Identification of the Genomic Breakpoints at 1p36.3 and 3q21.3 in Five MDS/AML(M4) Patients with t(1;3)(p36;q21) Translocation. GATA2 Mutation May Be Involved in Leukemogenesis.

Reciprocal translocation t(1;3)(p36;q21) is found in a subset of MDS/AML characterized by trilineage dysplasia, especially dysmegakaryopoiesis and a poor prognosis. In this leukemia, ectopic expression of MEL1 at 1p36.3 driven by the promoter of RPN1 at 3q21 is thought to be associated with the pathogenesis. Recently, we reported the identification of 2 kinds of the 1p36 breakpoint (BP) region in 3 patients with t(1;3), 1) a 70.7-kb region within the first intron of MEL1 in one patient, and 2) a 29.2-kb region in the 5′ region of MEL1 in the remaining two. However, the precise BP at 3q21 has not yet been determined. Here, we report that we have defined the 3q21 BP in 4 patients, and the 1p36.3 BP in 2 additional patients with FISH using bone marrow cells obtained from 4 patients (4 with MDS-related AML-M4 and one with CMML). To identify the BPs and deletions at 1p36.3 or at 3q21.3, we used 18 non-contig BAC/PAC probes and 7 contig BAC/PAC probes, respectively. FISH study revealed that the 3q21 BPs were clustered within RP11-475N22 probe in the 4 patients, in the 5′ region of GATA2. The 1p36.3 BP was found within the first intron of MEL1 in one patient, but in a 68.5-kb region which included a part of the first intron and a region of 5′ site of MEL1 in the other. Therefore, 3 BP regions at 1p36 were found among the 5 patients. No deletions were detected in the vicinity of the 1p36 BP or 3q21 BP in any of our 5 patients, although Lahortiga et al., detected a large deletion at the both BPs in their patients with MDS (RAEB) and t(1;3) (Oncogene 23:311–316, 2004). In Patient 1 (the 1p36 BP was in the first intron of MEL1) and Patient 3 (the 1p36 BP was in 5′ site of MEL1), the expression patterns of MEL1, ARPM2, and GATA2 which are located near the BPs were analyzed with RT-PCR. ARPM2 was not overexpressed in the two patients, while MEL1 was overexpressed in Patient 1, but not in Patient 3 when the expression level was compared with that of normal bone marrow cells. It is reported that GATA2, one of the zinc finger transcription factors, serves as a regulator of genes controlling proliferative capacity of early hematopoietic cells, and that two zinc finger domains of GATA2 are closely involved in inducing megakaryocytic differentiation. Interestingly, a deleted GATA2 transcript was detected in Patient 3 together with a wild type GATA2 transcript. The short GATA2 transcript contained 1009 nucleotides deletion from exon 3 to exon 6 with a frameshift, resulting in lacking the two zinc finger domains. Thus, there is the possibility that dysmegakaryopoiesis in this patient is associated with the expression of GATA2 without the zinc finger domains.