Differential cytokeratin and alpha-fetoprotein expression in morphologically distinct epithelial cells emerging at the early stage of rat hepatocarcinogenesis
Germain, L.; Goyette, R.; Marceau, N.
Cancer Research 45(2): 673-681
1985
ISSN/ISBN: 0008-5472 PMID: 2578305 Document Number: 256225
The various liver cell populations emerging during the transitory reappearance of .alpha.-fetoprotein (AFP) in serum of 3'-methyl-4-dimethylaminoazobenzene-ingesting rats were analyzed in situ and in vitro on isolated cell preparations in terms of their cytokeratin and AFP expression using single and double indirect immunofluorescence microscopy. A polyclonal guinea pig antibody raised against cow hoof prekeratin, which recognized a MW 52,000 cytokeratin, reacted with bile ductular epithelial cells and oval cells but not with hepatocytes. A monoclonal antibody against a MW 55,000 cytokeratin reacted not only with bile ductular and oval cells but also with hepatocytes. In contrast, a polyclonal antibody against porcine eye lens vimentin reacted with sinusoidal cells and stroma cells. To assess further the heterogeneity of the emerging cell populations, liver cells were isolated after 4 wk of treatment and fractionated according to cell size and ploidy level into 4 fractions (I-IV) by velocity sedimentation at 1 .times. g. A cell-type analysis using AFP and albumin as a functional markers revealed the presence of AFP-producing cells in fraction IV at a mean velocity equivalent to that of newborn diploid rat hepatocytes; most of the albumin-producing cells were distributed in Fractions I to III at velocities similar to those of adult tetraploid rat hepatocytes. A similar analysis based on the differential expression of MW 52,000 and MW 55,000 cytokeratins and vimentin in bile ductular and other diploid epithelial cells, hepatocytes, and mesenchymal cells showed that large cells in Fractions I to III were tetraploid hepatocytes; viable cells present in Fraction IV were diploid epithelial cells and mesenchymal cells in proportion of 62 and 38%, respectively. These cell populations could be solved further by changing the sedimentation time. A subsequent examination of the MW 55,000 cytokeratin-containing diploid epithelial cells in Fraction IV using double immunofluorescence microsocopy resolved 3 cell populations with respect to MW 52,000 cytokeratin and AFP expression, namely, 2 cell populations expressing either protein marker and a 3rd one containing both markers. These results suggest a ductular origin of oval cells and a possible relation to immature hepatocytes.