Diane E. Brattain

Differential sensitivity of subclasses of human colon carcinoma cell lines to the growth inhibitory effects of transforming growth factor-β1

In this study we have employed a model system comprising three groups of colon carcinoma cell lines to examine the growth-inhibitory effects of two molecular forms of transforming growth factor-beta (TGF-beta), TGF-beta 1 and TGF-beta 2. Aggressive, poorly differentiated colon carcinoma cells of group I did not respond to growth inhibitory effects of TGF-beta 1 or TGF-beta 2, while less aggressive, well-differentiated cells of group III displayed marked sensitivity to both TGF-beta 1 and TGF-beta 2 in monolayer culture as well as in soft agarose. One moderately well-differentiated cell line from group II which has intermediate growth characteristics failed to respond to TGF-beta 1 or TGF-beta 2, but the growth of two other cell lines in this group was inhibited. TGF-beta 1 and TGF-beta 2 were equally potent, 50% growth inhibition for responsive cell lines being observed at a concentration of 1 ng/ml (40 pM). Antiproliferative effects of TGF-beta 1 and TGF-beta 2 in responsive cell lines of groups II and III were associated with morphological alterations and enhanced, concentration-dependent secretion of carcinoembryonic antigen. Radiolabeled TGF-beta 1 bound to all three groups of colon carcinoma cells with high affinity (Kd between 42 and 64 pM). These data indicate for the first time a strong correlation between the degree of differentiation of colon carcinoma cell lines and sensitivity to the antiproliferative and differentiation-promoting effects of TGF-beta 1 and TGF-beta 2.

Different epidermal growth factor growth responses and receptor levels in human colon carcinoma cell lines

The growth response to epidermal growth factor (EGF) and the numbers and types of EGF receptors were studied in three human colon tumor cell lines from each of two groups of cell lines that differ markedly in their growth properties and extent of differentiation. Aggressively growing and poorly differentiated colon cells (group I) did not respond to EGF alone, while less aggressively growing and more differentiated cells (group III) responded with increased growth when EGF was added to their chemically defined, serum-free medium. The average number of EGF receptors (EGF-R) measured at the surface of group III cell lines by radioligand binding assays, was eight-fold higher than that measured for group I cell lines. These observations provide evidence for possible autocrine mechanisms that maintain available EGF-R levels in more differentiated group III colon tumor cells and down-regulate EGF-R levels in group I colon tumor cells.

Modulation of C-myc by transforming growth factor-β in human colon carcinoma cells☆

Previous work indicated that transforming growth factor-beta elicits proliferation-inhibitory and differentiation-like effects in the human colon carcinoma cell line MOSER. We report for the first time that the proto-oncogene c-myc is repressed in response to transforming growth factor-beta in a human colon carcinoma cell line. We also describe a subline of these cells which are relatively resistant to the transforming growth factor-beta-induced effects on proliferation in monolayer and in soft agarose, but which retain the ability to specifically bind transforming growth factor-beta. Analysis of molecular and cellular alterations in this subline may aid in elucidating the mechanism of action of transforming growth factor-beta.

Comparison of the antiproliferative effects of transforming growth factor-β,N,N-dimethylformamide and retinoic acid on a human colon carcinoma cell line

In this study we have compared the anti-proliferative effects of transforming growth factor-beta (TGF-beta), N,N-dimethylformamide (DMF) and retinoic acid (RA) on a moderately-differentiated colon carcinoma cell line (JVC). TGF-beta, DMF and RA inhibited the anchorage-independent growth and induced morphological changes in JVC cells. EC50 values of 40 pM TGF-beta, 0.5% DMF and 5 nM RA were obtained for growth inhibition. In addition all three agents enhanced cellular fibronectin levels in a time- and dose-dependent manner. Inhibition of cell proliferation as well as fibronectin induction by all three agents were reversible. Combinations of any two agents at suboptimal doses, added simultaneously to JVC cells gave additive inhibitory response on growth. These data indicate that the effects of TGF-beta in this colon carcinoma cell line are similar to those of the two differentiation promoting agents DMF and RA.

Comparison of the effects of transforming growth factor β, N,N-dimethylformamide, and retinoic acid on transformed and nontransformed fibroblasts☆

In order to compare the effects of transforming growth factor (TGF beta) with those of the differentiation promoters N,N-dimethylformamide (DMF) and retinoic acid (RA), the antiproliferative and fibronectin-inducing activities of the three agents were examined. AKR-2B mouse embryo fibroblasts and their chemically transformed counterpart AKR-MCA cells were used as the model system. Growth in monolayer culture of both cell lines was inhibited by TGF beta (EC50 approximately 1 ng/ml), DMF (EC50 approximately 0.5%), and RA (EC50 approximately 1 microM) in a concentration-dependent manner. Time-dependent elevation in fibronectin expression was also observed with all three agents. The EC50 for growth inhibition of both cell lines by TGF beta agreed well with that obtained for stimulation of fibronectin synthesis. A 3-h exposure to TGF beta is sufficient to obtain the maximal fibronectin level observed at 48 h in AKR-2 B cells but not in AKR-MCA cells. Our results indicate that in this system the effects of TGF beta are similar to those of the chemical differentiation inducers DMF and RA. Furthermore, our data also suggest that the TGF beta signal may be processed differently by nontransformed and transformed fibroblasts.

Retinoic acid restores normal growth control to a transformed mouse embryo fibroblast cell line

The effects of retinoic acid on a transformed mouse embryo fibroblast cell line (AKR-MCA) were examined. Treatment with retinoic acid restored a non-transformed phenotype to this transformed cell line in a dose dependent manner. Retinoic acid (RA) treated AKR-MCA cells showed a non-transformed morphology, a slower growth rate, and did not grow with anchorage independence. A 38,000 Da protein was phosphorylated to a high degree in the AKR-MCA transformed cell line compared to the non-transformed AKR-2B cell line. RA treatment greatly reduced the level of phosphorylation of this protein in AKR-MCA cells. Growth arrested AKR-MCA cells showed a mitogenic response to nutrient replenishment, but not to epidermal growth factor (EGF). Treatment of AKR-MCA cells with RA restored their ability to respond to EGF while the response to nutrient replenishment was lost. This pattern of growth control was similar to that of the non-transformed AKR-2B cells.