Tumor Necrosis Factor Receptor-associated Factor-6 and Ribosomal S6 Kinase Intracellular Pathways Link the Angiotensin II AT1 Receptor to the Phosphorylation and Activation of the IκB Kinase Complex in Vascular Smooth Muscle Cells

Abstract

Activation of NF-B transcription factors by locally produced angiotensin II (Ang II) is proposed to be involved in chronic inflammatory reactions leading to atherosclerosis development. However, a clear understanding of the signaling cascades coupling the Ang II AT1 receptors to the activation of NF-B transcription factors is still lacking. Using primary cultured aortic vascular smooth muscle cells, we show that activation of the IKK complex and NF-B transcription factors by Ang II is regulated by phosphorylation of the catalytic subunit IKK␤ on serine residues 177 and 181 in the activation T-loop. The use of pharmacological inhibitors against conventional protein kinases C (PKCs), mitogen-activated/extracellular signal-regulated kinase (MEK) 1/2, ribosomal S6 kinase (RSK), and silencing RNA technology targeting PKC␣, IKK␤ subunit, tumor growth factor ␤-activating kinase-1 (TAK1), the E3 ubiquitin ligase tumor necrosis factor receptor-associated factor-6 (TRAF6), and RSK isoforms, demonstrates the requirement of two distinct signaling pathway for the phosphorylation of IKK␤ and the activation of the IKK complex by Ang II. Rapid phosphorylation of IKK␤ requires a second messenger-dependent pathway composed of PKC␣-TRAF6-TAK1, whereas sustained phosphorylation and activation of IKK␤ requires the MEK1/2-ERK1/2-RSK pathway. Importantly, simultaneously targeting components of these two pathways completely blunts the phosphorylation of IKK␤ and the proinflammatory effect of the octapeptide. This is the first report demonstrating activation of TAK1 by the AT1R. We propose a model whereby TRAF6-TAK1 and ERK-RSK intracellular pathways independently and sequentially converge to the T-loop phosphorylation for full activation of IKK␤, which is an essential step in the proinflammatory activity of Ang II.

Characterization of a murine model of endothelial dysfunction induced by chronic intraperitoneal administration of angiotensin II

“…Moreover, the combined effect of AGII, oxidative stress, and inflammation induces fibrosis, as well as the proliferation and migration of vascular smooth muscle cells (VSMC), which further contribute to vascular remodeling ang hypertension 3 , 4 . The observed increase in blood pressure can be explained in part because AGII and ROS activate the ERK1/2 41 , 42 , JNK and NF-kB signaling pathways 43 – 45 , leading to the activation of matrix metalloproteinases (MMPs) and the production of growth factors like the epidermal growth factor (EGF), platelet-derived growth factor (PDGF), and insulin-like growth factor (IGF) 4 , 8 . These molecules promote the accumulation of extracellular matrix proteins (collagen and fibronectin) and the proliferation and migration of VSMC, which result in vascular remodeling 4 , 18 .…”

G Protein-Coupled Receptors Directly Bind Filamin A with High Affinity and Promote Filamin Phosphorylation

“…Ser/Thr kinase such as ribosomal S6 kinase activated upon AT1R activation is a known FLNa phosphorylating kinase. 50 , 56 Overall, kinases increase pFLNa levels in the cells and likely promote cytoskeletal assembly. Taken together, these two receptors seem to couple with filamin during or immediately after agonist activation.…”

Crucial Role of CD40 Signaling in Vascular Wall Cells in Neointimal Formation and Vascular Remodeling After Vascular Interventions

“…31 It has previously been shown that blockage of local vascular TRAF6 diminished vascular inflammation and intimal lesion formation upon injury. 31,32 Apart from linking CD40 to downstream signaling events, TRAF6 also serves as adaptor protein for other cell receptors in SMCs, including TNFR, TLR, IL-1R, and angiotensin II AT1R, 33–35 whereby it regulates the biological functions of a variety of proinflammatory cytokines. Thus, CD40-dependent expression of TRAF6 in SMCs may serve as a feedback mechanism to modulate itself or other TRAF6 dependent pathways that contribute to vascular response to injury and the development of neointimal formation.…”