GJB2 in human breast cancer and its role in breast cancer cell proliferation and migration. The RT-qPCR results revealed the upregulation of the GJB2 gene in invasive ductal carci-

Gap junction β-2 gene (GJB2, also known as connexin 26) is a member of the connexin family which forms gap junction channels. Many connexin genes have been considered to be tumor suppressor genes. However, the overexpression of GJB2 has been found to be associated with a poor prognosis in several human cancers. In our previous microarray study, we revealed the overexpression of GJB2 in breast cancer tissues. Hence, in this study, we investigated the expression of GJB2 in human breast cancer and its role in breast cancer cell proliferation and migration. The RT-qPCR results revealed the upregulation of the GJB2 gene in invasive ductal carcinoma (P<0.001) of the breast. Immunohistochemical analysis revealed an intense cytoplasmic and membrane staining. We observed that the staining for GJB2 was more intense in the majority of the estrogen receptor (ER)-negative breast cancer tissues compared to the normal breast tissues (P<0.0001). By contrast, the majority of the ER-positive breast cancer samples exhibited weak to moderate staining; however, this difference was not statistically significant compared to the normal tisues. The knockdown of GJB2 in human breast cancer cell lines using shRNA led to a significant decrease in the proliferative ability and an increase in the migratory ability of breast cancer cells. In addition, the knockdown of GJB‐2 led to a significant reduction in tumor volume and proliferation (as demonstrated by MIB-1 staining) in orthotopic xenografts in immunocompromised mice. On the whole, the findings of this study indicate that GJB2 may be an important regulator of breast tumorigenesis. Introduction The intercellular communication and passage of small molecules between neighbouring cells is mediated by gap junctions, which play a variety of important roles in various biological processes, including cell differentiation, homeostasis, morphogenesis and growth control (1-3). Connexins have been considered as tumor suppressors in many types of cancer (4-6). However, recent evidence indicates the involvement of connexins in promoting cell proliferation (7), regulating apoptosis (8), and promoting chemoresistance (9), migration (10), regulation of epithelial-mesenchymal transition (EMT) (11), tumor differentiation and angiogenesis (12-15). Gap Junction β-2 (GJB2, also known as connexin 26) is one of the members of 21 connexin family genes that form the gap junction channels, which is abundantly expressed in the skin, liver and breasts. A previous study indicated an association of the mutations in the GJB2 gene with neurosensory deafness (16). Previous studies have also revealed the overexpression of GJB2 in several carcinomas, including head and neck, colon, prostate and skin tumors (17-21). In breast cancer, GJB2 has been indicated to be a tumor suppressor due to its very low expression in breast tumor tissues, perhaps due to hypermethylation (22). By contrast, there are also studies indicating the overexpression of GJB2 in breast cancer tissues and its involvement in metastasis to the lymph node and its association with a poor prognosis (23,24). A high expression of GJB2 has also been detected in >50% of invasive breast cancer tissues when compared to normal human breast tissues. In addition, the expression of GJB2 has shown to be associated with a poor prognosis of lung and esophagus carcinoma (25-27). Collectively, these studies support a pro-tumorigenic role for GJB2. In view of these findings, we hypothesized that GJB2 may be associated with the hormonal status of breast tumors, which may be one of the reasons for the discrepancy in the reported role of GJB2 in breast cancer. In the present study, we examined the expression of GJB2 in breast cancer tissues of various hormonal statuses and investigated the role of GJB2 by knocking down its expression in breast cancer cells followed by in vitro and in vivo experiments. Our data revealed a negative association of GJB2 protein with the ER status of breast Gap junction β‐2 expression is negatively associated with the estrogen receptor status in breast cancer tissues and is a regulator of breast tumorigenesis ABHIJITH SHETTAR1, SUREKHA DAMINENI1, GEETASHREE MUKHERJEE2,3 and PATURU KONDAIAH1 1Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore, Karnataka 560012; 2Department of Pathology, Kidwai Memorial Institute of Oncology, Bangalore 560029 Karnataka, India Received July 11, 2017; Accepted June 13, 2018 DOI: 10.3892/or.2018. 6764 Correspondence to: Professor Paturu Kondaiah, Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, CV Raman Road, Bangalore, Karnataka 560012, India E-mail: paturu@iisc.ac. in Present address: 3Department of Histopathology, Tata Medical Center, Rajarhat, Kolkata 700160, India