Characterization of a human hepatoma cell line with acquired resistance to growth inhibition by transforming growth factor beta 1 (TGF- β1)

A new cell line (Hep 3B-TR), which is resistant to growth-inhibition by transforming growth factor beta 1 (TGF- β1) up to 10 ng/ml (400 p M), was isolated from parental Hep 3B human hepatoma cells, which are sensitive to growth-inhibition by TGF- β1. In the presence of TGF- β1 (1 to 10 ng/ml), the growth of the parental cell line (Hep 3B-TS) was inhibited by more than 95%. Under the same conditions, the growth rate of the resistant clone (Hep 3B-TR) however, was identical in the presence or absence of TGF- β1 and was almost the same as that of the Hep 3B-TS cells in the absence of TGF- β1. Affinity crosslinking with 5 p M¹²⁵I-labeled TGF- β1 showed that the TGF- β1 receptors type I (TGF- βRI) and type II (TGF- βRII) were not present on the cell surface of the Hep 3B-TR cells, whereas they were present on the sensitive HEP 3B-TS cells. Hep 3B-TS cells had detectable TGF- βRII mRNA, which was not found in Hep 3B-TR cells. RNA analysis showed different effects on the expression of TGF- β1, c-fos, c-myc, and protein disulfide isomerase (PDI) genes in the two cell lines in response to TGF- β1 protein. Addition of TGF- β1 (1 ng/ml) strongly increased the expression of TGF- β1 mRNA in Hep 3B-TS cells, but not in Hep 3B-TR cells. In Hep 3B-TS cells, c-fos mRNA was not detected either in the presence or absence of TGF- β1 protein. However, abundant c-fos mRNA was detected in Hep 3B-TR cells, which was not altered by TGF- β1 protein. TGF- β1 protein inhibited the expression of c-myc and PDI mRNAs in Hep 3B-TS cells, whereas although the c-myc and PDI mRNAs were much more abundant in Hep 3B-TR cells, their expression was not affected by TGF- β1 protein. These results suggest that the mechanisms of escape from growth-inhibition by TGF- β1 in Hep 3B-TR hepatoma cells probably involve loss of binding by TGF- β1 to its cell surface receptors.