A New Cellular Signaling Mechanism for Angiotensin II Activation of NF- B An I B–Independent, RSK–Mediated Phosphorylation of p65

Objective—Angiotensin II (Ang II) promotes vascular inflammation and remodeling via activation of nuclear factor B (NFB)–mediated transcription of proinflammatory genes such as interleukin-6 (IL-6). We examined the signaling mechanism whereby Ang II activates NFB in vascular smooth muscle cells (VSMCs). Methods and Results—Ang II treatment did not increase phosphorylation of inhibitor of B (I B ) or I B or decrease their levels. In contrast, mitogen-activated protein kinase kinase-1 (MEK1) inhibition (dominant-negative MEK1 adenovirus or inhibitor U0126) suppressed Ang II–induced NFB promoter activity, NFB DNA-binding activity, p65 phosphorylation, and led to 70% reduction in IL-6 transcription/production. The mechanism involved Ang II activation of Ras and MEK1. Signaling distal to MEK1 involved extracellular signal-regulated kinase (ERK) because inhibition of MEK1 suppressed the Ang II–induced activation of ribosomal S6 kinase (RSK), a substrate of ERK. Downregulation of RSK by small interfering RNA (SiRNA) in VSMCs was found to suppress Ang II–induced activation of NFB and p65 phosphorylation. Immunopurified RSK from Ang II–treated VSMCs phosphorylated recombinant glutathione S-transferase– p65 in vitro. Conclusion—We uncovered a nonclassical signaling pathway (Ras/MEK1/ERK/RSK) from Ang II to activation of NFB, a mechanism by which Ang II stimulates RSK-mediated phosphorylation of p65 to participate in vascular inflammation. (Arterioscler Thromb Vasc Biol. 2005;25:1148-1153.)