Melatonin, a novel selective ATF-6 inhibitor, induces human hepatoma cell apoptosis through COX-2 downregulation

World J Gastroenterol. 2017 Feb 14;23(6):986-998. doi: 10.3748/wjg.v23.i6.986.


Aim: To clarify the mechanisms involved in the critical endoplasmic reticulum (ER) stress initiating unfolded protein response pathway modified by melatonin.

Methods: Hepatoma cells, HepG2, were cultured in vitro. Flow cytometry and TUNEL assay were used to measure HepG2 cell apoptosis. Western blotting and quantitative reverse transcription-polymerase chain reaction methods were used to determine the protein and messenger RNA levels of ER stress and apoptosis related genes' expression, respectively. Tissue microarray construction from patients was verified by immunohistochemical analysis.

Results: In the present study, we first identified that melatonin selectively blocked activating transcription factor 6 (ATF-6) and then inhibited cyclooxygenase-2 (COX-2) expression, leading to enhanced liver cancer cell apoptosis under ER stress condition. Dramatically increased CCAAT-enhancer-binding protein homologous protein level, suppressed COX-2 and decreased Bcl-2/Bax ratio by melatonin or ATF-6 siRNA contributed the enhanced HepG2 cell apoptosis under tunicamycin (an ER stress inducer) stimulation. In clinical hepatocellular carcinoma patients, the close relationship between ATF-6 and COX-2 was further confirmed.

Conclusion: These findings indicate that melatonin as a novel selective ATF-6 inhibitor can sensitize human hepatoma cells to ER stress inducing apoptosis.

Keywords: Activating transcription factor 6; Cyclooxygenase-2; Endoplasmic reticulum stress; Hepatocellular carcinoma; Melatonin.

MeSH terms

  • Activating Transcription Factor 6 / antagonists & inhibitors*
  • Activating Transcription Factor 6 / genetics
  • Antioxidants / pharmacology*
  • Apoptosis / drug effects*
  • CCAAT-Enhancer-Binding Proteins / metabolism*
  • Cyclooxygenase 2 / metabolism*
  • Down-Regulation
  • Endoplasmic Reticulum Stress / drug effects*
  • Hep G2 Cells
  • Humans
  • In Situ Nick-End Labeling
  • Liver Neoplasms
  • Melatonin / pharmacology*
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • RNA Interference
  • RNA, Messenger / metabolism
  • RNA, Small Interfering
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction
  • Tunicamycin / pharmacology
  • Unfolded Protein Response / drug effects*
  • bcl-2-Associated X Protein / metabolism


  • ATF6 protein, human
  • Activating Transcription Factor 6
  • Antioxidants
  • BAX protein, human
  • BCL2 protein, human
  • CCAAT-Enhancer-Binding Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • RNA, Messenger
  • RNA, Small Interfering
  • bcl-2-Associated X Protein
  • Tunicamycin
  • CEBPE protein, human
  • Cyclooxygenase 2
  • PTGS2 protein, human
  • Melatonin