Absence of IRF-4 expression in leukemia cells is not due to promoter alterations
We have previously demonstrated a lack of IRF-4 expression in leukemia patients and specifically in CML T-cells (3). Here, we demonstrate the absence of IRF-4 expression in various hematopoietic cell lines, such as Jurkat, a T-cell leukemia, CML-T1, a bcr-abl-positive T-cell line, K-562, a bcr-abl-positve erythroleukemia, U-937, a monocytic leukemia, EM-2 and LAMA-84, bcr-abl-positve myeloid leukemia, but not in SD-1, a bcr-abl-positive acute lymphoblastic leukemia (pre B-ALL), RPMI-8226, a multiple myeloma and BV-173, a bcr-abl-positive B-cell line (Figures 1A and 5D). After sequencing of the IRF-4 promoter, it could be excluded that absence of IRF-4 expression in any of the above cell lines was due to genetic aberrations. However, 2 bp changes (nucleotide −1081, T→C and −1068, A→C) could be detected in both the IRF-4-positive BV-173 and the IRF-4-negative LAMA-84, EM-2 and K-562 (Figure 1B). At position −116 an A→C substitution was found in EM-2, K-562 and CML-T1, whereas Jurkat, BV-173 and SD-1 exhibited a mixed A/C sequence and U-937, LAMA-84 and RPMI-8226 no substitution at all (Figure 1B). Consequently, these alterations are unlikely to affect IRF-4 expression.