Elevation of c-abl-mRNA in human leukemic B lymphoblasts

Analysis of v-abl-homologous transcripts in peripheral blood leukocytes from 20 leukemia patients revealed a 5-kb species as the major abl-mRNA present. Elevated levels of this 5-kb transcript, together with detectable levels of 2- and 10-kb abl-homologous species, were observed in mRNA samples from two patients, one with Philadelphia chromosome (Ph')-positive chronic myeloid leukemia (CML) in lymphoid blast crisis, and the other with childhood Burkitt-type B-lymphoblastic leukemia. These abl-homologous transcripts differed from the aberrant 8-kb abl-mRNA reported by others in Ph'-positive CML patients in both size and extent of v-abl-homology. No alteration in the organization of v-abl-homologous sequences was detected in the genomic DNA of the Ph'-positive CML patient. Karyotypic analysis of the Burkitt-type B-lymphoblastic leukemia patient revealed the presence of an 8,14 translocation together with a number of other chromosomal aberrations. However, no abnormality of chromosome 9 could be detected. Hence, the observed increase in c-abl transcription is not consistently associated with either gross gene rearrangement or presence of the Ph'. The high levels of c-abl mRNA may be a function of the cell type involved (early lymphoid blast), suggesting that failure to down-regulate c-abl may be a factor in the onset of pre- or early B-lymphoid leukemias.