Expression of CDK 4, Connexin 32, and PCNA in N-diethylnitrosamine-Induced Lesions of Rat Liver

ABSTRACT

Cellular altered foci (CAF), hyperplastic nodules (HN) including regenerating and adenomatous nodules, and hepatocellular carcinomas (HCC) were induced in Sprague-Dawley rat liver by prolonged administration of N-diethylnitrosamine (DEN, 200 ppm). Immunohistochemical expression of connexin 32 (Cx 32), cyclin-dependent kinase 4 (CDK 4), and proliferating cell nuclear antigen (PCNA) was assessed for the evaluation of preneoplastic potential of CAF. Regardless the duration of DEN administration, basophilic cell foci were the most frequently observed lesion in both CAF and cellular expanding hyperplastic nodules. Eosinophilic cell foci, however, were concomitantly increased with adenomatous nodules in later experimental groups. Cx 32 showed perimembranous spot-like expression. Its number was 7.25 2.10 per cell in normal hepatocytes. CAF and adenomatous nodules showed markedly decreased Cx 32 spots. Moreover, its reduction was more prominent in HCC. PCNA-labelled hepatocytes were scattered in the most CAF, showing no significant difference between each CAF. PCNA labelling index (LI) in adenomatous nodule and HCC was markedly increased. CDK 4 was localized in the cytoplasm and/or nucleus of hepatocytes. Eosinophilic cell foci revealed more nuclear expression of CDK 4 than other types of CAF, of which expression incidence was comparable to that of adenomatous nodule. Nuclear CDK 4 expression in HN and HCC was increased, although significant difference between regenerating nodule and adenomatous nodule was not seen. In conclusion, the incidence of CDK 4 was concomitantly increased with PCNA LI, however, reciprocally decreased with Cx 32 in accordance with the advance of DEN-induced HCC in rat. Phenotypically altered foci manifested as CAF are early valuable preneoplastic marker lesion for evaluation. In addition, basophilic cell foci can be considered a discernible marker of cellular expansion within nodules. However, eosinophilic cell foci might be an indeterminate marker for the advance of DEN-induced HCC in rat.