REGULATORY EFFECTS OF GALACTOSE ON GALACTOSE-1-PHOSPHATE URIDYLTRANSFERASE ACTIVITY ON HUMAN HEPATOBLASTOMA HEPG2 CELLS

Galactose-1-phosphate uridyltransferase (GALT) deficiency results in g alactosemia in man. We have studied the regulation of the GALT gene ex pression on the HepG2 cell line by growing the cells in glucose or gal actose medium. No difference of K-m values was observed in glucose or galactose media but the V-max value with galactose was 50% higher than that with glucose. Also in galactose medium, an increased GALT specif ic activity was detected suggesting the production of more enzyme prot eins. Yet, slot dot quantification of GALT mRNA revealed a decreased a mount of these transcripts in cells cultured with galactose or inosine while Northern blot analysis revealed the normal 1.4 kb transcript in all culture media used. Finally, IEF gel analysis displayed different isozymic patterns for the GALT enzyme in cells grown in glucose, gala ctose or inosine media. With glucose-free media, the major band of GAL T corresponds to that found in human liver. Altogether, these results suggest that the control of GALT gene expression in HepG2 cells is loc ated at the post-transcriptional level and correlated to the growth ra te of the cell.