Expression of MAS1 in breast cancer

MAS1 is a receptor for angiotensin 1‐7 (A1‐7), which is derived from angiotensin II (A‐II) by the action of angiotensin converting enzyme (ACE) 2. MAS1 induces anti‐A‐II phenotypes, such as vessel dilation and depression of blood pressure. Using immunohistochemistry, we examined the role of MAS1 in 132 cases of invasive ductal carcinoma (IDC) of the breast. While benign mammary tissues expressed MAS1 at high levels, MAS1 expression was attenuated in all IDC, especially in scirrhous IDC. The decrease in MAS1 expression was associated with tumor growth, lymph node metastasis, and grade. MAS1 expression was inversely associated with the proliferation index and epidermal growth factor receptor and human epidermal growth factor receptor‐2 expression. Of the 132 cases, 12 (9.1%) were triple‐negative breast cancer (TNBC) cases. All TNBC cases (the 12 cases and the additional 36 cases using a tissue array) expressed MAS1. Using the TNBC cell lines 4T1 and MDA‐MB‐468, which expresses MAS1, we found that cell growth, anti‐apoptotic survival and invasion were suppressed by MAS1 activation with A1‐7 treatment and enhanced by MAS1 knockdown. In contrast, synergic effect was found between tamoxifen and A1‐7 in a luminal A breast cancer cell line, MCF‐7. Combination treatment with cisplatin, an ACE2 activator, and an A‐II type 1 receptor blocker showed synergic effects on tumor growth inhibition of 4T1 tumors in a syngeneic mouse model. These findings suggest that MAS1 might act as an inhibitory regulator of breast cancer and may be a possible molecular target for this malignancy. MAS1 expression is reduced in IDC, especially scirrhous type in comparison with that in benign breast tissues and DCIS. In contrast, MAS1 expression is retained in triple‐negative breast cancer cases. MAS1 is a hopeful molecular target for triple‐negative breast cancer.