A new cellular signaling mechanism for angiotensin II activation of NF-kappaB: An IkappaB-independent, RSK-mediated phosphorylation of p65.
ABSTRACT 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).
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.
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.
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ABSTRACT: The p90 ribosomal S6 kinase (RSK) constitute a family of serine/threonine kinases activated downstream of the Ras/mitogen-activated protein kinase (MAPK) pathway. In mammals, four RSK genes have been identified (RSK1, RSK2, RSK3 and RSK4), and RSK orthologues have also been described in D. melanogaster and C. elegans, but not in yeast or plants. The RSK isoforms are composed of two distinct and functional kinase domains that are activated in a sequential manner by a series of phosphorylation events. These enzymes were among the first substrates of extracellular signal-regulated kinase (ERK) to be discovered and have proven to be ubiquitous and multifunctional mediators of ERK signal transduction. While the RSK isoforms promote cell survival though the inactivation of several apoptotic effectors, they also appear to mediate cell growth and proliferation by simultaneously regulating substrates involved in gene transcription and mRNA translation. RSK1-4 are ubiquitously expressed in cell lines and tissues, and at present, little is known about specific and overlapping functions of individual RSK isoforms. The upregulation of RSK1 and RSK2 expression in different types of cancer suggest that they may be involved in oncogenesis and could potentially be targeted in anti-cancer therapies. The recent identification of specific RSK inhibitors will likely help addressing the biological functions of the RSK isoforms and their contributions in pathological conditions.Frontiers in Bioscience 02/2008; 13:4258-75. · 3.52 Impact Factor
Article: Proinflammatory protein CARD9 is essential for infiltration of monocytic fibroblast precursors and cardiac fibrosis caused by Angiotensin II infusion.[show abstract] [hide abstract]
ABSTRACT: Angiotensin II (Ang II)-induced cardiac remodeling with the underlying mechanisms involving inflammation and fibrosis has been well documented. Cytosolic adaptor caspase recruitment domain 9 (CARD9) has been implicated in the innate immune response. We aimed to examine the role of CARD9 in inflammation and cardiac fibrosis induced by Ang II. Two-month-old CARD9-deficient (CARD9(-/-)) and wild-type (WT) male mice were infused with Ang II (1,500 ng/kg/min) or saline for 7 days. Heart sections were stained with hematoxylin and eosin and Masson trichrome and examined by immunohistochemistry; and activity and protein levels were measured in macrophages obtained from mice. WT mice with Ang II infusion showed a marked increase in CARD9(+) macrophages in the heart, but CARD9(-/-) mice showed significantly suppressed macrophage infiltration and expression of proinflammatory cytokines, including interleukin-1β (IL-1β) and connective tissue growth factor (CTGF). Importantly, Ang II-induced cardiac fibrosis (extracellular matrix and collagen I deposition) was diminished in CARD9(-/-) hearts, as was the expression of transforming growth factor-β (TGF-β) and level of myofibroblasts positive for α-smooth muscle actin (α-SMA). Furthermore, Ang II activation of nuclear factor-κB (NF-κB), JNK and p38 mitogen-activated protein kinases (MAPKs) in WT macrophages was reduced in CARD9(-/-) macrophages. CARD9 plays an important role in regulating cardiac inflammation and fibrosis in response to elevated Ang II.American Journal of Hypertension 03/2011; 24(6):701-7. · 3.18 Impact Factor