Correlation of P-cadherin and β-catenin expression and phosphorylation with carcinogenesis in rat tongue cancer induced with 4-nitroquinoline 1-oxide

Abstract 

Using biochemical and immunohistochemical techniques, we have investigated P-cadherin, β-catenin, c-src and c-met protein expression, and phosphorylation of β-catenin in a rat model of tongue cancer induced with 4-nitroquinoline 1-oxide. Six-week-old male Sprague–Dawley rats were given either normal drinking water (controls) or 50 ppm 4NQO solution as drinking water for 16 and 20 weeks. This treatment produced dysplasia and well-differentiated squamous cell cancer in rat tongues after 16 and 20 weeks, respectively. In controls, P-cadherin and β-catenin were expressed only in cell membranes of tongue suprabasal epithelial cells, whereas strong reaction to P-cadherin antibody was observed during carcinogenesis, especially in nests of cancer cells. However, dysplastic and cancer cells expressed β-catenin not only in cell membranes but also in the nuclear and cytoplasmic compartments. During carcinogenesis, immunohistochemical reaction to phosphotyrosine increased gradually. Reaction to the c-src product was strongest at the dysplastic stage and, to the c-met product, at the cancer stage. In addition, western blotting analysis showed a marked increase in the expression of β-catenin and phosphotyrosine in dysplastic and cancer cells compared with the controls. Using immunoprecipitation and western blotting techniques, we found that phosphorylated β-catenin gradually increased during carcinogenesis. These experiments demonstrate that cell–cell adhesion in epithelial cells was reduced by phosphorylation of β-catenin and that β-catenin overexpression in nuclear and cytoplasmic compartments during carcinogenesis and the production of the c-met product that is associated with the phosphorylation of β-catenin in tongue cancer.

Keywords:  Rat, Tongue cancer, 4-Nitroquinoline 1-oxide, P-cadherin, β-Catenin, Phosphorylation