Distinct Patterns of Colocalization of the CCND1 and CMYC Genes With Their Potential Translocation Partner IGH at Successive Stages of B-Cell Differentiation.

The immunoglobulin heavy chain (IGH) locus is submitted to intra-chromosomal DNA breakages and rearrangements during normal B cell differentiation that create a risk for illegitimate inter-chromosomal translocations leading to a variety of B-cell malignancies. In most Burkitt's and Mantle Cell lymphomas, specific chromosomal translocations juxtapose the IGH locus with a CMYC or Cyclin D1 (CCND1) gene, respectively. 3D-fluorescence in situ hybridization was performed on normal peripheral B lymphocytes induced to mature in vitro from a naive state to the stage where they undergo somatic hypermutation (SHM) and class switch recombination (CSR). The CCND1 genes were found very close to the IGH locus in naive B cells and further away after maturation. In contrast, the CMYC alleles became localized closer to an IGH locus at the stage of SHM/CSR. The colocalization observed between the two oncogenes and the IGH locus at successive stages of B-cell differentiation occurred in the immediate vicinity of the nucleolus, consistent with the known localization of the RAGs and AID enzymes whose function has been demonstrated in IGH physiological rearrangements. We propose that the chromosomal events leading to Mantle Cell lymphoma and Burkitt's lymphoma are favored by the colocalization of CCND1 and CMYC with IGH at the time the concerned B cells undergo VDJ recombination or SHM/CSR, respectively. J. Cell. Biochem. 117: 1506-1510, 2016. © 2016 Wiley Periodicals, Inc.