Clonal heterogeneity of the sensitivity of human colon carcinoma cell lines to TGE beta isoforms

Spontaneously arising, TGF beta 1-resistant colonies were isolated directly from the soft agarose plates of MOSER human colon carcinoma cells grown in the presence of TGF beta 1 but in the absence of serum. The colonies were cloned by limiting dilution and screened in a monolayer proliferation assay for sensitivity to TGF beta 1 and TGF beta 2 isoforms. Cell clones selectively sensitive or resistant to these isoforms in the growth inhibition assay displayed similar differential sensitivities to TGF beta isoforms for production of the extracellular matrix proteins laminin and fibronectin, as well as for the expression of the colon cell differentiation marker carcinoembryonic antigen. Differential receptor binding profiles for TGF beta 1 and TGF beta 2 were observed among the clones. The isolation of cell clones selectively resistant or sensitive to TGF beta isoforms as well as the identification of differential receptor binding profiles among the clones indicate the heterogeneity of TGF beta responsiveness that exists naturally in human colon tumor cells and stress the importance of defining mechanisms underlying differential responsiveness to TGF beta isoforms.

Transforming growth factor beta isoform-specific differences in interactions with type I and II transforming growth factor beta receptors

Here we describe human colon carcinoma cell clones, isolated from a transforming growth factor beta (TGF-beta)-responsive parental cell line, which display differential sensitivities to TGF-beta 1 and TGF-beta 2 isoforms. In a monolayer proliferation assay, some clones were sensitive to both isoforms (IC50 = 0.1-0.6 ng/ml; S1S2) while others were resistant to both isoforms (IC50 > 5 ng/ml; R1R2). Still other clones (R1S2) were sensitive to TGF-beta 2 (IC50 = 0.1-0.2 ng/ml), but were resistant to TGF-beta 1 (IC50 > or = 5 ng/ml). In S1S2 cells, both TGF-beta isoforms resulted in a repression of c-myc mRNA expression, a concentration-dependent increase in fibronectin levels, and an enhanced production of the colon cell differentiation marker carcinoembryonic antigen. In contrast, R1R2 cells did not display these responses, or did so only to a limited extent. In R1S2 cells, TGF-beta 2 elicited these responses, yet TGF-beta 1 was essentially without effect. Receptor cross-linking experiments indicated that TGF-beta resistance in this model system was not generally associated with a complete lack of expression of either type I or II receptors. Moreover, the R1S2 type clones were heterogeneous, although the majority of them displayed binding to type I receptors by TGF-beta 2 but not by TGF-beta 1. These data suggest that either the TGF-beta 1 and TGF-beta 2 isoforms differ with respect to their ability to interact with the type I and II classes of receptors, or the TGF-beta 1 and TGF-beta 2 isoforms can interact with distinct receptor proteins of the type I and II classes in this model system.