The calcium-activated chloride channel hCLCA2 has been identified as a candidate tumor suppressor in human breast cancer. We found that hCLCA2 was highly expressed in 12/12 normal breast samples but downregulated in 8/12 tumor samples. Expression was also reduced in breast cancer cell lines corresponding to the malignant character of the cell line. While immortalized cell lines had a uniformly high level of expression, hCLCA2 was downregulated by about 200-fold in highly metastatic cell lines such as MDA-MB231 but only ten- to thirtyfold in nonmetastatic tumor cell lines such as SKBR3 and MCF-7. Surprisingly however, the hCLCA2 gene remained inducible in tumor cell lines by multiple forms of stress, including starvation, detachment, and DNA damage, in parallel with p21 and Bax. Induction was stronger in anoikis-sensitive, nonmetastatic cells than in anoikis-resistant, metastatic cells. Inhibitors of the PI3 kinase survival pathway enhanced induction, as did ectopic expression of a dominant negative subunit of PI3 kinase. The gene was also highly expressed in permanently arrested cells. Ectopic expression in MCF-7 tumor cells inhibited colony formation by about twentyfold, enhanced sensitivity to detachment, and increased the frequency of multinuclear giant and senescent-like cells. These results demonstrate that hCLCA2 is a stress-inducible growth inhibitor that promotes permanent arrest or death in response to prolonged interruption of survival signaling.
[Proc Amer Assoc Cancer Res, Volume 46, 2005]