Hybrid formation between the intracellular faces of the bradykinin B2 and angiotensin II AT1 receptors and signal transduction

Gene Polymorphisms of Angiotensin II Type 1 Receptor and Angiotensin-Converting Enzyme in Two Ethnic Groups Living in Zhejiang Province, China

Polymorphisms of ACE insertion/deletion (I/D) and angiotensin II type 1 receptor (AT1R) 1166A-C have been associated with many diseases, and distributions of their genotypes vary in different races and populations. The aim of this study was to investigate distributions of angiotensin-converting enzyme (ACE) and AT1R genotypes in Han and She populations in ZheJiang province. We determined ACE and AT1R genotypes in 189 Han and 163 She individuals. DNA was extracted from peripheral blood samples. Analyses of ACE and AT 1R genotypes were performed by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). The frequencies of ACE genotypes and alleles among the Han sample (41.3%II, 41.3%ID, 17.5%DD; 61.9%I allele, 38.1%D allele) were similar to those among She individuals (39.9%II, 39.3%ID, 20.9%DD; 59.5%I allele, 40.5%D allele), with p=0.660; p=0.421. However, significant differences in the distributions of ACE polymorphism between men and women among She population were observed, with p=0.042, p=0.014. AT1R genotype and allele frequencies in the Han population were (88.4%AA, 11.1%AC, 0.5%CC) and (93.9%A allele, 6.1%C) allele respectively. In the She population they were (78.0%AA, 21.3%AC, 0.6%CC) and (89.0%A allele, 11.0%C allele). The significant differences were found between Han and She populations with p=0.031, p=0.018, and within subgroups of women, with p=0.010, p=0.021. There were no significant differences within subgroups of men (p=0.476, p=0.261). The genotype distributions or allele frequencies of ACE and AT1R were significantly different between the samples of the She and Han populations.

Angiotensin II Type 1 Receptor Gene A1166C Polymorphism Was Not Associated With Acute Coronary Syndrome in an Iranian Population

Background

There are very limited data for Iranian populations on the predisposing genetic factors for acute coronary syndrome (ACS).

Objectives

The objective of the present study was to investigate the association of the angiotensin II type 1 receptor (AT1R) gene polymorphism and ACS in an Iranian population.

Patients and Methods

This cross-sectional study was conducted among 263 subjects (97 men and 166 women). Patients (n = 128) aged 30 - 80 years with chest pain were recruited from the emergency department of Ghaem Hospital (Mashhad, Iran). A 12-lead electrocardiograph plus creatine kinase MB (CK-MB) levels were used as the basis for the diagnosis of myocardial ischemia. The control group was selected from age-matched healthy subjects (n = 135). Non-enzymatic kits were used for extraction of DNA from blood samples. Polymerase chain reaction (PCR) was performed to amplify the DNA fragments. For restriction fragment length polymorphism (RFLP) determination, the DdeI enzyme was used to digest the amplified DNA fragments. Statistical analyses were performed using SPSS version 13.0.

Results

There was no statistical difference in the genotype frequency of patients and healthy subjects with regard to age and gender (P > 0.05).

Conclusions

The AT1R A1166C polymorphism appeared not to be associated with the presence of ACS in the population studied.

Association between angiotensin II type 1 receptor polymorphism and sudden cardiac death in myocardial infarction

Objective. The renin-angiotensin system is involved in the pathogenesis of coronary artery disease and myocardial infarction (MI). Angiotensin II (Ang II) has many adverse effects such as vasoconstriction and vascular remodeling, and these actions are mediated by the angiotensin II type 1 receptor (AT1R). Patients and Methods. A total of 1376 patients were recruited from January 2010 to April 2012. The study group consisted of 749 patients with ACS (317 females and 432 males) and of 627 healthy controls. Results. The ACS patients demonstrated a lower proportion of AA genotypes and AC genotypes but higher proportions of CC genotypes than the control population. The AT1R CC genotype conferred a 2.76-fold higher risk of MI compared with the genotype AC and AA. In addition, the CC genotype was also associated with a 4.08 times higher risk of left anterior descending artery infarction and a 3.07 times higher risk of anterior wall infarction. We also found that the CC genotype was independently associated with sudden cardiac death. In Summary. This study demonstrated that the AT1R CC genotype is an independent risk factor for ACS incidence, and this genotype is associated with a greater ACS severity and greater risk of sudden cardiac death.

Kinin-mediated inflammation in neurodegenerative disorders

The mediatory role of kinins in both acute and chronic inflammation within nervous tissues has been widely described. Bradykinin, the major representative of these bioactive peptides, is one of a few mediators of inflammation that directly stimulates afferent nerves due to the broad expression of specific kinin receptors in cell types in these tissues. Moreover, kinins may be delivered to a site of injury not only after their production at the endothelium surface but also following their local production through the enzymatic degradation of kininogens at the surface of nerve cells. A strong correlation between inflammatory processes and neurodegeneration has been established. The activation of nerve cells, particularly microglia, in response to injury, trauma or infection initiates a number of reactions in the neuronal neighborhood that can lead to cell death after the prolonged action of inflammatory substances. In recent years, there has been a growing interest in the effects of kinins on neuronal destruction. In these studies, the overexpression of proteins involved in kinin generation or of kinin receptors has been observed in several neurologic disorders including neurodegenerative diseases such Alzheimer's disease and multiple sclerosis as well as disorders associated with a deficiency in cell communication such as epilepsy. This review is focused on recent findings that provide reliable evidence of the mediatory role of kinins in the inflammatory responses associated with different neurological disorders. A deeper understanding of the role of kinins in neurodegenerative diseases is likely to promote the future development of new therapeutic strategies for the control of these disorders. An example of this could be the prospective use of kinin receptor antagonists.

Angiotensin II type 1 receptor gene polymorphism in myocardial infarction patients

Introduction. Acute myocardial infarction is commonly known as heart attack. It is a multifactorial disease influenced by environmental and genetic factors.The objective of the present study was to investigate the association of the angiotensin II type 1 receptor gene A/C polymorphism in South Indian myocardial infarction patients.

Subjects and methods. The present study included a total number of 221 subjects (107 myocardial infarction patients and 114 age- and sex-matched controls). Demographic and clinical characteristics were collected. Lipid profiles were estimated. DNA was isolated and the angiotensin II type 1 receptor gene A/C polymorphism was determined by polymerase chain reaction.

Results. Comparison of the lipid profiles between patients and controls showed that patients had statistically highly significant values (p=0.0001).The CC genotype of the angiotensin II type 1 receptor was not associated with myocardial infarction patients when compared to controls. CC vs. AA was χ2 = 2.08, odds ratio 2.30, 95% confidence interval 0.72 — 7.23, and p value was 0.14.

Conclusion. The angiotensin II type 1 receptor CC genotype is not a risk factor for myocardial infarction in patients in a South Indian population.

Modulation by bradykinin of angiotensin type 1 receptor-evoked RhoA activation of connective tissue growth factor expression in human lung fibroblasts

The mechanisms regulating the opposing physiological actions of bradykinin (BK) and angiotensin II (AngII) are not well understood. Here we investigate signaling interactions between these two effectors. Connective tissue growth factor (CTGF) expression in IMR-90, human lung fibroblasts, is used as the endpoint target. In these cells the BK B2 receptor (BKB2R) is expressed constitutively, while no binding of AngII is detected. An inducible expression system is used to insert AngII receptor 1 (AT1R) and to obtain a signal level in response to AngII at the magnitude of BK. AngII and BK activate G protein-coupled targets, arachidonate release from cellular phospholipid stores, and intracellular phosphatidylinositol turnover equally. Both activate ERK, JNK, and p38 equally. However, AngII activates, whereas BK inactivates, RhoA. AngII induces a rapid (1 h) CTGF mRNA expression. RhoA siRNA and RhoA activation inhibitor, Y-27632, markedly reduce the AngII effect. Simultaneous treatment with BK and AngII attenuates the AT1R action. Additionally, BK in the absence of AngII lowers CTGF mRNA expression below basal levels over a span of 4 h. An AT1R/BKB2R chimera lacking heterotrimeric G protein coupling continues to activate MAP kinases to the same extent as wild-type (WT) AT1R and BKB2R. However, the increase of CTGF mRNA expression by this mutant is low, almost identical with that obtained by the simultaneous treatment of the WT AT1R-expressing cells with BK and AngII. In this context the chimeric receptor displays the characteristics of both receptors. These data demonstrate that, in human lung fibroblasts, BK modulates the action of AngII through the small G protein RhoA, but in a Galphai/Galphaq-independent manner.

Microarray and phosphokinase screenings leading to studies on ERK and JNK regulation of connective tissue growth factor expression by angiotensin II 1a and bradykinin B2 receptors in Rat1 fibroblasts

Rat1 fibroblasts stably transfected with the rat angiotensin II (AngII) AT1a and bradykinin (BK) B2 receptor cDNAs gained the ability to bind Ang II and BK. Wild-type Rat1 cells bound neither ligand. Exposure to either effector led to characteristic Galphai and Galphaq signal cascades, the release of arachidonic acid (ARA), and the intracellular accumulation of inositol phosphates (IP). Microarray analyses in response to BK or AngII showed that both receptors markedly induce the CCN family genes, CTGF (CCN2) and Cyr61 (CCN1), as well as the vasculature-related genes, Cnn1 and Egr1. Real time PCR confirmed the increased expression of connective tissue growth factor (CTGF) mRNA. Combined sequence-based analysis of gene promoter regions with statistical prevalence analyses identified CREB, SRF, and ATF-1, downstream targets of ERK, and JNK, as prominent products of genes that are regulated by ligand binding to the BK or AngII receptors. The binding of AngII or BK markedly stimulated the phosphorylation and thus the activation of ERK2, JNK, and p38MAPK. A BKB2R and an AT1aR chimera which displayed only negligible G-protein-related signaling were constructed. Both mutant receptors continued to activate these kinases and stimulate CTGF expression. Inhibitors of ERK1/2 and JNK but not p38MAPK inhibited the BK- and AngII-stimulated expression of CTGF in cells expressing either the WT or mutant receptors, illustrating that ERK and JNK participate in the control of CTGF expression in a manner that appears to be independent of G-protein. Conversely, addition of BK or AngII to the cell line expressing WT AT1aR and BKB2R downregulated the expression of collagen alpha1(I) (COL1A1) mRNA. However, these effectors did not have this effect in cells expressing the mutant receptors. Thus, a robust G-protein related response is necessary for BK or AngII to affect COL1A1 expression.

Tyrosine kinase and mitogen-activated protein kinase/extracellularly regulated kinase differentially regulate intracellular calcium concentration responses to angiotensin II/III and bradykinin in rat cortical thick ascending limb

The cortical thick ascending limb (CTAL) coexpresses angiotensin (Ang) II/Ang III receptor type 1A (AT(1A)-R) and bradykinin (BK) receptor type 2 (B2-R). In several cell types, these two receptors share the same signaling pathways, although their physiological functions are often opposite. In CTAL, little is known about the intracellular transduction events leading to the final physiological response induced by these two peptides. We investigated and compared in this segment the action of Ang II/III and BK on intracellular calcium concentration ([Ca2+]i) response and metabolic CO2 production, an index of Na+ transport, by using inhibitors of protein kinase C (bisindolylmaleimide), Src tyrosine kinase (herbimycin A and PP2), and MAPK/ERK (PD98059 and UO126). Ang II/III and BK (10(-7) mol/liter) released Ca2+ from the same intracellular pools but activated different Ca2+ entry pathways. Ang II/III- or BK-induced [Ca2+]i increases were similarly potentiated by bisindolylmaleimide. Herbimycin A and PP2 decreased similarly the [Ca2+]i responses induced by Ang II/III and BK. In contrast, PD98059 and UO126 affected the effects of BK to a larger extent than those of Ang II/III. Especially, the Ca2+ influx induced by BK was more strongly inhibited than that induced by Ang II/III in the presence of both compounds. The Na+ transport was inhibited by BK and stimulated by Ang II/III. The inhibitory action of BK on Na+ transport was blocked by UO126, whereas the stimulatory response of Ang II/III was potentiated by UO126 but blocked by bisindolylmaleimide. These data suggest that the inhibitory effect of BK on Na+ transport seems to be directly mediated by an increase in Ca2+ influx dependent on MAPK/ERK pathway activation. In contrast, the stimulatory effect of Ang II/III on Na+ transport is more complex and involves PKC and MAPK/ERK pathways.

K317, R319, and E320 within the proximal C-terminus of the bradykinin B2 receptor form a motif important for phospholipase C and phospholipase A2 but not connective tissue growth factor related signaling

We showed previously that large domain exchanges between the bradykinin B2 (BKB2) and angiotensin II type 1a (AT1a) receptors can result in functional hybrids. However, when we proceeded to exchange the entire bradykinin B2 receptor (BKB2R) C-terminal tail with the AT1aR C-terminus, the hybrid, while continuing to bind BK and be endocytosed as wild type (WT) BKB2R, lost much of its ability to activate phosphatidylinositol (PI) turnover or the release of arachidonic acid (ARA). In this study, we constructed chimeric receptors within the proximal C-terminus between the BKB2R and AT1aR or bradykinin B1 receptor (BKB1R). The mutant and WT receptor cDNAs were stably transfected into Rat-1 cells. Also, point mutations were generated to evaluate the role of the individual residues within this region. These chimeric studies revealed that the proximal portion of the BKB2R C-tail is crucial for G protein-linked BKB2R functions. This region could not be swapped with the AT1aR to obtain a BK activated PI turnover or ARA release. Further studies demonstrated that the distal portion (325-330) of this region is exchangeable; however, the middle portion (317-324) is not. Small motif exchanges within this section identified the KSR and EVY motifs as crucial for G(alphaq), G(alphai) related signaling of the BKB2R. Point mutations then showed that the charged amino acids K317, R319, and E320 are the residues critical for linking to PI turnover and ARA release. However, these proximal chimeras showed normal receptor uptake. Interestingly, while apparently not activating G protein-linked signaling, the proximal tail AT1aR exchange mutant and the entire C-terminus exchange hybrid continued to cause a substantial bradykinin effected increase in connective tissue growth factor (CTGF) mRNA level, as WT BKB2R.

Chimeric exchanges within the bradykinin B2 receptor intracellular face with the prostaglandin EP2 receptor as the donor: importance of the second intracellular loop for cAMP synthesis

The prostaglandin E2 (PGE(2)) EP2 receptor (EP2R) type is G protein coupled (GPCR) and links to Galphas. Through this receptor PGE(2) activates cAMP production. The bradykinin (BK) B2 receptor (BKB2R) is also a GPCR but links to Galphaq and Galphai and does not activate cAMP production in response to bradykinin. In an attempt to convert the BKB2R into a Galphas-linked adenylate cyclase-activating receptor we proceeded to make global and discrete motif replacements of the intracellular (IC) face of the BKB2R with the corresponding regions of the human EP2R. With this approach we produced hybrid receptors which, when stably transfected into wild type (WT) Rat-1 cells, bound BK but produced cAMP. Replacement of the second loop (IC2), third loop (IC3), the entire C terminus, and the distal C terminus resulted in receptors which bound BK. However, only the IC2 and IC3 exchanges resulted in cAMP-producing receptors. Of these two regions, the IC2 exchange was by far the better cAMP-generating receptor, producing cAMP at approximately 6.6-fold above WT BKB2R or approximately one fourth the amount produced by WT EP2R-transfected Rat-1 cells. Both human and rat EP2R and human beta2-adrenergic receptor exchanges of the IC2 produced equal quantities of cAMP. Focusing on the rBKB2R/hEP2R IC2 chimeras, the region consisting of residues 136-147 (BKB2R residue numbering) proved to contain a cAMP-generating motif. Within this region, the proximal six amino acids from the EP2R (HPYFYQ) at position 136-141 proved crucial for cAMP production (10-fold over WT BKB2R). The distal part of this region, the six residues at 142-147, played no role in cAMP production. On the other hand, the ALV motif of the BKB2R IC2, residues 133-135, proved important with respect to phosphatydilinositol (PI) turnover. Replacing the entire IC2 of BKB2R resulted in poor PI turnover, while including the AVL of BKB2R retained approximately half of the WT PI turnover. With respect to receptor uptake, all the IC2 mutants endocytosed as WT BKB2R (60% in 1h). However, the exchange of the distal and the whole C termini resulted in a marked drop in endocytosis (30% in 1h). These results demonstrate that the construction of a cAMP-producing BKB2/EP2 receptor hybrid is possible, with the IC2 region distal to DRYLALV proving important to Galphas linkage and the LALV motif within the IC2 of BKB2R and the region proximal to it proving important for Galphaq and Galphai linkage. Additionally, our results confirm the importance of the distal C terminus in determining receptor uptake.