Mechanism of [Ca2+]i rise induced by angiotensin 1-7 in MDCK renal tubular cells

Angiotensin-(1-7) mediated calcium signalling by MAS

The G protein-coupled receptor, MAS, is the receptor of the endogenous ligand, Angiotensin (Ang)-(1-7). It is a promising drug target since the Ang-(1-7)/MAS axis is protective in the cardiovascular system. Therefore, a characterization of MAS signalling is important for developing novel therapeutics for cardiovascular diseases. In this paper, we show that Ang-(1-7) increases intracellular calcium in transiently MAS-transfected HEK293 cells. The calcium influx induced by the activation of MAS is dependent on plasma membrane Ca²⁺ channels, phospholipase C, and protein kinase C. Specifically, we could demonstrate that MAS employs non-selective, transient receptor potential channels (TRPs) for calcium entry.

NHERF4 hijacks Mas-mediated PLC/AKT signaling to suppress the invasive potential of clear cell renal cell carcinoma cells

The Mas receptor has been reported to promote migration and invasion of clear cell renal cell carcinoma (ccRCC) cells via Ang-(1-7)-dependent AKT signaling. However, the mechanism underlying the regulation of Mas function remains unknown. Here, eight PDZ domain-containing proteins were identified as Mas interactors using surface plasmon resonance (SPR) coupled to mass spectrometry (MS). NHERF4 was the only downregulated gene across multiple independent ccRCC datasets. GST pull-down and co-immunoprecipitation assays confirmed physical interaction between NHERF4 and Mas. Using NHERF4 overexpression and knockdown assays, we found that NHERF4 inhibited Mas-induced migration, invasion and in vivo metastasis of ccRCC cells. Mechanistically, NHERF4 suppressed Mas-stimulated AKT phosphorylation and the PLC/Ca²⁺ response. We further demonstrated that NHERF4 compromised Mas-mediated migration and invasion of ccRCC cells via regulation of the PLC/AKT signaling axis. Analysis of the ccRCC dataset revealed that low levels of NHERF4 expression were correlated with higher TNM stage, and independently predicted poor prognosis of ccRCC patients. Overall, our study identified NHERF4 as a novel regulator of ccRCC invasiveness, and a prognostic biomarker, which may be beneficial for determining optimal therapeutic strategies for ccRCC patients.

The effects of angiotensin-(1-7) on the exchanger NHE3 and on [Ca2+]i in the proximal tubules of spontaneously hypertensive rats

The acute effects of angiotensin-1-7 [ANG-(1-7)] on the reabsorptive bicarbonate flow (J[Formula: see text]) were evaluated using stationary microperfusion in vivo in the proximal tubules of spontaneously hypertensive rats (SHR) and their normotensive controls, Wistar-Kyoto (WKY) rats, using a microelectrode sensitive to H⁺ In WKY rats, the control J[Formula: see text] was 2.40 ± 0.10 nmol·cm^-2·s^-1 (n = 120); losartan (10^-7 M) or A779 (10^-6 M, a specific Mas antagonist), alone or in combination with losartan, decreased the J[Formula: see text] ANG-(1-7) had biphasic effects on J[Formula: see text]: at 10^-9 M, it inhibited, and at 10^-6, it stimulated the flow. S3226 [10^-6 M, a specific Na⁺-H⁺ exchanger 3 (NHE3) antagonist] decreased J[Formula: see text] and changed the stimulatory effect of ANG-(1-7) to an inhibitory one but did not alter the inhibitory action of ANG-(1-7). In SHR, the control J[Formula: see text] was 2.04 ± 0.13 nmol·cm^-2·s^-1 (n = 56), and A779 and/or losartan reduced the flow. ANG-(1-7) at 10^-9 M increased J[Formula: see text], and ANG-(1-7) at 10^-6 M reduced it. The effects of A779, losartan, and S3226 on the J[Formula: see text] were similar to those found in WKY rats, which indicated that in SHR, the ANG-(1-7) action on the NHE3 was via Mas and ANG II type 1. The cytosolic calcium in the WKY or SHR rats was ~100 nM and was increased by ANG-(1-7) at 10^-9 or 10^-6 M. In hypertensive animals, a high plasma level of ANG-(1-7) inhibited NHE3 in the proximal tubule, which mitigated the hypertension caused by the high plasma level of ANG II.

Renin-angiotensin system in the kidney: What is new?

The renin-angiotensin system (RAS) has been known for more than a century as a cascade that regulates body fluid balance and blood pressure. Angiotensin II(Ang II) has many functions in different tissues; however it is on the kidney that this peptide exerts its main functions. New enzymes, alternative routes for Ang IIformation or even active Ang II-derived peptides have now been described acting on Ang II AT₁ or AT₂ receptors, or in receptors which have recently been cloned, such as Mas and AT₄. Another interesting observation was that old members of the RAS, such as angiotensin converting enzyme (ACE), renin and prorenin, well known by its enzymatic activity, can also activate intracellular signaling pathways, acting as an outside-in signal transduction molecule or on the renin/(Pro)renin receptor. Moreover, the endocrine RAS, now is also known to have paracrine, autocrine and intracrine action on different tissues, expressing necessary components for local Ang II formation. This in situ formation, especially in the kidney, increases Ang II levels to regulate blood pressure and renal functions. These discoveries, such as the ACE2/Ang-(1-7)/Mas axis and its antangonistic effect rather than classical deleterious Ang II effects, improves the development of new drugs for treating hypertension and cardiovascular diseases.