Increased tyrosine kinase activites may lead to the phenotypic differences of gastric cancer cells.

ABSTRACT

BACKGROUND: The aim of this study was to elucidate possible mechanisms responsible for the phenotypic difference in gastric cancer cells between the intestinal type and the diffuse type. MATERIALS AND METHODS: The gastric cancer cell lines MKN7 and KATO-III were used. Expression of adhesion molecules and protein tyrosine phosphorylation were examined by immunoblotting. Protein-protein interactions were determined by immunoblotting following immunoprecipitation. ERK activity was assessed by immunoblotting using anti-phospho-ERK antibody. RESULTS: E-cadherin expression in KATO-III was decreased compared to that in MKN7. The expression of alpha-, beta- and gamma-catenin was not significantly different; beta- and gamma-catenin were highly tyrosine phosphorylated in KATO-III but not in MKN7. In KATO-III, a number of tyrosine phosphorylated proteins, including extracellular signal-regulated protein kinases (ERKs) and epidermal growth factor receptor (EGFR), were observed irrespective of EGF stimulation and induction of ERK activity and EGFR tyrosine phosphorylation by EGF were less than that in MKN7. CONCLUSION: Increased tyrosine kinase activities may cause diminished expression of E-cadherin and tyrosine phosphorylation of catenins, resulting in the abrogated cell-cell adhesion in gastric cancer cells.