Melanoma cells produce a cell-specific proteoglycan, mel-PG, which is an integral chondroitin sulfate proteoglycan that can be released into the medium as a result of the proteolytic cleavage of the trans-membrane form. The effect of transforming growth factor β1 (TGF-β1) on proteoglycan production was studied in three melanoma cell linea at various stages of differentiation: SK-mel-1.36-1-5 (early), SK-mel-3.44 (intermediate), and SK- mel-23 (late). The main effect of TGF-β1 was to increase the synthesis and shedding of melPG into the medium without affecting the amount present in the cell membranes nor the balance between the proteoglycan and the glycoprotein forms of mel-PG. After TGF-β1 treatment, there was an increase in the amount of mel-PG present in the medium as observed in metabolic labeling, immunoprecipitation, and pulse-chase experiments. This effect was more pronounced in the SK-mel-1.36-1-5 than in the SK-mel-3.44 cell line, whereas the SK-mel-23 cells did not contain mel-PG either in the presence or in the absence of TGF-β1. Characterization of mel-PG purified from the medium from control and TGF-β1-treated cells showed that the factor increased slightly the GAG chain length in SK-mel-1.36-1-5, but not in SK-mel-3.44 cells, without modifying the degree of sulfation.
- transforming growth factor β