Impaired actin filaments decrease cisplatin sensitivity via dysfunction of volume-sensitive Cl- channels in human epidermoid carcinoma cells.

Cisplatin is a widely used platinum-based anticancer drug in the chemotherapy of numerous human cancers. However, cancer cells acquire resistance to cisplatin. So far, functional loss of volume-sensitive outwardly rectifying (VSOR) Cl- channels has been reported to contribute to cisplatin resistance of cancer cells. Here, we analyzed protein expression patterns of human epidermoid carcinoma KB cells and its cisplatin-resistant KCP-4 cells. Intriguingly, KB cells exhibited higher ß-actin expression and clearer actin filaments than KCP-4 cells. The ß-actin knockdown in KB cells decreased VSOR Cl- currents and inhibited the regulatory volume decrease (RVD) process after cell swelling. Consistently, KB cells treated with cytochalasin D, which depolymerizes actin filaments, showed smaller VSOR Cl- currents and slower RVD. Cytochalasin D also inhibited cisplatin-triggered apoptosis in KB cells. These results suggest that the disruption of actin filaments cause the dysfunction of VSOR Cl- channels, which elicits resistance to cisplatin in human epidermoid carcinoma cells.

Volume-sensitive outwardly rectifying Cl(-) channels contribute to butyrate-triggered apoptosis of murine colonic epithelial MCE301 cells.

Butyrate is a fatty acid with an important role in the maintenance of colonic homeostasis. It induces apoptosis in colonic epithelial cells and contributes to the pathogenesis of ulcerative colitis. However, just how how butyrate triggers apoptosis is poorly understood. In our model system of mouse colonic epithelial MCE301 cells, whole-cell patch-clamp recordings revealed the presence of swelling-activated outwardly rectifying chloride ion (Cl(-)) currents. These currents exhibited time-dependent inactivation upon strong depolarization, a low field strength anion selectivity (I(-) > Br(-) > Cl(-) > F(-)), and a sensitivity to 4-(2-butyl-6,7-dichloro-2-cyclopentylindan-1-on-5-yl)oxybutyric acid (DCPIB), a specific blocker of volume-sensitive outwardly rectifying (VSOR) Cl(-) channels. The results of flow cytometric analysis and caspase 3/7 assays demonstrated that exposure of MCE301 cells to sodium butyrate for 16 h triggered apoptotic cell shrinkage, phosphatidylserine exposure, and caspase 3/7 activation. Importantly, the VSOR Cl(-) channel blocker was able to inhibit sodium butyrate-induced apoptotic processes. These results suggest that activation of the VSOR Cl(-) channel is essential for sodium butyrate-triggered apoptosis in MCE301 cells.