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Principal Investigator: Dr. Randolph C. Elble
Contact Information: E-mail: rce3@cornell.edu - Phone: 3-3324
Sponsor: Philip Morris
Grant Number:
Title: Tumor Suppression by a Stress-Inducible Chloride Channel
Annual Direct Cost: $187,655
Project Period: 9/14/04 - 9/13/05
Tumor cells commonly activate survival pathways and inactivate arrest and apoptosis mechanisms, and there is increasing evidence that ion channels are important in these functions. We have discovered that expression of the calcium-activated chloride channel CLCA2 is greatly downregulated in proliferating breast cancer cells relative to normal ductal epithelial cells. Forced re-expression inhibits cancer cell proliferation and sensitizes cells to detachment-induced apoptosis, anoikis. Further, the CLCA2 mRNA is strongly but transiently induced in breast cancer cell lines by detachment and also by chemotherapeutic drugs. Preliminary results suggest that CLCA2 is regulated by the P13K/AKT pathway by both transcriptional regulation and by direct phosphorylation. The promoter region of CLCA2 contains several binding sites for pro-apoptotic, AKT-regulated forkhead (FKH) transcription factors. In addition, CLCA proteins contain a consensus AKT- phosphorylation site that may allow I channel inactivation. We propose that CLCA2 is an effector of cell cycle arrest or part of the apoptotic cascade, that tumor cells must lose its expression to escape the primary tumor, and that its expression and activity are regulated by the P13K/AKT survival pathway. Our specific aims are (1) to establish the generality and timing of CLCA2 downregulation in breast and other cancers using tumor tissue microarrays; (2) to determine the mechanism whereby CLCA2 inhibits proliferation and sensitizes tumor cells to apoptosis; (3) to determine how CLCA2 is linked to known survival and apoptosis regulatory pathways; and (4) to find whether suppression of CLCA2 expression confers faster growth or resistance to apoptosis. The mechanistic studies ask whether CLCA2 effects on anoikis involve a chloride current and changes in intracellular pH. They will be conducted in collaboration with Dr. Michael Kotlikoff, an authority on calcium-activated chloride currents. The finding that a calcium-activated chloride channel is regulated by these pathways and can in turn induce cell death would open an entirely new front of attack on breast cancer, one based upon stimulation of plasma membrane chloride conductance to thwart metastasis. This study will provide the foundation for that approach.
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