Over-expression of the mitogen-activated protein kinase (MAPK) kinase (MEK)-MAPK in hepatocellular carcinoma: its role in tumor progression and apoptosis

BMC Gastroenterol. 2003 Aug 8;3:19. doi: 10.1186/1471-230X-3-19.

Abstract

Background: Hepatocellular carcinoma (HCC) is one of the most common malignancies in South East Asia. Although activation of the MEK-MAPK is often associated with cellular growth, the role of MEK-MAPK in growth and survival of hepatocarcinoma cells has not been established.

Methods: Immuno-histochemistry was used to localize phosphorylated MAPK and MEK1/2 in the tissues. 3-(4,5-dimethylthiazol-2-y1)-2,5-diphenyltetrazolium bromide (MTT) assay and ELISA were used to determine cell viability and cell proliferation. Deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay was used to detect apoptotic cells. Western blots analysis was performed to determine the levels of proteins involved in the MEK-MAPK and apoptotic pathways. Transfection study was performed to assess the role of MEK-MAPK pathway in growth and survival of liver cancer cells.

Results: We report that phosphorylation of MEK1/2 at Ser217/221 was detected by immuno-histochemistry in 100% (46 of 46) of HCCs examined. A positive signal was localized in the nuclei of hepatocarcinoma cells but not in dysplastic hepatocytes or stromal cells. Over-expression and phosphorylation of MAPK was also detected in 91% (42 of 46) and 69% (32 of 46) of HCCs examined, respectively. The percentage of cells showing positively for phosphorylated MEK1/2 increased with advancing tumor stage. In vitro, treatment of human HepG2 and Hep3B cells with MEK1/2 specific inhibitors U0126 and PD98059 led to growth inhibition and apoptosis. U0126 induced the release of cytochrome c and increased the cleavage of caspase-3, caspase-7, and poly ADP-ribose polymerase (PARP). Inhibition of phosphatidylinositol 3-kinase (PI-3K), c-Jun N-terminal kinase (JNK) and p38 kinase activities caused only a mild apoptosis in HepG2 and Hep3B cells. Activated MEK1-transfected cells were more resistant to UO126-induced apoptosis in vitro and formed larger tumors in SCID mice than mock-transfected cells.

Conclusion: In conclusion, our results demonstrate that MEK-MAPK plays an important role in the growth and survival of liver cancer cells and suggest that blocking MEK-MAPK activity may represent an alternative approach for the treatment of liver cancer.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects*
  • Carcinoma, Hepatocellular / enzymology*
  • Carcinoma, Hepatocellular / pathology
  • Cell Line, Tumor
  • Disease Progression
  • Disease-Free Survival
  • Humans
  • Liver Neoplasms / enzymology*
  • Liver Neoplasms / pathology
  • Mice
  • Mice, SCID
  • Mitogen-Activated Protein Kinase Kinases / antagonists & inhibitors
  • Mitogen-Activated Protein Kinase Kinases / metabolism*
  • Mitogen-Activated Protein Kinases
  • Phosphorylation

Substances

  • Mitogen-Activated Protein Kinases
  • Mitogen-Activated Protein Kinase Kinases