Background: Melatonin, which is mainly produced by the pineal gland, has a good inhibitory effect on cellgrowth of multiple cancer types. However, the underlying molecular mechanisms of anti-tumor activity for coloncancer have not been fully elucidated. In this study, we investigated the effects of melatonin on migration inhuman colon cancer RKO cells and the potential molecular mechanisms. Materials and
Methods: The viability ofRKO cells was investigated by MTT assay after treatment with melatonin, SB203580 (p38 inhibitor) and phorbol12-myristate 13-acetate (PMA, MAPK activator) alone or in combination for 48h. The effects of melatonin, andML-7, a selective inhibitor of myosin light chain kinase (MLCK), and SB203580, and PMA on the migration ofRKO cells were analyzed by in vitro scratch-wound assay. The relative mRNA levels of MLCK was assessed byreal-time quantitative RT-PCR. Western blotting analysis was performed to examine the expression of MLCK,phosphorylation of myosin light chain (pMLC) and p38 (pp38).
Results: The proliferation and migration ofhuman colon cancer RKO cells were inhibited significantly after treatment with melatonin. The expression levelsof MLCK and phosphorylation of MLC of RKO cells were reduced, and real-time quantitative RT-PCR showedthat melatonin had significant effects on suppressing the expression of MLCK. Furthermore, the phosphorylationlevel of p38, which showed the same trend, was also reduced when cells were treated by melatonin. In addition,ML-7 (25umol/l) could down-regulate the phosphorylation of p38.
Conclusions: Melatonin could inhibit theproliferation and migration of RKO cells, and further experiments confirmed that p38 MAPK plays an importantrole in regulating melatonin-induced migration inhibition through down-regulating the expression and activityof MLCK.