Characterization of CACNA2D3 as a putative tumor suppressor gene in the development and progression of nasopharyngeal carcinoma

Apart from -catenin accumulation, loss of 3p21 is one of the most frequent genetic alterations in numerous malignancies including nasopharyngeal carcinoma (NPC). Herein, we characterized a novel candidate tumor suppressor gene (TSG) CACNA2D3, a voltage-dependent subunit alpha 2 delta 3 of a calcium channel complex. Downregulation of CACNA2D3 was frequently detected in primary NPCs and NPC cell lines compared with their nontumorigenic counterparts. Attenuated CACNA2D3 expression may be associated with loss of heterozygosity (LOH) at intragenic single-nucleotide polymorphism sites (rs589281, rs1449325 and rs6797113) and/or epigenetic silencing by methylation and histone deacetylation. Given the extensive effects of calcium in cancer, we then investigated the tumor suppressive role and underlying mechanism of CACNA2D3 in the development and progression of NPC. CACNA2D3 was stably transfected into NPC cell lines (C666 and SUNE1) at levels comparative with the normal nasopharynx, alongside siRNA-mediated silencing in an immortalized nasopharyngeal epithelial cell line (NP69) to conduct in vivo and in vitro functional assays. Our findings show that CACNA2D3-mediated increase in intracellular calcium (Ca2+) can induce mitochondrial-mediated apoptosis and activation of NLK (through the Wnt/Ca2+ pathway) to antagonize Wnt signaling-mediated anchorage-dependent and independent cell proliferation (via CCND1 and CMYC), invasion (via MMP7) and epithelial-to-mesynchemal transition (via SNAIL). As the expression pattern of calcium channels and their degree of functionality can change with the progression of cancer, CACNA2D3 may indeed be a promising biomarker for NPC. Our study also warrants further exploration in the potential therapeutic use of existing epigenetic targeting drugs (e.g., 5-azacytidine, SAHA) to reconstitute CACNA2D3-associated tumor suppression in NPC. What's new? Calcium has been involved in diverse cellular processes associated with cancer development. Despite growing evidence for the potential tumor suppressive properties of CACNA2D3an auxiliary member of the alpha-2/delta subunit family of the voltage-dependent calcium channel complexthe mechanism underlying its role in Nasopharyngeal Carcinoma (NPC) remains unclear. Here the authors demonstrate for the first time that CACNA2D3-mediated increase in intracellular calcium activates NLK via the Wnt/Ca2+ non-canonical Wnt pathway. The observed epigenetic silencing of CACNA2D3 may also be required for accumulated -catenin to effectively activate Wnt-associated oncogenes known to promote apoptosis evasion, cell proliferation, invasion, metastasis, and epithelial-to-mesynchemal transition.