Fig. 1. Melatonin prevents apoptosis induced by VvhA via MT₂.

a Dose responses of rVvhA for 24 h in cell counting assay are shown. Data represent means ± S.E. n = 5. *p < 0.05 vs. 0 pg/mL. **P < 0.01 vs. 0 pg/mL. b Time responses of 50 pg/mL of rVvhA in cell counting assay are shown. Error bars represent the means ± S.E. n = 5. *p < 0.01 vs. 0 h. c Cells were treated with melatonin at various concentrations (10–100 µM) for 30 min prior to rVvhA (50 pg/mL) exposure for 24 h. *p < 0.01 vs. vehicle. ^#p < 0.01 vs. rVvhA alone. d Cells were incubated with melatonin (1 µM) for 30 min prior to rVvhA exposure for 24 h. Percentages of total apoptotic cells were measured by using Annexin V/PI staining and flow cytometry. n = 4. *p < 0.01 vs. control. ^#p < 0.01 vs. rVvhA alone. e Expression of MT₁ and MT₂ mRNAs in HCT116 cells. A representative 1% agarose gel following RT–PCR is shown. n = 3. f Cells transfected with siRNAs for non-targeting (nt) control and MT₂ were incubated with melatonin (1 µM) for 30 min prior to rVvhA exposure for 24 h. Percentages of total apoptotic cells were measured by using Annexin V/PI staining and flow cytometry. n = 4. *p < 0.01 vs. nt siRNA alone. ^#p < 0.01 vs. rVvhA + nt siRNA. ^$p < 0.01 vs. rVvhA + melatonin + nt siRNA