Voltage-gated sodium channel Na1.5 promotes tumor progression and enhances chemosensitivity to 5-fluorouracil in colorectal cancer.

Na1.5, encoded by SCN5A, has been associated with metastasis in colorectal cancer (CRC). Here, we investigated the mechanism by which Na1.5 regulates tumor progression and whether Na1.5 influences chemosensitivity to 5-fluorouracil (5-FU) in CRCs. CRC cases were evaluated for Na1.5 expression. Elevated Na1.5 expression was associated with poor prognosis in CRCs, whereas stage II/III patients with upregulated SCN5A expression could have better survival after receiving 5-FU-based adjuvant chemotherapy. In CRC cells, SCN5A knockdown reduced the proliferation, migration and invasion. According to RNA sequencing, SCN5A knockdown inhibited both the cell cycle and epithelial-mesenchymal transition. In addition, Na1.5 stabilized the KRas-calmodulin complex to modulate Ras signaling, promoting Ca influx through the Na-Ca exchanger and Ca release-activated calcium channel. Meanwhile, SCN5A knockdown increased the 50% inhibitory concentration to 5-FU by upregulating 5-FU-stimulated apoptosis in CRCs. In conclusion, Na1.5 could progress to proliferation and metastasis through Ca/calmodulin-dependent Ras signaling in CRC, and it could also enhance 5-FU-stimulated apoptosis. Clinically, patients with stage II/III CRCs with elevated SCN5A expression demonstrated poor prognosis, yet those patients could benefit more from 5-FU-based chemotherapy than patients with lower SCN5A expression.