A new cellular signaling mechanism for angiotensin II activation of NF-kappaB: An IkappaB-independent, RSK-mediated phosphorylation of p65.
OBJECTIVE
Angiotensin II (Ang II) promotes vascular inflammation and remodeling via activation of nuclear factor kappaB (NF-kappaB)-mediated transcription of proinflammatory genes such as interleukin-6 (IL-6). We examined the signaling mechanism whereby Ang II activates NF-kappaB in vascular smooth muscle cells (VSMCs).


RESULTS
Ang II treatment did not increase phosphorylation of inhibitor of kappaBalpha (IkappaBalpha) or IkappaBbeta 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-kappaB promoter activity, NF-kappaB 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-kappaB and p65 phosphorylation. Immunopurified RSK from Ang II-treated VSMCs phosphorylated recombinant glutathione S-transferase-p65 in vitro.


CONCLUSIONS
We uncovered a nonclassical signaling pathway (Ras/MEK1/ERK/RSK) from Ang II to activation of NF-kappaB, a mechanism by which Ang II stimulates RSK-mediated phosphorylation of p65 to participate in vascular inflammation.
Zhang
Liping
L
Department of Internal Medicine, The University of Texas Medical Branch, Galveston 77555-1064, USA.
Ma
Yewei
Y
Zhang
Jiqiang
J
Cheng
Jizhong
J
Du
Jie
J
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000166:cytology; D002478:Cells, Cultured; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D010766:Phosphorylation / Q000187:drug effects; D034741:RNA, Small Interfering; D051381:Rats; D017207:Rats, Sprague-Dawley; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D051996:Transcription Factor RelA / Q000378:metabolism*; D014657:Vasculitis / Q000378:metabolism*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D018631:ras Proteins / Q000378:metabolism
D034741:RNA, Small Interfering; D051996:Transcription Factor RelA; D014662:Vasoconstrictor Agents; D000804:Angiotensin II; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C512963:Rps6ka1 protein, rat; D048049:Extracellular Signal-Regulated MAP Kinases; D048369:MAP Kinase Kinase 1; D018631:ras Proteins