Genomic organization of the JEM-1 (BLZF1) gene on human chromosome 1q24: Molecular cloning and analysis of its promoter region

The Jem-1 (JEM-1, HGMW-approved symbol BLZF1) gene mapping to human chromos ome 1q24 codes for a ubiquitously expressed 3-kb mRNA, translated in a 45-k Da nuclear protein. Recent studies have shown a deficient expression of thi s gene in acute promyelocytic leukemia (APL). However, treatment with retin oids was able to upregulate JEM-1 mRNA in maturing NB4 leukemia cells. Here , we report the characterization of the structural organization of JEM-1. B y hybridization screening of a human genomic library derived from blood mon onuclear cells, five overlapping genomic DNA clones were isolated. These cl ones extend over 34 kb of the human genome and comprise the complete JEM-1 gene and a 4-kb 5'flanking region. Determination of the exon-intron structu re of Jem-1 revealed seven exons whose junctions with introns exhibited typ ical splice sequences. A shorter transcript (Jem-1s, 1.3 kb) generated by e xon 3 extension and polyadenylation was identified. Its translation generat ed a 23-kDa protein that exhibited a cytoplasmic localization. 5'RACE-PCR i dentified a major transcription start site (TSS) located at 403 nt upstream of the ATG, Computer analysis of the 1.8-kb 5'flanking region showed that it lacks a TATA box, Inr motifs or DPE motifs, but it contains a typical CC AAT box located 95 bp upstream of the TSS. Sequencing also revealed potenti al cia-acting elements for multiple transcription regulators including Sp1, GATA, C/EBP, AP-1, and Pu1, No retinoic acid receptor elements or retinoic X receptor elements were detected. This 1.8-kb DNA sequence showed a stron g constitutive promoter activity determined by a luciferase-reporter gene a ssay in transiently transfected HeLa cells. Retinoids further increased luc iferase expression 2.7-fold. We demonstrated that the 1-kb distal sequence contains yet unidentified elements reducing constitutive transcription. Thu s, the maximal constitutive promoter activity was assigned to a -432 + 101 region overlapping the TSS, These data support the idea of a constitutive e xpression of JEM-1, but a negative regulation in APL released by retinoids, (C) 2000 Academic Press.