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

Objective—Angiotensin II (Ang II) promotes vascular inflammation and remodeling via activation of nuclear factor &kgr;B (NF-&kgr;B)–mediated transcription of proinflammatory genes such as interleukin-6 (IL-6). We examined the signaling mechanism whereby Ang II activates NF-&kgr;B in vascular smooth muscle cells (VSMCs). Methods and Results—Ang II treatment did not increase phosphorylation of inhibitor of &kgr;B&agr; (I&kgr;B&agr;) or I&kgr;B&bgr; 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 NF-&kgr;B promoter activity, NF-&kgr;B 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 NF-&kgr;B 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 NF-&kgr;B, a mechanism by which Ang II stimulates RSK-mediated phosphorylation of p65 to participate in vascular inflammation.

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