Department of Medicine, University of Okayama, 2-5-1 Shikatacho, Okayama 700-8558, Japan.
OBJECTIVE: In previous studies, we demonstrated overexpression of the dominant-negative isoform of the transcription factor Ikaros, Ik-6, in patients with blast crisis of chronic myelogenous leukemia and B-cell acute lymphoblastic leukemia. In the present study, we analyzed expression of the Ikaros family genes Ikaros, Aiolos, and Helios in a panel of human T-cell leukemia/lymphoma cell lines and bone marrow samples of patients with T-cell acute lymphoblastic leukemia. MATERIALS AND METHODS: We performed reverse transcriptase polymerase chain reaction, sequencing analysis, immunoblotting, and Southern blotting. RESULTS: We found overexpression of novel short isoforms of Helios (Hel-5 and Hel-6) in the HD-Mar cell line. Southern blot analysis suggested that there might be a small deletion in the Helios locus of HD-Mar. In addition, we observed decreased expression of more than one Ikaros family gene in 3 of 9 patients with T-cell acute lymphoblastic leukemia. Moreover, one of the patients overexpressed novel short isoforms of Helios (Hel-7 and Hel-8). CONCLUSION: This study provides the first evidence of an Ikaros family member (other than Ikaros) of which novel short isoforms become overexpressed in human leukemia.