Molecular analysis of Evi1, a zinc finger oncogene involved in myeloid leukemia

Identification of two critically deleted regions within chromosome segment 7q35-q36 in EVI1 deregulated myeloid leukemia cell lines

Chromosomal rearrangements involving the EVI1 proto-oncogene are a recurrent finding in myeloid leukemias and are indicative of a poor prognosis. Rearrangements of the EVI1 locus are often associated with monosomy 7 or cytogenetic detectable deletions of part of 7q. As EVI1 overexpression alone is not sufficient to induce leukemia, loss of a 7q tumour suppressor gene might be a required cooperating event. To test this hypothesis, we performed high-resolution array comparative genomic hybridization analysis of twelve EVI1 overexpressing patients and three EVI1 deregulated cell lines to search for 7q submicroscopic deletions. This analysis lead to the delineation of two critical regions, one of 0.39 Mb on 7q35 containing the CNTNAP2 gene and one of 1.33 Mb on chromosome bands 7q35-q36 comprising nine genes in EVI1 deregulated cell lines. These findings open the way to further studies aimed at identifying the culprit EVI1 implicated tumour suppressor genes on 7q.

The evi-1 oncoprotein inhibits c-Jun N-terminal kinase and prevents stress-induced cell death

Evi-1 encodes a nuclear protein involved in leukemic transformation of hematopoietic cells. Evi-1 possesses two sets of zinc finger motifs separated into two domains, and its characteristics as a transcriptional regulator have been described. Here we show that Evi-1 acts as an inhibitor of c-Jun N-terminal kinase (JNK), a class of mitogen-activated protein kinases implicated in stress responses of cells. Evi-1 physically interacts with JNK, although it does not affect its phosphorylation. This interaction is required for inhibition of JNK. Evi-1 protects cells from stress-induced cell death with dependence on the ability to inhibit JNK. These results reveal a novel function of Evi-1, which provides evidence for inhibition of JNK by a nuclear oncogene product. Evi-1 blocks cell death by selectively inhibiting JNK, thereby contributing to oncogenic transformation of cells.

cDNA cloning, expression pattern, and chromosomal localization of Mlf1, murine homologue of a gene involved in myelodysplasia and acute myeloid leukemia

The NPM-MLF1 fusion protein is expressed in blasts from patients with myelodysplasia/acute myeloid leukemia (MDS/AML) containing the t(3;5) chromosomal rearrangement. Nucleophosmin (NPM), a previously characterized nucleolar phosphoprotein, contributes to two other fusion proteins found in lympho-hematopoietic malignancies, anaplastic large cell lymphoma (NPM-ALK) and acute promyelocytic leukemia (NPM-RARalpha). By contrast, the function of the carboxy-terminal fusion partner, myelodysplasia/myeloid leukemia factor 1 (MLF1), is unknown. To aid in understanding normal MLF1 function, we isolated the murine cDNA, determined the chromosomal localization of Mlf1, and defined its tissue expression by in situ hybridization. Mlf1 was highly similar to its human homologue (86% and 84% identical nucleotide and amino acid sequence, respectively) and mapped to the central region of chromosome 3, within a segment lacking known mouse mutations. Mlf1 tissue distribution was restricted during both development and postnatal life, with high levels present only in skeletal, cardiac, and selected smooth muscle, gonadal tissues, and rare epithelial tissues including the nasal mucosa and the ependyma/choroid plexus in the brain. Mlf1 transcripts were undetectable in the lympho-hematopoietic organs of both the embryonic and adult mouse, suggesting that NPM-MLF1 contributes to the genesis of MDS/AML in part by enforcing the ectopic overexpression of MLF1 within hematopoietic tissues.

KRAB-independent suppression of neoplastic cell growth by the novel zinc finger transcription factor KS1

The study of zinc finger proteins has revealed their potential to act as oncogenes or tumor suppressors. Here we report the molecular, biochemical, and functional characterization of KS1 (KRAB/zinc finger suppressor protein 1), a novel, ubiquitously expressed zinc finger gene initially isolated from a rat pancreas library. KS1 contains 10 C2H2 zinc fingers, a KRAB-A/B motif, and an ID sequence that has been shown previously to participate in growth factor-regulated gene expression. Northern blot analysis using pancreatic cell lines demonstrates that KS1 mRNA is inducible by serum and epidermal growth factor, suggesting a role for this gene in cell growth regulation. Biochemical analysis reveals that KS1 is a nuclear protein containing two transcriptional repressor domains, R1 and R2. R1 corresponds to the KRAB-A motif, whereas R2 represents a novel sequence. Transformation assays using NIH3T3 cells demonstrate that KS1 suppresses transformation by the potent oncogenes Ha-ras, Galpha12, and Galpha13. Deletion of the R1/ KRAB-A domain does not modify the transformation suppressive activity of KS1, whereas deletion of R2 abolishes this function. Thus, KS1 is a novel growth factor-inducible zinc finger transcriptional repressor protein with the potential to protect against neoplastic transformation induced by several oncogenes.