Enforced expression of MIR142, a target of chromosome translocation in human B-cell tumors, results in B-cell depletion.

MicroRNA142 (MIR142) is a target of chromosome translocations and mutations in human B-cell lymphomas. We analyzed an aggressive B-cell lymphoma carrying t(8;17)(q24;q22) and t(6;14)(p21;q32), and sought to explore the role(s) of MIR142 in lymphomagenesis. t(8;17)(q24;q22) involved MYC on 8q24 and pri-MIR142 on 17q22. MYC was activated by a promoter substitution by t(8;17)(q24;q22). t(8;17)(q24;q22) was an additional event after t(6;14) (p21;q32), which caused the over-expression of CCND3. Southern blot analyses revealed that the MIR142 locus was deleted from the affected allele, whereas Northern analyses showed over-expression of MIR142 in tumor cells. Although previous studies reported an over-expression of mutations in MIR142 in B-cell lymphomas, limited information is available on the functions of MIR142 in lymphomagenesis. Therefore, we generated bone marrow transplantation (BMT) and transgenic (Eµ/mir142) mice, which showed enforced expression in hematopoietic progenitor cells and B cells, respectively. BMT mice showed decreased numbers of all lineage-positive cells, particularly B cells, in peripheral blood. Eµ/mir142 mice showed decreased numbers of IgM-positive splenocytes, and exhibited altered B-cell phenotypic changes induced by lipopolysaccharide. Our results suggest that over-expression of MIR142 alters B-cell differentiation, implying multi-step lymphomagenesis together with MYC activation and CCND3 over-expression.

Acute leukemia showing t(8;22)(p11;q11), myelodysplasia, CD13/CD33/CD19 expression and immunoglobulin heavy chain gene rearrangement.

t(8;22)(p11;q11) is a rare but recurrent chromosome translocation that has been reported in 11 cases of myeloproliferative neoplasm or B-acute lymphoblastic leukemia. This translocation results in an in-frame fusion of FGFR1 on 8p11 and BCR on 22q11, and causes constitutive activation of the tyrosine kinase of the BCR/FGFR1 chimera protein. Here, we report the twelfth case of hematological tumor bearing t(8;22)(p11;q11). The bone marrow showed hypoplastic and tri-lineage dysplasia with 24.4% abnormal cells. The abnormal cells were not defined as myeloid or lymphoid morphologically, lacking a myeloperoxidase reaction. Flow cytometric analysis of the bone marrow cells revealed that the abnormal cells expressed CD13, CD33, CD34, and CD19, and that a fraction of the abnormal cells was positive for CD10. Southern blot analysis of the bone marrow cells showed rearrangement of the immunoglobulin heavy chain gene, a genetic hallmark of B-cell differentiation. Previously reported cases with t(8;22)(p11;q11) suggested an association between myeloid and B-lymphoid tumors, whereas other chromosome translocations involving FGFR1 on 8p11 showed a link between myeloid and T-lymphoid tumors. Our observation supports that t(8;22)(p11;q11) might define a dual myeloid and B-lymphoid disorder.

Molecular cloning of IGλ rearrangements using long-distance inverse PCR (LDI-PCR).

OBJECTIVES: Malignant cells of mature B-cell origin show tumor-specific clonal immunoglobulin gene (IG) rearrangements, including V(D)J recombinations, nucleotide mutations, or translocations. Rapid molecular cloning of the breakpoint sequence by long-distance inverse PCR (LDI-PCR) has so far been applied to rearrangements targeted to IGH joining, IGH switch, and IGκ regions. We tended to apply LDI-PCR method for cloning of IGλ rearrangements. METHODS: To identify which IGλ isotype segment was rearranged, we performed Southern blot analysis using isotype-specific probes. We set inverse primers on the telomeric side of each joining region and amplified rearranged bands detected by Southern blot analysis as corresponding PCR products. RESULTS: All germline IGλ segments were successfully amplified as expected PCR products. We determined breakpoint sequences of five chromosome translocations involving IGλ locus: three novel t(8;22)(q24;q11), one known t(3;22)(q27;q11), and one partially known t(11;22)(q13;q11). Two of the three t(8;22)(q24;q11) were involved in Jλ with a recombination signal sequence and one of three in the first exon of IGLL5, which lies upstream of Jλ1. Three 8q24 breakpoints were widespread at 132, 260 and 366 kb downstream of MYC locus. The t(3;22)(q27;q11) showed a juxtaposition of Jλ2 and the first intron of BCL6, as previously reported. In t(11;22)(q13;q11), 3'UTR of cyclin D1 fused to the constant region of λ7 with nucleotide mutations. We also amplified four Vλ/Jλ recombination sequences. CONCLUSION: Our method is a useful tool for molecular analysis of genetic events in IGλ.

Bone marrow large B cell lymphoma bearing cyclin D3 expression: clinical, morphologic, immunophenotypic, and genotypic analyses of seven patients.

We report seven large B cell lymphoma patients showing the involvement of tumor cells with cyclin D3 (CCND3) expression in bone marrow (BM) at the initial diagnosis. All patients presented with B symptoms, splenomegaly, and anemia/thrombocytopenia lacking hemophagocytosis in the BM. Five of the seven patients had suffered from immunological diseases or cancers. The tumor cells were divided into those with a lymphoplasmacytoid or blastoid appearance. Six cases were confirmed to express CD5 antigen on tumor cells. Three cases presented a chromosomal translocation between CCND3 and the immunoglobulin heavy chain (IGH) loci, t(6;14)(p21;q32). Three and two cases showed unmutated and mutated sequences of the variable region of IGH (VH), respectively, and one case showed deletion of an entire segment of VH. Two cases with t(6;14)(p21;q32) showed an unmutated VH sequence and chromosomal translocation within the switch region of IGH. Further studies are required to determine whether CCND3 expression is associated with a unique subset of diffuse large B cell lymphoma.