FUNCTIONAL-CHARACTERIZATION OF THE RAT BETA-GLUTAMYL TRANSPEPTIDASE PROMOTER THAT IS EXPRESSED AND REGULATED IN THE LIVER AND HEPATOMA-CELLS

gamma-Gylutamyl transpeptidase (GGT) is an enzyme encoded by multiple mRNAs (mRNA(I) to mRNA(IV)) that, in the rat, are transcribed from a s ingle copy gene in a tissue specific manner. In the liver, GGT express ion is up-regulated in transformed cells, and this induction is the mo st widely used marker of liver cell transformation. We characterized t he GGT mRNA species expressed in the liver (mRNA(III)), and we report that this mRNA differs from the other GGT mRNA species by a 275-base a lternate 5'-end sequence. Its transcription occurs on a specific promo ter (promoter III) that maps on the GGT gene upstream of the two promo ters coding for the GGT mRNA(I) and mRNA(II). In hepatoma cells, mRNA( III) expression is related to the differentiation state of the cells. We have shown that, in Reuber H-35-derived cell lines, the GGT mRNA(II I) is transcribed in cells that express a differentiated phenotype (Fa o), but not in the dedifferentiated C2 and H5 variants. Moreover, we o bserved a reexpression of the GGT mRNA(III) species in the C2 Rev7 var iant, which has reverted from C2 toward a differentiated hepatocyte ph enotype. In the proximal promoter III region, we identified a sequence that strongly enhances transcriptional activity in Fao and C2 Rev7 ce lls, but not in the dedifferentiated C2 variant. This motif interacts with nuclear proteins belonging to the NF-1 and NF-Y families that gov ern GGT promoter III expression in differentiated hepatoma cells.