We have examined the effects of transforming growth factor β1 (TGF-β1) on the growth of paired murine melanoma cell clones that differ with respect to their experimental metastatic potential. Neither poorly (clone 16) nor highly (clone M2) metastatic cells were capable of anchorage-independent growth in 0.3% agar/Dulbecco's modified Eagle's medium in the absence of serum. However, both clones were capable of anchorage-independent growth in 0.3% agar/Dulbecco's modified Eagle's medium containing 10% calf serum. Colony formation in the presence of 10% calf serum was enhanced in a dose-dependent manner by TGF-β1 (half-maximal dose, 0.1 ng/ml) and was 5- to 10-fold greater than colony formation in the presence of 10% calf serum alone. Under anchorage-dependent (monolayer) conditions, neither clone grew in the absence of serum or in medium containing less than 1% calf serum. The monolayer growth of poorly metastatic cells (clone 16) was enhanced in a dose-dependent manner by TGF-β1 in medium supplemented with calf serum. Growth was 3.5-fold and 2.3-fold greater than untreated controls after 5 days in submitogenic (0.5%) and mitogenic (10%) concentrations of calf serum, respectively. In contrast, TGF-β1 had no effect on the monolayer growth of highly metastatic cells (clone M2) either in submitogenic (0.5%) or mitogenic (10%) concentrations of serum. TGF-β1 did not directly stimulate DNA synthesis by either poorly or highly metastatic cells when measured 24 h after TGF-β1 treatment. The ability of TGF-β1 to stimulate the anchorage-independent growth of metastatic melanoma cells suggests that this potent growth factor may play a role in the growth of these cells in vivo. In addition, the differential sensitivity of poorly and highly metastatic cells to TGF-β1 may be relevant to their metastatic potential in vivo. While the mechanism(s) by which TGF-β1 stimulates the growth of these cells remains unknown, these differentially metastatic clones of the K-1735 murine melanoma should provide a useful model in which to study the effects of transforming growth factor β on the metastatic phenotype.

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This research was supported by NIH Grants CA21463 and CA29995 and a grant from the Leukemia Task Force.

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