[Role of calcium signal in apoptosis and protective mechanism of colon cancer cell line SW480 in response to 5-aminolevulinic acid-photodynamic therapy].

BACKGROUND & OBJECTIVE: Photodynamic therapy (PDT) for tumors is based on the tumor-selective accumulation of a photosensitizer, followed by irradiation with visible light, which induces cell death and apoptosis. As an important second messenger, free calcium is involved in the regulation of several cellular processes. However, the role of calcium signal in the cells after PDT is less clear. This study was to explore the role of calcium signal in apoptosis and protective mechanism of colon cancer cell line SW480 in response to 5-aminolevulinic acid (ALA)-PDT. METHODS: SW480 cells were divided into control group, light group, ALA group, and ALA-PDT group. Cell apoptosis was detected by TUNEL assay. The changes of intracellular Ca(2+) concentration were observed by confocal laser scanning microscopy (CLSM). Intracellular cAMP and cGMP concentrations were detected by radioimmunoassay. The expression of calmodulin in SW480 cells was detected by reverse transcription-polymerase chain reaction (RT-PCR). The expression of protein products and phosphorylated protein products of MEK and ERK1/2 was detected by Western blot. RESULTS: Apoptosis indexes of SW480 cells at 30 min and 60 min after PDT were (25.26+/-5.04)% and (50.45+/-7.85)%, respectively. CLSM revealed that intracellular Ca(2+) concentration was 100.00+/-19.83 at 10 min after PDT, but 185.40+/-18.90 at 20 min after PDT (P<0.01). cAMP concentration of ALA-PDT group was (3.215+/-0.245) pmol/L at 30 min after irradiation, which was significantly higher than those of other groups (P<0.001). The relative contents of CaM gene of ALA-PDT group at 30, 60 and 90 min after PDT were significantly higher than those of control group, light group, and ALA group (12.60+/-1.84, 11.39+/-1.13, and 12.77+/-1.35 vs. 3.97+/-0.29, 4.28+/-0.39, and 4.51+/-0.44, P<0.001). ERK pathway of SW480 cells was activated after ALA-PDT. CONCLUSIONS: Calcium signal plays an important role in ALA-PDT-induced apoptosis of SW480 cells, and can induce protective mechanism of SW480 cells by activating ERK pathway.