Clonal analysis of neoplastic transformation in cultured diploid rat liver epithelial cells

Expression of TGF-alpha mRNA, which correlates well with the ability of cells to condition medium with an EGF-like activity, clonally segregates best with tumorigenicity among the several single phenotypes considered in this study. The results of unreported studies in which we have analyzed the quantitative relationships between the expression of selected phenotypes and tumorigenicity, suggest that the elevated expression of myc and TGF-alpha mRNAs interact in their associations with tumor yield. These results suggest that elevated myc expression sensitizes hepatic epithelial cells to the possible tumorigenic action of TGF-alpha. This observation may explain why the correlation between the qualitative expression of TGF-alpha and tumorigenicity, described here, is not perfect. Conventionally applied markers of transformation in hepatocytes in vivo and in cultured liver epithelial cells in vitro that we studied -histochemical expression of GGT, ability to grow in medium containing low levels of calcium, and ability to grow in soft agar- clonally segregated with tumorigenicity poorly in liver epithelial cells transformed in vitro. We conclude that these phenotypes are not adequate markers for determining the lineage of hepatic epithelial neoplasms (including, probably hepatocellular cancers arising in vivo). This study appears to be the first to attempt to analyze clonally the association of these markers with tumorigenicity, and to quantify the sensitivity, specificity, and predictive value of the associations. Our study suggests that the relatively weak associations of these phenotypes with tumorigenicity may be related only to their stronger associations with expression of TGF-alpha, or to some other property that is strongly associated with tumorigenicity. Expression of TGF-alpha is more strongly associated with expression of GLC, for example, than is the GLC phenotype with tumorigenicity. At least for GLC, autocrine stimulation by TGF-alpha is likely, since EGF increases growth of WB cells in low calcium medium. This observation may explain the perfect correlation between expression of TGF-alpha and GLC. EGF also stimulates lactate dehydrogenase, pyruvate kinase, and glucose 6-phosphate dehydrogenase in WB cells. However, quantitative correlation between GGT activity and TGF-alpha is less strong. Thus, our data from these studies suggest that the tumorigenic phenotype of cultured hepatic epithelial cells is intimately dependent on the expression of the TGF-alpha gene, possibly producing autocrine stimulation of growth via the cells' EGF receptors. This is the most simple view of the potential relationship between TGF-alpha expression and tumorigenicity in liver epithelial cells.(ABSTRACT TRUNCATED AT 400 WORDS)