, in rat adrenal glomerulosa cells, specific Rho/Rho-associated kinase-dependent activation of p44(mapk) (ERK1) and an intact cytoskeletal organization are necessary in mediating basal cell proliferation, whereas activation of p42/p44(mapk), p38 MAPK, and Rac are essential in mediating Ang II-induced protein synthesis (steroidogenic acute regulatory protein and 3beta-hydroxysteroid dehydrogenase).