Retroviral insertions 90 kilobases proximal to the Evi-1 myeloid transforming gene activate transcription from the normal promoter.

Abstract

The inappropriate production of the Evi-1 zinc finger protein occurs in retrovirus-induced murine myeloid leukemias and human acute myelogenous leukemias. In murine leukemias, expression of the Evi-1 gene is associated with retroviral insertions either in the Evi-1 locus, which is immediately 5' of the coding region of the gene, or in the genetically linked Cb-1/fim-3 locus. In these studies, we demonstrate by chromosomal walking and pulse field electrophoresis that the Cb-1/fim-3 locus is located 90 kb 5' of the Evi-1 locus. Primary structure analysis of Evi-1 cDNA clones from a Cb-1/fim-3 rearranged cell line (DA-3) demonstrates that transcription initiates 5' of the Evi-1 locus and that the first noncoding exon of the gene is 681 bp larger than previously defined. S1 nuclease protection studies reveal multiple transcription initiation sites within this region. Comparable transcriptional initiation sites were identified in RNA from kidney and ovary, in which the gene is normally expressed, suggesting that retroviral insertions in the Cb-1/fim-3 locus activate transcription from the normal promoter. In one myeloid cell line (DA-3), a single long terminal repeat (LTR) is present in the Cb-1/fim-3 locus. No stable transcripts were detectable from this LTR. In cells with retroviral insertions in the Cb-1/fim-3 locus, one allele of the Evi-1 locus becomes hypermethylated in the 5' region of the gene. Together, these results are most consistent with an LTR-mediated, long-range cis activation of Evi-1 gene expression.