The apoptotic effect of Zoledronic acid on the nasopharyngeal carcinoma cells via ROS mediated chloride channel activation.

Zoledronic acid (ZA), a third-generation bisphosphonate, has been applied for treatment of bone metastases caused by malignant tumors. Recent studies have found its anti-cancer effects on various tumor cells. One of the mechanisms of anti-cancer effects of ZA is induction of apoptosis. However, the mechanisms of ZA-induced apoptosis in tumor cells have not been clarified clearly. In this study, we investigated the roles of chloride channels in ZA-induced apoptosis in nasopharyngeal carcinoma CNE-2Z cells. Apoptosis and chloride current were induced by ZA and suppressed by chloride channel blockers. After the knockdown of ClC-3 expression by ClC-3 siRNA, ZA-induced chloride current and apoptosis were significantly suppressed, indicating that the chloride channel participated in ZA-induced apoptosis may be ClC-3. When reactive oxygen species (ROS) generation was inhibited by the antioxidant N-acetyl-L-cysteine (L-NAC), ZA-induced apoptosis and chloride current were blocked accordingly, suggesting that ZA induces apoptosis through promoting ROS production and subsequently activating chloride channel.

Estradiol activates chloride channels via estrogen receptor-α in the cell membranes of osteoblasts.

Estrogen plays important roles in regulation of bone formation. Cl- channels in the ClC family are expressed in osteoblasts and are associated with bone physiology and pathology, but the relationship between Cl- channels and estrogen is not clear. In this study the action of estrogen on Cl- channels was investigated in the MC3T3-E1 osteoblast cell line. Our results show that 17ß-estradiol could activate a current that reversed at a potential close to the Cl- equilibrium potential, with a sequence of anion selectivity of I- > Br- > Cl- > gluconate, and was inhibited by the Cl- channel blockers 5-nitro-2-(3-phenylpropylamino)-benzoate and 4,4'-diisothiocyano-2,2'-stilbene disulfonic acid. Knockdown of ClC-3 Cl- channel expression by a specific small interfering RNA to ClC-3 attenuated activation of the 17ß-estradiol-induced Cl- current. Extracellular application of membrane-impermeable 17ß-estradiol-albumin conjugates activated a similar current. The estrogen-activated Cl- current could be inhibited by the estrogen receptor (ER) antagonist fulvestrant (ICI 182780). The selective ERα agonist, but not ERß agonist, activated a Cl- current similar to that induced by 17ß-estradiol. Silencing ERα expression prevented activation of estrogen-induced currents. Immunofluorescence and coimmunoprecipitation experiments demonstrated that ClC-3 Cl- channels and ERα were colocalized and closely related in cells. Estrogen promoted translocation of ClC-3 and ERα to the cell membrane from the nucleus. In conclusion, our findings show that Cl- channels can be activated by estrogen via ERα on the cell membrane and suggest that the ClC-3 Cl- channel may be one of the targets of estrogen in the regulation of osteoblast activity.