AT2 receptors cross talk with AT1 receptors through a nitric oxide- and RhoA-dependent mechanism resulting in decreased phospholipase D activity

ANG II activation of phospholipase D (PLD) is required for ERK and NAD(P)H oxidase activation, both of which are involved in hypertension. Previous findings demonstrate that ANG II stimulates PLD activity through AT1 receptors in a RhoA-dependent mechanism. Additionally, endogenous AT2 receptors in preglomerular smooth muscle cells attenuate ANG II-mediated PLD activity. In the present study, we examined the signal transduction mechanisms used by endogenous AT2 receptors to modulate ANG II-induced PLD activity through either PLA2 generation of lysophosphatidylethanolamine or Gαi-mediated generation of nitric oxide (NO) and interaction with RhoA. Blockade of AT2 receptors, Gαi and NO synthase, but not PLA2, enhanced ANG II-mediated PLD activity in cells rich in, but not poor in, AT2 receptors. Moreover, NO donors, a direct activator of guanylyl cyclase and a cGMP analog, but not lysophosphatidylethanolamine, inhibited ANG II-mediated PLD activity, whereas an inhibitor of guanylyl cyclase augmented ANG II-induced PLD activity. AT2 receptor- and NO-mediated attenuation of ANG II-induced PLD activity was completely lost in cells transfected with S188A RhoA, which cannot be phosphorylated on serine 188. Therefore, our data indicate that AT2 receptors activate Gαi, subsequently stimulating NO synthase and leading to increased soluble guanylyl cyclase activity, generation of cGMP, and activation of a protein kinase, resulting in phosphorylation of RhoA on serine 188. Furthermore, because AT2 receptors inhibit AT1 receptor signaling to PLD via modulating RhoA activity, AT2 receptor signaling can potentially regulate multiple vasoconstrictive signaling systems through inactivating RhoA.