Background: Recent human and animal studies have demonstrated the oncostatic properties of N-acetyl-5-methoxytryptamine (melatonin) in different types of cancer. However, in few cancer cell lines including colorectal cancer cell line (HT-29), acute T cell leukemia cell line (JURKAT) and cervical cancer cell line (HeLa), precise oncostatic mechanism induced by melatonin is yet to be described.
Objectives: The aim of this study is to investigate the effects of melatonin in HT-29, JURKAT and HeLa cells and to determine the underlying molecular mechanism.
Methods: Cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay while cell cycle, apoptosis and membrane potential were analysed by flow cytometry. Reactive oxygen species (ROS) was detected by 2',7'‑dichlorofluorescein diacetate (DCFH-DA) staining. Protein expressions were determined by western blot.
Results: Our results showed that melatonin suppressed cell proliferation, increased the number of sub G1 hypodiploid cells and cell cycle arrest in HT-29, JURKAT and HeLa cells. Besides that, melatonin also induced early and late apoptosis, although there was marked variations in responses between different cell lines (sensitivity; HeLa > HT-29 >JURKAT). Apart from that, staining with DCHF-DA demonstrated ROS production that was induced in a dose dependent manner in HeLa, HT-29 and JURKAT cells. Moreover, the apoptotic process and oncostatic effect of melatonin was seen to be associated with extracellular-signal-regulated kinase (ERK) and stress-activated protein kinase/c-Jun NH (2)-terminal kinase (SAPK-JNK) signalling cascades in HeLa cells. In HT-29 and JURKAT cells, melatonin induced apoptosis via activation of p38 mitogen-activated protein kinases (p38), ERK and SAPK-JNK signalling pathways. In all three cell lines, apoptotic event was triggered by mammalian target of rapamycin (mTOR)-mediated activation of the downstream target rapamycin-insensitive companion of mTOR (RICTOR) and/or regulatory-associated protein of mTOR (RAPTOR) proteins.
Conclusions: Our findings confirm that melatonin induces apoptosis through reactive oxygen species-mediated dysregulated mitogen-activated protein kinase (MAPK) and mTOR signalling pathways in these cancer cell lines.