thapsigargin and Stomach-Neoplasms

We studied potential interactions between the endoplasmic reticulum (ER) stress response and the MEK/ERK pathway. Induction of ER stress did not trigger significant apoptosis, but caused rapid activation of ERK1/2 in gastric cancer cells. Inhibition of MEK enhanced ER stress-induced apoptosis via a caspase-dependent, mitochondria-mediated mechanism. This was associated with blockage of ER stress-mediated up-regulation of GRP78. The latter appeared to be critical in antagonizing the apoptosis-inducing potential of ER stress. Thus, activation of MEK/ERK by ER stress is necessary for induction of GRP78 that protects against apoptosis in gastric cancer cells submitted to ER stress.

Topics: Activating Transcription Factor 6; Adenocarcinoma; Antiviral Agents; Apoptosis; Blotting, Western; Caspases; eIF-2 Kinase; Endoplasmic Reticulum; Endoplasmic Reticulum Chaperone BiP; Endoribonucleases; Enzyme Inhibitors; Heat-Shock Proteins; Humans; MAP Kinase Kinase 1; Membrane Potential, Mitochondrial; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Molecular Chaperones; Protein Serine-Threonine Kinases; RNA, Small Interfering; Stomach Neoplasms; Thapsigargin; Tumor Cells, Cultured; Tunicamycin; Up-Regulation

After incubation with 2-butylamino-2-demethoxy-hypocrellin A (2-BA-2-DMHA), photodynamically induced change in the cytoplasmic free calcium concentration ([Ca(2+)](i)) and its effect on cell damage were investigated in human gastric cancer (MGC-803). Fluorescence spectrophotometry measurement indicated that the photosensitization of MGC-803 by 2-BA-2-DMHA caused an increase in intracellular calcium [Ca(2+)](i), and this increase in [Ca(2+)](i) showed a dependence on the concentration of 2-BA-2-DMHA, light dose and extracellular [Ca(2+)](e). This phenomenon of intracellular calcium accumulation was further confirmed by using laser scanning confocal microscopy (LSCM). Furthermore, the results from MTT assay and flow cytometry analysis suggested that chelation of extracellular calcium by EGTA or intracellular calcium by BAPTA could inhibit photodynamically induced cell killing, while increase of [Ca(2+)](i) by thapsigargin (TG), a highly specific inhibitor of the Ca(2+)-ATPase, or by A23187, a calcium ionophore could enhance this action. Meanwhile, the nucleus morphology was also investigated by fluorescence microscopy. The results indicated that the increase in intracellular Ca(2+) concentration was responsible for 2-BA-2-DMHA photodynamically induced damage to MGC-803.

Topics: Calcimycin; Calcium; Cell Survival; Chelating Agents; Egtazic Acid; Enzyme Inhibitors; Fluorescent Dyes; Fura-2; Humans; Ionophores; Light; Microscopy, Confocal; Microscopy, Fluorescence; Perylene; Photochemotherapy; Photosensitizing Agents; Quinones; Stomach Neoplasms; Thapsigargin; Tumor Cells, Cultured