Molecular mechanisms underlying Ca²⁺-mediated motility of human pancreatic duct cells

We recently reported that transforming growth factor-β (TGF-β) induces an increase in cytosolic Ca²⁺ ([Ca²⁺] _cyt) in pancreatic cancer cells, but the mechanisms by which TGF-β mediates [Ca²⁺]_cyt homeostasis in these cells are currently unknown. Transient receptor potential (TRP) channels and Na ⁺/Ca²⁺ exchangers (NCX) are plasma membrane proteins that play prominent roles in controlling [Ca²⁺]_cyt homeostasis in normal mammalian cells, but little is known regarding their roles in the regulation of [Ca²⁺]_cyt in pancreatic cancer cells and pancreatic cancer development. Expression and function of NCX1 and TRPC1 proteins were characterized in BxPc3 pancreatic cancer cells. TGF-β induced both intracellular Ca²⁺ release and extracellular Ca²⁺ entry in these cells; however, 2-aminoethoxydiphenyl borate [2-APB; a blocker for both inositol 1,4,5-trisphosphate (IP₃) receptor and TRPC], LaCl₃ (a selective TRPC blocker), or KB-R7943 (a selective inhibitor for the Ca²⁺ entry mode of NCX) markedly inhibited the TGF-β-induced increase in [Ca²⁺]_cyt. 2-APB or KB-R7943 treatment was able to dose-dependently reverse membrane translocation of PKCα induced by TGF-β. Transfection with small interfering RNA (siRNA) against NCX1 almost completely abolished NCX1 expression in BxPc3 cells and also inhibited PKCα serine phosphorylation induced by TGF-β. Knockdown of NCX1 or TRPC1 by specific siRNA transfection reversed TGF-β-induced pancreatic cancer cell motility. Therefore, TGF-β induces Ca²⁺ entry likely via TRPC1 and NCX1 and raises [Ca ²⁺]_cyt in pancreatic cancer cells, which is essential for PKCα activation and subsequent tumor cell invasion. Our data suggest that TRPC1 and NCX1 may be among the potential therapeutic targets for pancreatic cancer.