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 chromosome 1q24 codes for a ubiquitously expressed 3-kb mRNA, translated in a 45-kDa nuclear protein. Recent studies have shown a deficient expression of this gene in acute promyelocytic leukemia (APL). However, treatment with retinoids was able to upregulate JEM-1 mRNA in maturing NB4 leukemia cells. Here, we report the characterization of the structural organization of JEM-1. By hybridization screening of a human genomic library derived from blood mononuclear cells, five overlapping genomic DNA clones were isolated. These clones 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 structure of Jem-1 revealed seven exons whose junctions with introns exhibited typical splice sequences. A shorter transcript (Jem-1s, 1.3 kb) generated by exon 3 extension and polyadenylation was identified. Its translation generated a 23-kDa protein that exhibited a cytoplasmic localization. 5'RACE-PCR identified 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 CCAAT box located 95 bp upstream of the TSS. Sequencing also revealed potential cis-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 strong constitutive promoter activity determined by a luciferase-reporter gene assay in transiently transfected HeLa cells. Retinoids further increased luciferase expression 2.7-fold. We demonstrated that the 1-kb distal sequence contains yet unidentified elements reducing constitutive transcription. Thus, the maximal constitutive promoter activity was assigned to a -432 + 101 region overlapping the TSS. These data support the idea of a constitutive expression of JEM-1, but a negative regulation in APL released by retinoids.

Expression patterns of the JEM-1 gene in normal and tumor cells: ubiquity contrasting with a faint, but retinoid-induced, mRNA expression in promyelocytic NB4 cells.

The JEM-1 gene, recently identified in acute promyelocytic leukemia (APL) cells, codes for a novel nuclear factor (Duprez et al Oncogene 1997; 14: 1563-1570). JEM-1 is kept silent in the APL cell line NB4, but up-regulated (3 kb transcript) during cell maturation. Here, we show that retinoic acid (RA)-induced JEM-1 expression is biphasic (peaks at 6 h and 48 h) and associated with the later stages of maturation. Retinoids, which cooperates with cAMP to induce maturation, also cooperates with cAMP to up-regulate JEM-1, either in maturation-responsive NB4 cells or in NB4-R1 resistant subclones. APL patients showed a low, yet variable, level of JEM-1 mRNA in bone marrow. RA treatment induced an increase in the level of JEM-1 mRNA, as detected by a semi-quantitative PCR. This increase can result from both gene up-regulation or replacement of leukemia cells by differentiated ones. Analysis of JEM-1 expression patterns in normal and tumor cells revealed that JEM-1 expression was ubiquitous. Cell lines derived from monocytic and erythroid leukemias, expressed low and high amounts of JEM-1 mRNA, respectively. Using a JEM cDNA probe, distinct profiles of expression and different transcript sizes (4 kb, 3 kb and 2 kb) were also identified in tumour and normal non-hematopoietic tissues, while interestingly only the 3kb transcript was up-regulated in NB4 cells. This work identifies JEM-1 as a novel ubiquitous gene whose expression is low in APL cells, but can be restored by RA treatment, concomitant with cell maturation.