title: A novel intron element operates posttranscriptionally To regulate human N-myc expression.
abstract: Precisely regulated expression of oncogenes and tumor suppressor genes is essential for normal development, and deregulated expression can lead to cancer. The human N-myc gene normally is expressed in only a subset of fetal epithelial tissues, and its expression is extinguished in all adult tissues except transiently in pre-B lymphocytes. The N-myc gene is overexpressed due to genomic amplification in the childhood tumor neuroblastoma. In previous work to investigate mechanisms of regulation of human N-myc gene expression, we observed that N-myc promoter-chloramphemicol acelyltransferase reporter constructs containing sequences 5' to exon 1 were active in all cell types examined, regardless of whether endogenous N-myc RNA was detected. In contrast, inclusion of the first exon and a portion of the first intron allowed expression only in those cell types with detectable endogenous N-myc transcripts. We investigated further the mechanisms by which this tissue-specific control of N-myc expression is achieved. Using nuclear run-on analyses, we determined that the N-myc gene is actively transcribed in all cell types examined, indicating a posttranscriptional mode of regulation. Using a series of N-myc intron 1 deletion constructs, we localized a 116-bp element (tissue-specific element [TSE]) within the first intron that directs tissue-specific N-myc expression. The TSE can function independently to regulate expression of a heterologous promoter-reporter minigene in a cell-specific pattern that mirrors the expression pattern of the endogenous N-myc gene. Surprisingly, the TSE can function in both sense and antisense orientations to regulate gene expression. Our data indicate that the human N-myc TSE functions through a posttranscriptional mechanism to regulate N-myc expression.
authors.affiliation: Department of Experimental Pathology, Department of Pediatrics, University of Utah School of Medicine, Salt Lake City, Utah 84112, USA.
authors.forename: L E
authors.initials: LE
authors.lastname: Sivak
authors.forename: G
authors.initials: G
authors.lastname: Pont-Kingdon
authors.forename: K
authors.initials: K
authors.lastname: Le
authors.forename: G
authors.initials: G
authors.lastname: Mayr
authors.forename: K F
authors.initials: KF
authors.lastname: Tai
authors.forename: B T
authors.initials: BT
authors.lastname: Stevens
authors.forename: W L
authors.initials: WL
authors.lastname: Carroll
mesh_terms: D000328:Adult; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D005091:Exons; D015972:Gene Expression Regulation, Neoplastic; D018922:HL-60 Cells; D006801:Humans; D007438:Introns; D020014:K562 Cells; D009447:Neuroblastoma; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D012313:RNA; D012323:RNA Processing, Post-Transcriptional; D014158:Transcription, Genetic; D020298:U937 Cells
chemical_list: D016271:Proto-Oncogene Proteins c-myc; D012313:RNA; D015500:Chloramphenicol O-Acetyltransferase