Activation of c-myb is an early bone-marrow event in a murine model for acute promonocytic leukemia.
Insertional mutagenesis of c-myb by Moloney murine leukemia virus occurs in 100% of promonocytic leukemias (MMLS) induced by the virus. These leukemias, which resemble acute monocytic leukemia-M5 in humans are induced only in mice undergoing a peritoneal chronic inflammatory response. We have found that two leukemia-specific gag-myb mRNAs in MML provide molecular markers for detection of preleukemic cells in hematopoietic tissue in vivo. The two aberrant RNAs result from splicing of gag to either exon 3 or 4 of c-myb, depending on the site of proviral integration. After reverse transcription-PCR with nested primers and hybridization with specific gag-myb junction probes, one cell, having aberrant c-myb message, could be detected in a minimum of 10(5) liver cells or 10(6) spleen or bone-marrow cells. This approach was used to examine hematopoietic tissues of mice after pristane injection to induce inflammation and virus inoculation. Cells with gag-myb mRNAs could be detected as early as 2 weeks after virus inoculation. In mice receiving both pristane and virus, there was evidence of preleukemic cells in 83% of the mice by 3 weeks after virus infection. Furthermore, 100% of the mice were positive for preleukemic cells by 8 weeks, even though only 50% of mice have been shown to succumb to MML (peak time for disease latency is 12-16 weeks). Cells with these aberrant c-myb messages were initially detected in the bone marrow, but during intermediate stages of disease development these cells disseminated to the spleen, liver, and granuloma. At preleukemic times, from 3 to 8 weeks after virus infection, a lower percentage of mice were positive in the group that did not receive pristane compared with mice in the group receiving pristane. However, at 18 weeks, 100% of the mice in the group receiving virus only had evidence of cells expressing gag-myb RNA in their spleens and/or bone marrow; it is of interest that mice inoculated with virus alone never develop MML. This approach for detecting preleukemic cells will now allow the study of mechanisms by which these preleukemic cells progress to a more transformed state and, perhaps, to a more differentiated state.
Nason-Burchenal
K
K
Laboratory of Genetics, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
Wolff
L
L
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D001853:Bone Marrow / Q000502:physiology*; D005260:Female; D015750:Genes, gag; D007942:Leukemia, Experimental / Q000235:genetics* / Q000473:pathology; D015473:Leukemia, Promyelocytic, Acute / Q000235:genetics* / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D008979:Moloney murine leukemia virus / Q000235:genetics*; D016254:Mutagenesis, Insertional; D009367:Neoplasm Staging; D009838:Oligodeoxyribonucleotides; D009857:Oncogenes; D009928:Organ Specificity; D016133:Polymerase Chain Reaction / Q000379:methods; D012313:RNA / Q000235:genetics / Q000302:isolation & purification
D009838:Oligodeoxyribonucleotides; D012313:RNA