REGULATION OF ACTIVITY LEVELS OF GLYCOLIPID SULFOTRANSFERASES BY TRANSFORMING GROWTH-FACTOR-ALPHA IN RENAL-CELL CARCINOMA-CELLS

Accumulation of sulfolipids associated with markedly elevated levels o f glycolipid sulfotransferase activities was previously demonstrated i n human renal cell carcinoma cells. To explore the regulation mechanis ms of sulfoglycolipid synthesis in renal cancer, effects of various gr owth factors on the metabolic enzymes of sulfoglycolipids were investi gated by using a human renal cell carcinoma cell line, SMKT-R3. Among the growth factors tested, transforming growth factor alpha (TGF-alpha ) and epidermal growth factor (EGF) were found to increase the sulfotr ansferase activity markedly (about 300%), but did not change that of a rylsulfatase A, which hydrolyzes sulfoglycolipids. The augmented effec ts of TGF-alpha was abolished by cycloheximide. Since TGF-alpha is kno wn to bind to the same receptor as EGF, SMKT-R3 cells were investigate d for the EGF receptor by affinity cross-linking with I-125-EGF. A rad iolabeled protein with a molecular mass of 175 kDa corresponding to th e ligand-receptor complex was immunoprecipitated with a monoclonal ant i-EGF receptor antibody. When production of the growth factors was exa mined immunochemically, the cells were found to secrete TGF-alpha at a low level and retain it in a membrane-bound form, whereas EGF was not detected. These observations suggest that the sulfotransferase activi ties are regulated through the autocrine, paracrine, and/or juxtacrine modes of intercellular stimulation by TGF-alpha in human renal cancer cells.