Gα_12/13-mediated production of reactive oxygen species is critical for angiotensin receptor-induced NFAT activation in cardiac fibroblasts

Angiotensin II (Ang II) activates multiple signaling pathways leading to hyperplasia of cardiac fibroblasts. Reactive oxygen species (ROS) produced by Ang II stimulation are assumed to play pivotal roles in this process. Here, we show that ROS mediate Ang II-induced activation of nuclear factor of activated T cells (NFAT) in rat cardiac fibroblasts. Ang II-induced NFAT activation was suppressed by diphenyleneiodonium (an NADPH oxidase inhibitor), dominant negative (DN)-Rac, DN-p47_phox, and an inhibitor of Gα_12/13 (Gα_12/13-specific regulator of G protein signaling domain of p115RhoGEF, p115-regulator of G protein signaling (RGS)). Stimulation of Ang II receptor increased the intracellular ROS level in a Rac- and p47_phox-dependent manner. Because p115-RGS suppressed Ang II-induced Rac activation, Ang II receptor-coupled Gα_12/13 mediated NFAT activation through ROS production by Rac activation. Ang II-induced nuclear translocation of the green fluorescent protein (GFP)-tagged amino-terminal region of NFAT4 (GFP-NFAT4) was suppressed by p115-RGS or BAPTA but not by diphenyleneiodonium. The expression of constitutively active (CA)-Gα₁₂, CA-Gα₁₃, or CA-Rac increased the nuclear translocation of GFP-NFAT4. These results suggest that NFAT activity is regulated by both Ca²⁺-dependent and ROS-dependent pathways. Furthermore, activation of c-Jun NH₂-terminal kinase (JNK) induced by Ang II stimulation is required for NFAT activation because Ang II-induced NFAT activation was inhibited by SP600125, a selective JNK inhibitor. These results indicate that Ang II stimulates the nuclear translocation and activation of NFAT by integrated pathways including the activation of Gα_12/13, Rac, NADPH oxidase, and JNK and that Gα_12/13-mediated ROS production is essential for NFAT transcriptional activation.