Transcriptional Regulation ofN-Acetylglucosaminyltransferase V by the srcOncogene

Abstract

Transformation of baby hamster kidney fibroblasts by the Rous sarcoma virus causes a significant increase in the GlcNAcbeta(1, 6)Man-branched oligosaccharides by elevating the activity and mRNA transcript levels encoding N-acetylglucosaminyltransferase V (GlcNAc-T V). Elevated activity and mRNA levels could be inhibited by blocking cell proliferation with herbimycin A, demonstrating that Src kinase activity can regulate GlcNAc-T V expression. 5' RACE analysis was used to identify a 3-kilobase 5'-untranslated region from GlcNAc-T V mRNA and locate a transcriptional start site in a 25-kilobase pair GlcNAc-T V human genomic clone. A 6-kilobase pair fragment of the 5' region of the gene contained AP-1 and PEA3/Ets binding elements and, when co-transfected with a src expression plasmid into HepG2 cells, conferred src-stimulated transcriptional enhancement upon a luciferase reporter gene. This stimulation by src could be antagonized by co-transfection with a dominant-negative mutant of the Raf kinase, suggesting the involvement of Ets transcription factors in the regulation of GlcNAc-T V gene expression. The src-responsive element was localized by 5' deletion analysis to a 250-base pair region containing two overlapping Ets sites. src stimulation of transcription from this region was inhibited by co-transfection with a dominant-negative mutant of Ets-2, demonstrating that the effects of the src kinase on GlcNAc-T V expression are dependent on Ets.