A Novel Cellular Model to Study Angiotensin II AT2 Receptor Function in Breast Cancer Cells

AT2 Receptor Mediated Activation of the Tyrosine Phosphatase PTP1B Blocks Caveolin-1 Enhanced Migration, Invasion and Metastasis of Cancer Cells

The renin–angiotensin receptor AT2R controls systemic blood pressure and is also suggested to modulate metastasis of cancer cells. However, in the latter case, the mechanisms involved downstream of AT2R remain to be defined. We recently described a novel Caveolin-1(CAV1)/Ras-related protein 5A (Rab5)/Ras-related C3 botulinum toxin substrate 1 (Rac1) signaling axis that promotes metastasis in melanoma, colon, and breast cancer cells. Here, we evaluated whether the anti-metastatic effect of AT2R is connected to inhibition of this pathway. We found that murine melanoma B16F10 cells expressed AT2R, while MDA-MB-231 human breast cancer cells did not. AT2R activation blocked migration, transendothelial migration, and metastasis of B16F10(cav-1) cells, and this effect was lost when AT2R was silenced. Additionally, AT2R activation reduced transendothelial migration of A375 human melanoma cells expressing CAV1. The relevance of AT2R was further underscored by showing that overexpression of the AT2R in MDA-MB-231 cells decreased migration. Moreover, AT2R activation increased non-receptor protein tyrosine phosphatase 1B (PTP1B) activity, decreased phosphorylation of CAV1 on tyrosine-14 as well as Rab5/Rac1 activity, and reduced lung metastasis of B16F10(cav-1) cells in C57BL/6 mice. Thus, AT2R activation reduces migration, invasion, and metastasis of cancer cells by PTP1B-mediated CAV1 dephosphorylation and inhibition of the CAV1/Rab5/Rac-1 pathway. In doing so, these observations open up interesting, novel therapeutic opportunities to treat metastatic cancer disease.

Angiotensin II receptor blockers induce autophagy in prostate cancer cells

Angiotensin II receptor blockers (ARBs) are anti-hypertensive drugs that competitively inhibit the binding of angiotensin II to its receptor, resulting in blood vessel dilation and the reduction of blood pressure. These antagonists are also known as sartans, and are a group of pharmaceuticals that possess tetrazole or imidazole groups. In the present study, the anticancer and antimetastatic effects of the ARBs fimasartan, losartan, eprosartan and valsartan on the human prostate cancer PC-3, DU-145 and LNCap-LN3 cell lines were investigated in vitro. The proliferation of the prostate cancer cells was inhibited following treatment with 100 µM ARB. In particular, treatment with fimasartan resulted in marked anti-proliferative activity compared with the other ARBs. With respect to the molecular mechanism of the growth inhibition exhibited by the ARBs, 3-methyladenin (3-MA), an autophagy inhibitor, was revealed to increase the survival rate of PC-3 cells when cell death inhibitors were pretreated with fimasartan. In addition, the ARBs induced autophagy with increased expression levels of autophagy protein (Atg) 5-12, Atg 16-like-1, beclin-1 and microtubule-associated protein 1A/1B-light chain 3 (LC3). Notably, the enhanced expression of LC3-II (a 6.7-fold increase at 72 h) was observed in PC3 cells treated with fimasartan. This was supported by the observation of the time-dependent accumulation of LC3-positive foci in PC-3. In addition, a migration assay indicated that the ARBs induced anti-metastatic effects in PC-3 and DU-145 cells. The aforementioned results suggest that ARBs may induce autophagy-associated cell death and anti-metastatic activity in prostate cancer cells. Thus, ARBs may be a potential medication for patients with prostate cancer and hypertension.

G-protein coupled receptors of the renin-angiotensin system: new targets against breast cancer?

G-protein coupled receptors (GPCRs) constitute the largest family of membrane receptors, with high potential for drug discovery. These receptors can be activated by a panel of different ligands including ions, hormones, small molecules, and vasoactive peptides. Among those, angiotensins [angiotensin II (AngII) and angiotensin 1–7] are the major biologically active products of the classical and alternative renin-angiotensin system (RAS). These peptides bind and activate three different subtypes of GPCRs, namely AT1, AT2, and Mas receptors, to regulate cardiovascular functions. Over the past decade, the contribution of several RAS components in tumorigenesis has emerged as a novel important concept, AngII being considered as harmful and Ang1–7 as protective against cancer. Development of selective ligands targeting each RAS receptor may provide novel and efficient targeted therapeutic strategies against cancer. In this review, we focus on breast cancer to summarize current knowledge on angiotensin receptors (AT1, AT2, and Mas), and discuss the potential use of angiotensin receptor agonists and antagonists in clinics.