Overexpression of C-NEU and C-MET during rat liver cholangiocarcinogenesis: A link between biliary intestinal metaplasia and mucin-producing cholangiocarcinoma

Based on limited but compelling immunohistochemical data demonstrating indi vidual overexpression of the tyrosine kinase growth factor receptors, c-erb B-2 and c-met, in significant percentages of human cholangiocarcinoma (ChC) , we investigated if combined overexpression of both c-neu, the rat homolog ue of c-erbB-2, and c-met, the receptor for hepatocyte growth factor/scatte r factor (HGF/SF), might represent a characteristic, early event associated with furan-induced cholangiocarcinogenesis in rat liver. Specifically, thr ough the use of immunohistochemistry, ill situ hybridization (ISH), and Wes tern and Northern blotting, we found that both c-neu and c-met are prominen tly overexpressed in intestinal metaplastic lesions in early putative preca ncerous cholangiofibrotic tissue formed in the livers of rats after 6 weeks of furan treatment when compared with normal and hyperplastic intrahepatic biliary epithelia. We further demonstrated that c-neu and c-met are concor dantly overexpressed in neoplastic glandular epithelia in later-developed p rimary "intestinal-type" of ChC formed in the livers of furan-treated rats, as well as in subsequently derived transplantable mucin-producing tumors. Overexpression of c-neu and c-met correlated with increased proliferating c ell nuclear antigen (PCNA)-labeling indices, which were determined to be th ree to four times higher in intestinal metaplastic glands in precancerous c holangiofibrotic tissue and in neoplastic glands in the primary "intestinal type" of ChC than in hyperplastic bile ductular structures within either c holangiofibrotic or bile duct-ligated (BDL) livers. The c-neu and c-met rec eptor proteins overexpressed in different iii vivo passages of a transplant able ChC each contained immunoreactive phosphotyrosines, indicating an acti vated state. However, we did not detect evidence of either gene amplificati on of c-neu or c-met or of a common transmembrane-activating mutation in c- neu expressed in transplantable ChC, Our findings indicate that altered exp ression of c-neu and c-met occurs relatively early in the process of furan- induced cholangiocarcinogenesis in rat liver and may play a potentially imp ortant role in its pathogenesis, They further indicate a common alteration in tyrosine kinase growth factor receptor expression linking early putative precancerous intestinal metaplastic lesions in liver to later-developed mu cin-producing biliary cancer.