The human angiotensin II type 1 receptor +1166 A/C polymorphism attenuates microrna-155 binding

The adverse effects of angiotensin II (Ang II) are primarily mediated through the Ang II type 1 receptor (AT1R). A silent polymorphism (+1166 A/C) in the human AT1R gene has been associated with cardiovascular disease, possibly as a result of enhanced AT(1)R activity. Because this polymorphism occurs in the 3'-untranslated region of the human AT1R gene, the biological importance of this mutation has always been questionable. Computer alignment demonstrated that the +1166 A/C polymorphism occurred in a cis-regulatory site, which is recognized by a specific microRNA (miRNA), miR-155. miRNAs are noncoding RNAs that silence gene expression by base-pairing with complementary sequences in the 3'-untranslated region of target RNAs. When the +1166 C-allele is present, base-pairing complementarity is interrupted, and the ability of miR-155 to interact with the cis-regulatory site is decreased. As a result, miR-155 no longer attenuates translation as efficiently as demonstrated by luciferase reporter and Ang II radioreceptor binding assays. In situ hybridization experiments demonstrated that mature miR-155 is abundantly expressed in the same cell types as the AT1R (e.g. endothelial and vascular smooth muscle). Finally, when human primary vascular smooth muscle cells were transfected with an antisense miR-155 inhibitor, endogenous human AT1R expression and Ang II-induced ERK1/2 activation were significantly increased. Taken together, our study demonstrates that the AT1R and miR-155 are co-expressed and that miR-155 translationally represses the expression of AT1R in vivo. Therefore, our study provides the first feasible biochemical mechanism by which the +1166 A/C polymorphism can lead to increased AT1R densities and possibly cardiovascular disease.     

A novel angiotensin II type 1 receptor-associated protein induces cellular hypertrophy in rat vascular smooth muscle and renal proximal tubular cells

Angiotensin II stimulates cellular hypertrophy in cultured vascular smooth muscle and renal proximal tubular cells. This effect is believed to be one of earliest morphological changes of heart and renal failure. However, the precise molecular mechanism involved in angiotensin II-induced hypertrophy is poorly understood. In the present study we report the isolation of a novel angiotensin II type 1 receptor-associated protein. It encodes a 531-amino acid protein. Its mRNA is detected in all human tissues examined but highly expressed in the human kidney, pancreas, heart, and human embryonic kidney cells as well as rat vascular smooth muscle and renal proximal tubular cells. Protein synthesis and relative cell size analyzed by flow cytometry studies indicate that overexpression of the novel angiotensin II type 1 receptor-associated protein induces cellular hypertrophy in cultured rat vascular smooth muscle and renal proximal tubular cells. In contrast, the hypertrophic effects was reversed in renal proximal tubular cell lines expressing the novel gene in the antisense orientation and its dominant negative mutant, which lacks the last 101 amino acids in its carboxyl-terminal tail. The hypertrophic effects are at least in part mediated via protein kinase B activation or cyclin-dependent kinase inhibitor, p27(kip1) protein expression level in vascular smooth muscle, and renal proximal tubular cells. Moreover, angiotensin II could not stimulate cellular hypertrophy in renal proximal tubular cells expressing the novel gene in the antisense orientation and its mutant. These findings may provide new molecular mechanisms to understand hypertrophic agents such as angiotensin II-induced cellular hypertrophy.     

Selective down-regulation of angiotensin II receptor type 1A signaling by protein tyrosine phosphatase SHP-2 in vascular smooth muscle cells

The heptahelical AT(1) G-protein-coupled receptor lacks inherent tyrosine kinase activity. Angiotensin II binding to AT(1) nevertheless activates several tyrosine kinases and stimulates both tyrosine phosphorylation and phosphatase activity of the SHP-2 tyrosine phosphatase in vascular smooth muscle cells. Since a balance between tyrosine kinase and tyrosine phosphatase activities is essential in angiotensin II signaling, we investigated the role of SHP-2 in modulating tyrosine kinase signaling pathways by stably transfecting vascular smooth muscle cells with expression vectors encoding wild-type SHP-2 protein or a catalytically inactive SHP-2 mutant. Our data indicate that SHP-2 is an efficient negative regulator of angiotensin II signaling. SHP-2 inhibited c-Src catalytic activity by dephosphorylating a positive regulatory tyrosine 418 within the Src kinase domain. Importantly, SHP-2 expression also abrogated angiotensin II-induced activation of ERK, whereas expression of catalytically inactive SHP-2 caused sustained ERK activation. Thus, SHP-2 likely regulates angiotensin II-induced MAP kinase signaling by inactivating c-Src. These SHP-2 effects were specific for a subset of angiotensin II signaling pathways, since SHP-2 overexpression failed to influence Jak2 tyrosine phosphorylation or Fyn catalytic activity. These data show SHP-2 represents a critical negative regulator of angiotensin II signaling, and further demonstrate a new function for this phosphatase in vascular smooth muscle cells.     

Monocyte chemoattractant protein-1 mediates angiotensin II-induced vascular smooth muscle cell proliferation via SAPK/JNK and ERK1/2

Abnormal vascular smooth muscle cells proliferation is the pathophysiological basis of cardiovascular diseases, such as hypertension, atherosclerosis, and restenosis after angioplasty. Angiotensin II can induce abnormal proliferation of vascular smooth muscle cells, but the molecular mechanisms of this process remain unclear. Here, we explored the role and molecular mechanism of monocyte chemotactic protein-1, which mediated angiotensin II-induced proliferation of rat aortic smooth muscle cells. 1,000 nM angiotensin II could stimulate rat aortic smooth muscle cells' proliferation by angiotensin II type 1 receptor (AT(1)R). Simultaneously, angiotensin II increased monocyte chemotactic protein-1 expression and secretion in a dose-and time-dependent manner through activation of its receptor AT(1)R. Then, monocyte chemotactic protein-1 contributed to angiotensin II-induced cells proliferation by CCR2. Furthermore, we found that intracellular ERK and JNK signaling molecules were implicated in angiotensin II-stimulated monocyte chemotactic protein-1 expression and proliferation mediated by monocyte chemotactic protein-1. These results contribute to a better understanding effect on angiotensin II-induced proliferation of rat smooth muscle cells.     

Mechanisms linking angiotensin II and atherogenesis

PURPOSE OF REVIEW: The concept that angiotensin II plays a central role in early atherogenesis, progression to atherosclerotic plaque, and the most serious clinical sequelae of coronary artery disease is the subject of considerable current interest. Results from recent large clinical trials confirm that blunting of the renin-angiotensin system through either angiotensin converting enzyme inhibition or angiotensin II type 1 receptor blockade incurs significant beneficial outcomes in patients with coronary artery disease. The exact mechanisms for these effects are not yet clear, but are suggested by studies demonstrating that suppression of the renin-angiotensin system is associated with muted vascular oxidative stress. RECENT FINDINGS: As most of the biological effects of the renin-angiotensin system occur through stimulation of the angiotensin II type 1 receptor, the focus of this review is on changes in the vascular wall mediated by this receptor and primarily related to endothelial and vascular smooth muscle cells, monocyte/macrophages and platelets. The interactions between angiotensin II and nitric oxide exert particular demands on the vascular capacity to adapt to dyslipidemia, hypertension, estrogen deficiency and diabetes mellitus that appear to exacerbate atherogenesis. Associated with each of these conditions is angiotensin II-mediated stimulation of macrophages, platelet aggregation, plasminogen activator inhibitor 1, endothelial dysfunction, vascular smooth muscle cell proliferation and migration, apoptosis, leukocyte recruitment, fibrogenesis and thrombosis. SUMMARY: Inhibition of the actions of angiotensin II serves a dual purpose: indirectly through reduction of mechanical stress on the vascular wall, and directly by diminished stimulation for vascular restructuring and remodeling. Collectively, data from studies published over the last year confirm and extend the notion that angiotensin II is a true cytokine prevalent at all stages of atherogenesis.