REGULATION OF GLYCOLIPID SULFOTRANSFERASE BY TYROSINE KINASES IN HUMAN RENAL-CANCER CELLS

Glycolipid sulfotransferase activity in a human renal cancer cell line , SMKT-R3, is enhanced by the action of growth factors such as ECF, TG F-alpha and HGF, whose receptors possess tyrosine kinase domains. We i nvestigated whether tyrosine kinases are involved in the regulation of the sulfotransferase in the cells by using specific tyrosine kinase i nhibitors. Genistein and tyrphostin 51 not only cancelled the enhancem ent of the sulfotransferase by EGF but also reduced the enzyme level t o a point much lower than that seen in non-treated cells, whereas they did not affect the sulfotransferase activity in vitro. The activity-r educing effects of genistein were dose- and time-dependent. Genistein also inhibited the cell growth of SMKT-R3 cells. Western blotting usin g anti-phosphotyrosine monoclonal antibody revealed a tyrosine-phospho rylated protein with an apparent molecular mass of 116 kDa in the non- treated cells. The EGF receptor was tyrosine-phosphorylated by the add ition of EGF. The phosphorylations of the 116 kDa protein and EGF rece ptor were attenuated by co-incubation with genistein. These results in dicate that tyrosine kinases including the EGF receptor are involved i n the growth of SMKT-R3 cells and in the regulatory mechanisms of glyc olipid sulfotransferase in the cells.