Aldehyde dehydrogenase isozymes in rat hepatoma-mouse fibroblast hybrids

Regulation of expression of liver-specific enzymes. I. Detection in mammalian tissues and cultured cells

Nineteen enzymes showing highest activity in liver were examined in human and rodent tissues and cultured cells using starch-gel electrophoresis. The rat hepatoma line Faza 967 strongly expressed 13 of these enzymes. A series of somatic cell hybrids, constructed between Faza and cells of non-hepatic origin derived from man or from Chinese hamster, were examined for expression of these enzymes. Some of the human/rat hybrids continued to produce rat liver-specific enzymes, and the human forms of the enzymes glutamate-pyruvate transaminase, alpha-glycerophosphate dehydrogenase, alcohol dehydrogenase and pyruvate kinase L were reexpressed in a few cases.

Expression of human hepatic genes in mouse hepatoma--human amniocyte hybrids

Human liver-specific gene products are expressed by hybrid cells resulting from the fusion of human amniocytes with mouse hepatoma cells. Amniocytes grown from human amniotic fluid have no detectable levels of secreted human albumin, transferrin, alpha-1 antitrypsin, or ceruloplasmin, while the mouse hepatoma line, HH--, secretes several mouse liver-specific gene products including transferrin and albumin. Fifty-five hybrids were isolated and analyzed for the expression of serum proteins by Ouchterlony double diffusion and Laurell immunoelectrophoresis. All hybrids continued to express mouse albumin and transferrin, and 29 hybrids from this series were found to express one or more human serum proteins. Activation of the human amniocyte genome provides a model for prenatal diagnosis of serum protein abnormalities.

The expression of differentiated functions in somatic cell hybrids: retention and activation of C3 production

Rat and mouse fibroblasts which do not secrete the third component of complement (or secrete it at a very low rate), were respectively hybridized with mouse and rat hepatoma cells which actively produce C3. These interspecific hybrids actively secrete both mouse and rat C3. The production of C3 coded by the hepatoma cell genome is thus retained, but in addition, the secretion of C3 coded by the fibroblast genome is activated. On the other hand, intraspecific hybrids have been isolated from normal diploid C3 producing cells and non-producing cells. These cell hybrids also retain the capacity to secret C3. Retention of C3 production thus does not appear to be peculiar to hybrides derived from hepatoma cells.

The control of serum protein synthesis in hepatoma-fibroblast hybrids

Hybrids between mouse hepatoma cells (which secrete several serum proteins) and mouse or rat fibroblasts (which do not secrete these proteins) produce transferrin and the third component of complement (C3) like the parental hepatoma cells, while they do not secrete either albumin or alpha-fetoprotein (AFP). This lack of albumin and AFP secretion is probably due to a lack of synthesis, rather than to a simple defect in secretion. The cessation of albumin and AFP production is not dependent upon the parental fibroblast nor upon the selection conditions; it is best explained by a shut-off synthesis and could thus reflect the existence of a regulatory mechanism. This would imply a difference between the control of albumin and AFP synthesis and that of transferrin and C3 synthesis. On the other hand, in agreement with Peterson and Weiss (1972), hybrids between rat hepatoma cells and mouse fibroblasts continue to product rat albumin. This suggests that the mouse hepatoma cells differ from the rat hepatoma cells in the way they control albumin production.