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Tumor suppression by a proapoptotic calcium-activated chloride channel in mammary epithelium
1Cancer Biology Laboratories and Department of Molecular Medicine, Cornell University College of Veterinary Medicine, Ithaca, New York 14853, USA. rce3@cornell.edu
Abstract:
Little is known of the roles played by ion channels in cancer. Here we describe a pair of closely related calcium-activated chloride channels whose differential regulation in normal, apoptotic, and transformed mouse cells suggests that channel function is proapoptotic and antineoplastic. While mCLCA1 predominates over mCLCA2 under normal physiological conditions, this relationship is reversed by apoptotic stress both in developing mammary gland and in cultured HC11 mammary epithelial cells. Consistent with an apoptosis-promoting role, splicing of mCLCA2 is disrupted in apoptosis-resistant tumor cell lines and in HC11 cells selected for resistance to detachment-induced apoptosis (anoikis). Unexpectedly, mCLCA1 message is also down-regulated in these cells by at least 30-fold. These results suggest that both genes antagonize survival of mammary tumor cells by sensitizing them to anoikis. When MCF7 or HEK293 tumor cells were transfected with plasmids encoding either mCLCA1 or mCLCA2, colony formation was greatly reduced relative to a vector-transfected control, demonstrating that calcium-sensitive chloride channel (CLCA) expression is deleterious to tumor cell survival. Furthermore, mammary epithelial cells overexpressing mCLCA2 had twice the rate of apoptosis of normal cells when subjected to serum starvation and formed multinuclear giants at a high frequency in normal culture, suggesting that mCLCA2 can promote either apoptosis or senescence.
Insights
Calcium-activated chloride channels (CLCA) show anti-cancer properties. Their differential regulation in normal and tumor cells suggests a role in promoting apoptosis and inhibiting tumor growth.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- The role of ion channels in cancer remains largely undefined.
- Calcium-activated chloride channels (CLCA) are a family of channels with largely unknown functions in cellular processes.
Purpose of the Study:
- To investigate the role of calcium-activated chloride channels (CLCA) in cancer.
- To explore the differential regulation and function of mCLCA1 and mCLCA2 in normal, apoptotic, and transformed cells.
Main Methods:
- Differential expression analysis of mCLCA1 and mCLCA2 in normal, apoptotic, and transformed mouse mammary cells.
- Analysis of mCLCA2 splicing in apoptosis-resistant tumor cell lines and anoikis-resistant cells.
- Transfection of tumor cells (MCF7, HEK293) with mCLCA1 or mCLCA2.
- Overexpression of mCLCA2 in mammary epithelial cells followed by serum starvation and culture.
Main Results:
- mCLCA1 and mCLCA2 expression is differentially regulated by apoptotic stress, with mCLCA2 levels increasing.
- Disrupted splicing of mCLCA2 and down-regulation of mCLCA1 were observed in apoptosis-resistant and anoikis-resistant cells.
- Expression of mCLCA1 or mCLCA2 significantly reduced tumor cell colony formation.
- Overexpression of mCLCA2 increased apoptosis rates and induced multinucleation in mammary epithelial cells.
Conclusions:
- Both mCLCA1 and mCLCA2 function as proapoptotic and antineoplastic factors.
- These genes antagonize mammary tumor cell survival by sensitizing cells to anoikis.
- CLCA channel expression is detrimental to tumor cell survival and may promote apoptosis or senescence.