Intergenic splicing of MDS1 and EVI1 occurs in normal tissues as well as in myeloid leukemia and produces a new member of the PR domain family.

Abstract

The EVII gene, located at chromosome band 3q26, is overexpressed in some myeloid leukemia patients with breakpoints either 5' of the gene in the t(3;3)(q21;q26) or 3' of the gene in the inv(3)(q21q26). EVIl is also expressed as part of a fusion transcript with the transcription factorAMLI in the t(3;21)(q26;q22), associated with myeloid leukemia. In cells with t(3;21), additional fusion transcripts are AMLIMDSl andAMLI-MDSI-EV71.MDSJ is located at 3q26 170-400 kb upstream (telomeric) The protooncogene EVI1 was initially identified and described in the mouse. It is activated in murine myeloid leukemia by proviral insertion in the evil common integration site (1, 2). EVIl is not normally expressed in hematopoietic cells. In humans, the gene can be activated in myeloid leukemias and myelodysplastic diseases by chromosomal rearrangements either 5' of the gene in the t(3;3)(q21;q26) or 3' of the gene in the inv(3)(q21q26) by juxtaposition of the gene to enhancer elements of the ribophorin gene located at 3q21 (3-5). Activation of EVIl can also occur in the t(3;21)(q26;q22) as part of the fusion mRNA,AMLl-EV71, that is transcribed from the der(3) chromosome (6, 7). Abnormal expression of EVI1 has also been detected in patients with myeloid leukemia and a cytogenetically normal karyotype (8), suggesting that inappropriate activation of this gene occurs through various mechanisms.EV71 is a nuclear protein containing a seven-zinc-finger domain at the N-terminal end, a three-finger domain in the central part of the molecule, and an acidic domain distal to the second group of zinc fingers (9). The human and mouse open reading frames are 91% homologous at the DNA level and 94% homologous at the amino acid level. The second exon of the gene, in frame although not translated, is highly conserved between the two species. The open reading frame starts in the third exon of the gene, where the first ATG is located (9). A The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. putative promoter has been identified, by genomic sequencing and Si protection analysis, immediately upstream of the first exon of the murine cDNA (10).MDS1 was cloned as one of the partner genes of AML1 in the t(3;21)(q26;q22), associated with therapy-related acute myeloid leukemia and myelodysplastic syndrome as well as with chronic myeloid leukemia in blast crisis (11,12). In this translocation, AML1, located at 21q22, is fused to several genes, EAP, MDS1, and EVIl, all of which are located at 3q26200-400 kb apart (7), and chimeric cDNAs have been isolated from cells with t(3;21) in which AML1 is fused to EAP, to MDS1, to EVI1, or to MDS1 and EVIl in the same transcript, producing, in the latter case, a very complex chimeric gene. Only the 3' region of MDS1 that is fused to AML1 has been isolated and sequenced. The nature of MDS1 is somewhat controversial; MDS1 has been described as a unique ge...

The EVI1 gene in myeloid leukemia

“…Analysis of the sequence showed that the clones contained an open reading frame in which MDS1 was spliced in-frame to the second exon of EVI1, resulting in a new gene which we named MDS1/EVI1. 80 The predicted translation of this longer ORF adds about 200 amino acids upstream of the previously reported start site of EVI1. 80 Analysis of the multiple tissue Northern blot with the MDS1 probe showed that, in addition to the 5.8 and 6.2 kb bands corresponding to MDS1/EVI1, three unique transcripts of about 1, 1.5 and 2 kb were also identified by the probe.…”

“…80 The predicted translation of this longer ORF adds about 200 amino acids upstream of the previously reported start site of EVI1. 80 Analysis of the multiple tissue Northern blot with the MDS1 probe showed that, in addition to the 5.8 and 6.2 kb bands corresponding to MDS1/EVI1, three unique transcripts of about 1, 1.5 and 2 kb were also identified by the probe. This indicated that MDS1 can also be expressed as a unique gene encoding a small protein, presumably with transcripts of 1 to 2 kb.…”

“…The two alternative isoforms of MDS1 result in two predicted proteins differing in their C-terminus by about 10-15 amino acids. 80 The pattern of expression of MDS1 is very similar to that of EVI1, with prominent bands in several tissues.…”

“…25 Analysis of a multiple tissue Northern blot with MDS1 revealed two large bands of 5.8 and 6.2 kb identical in size to those observed with an EVI1 probe. 80 This suggested that MDS1 could be expressed in normal tissues as a transcript including EVI1. The existence of this MDS1/EVI1 transcript was confirmed with the isolation and sequencing of cDNA clones from normal human pancreas and kidney libraries.…”

“…18 The homology is concentrated mainly within three blocks of about 15 amino acids each, which are evenly spaced (Figure 4). The domain has been named the PR domain, 80 and its conservation among the various proteins …”