title: CAD, a c-Myc target gene, is not deregulated in Burkitt's lymphoma cell lines.
abstract: Although the Myc family of transcription factors is upregulated in many human tumors, it is unclear which genes are targets for the deregulated Myc. Previous studies suggest that hamster and rat carbamoyl phosphate synthase, aspartate transcarbamylase, dihydroorotase Cad genes are regulated by c-Myc. In fact, of all putative target genes thought to be activated by c-Myc, only the Cad gene showed loss of growth regulation in rat cells nullizygous for c-Myc. However, it was unknown whether upregulation of CAD, which performs the first three rate-limiting steps of pyrimidine biosynthesis, contributes to c-Myc's role in human neoplasia. To explore this possibility, we cloned the human cad promoter. We found that c-Myc could bind to an E box in the human cad promoter in gel shift assays and that growth regulated transcription from the human cad promoter was dependent on this c-Myc binding site. However, the increased amount of c-Myc found in Burkitt's lymphoma cell lines did not lead to increased cad mRNA levels. Thus, we suggest that although c-Myc is clearly important for the normal transcriptional control of the cad promoter, it is unlikely that increased levels of CAD are important mediators of c-Myc-induced neoplasia. Therefore, an understanding of the mechanism by which overexpressed c-Myc contributes to the development of Burkitt's lymphoma requires the identification of additional c-Myc target genes.
authors.affiliation: Department of Oncology, McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, 53706, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Mac
authors.forename: P J
authors.initials: PJ
authors.lastname: Farnham
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001221:Aspartate Carbamoyltransferase / Q000096:biosynthesis / Q000235:genetics*; D001483:Base Sequence; D002051:Burkitt Lymphoma / Q000235:genetics* / Q000378:metabolism; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) / Q000096:biosynthesis / Q000235:genetics*; D003001:Cloning, Molecular; D006224:Cricetinae; D004080:Dihydroorotase / Q000096:biosynthesis / Q000235:genetics*; D015536:Down-Regulation / Q000235:genetics*; D016193:G1 Phase / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D018390:Gene Targeting; D016259:Genes, myc; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000096:biosynthesis / Q000235:genetics*; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid; D016196:S Phase / Q000235:genetics; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D014407:Tumor Cells, Cultured
chemical_list: C033626:CAD trifunctional enzyme; D009097:Multienzyme Complexes; D009363:Neoplasm Proteins; D001221:Aspartate Carbamoyltransferase; D004080:Dihydroorotase; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing)