Changes in pRb expression in the rat tongue during 4-nitroquinoline 1-oxide-induced carcinogenesis

Abstract

We investigated immunohistochemical expression of pRb, cyclin D 1, and cdk 4 in rat tongue carcinoma induced by 4-nitroquinoline 1-oxide. pRb expression in carcinoma decreased compared with that in dysplastic lesions, while expression of cyclin D 1 and cdk 4 increased gradually during the course of carcinogenesis. Phosphorylation of pRb was analyzed by immunoblotting using the G 3-245 antibody, which recognizes both phosphorylated (pp 110^<RB>) and unphosphorylated pRb (p 110^<RB>). Although expression of pp 110^<RB> notably increased in the dyspiastic membrane, it almost disappeared in carcinoma. p 110^<RB> was also expressed in control and dysplastic membranes, but not in carcinoma. We found there was a decrease of pRb and an increase of cdk 4 and cyclin D 1 in the premalignant stage. A decrease in the amount of pRb and an increase in its phosphorylation may prevent G 1 arrest and consequently accelerate proliferation of chemically injured cells.