Mechanisms causing chromosomal translocation and its biological consequence in multiple myeloma

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1.Establishment of the MUM1 transgenic mice : An Eμ-SV-MUM1-myc tag-hGH construct was used for establishing transgenic mice in mature B-cells. During a long-term follow-up, no B-cell malignancy has developed in this experimental system.2.Identification of the target genes regulated by MUM1/IRF4 and by MAFB, which are deregulated in multiple myeloma : a)MUM1 : MUM1-expressing mouse proB-cell line, BaF3, grew faster than its parent cells, suggesting that MUM1 provides the B-cells with a growth advantage by regulating its downstream target genes. By means of cDNA array analysis, we identified monokine induced by IFNγ(Mig) as one of the directly regulated genes by MUM1. A reporter assay using Mig gene promoter sequences has resulted in the elevated luciferase activity when transfected with MUM1 together with PU.1, indicating their cooperation in terms of Mig transcription. MUM1 also directly binds to Mig promoter sequences, proven by chromosome immunoprecipitation assay. Interestingly, MUM1-positive B-cell chronic lymphocytic leukemia cells also expressed Mig and its receptor, CXCR3, and neutralizing anti-CXCR3 or anti-Mig antibodies partially inhibited their proliferation, suggesting that Mig and CXCR3 constitute an which is a downstream executer of the Phosphatidyl inositol 3 kinase-Akt signaling, is positively regulated by MAFB. Ectopic expression of the ARK5 resulted in the resistance against hypo-nutritional condition and in the promoted adhesion to fibronectin.3.Mutation analysis of the non-homologous end joining (NHEJ) protein associated with the repair of the double strand DNA breaks : Out of 14 multiple myeloma cell lines, one, one, and two harbored missense mutations of the Ku80, Ligase 4 and DNA-PKcs, in spite of the absence of mutation in Ku70 and XRCC4 genes. Since the remaining alleles kept the wild-type seguences, dominant-negative effect of the mutated proteins remains to be clarified further in myeloma cells.