We have used single- and double-label immunocytochemistry to examine the distribution of AGp110, integrin alpha 5 beta 1 and fibronectin in adult rat liver during carcinogenesis induced by aflatoxin B1 or diethylnitrosamine. In normal liver fibronectin and the fibronectin integrin receptor alpha 5 beta 1 are localized on all three domains of the parenchymal cell surface: sinusoidal, lateral and canalicular. In contrast, AGp110, a non-integrin monomeric glycoprotein with fibronectin receptor properties, is confined to the bile canalicular (apical) plasma membrane of hepatocytes. Hepatocarcinogenesis induced by aflatoxin B1 causes altered cell foci to form in the parenchyma, followed by enlargement of these foci to form pre-neoplastic nodules and finally hepatocellular carcinomas of either poorly differentiated, trabecular or adenocarcinoma morphology. Expression of AGp110 decreased to a minimal level, at first selectively in altered cell foci, from the 9th week of treatment, and then indiscriminately in poorly differentiated carcinomas. The same lesions that were deficient in AGp110 also displayed a reduced level of fibronectin and alpha 5 beta 1, although the observed change in AGp110 demarcated altered foci and poorly differentiated tumour lesions more sharply, since expression of alpha 5 beta 1 and fibronectin, though substantially reduced, was still faintly apparent on the cell surface. Small acinar structures, observed in late hyperplastic nodules and in trabecular carcinomas, exhibited even, pericellular staining of fibronectin and alpha 5 beta 1, including prominent staining of the lumen area, whereas staining of AGp110 appeared to be confined to the lumen. In larger ducts of overt adenocarcinomas, fibronectin and alpha 5 beta 1 were distributed along the basal surface of the epithelium and AGp110 on the apical domain.(ABSTRACT TRUNCATED AT 250 WORDS)

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