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 3 beta-hydroxysteroid dehydrogenase).