Mechanisms of Chromosomal Translocations in Malignant Lymphomas

Abstract

Recurring and highly consistent chromosomal abnormalities are a feature of many hematopoietic neoplasms. They are carried throughout the malignant cells indicating that they occurred prior to clonal expansion. Over the last decade it has become clear that distinct translocations play a major role in the pathogenesis of malignant lymphomas. The main cytogenetic changes are exhibited by deletions, translocations and inversions of genetic material, resulting in loss of tumor suppressor genes, activation of proto-oncogene products or creation of tumor-specific fusion proteins.

Molecular genetic analyses of chromosomal translocations in lymphomas have demonstrated rearrangements of immunoglobulin (Ig) and T-cell receptor (TCR) genes as a consequence of chromosomal breakage. The frequent involvement of Ig and TCR genes in lymphoid chromosome translocations suggests a role of site specific recombinases in aberrant recombination. Additional mechanisms may be involved in this process: Polypurine stretches (Alu-elements) can act as targets for endonucleases and breakpoint binding proteins can stimulate homologous site-specific recombination in conjunction with nucleases. The putative molecular mechanisms leading to a new chromosomal translocation t(14;18)(qll;q23) in a T-cell line established from a patient with ataxia telangiectasia will be discussed. The characterization of these molecular events will not only provide further insight into the pathogenesis of lymphoid tumors but will enable the development of diagnostic probes for the detection of cytogenetic abnormalities.