HIV-1 Tat Activates Dual Nox Pathways Leading to Independent Activation of ERK and JNK MAP Kinases

Abstract

Human immunodeficiency virus, type 1 Tat is known to exert pleiotropic effects on the vascular endothelium through mitogen-activated protein (MAP) kinases, although the signaling pathways leading to MAP kinase activation are incompletely understood. We focused on proximal pathways potentially governing downstream MAP kinase activity by Tat. Within 2 min, Tat activated both Ras and Rho GTPases in endothelial cells, leading to ERK phosphorylation by 10 min. Notably, Rac1 was necessary for downstream activation of RhoA and both Rac1 and RhoA acted upstream of the Ras/ERK cassette. Antioxidants and the oxidase inhibitor diphenylene iodonium blocked ERK phosphorylation, but specific interference with the canonical Nox2 oxidase had no effect on ERK. Instead, knock down of the novel oxidase Nox4 completely suppressed Tat-dependent Ras and ERK activation downstream of Rac1 and RhoA. Conversely, interference with Rac1, PAK1, and Nox2 blocked JNK phosphorylation, whereas RhoA(N19) and Nox4 knock down did not. Further, knock down of Nox2, but not Nox4, blocked Tat-induced cytoskeletal rearrangement, whereas knock down of Nox4, but not Nox2, blocked Tat-dependent proliferation. Rac1, therefore, bifurcates Tat signaling, leading to concurrent but separate Nox4-dependent Ras/ERK activation, and Nox2-dependent JNK activation. Tat signaling, therefore, provides an example of Nox-specific differential control of MAP kinase pathways.

Nox4-Derived H2O2 Mediates Endoplasmic Reticulum Signaling through Local Ras Activation

“…To gain further support for the role of Nox4 in specific ER signaling events, we examined the involvement of other known signaling pathways, focusing on the agonist Tat. When stimulated acutely with Tat, RhoA and Ras are transiently activated (44). Under these conditions, RhoA acts upstream of Nox4, which in turn leads to downstream Ras activation.…”

NADPH oxidase-4 mediates protection against chronic load-induced stress in mouse hearts by enhancing angiogenesis

“…[17][18][19][20]. These differences in regulation, activation mechanism, subcellular location, and ROS generation translate into isoform-specific actions in isolated cellular models (9,19,22,33). In the heart, previous studies in mouse models of defective Nox2 activation or its deletion showed that Nox2 is detrimental during remodeling, causing increased hypertrophy, apoptosis, and contractile dysfunction (10)(11)(12)(13)(14)(15).…”

Hepatitis C Virus (HCV) Proteins Induce NADPH Oxidase 4 Expression in a Transforming Growth Factor β-Dependent Manner: a New Contributor to HCV-Induced Oxidative Stress

“…Although Nox4 is a constitutively active ROS-generating enzyme, increased expression of mRNA, protein, and ROS has been detected in response to inflammatory stimuli. Recent work suggests that Nox4-derived ROS are involved in transforming growth factor ␤ (TGF-␤)-induced fibrosis, ER stress, human immunodeficiency virus type 1-activated cell signaling, beta interferon-regulated transcription, and Toll-like receptor 4-mediated pathways (10,14,(51)(52)(53)72). However, little is known about the function of Nox4 in the liver under inflammatory conditions.…”