**6.4. AQP 5**

Immunohistochemical analysis shows significant overexpression of AQP 5 in breast tumors from early breast cancer patients, and was correlated with the disease prognosis particularly in patients with ER/PR+ve tumors [142]. This observation was also confirmed by another group who showed that AQP 5 was not detectable in normal breast tissues, but was expressed mainly in the cell membrane of mammary carcinoma and associated with cellular differentiation, lymph node invasion and tumor stage [133]. The 5-year survival rate was decreased from 80% in AQP 5 −ve patients to 50% in AQP5+ve patients, suggesting that its expression was associ‐ ated with short overall survival [133]. In another report, AQP 5 expression was observed in the ductal epithelial cells of human breast tissues with significant overexpression in invasive compared to benign tumors [143]. It was also expressed in MCF7 and MDA-MB-231 breast cancer cell lines (at mRNA and protein level); shRNA, or hyperosmotic stress-induced reduction in AQP 5 expression significantly reduced cell proliferation and migration toward fetal bovine serum (FBS) gradient. Some reports have suggested that AQP 5 induces tumori‐ genesis (at least in lung epithelial cells) upon phosphorylation of the cAMP protein kinase consensus site located in its cytoplasmic loop [144, 145].
