A specific distal promoter controls γ-glutamyl transpeptidase gene expression in undifferentiated rat transformed liver cells

Abstract

In rat undifferentiated hepatoma cells, the gamma-glutamyl transpeptidase (GGT) gene is transcribed into a 2.3 and a 2.6 kb mRNA which, in contrast with other rat GGT transcripts, are not detected in more differentiated liver cells or adult tissues. Analysis of the cDNA sequences obtained from H5 hepatoma cells reveals that these two transcripts differ from other GGT mRNAs by a 312-nt unique untranslated leader sequence; this sequence maps on the gene in a single exon 10 kb upstream from the GGT promoter IV transcription start site. We established that the 2.6 kb mRNA V-1 and the 2.3 kb GGT mRNA V-2 derive, by alternate splicing, from a primary transcript initiated on a distal promoter on the rat GGT gene. This gene appears to be transcribed from five promoters, and the specific expression of this new distal promoter in undifferentiated hepatoma cells requires binding of activator protein-1 and hepatic nuclear factor 3 specific transcription factors to a composite cis-element in the proximal region of the promoter. The distal GGT promoter, specifically expressed in undifferentiated liver cells, might reflect the expression of that gene in liver precursor cells before they differentiate in the hepatocytic or biliary lineage.

γ-Glutamyl transpeptidase is induced by 4-hydroxynonenal via EpRE/Nrf2 signaling in rat epithelial type II cells

“…mRNA V was first identified in rat undifferentiated hepatoma H5 and HTC cells [30]. Our results here show that GGT mRNA V (V-2) was expressed predominantly in rat lung, spleen, ovary, testicle, and embryo and to a lesser extent in liver, kidney, and brain but not in heart and thymus (Fig.…”

“…In this cell line, we observed that the AP-1/ hepatocyte nuclear factor (HNF) 3 overlapping site located between −27 and −48, which was reported to be essential for the basal expression of GGT mRNA in undifferentiated hepatoma H5 cells [30], is not involved in the basal activity of GP5. HNF3 is a member of the forkhead winged helix family, and its function is often controlled by regulatory factors which have binding sites overlapping with HNF3 motif [44].…”

“…We also noted a binding to this element in the absence of HNE treatment, and this binding can be associated with an effect of the EpRE observed under basal conditions. The promoter region from −98 to −150, which contains this EpRE, also contributes to the basal level of GP5 in hepatoma cells [30]; however, the specific contributions of the EpRE to this activity have not been demonstrated.…”

“…Transcription of the GGT gene from its distal promoter (GP5) was first detected in rat HTC and H5 hepatoma cells [30]. Promoter 5 generates an mRNA V primary transcript that, by alternative splicing of exon 2, giving rise to the V-1 and V-2 mature transcripts.…”

“…GGT mRNA V was first identified in undifferentiated rat hepatoma cells, and its transcription was regulated by the most distal promoter-promoter 5. With alternate splicing, two types of mRNA V, V-1 and V-2, are generated by GGT promoter 5 (GP5) [30]. Compared to V-1, V-2 does not have the 252 nucleotides (nt) corresponding to the second exon for the mRNA IV and V-1.…”