Gypenosides Induce Apoptosis by Ca²⁺ Overload Mediated by Endoplasmic-Reticulum and Store-Operated Ca²⁺ Channels in Human Hepatoma Cells

Abstract

Gypenosides (Gyps) are triterpenoid saponins contained in an extract from Gynostemma pentaphyllum Makino and reported to induce apoptosis in human hepatoma cells through Ca 2 + -implicated endoplasmic reticulum (ER) stress and mitochondria-dependent pathways. The mechanism underlying the Gyp-increased intracellular Ca 2 + channel (SOC) inhibitor 2-aminoethoxydiphenyl borate (2-APB), and ER Ca 2 + -release-antagonist 3,4,5-trimethoxybenzoic acid 8-(diethylamino) octyl ester (TMB-8). The strongest inhibitory effect was observed with TMB-8. EGTA, 2-APB, and TMB-8 also protected against Gyp-induced apoptosis in HepG2 cells. The combination of 2-APB and TMB-8 almost completely abolished the Gyp-induced Ca 2 + response and apoptosis. In contrast, the sarco/endoplasmic-reticulum-Ca 2 + -ATPase (SERCA) inhibitor thapsigargin slightly elevated Gyp-induced [Ca 2 + ] i increase and apoptosis in HepG2 cells. Exposure to 300 lg/mL Gyp for 24 hours upregulated protein levels of inositol 1,4,5-trisphosphate receptor and SOC and downregulated that of SERCA for at least 72 hours. Thus, Gyp-induced increase in [Ca 2 + ] i level and consequent apoptosis in HepG2 cells may be mainly due to enhanced Ca 2 + release from ER stores and increased store-operated Ca 2 + entry.

Inhibition of store-operated Ca2+ entry counteracts the apoptosis of nasopharyngeal carcinoma cells induced by sodium butyrate

“…A sustained increase in cytosolic Ca 2+ activity triggers apoptosis (34). The roles of SOCE, a major calcium-entry pathway for non-excitable cells, and those of the CRAC channel, a key channel in mediating SOCE, in apoptotic regulation appear to be paradoxical (7,16,17,34,35). Indeed, SOCE can serve as a pro-apoptotic or an anti-apoptotic factor in cancerous cells under different conditions (7,16,17,34,35).…”

“…The roles of SOCE, a major calcium-entry pathway for non-excitable cells, and those of the CRAC channel, a key channel in mediating SOCE, in apoptotic regulation appear to be paradoxical (7,16,17,34,35). Indeed, SOCE can serve as a pro-apoptotic or an anti-apoptotic factor in cancerous cells under different conditions (7,16,17,34,35). For example, enhanced SOCE resulted from upregulated Orai1 and Stim1 expression, which was observed in drug-resistant cancer cells, and impairing SOCE by using specific inhibitors or by knocking down Orai1 and Stim1 can sensitize the drug-resistant cells to chemotherapy (34,35).…”

“…In addition, enhanced SOCE commonly occurs during the cell apoptosis induced by anti-tumor or chemotherapeutic agents (17). The use of SOCE inhibitors or knocking down the expression of Orai1 or Stim1 can counteract the apoptosis induced by anti-tumor agents (7,16,17). In the present study, SOCE appeared to serve as a pro-apoptotic factor in NPC cells treated with NaBu, and inhibition of SOCE could attenuate the NaB-induced apoptosis in NPC cells, in accordance with previous results in colon cancer (17).…”

“…Sodium butyrate (NaBu) is the sodium salt of butyric acid, one of the short chain fatty acids, which is naturally produced by symbiotic bacteria in the gastrointestinal tract through fermenting dietary fibers (6)(7)(8). Histone deacetylases (HDACs) are key epigenetic regulators that can regulate the gene expression profile by directly interacting with other proteins such as transcription factors (6).…”

“…Under certain circumstances, including endogenous mutations and exogenous drugs stimulation, the Orai1/Stim1 CRAC channel may overexcite, and the aberrant overloaded intracellular Ca 2+ concentration would cause a series of pathological responses such as apoptosis (15,16). Interrupting the SOCE process by knocking down Orai1/Stim1 or blocking it with specific inhibitors could counteract the apoptosis of cells induced by anti-tumor agents such as cisplatin, gypenosides and oxaliplatin in several cancers (7,15,16). SOCE was also confirmed to be necessary for the apoptosis induced by NaBu in colon cancer cells (17).…”