TRPV6 Calcium Channel Targeting by Antibodies Raised against Extracellular Epitopes Induces Prostate Cancer Cell Apoptosis

Simple Summary The TRPV6 channel is upregulated in many cancers and is associated with bad prognosis. Despite this fact, no reliable tool to target TRPV6 is known so far. Two prospective antibodies have been generated capable of binding to TRPV6 and thereby transiently activating calcium currents. This transient activation of TRPV6 and increase in intracellular calcium led to the apoptosis induction of prostate cancer cells. Only cells showing no TRPV6 membrane expression avoided cell death. Thus, the activation of the TRPV6 channel per se is extremely efficient and is likely to be more prospective than its inhibition. The TRPV6 calcium channel is known to be up-regulated in various tumors. The efforts to target the TRPV6 channel in vivo are still ongoing to propose an effective therapy against cancer. Here, we report the generation of two antibodies raised against extracellular epitopes corresponding to the extracellular loop between S1 and S2 (rb79) and the pore region (rb82). These antibodies generated a complex biphasic response with the transient activation of the TRPV6 channel. Store-operated calcium entry was consequently potentiated in the prostate cancer cell line LNCaP upon the treatment. Both rb79 and rb82 antibodies significantly decreased cell survival rate in a dose-dependent manner as compared to the control antibodies of the same isotype. This decrease was due to the enhanced cell death via apoptosis revealed using a sub-G1 peak in a cell cycle assay, TUNEL assay, and a Hoechst staining, having no effects in the PC3M(trpv6-/-) cell line. Moreover, all TUNEL-positive cells had TRPV6 membrane staining as compared to the control antibody treatment where TRPV6-positive cells were all TUNEL negative. These data clearly demonstrate that TRPV6 channel targeting using rb79 and rb82 antibodies is fatal and may be successfully used in the anticancer therapies.