title: Rhom-2 expression does not always correlate with abnormalities on chromosome 11 at band p13 in T-cell acute lymphoblastic leukemia.
abstract: A frequent site for nonrandom recombination in T-cell acute lymphoblastic leukemia (T-ALL) is chromosome 11 at p13. The molecular characterization of a (7;11)(q35;p13) translocation showed that the translocation breakpoint was 2 kb 5' to the T-ALLbcr locus resulting in the juxtaposition of the T-cell receptor (TCR) beta gene to the rhom-2 gene locus. Northern blot analysis did not detect expression of the rhom-2 gene in the leukemic blasts of the (7;11) translocation. However, using a sensitive polymerase chain reaction (PCR)-based assay, the (7;11) translocation showed a trace expression of rhom-2 at a level of 0.01% of TCR-beta message. Because rhom-2 is considered a proto-oncogene, the significance of the trace expression of rhom-2 in the (7;11) translocation was investigated by comparing the level of rhom-2 expression in 7 additional T-ALLs, normal thymocytes, and CEM (pre-T) and HPB (mature-T) cell lines using the PCR assay. The CEM cells, normal thymocytes, and one patient, whose blasts had no cytogenetic abnormality of chromosome 11, did not express rhom-2 indicating that rhom-2 is not normally expressed in T cells. The other six T-ALLs fell into three categories: (1) two T-ALLs overexpressed rhom-2 in the presence of a translocation; (2) two T-ALLs had trace expression in the presence of a translocation; and (3) two T-ALLs had trace expression with no observable abnormalities on chromosome 11 at p13. Therefore, the data indicate that not all translocations at the T-ALLbcr locus result in overexpression of rhom-2. To account for the sharp contrast in rhom-2 expression seen in these T-ALLs, a model is proposed with a negative regulatory element in the T-ALLbcr locus that is disrupted in some of the cases leading to overexpression of rhom-2.
mesh_terms: D001483:Base Sequence; D015139:Blotting, Southern; D002675:Child, Preschool; D002869:Chromosome Aberrations; D002871:Chromosome Banding; D025063:Chromosome Disorders; D002880:Chromosomes, Human, Pair 11; D002897:Chromosomes, Human, Pair 7; D003001:Cloning, Molecular; D004273:DNA, Neoplasm / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D016130:Immunophenotyping; D015459:Leukemia-Lymphoma, Adult T-Cell / Q000235:genetics* / Q000276:immunology; D008297:Male; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D016133:Polymerase Chain Reaction / Q000379:methods; D000090063:Proto-Oncogene Mas; D011519:Proto-Oncogenes; D012194:RNA-Directed DNA Polymerase; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000235:genetics*; D015183:Restriction Mapping; D013601:T-Lymphocytes / Q000276:immunology; D014178:Translocation, Genetic
chemical_list: D004273:DNA, Neoplasm; C000715470:MAS1 protein, human; D009838:Oligodeoxyribonucleotides; D000090063:Proto-Oncogene Mas; D016693:Receptors, Antigen, T-Cell, alpha-beta; D012194:RNA-Directed DNA Polymerase