Mechanisms in Suppressing Chromosomal Translocations and Maintaining Genome Stability.

Abstract

Double strand breaks (DSBs) represent one of the most dangerous forms of DNA damage. DSBs are generated during normal metabolic processes, such as DNA replication, or upon exposure of cells to exogenous agents, such as ionizing radiation. In addition, DSBs are formed as intermediates during programmed DNA rearrangements that occur during early B and T lymphocyte development, a process known as V(D)J recombination. Unrepaired or mis-repaired DNA ends can engender detrimental outcomes for cells and organisms such as aberrant genomic events like chromosomal translocations. The classical nonhomologous end joining (cNHEJ) pathway is one of the major DNA DSB repair pathways operative in mammalian cells and is required for both general DSB repair and V(D)J recombination. The studies of my dissertation investigate the functions of DNA nucleases in the repair of double strand breaks during V(D)J recombination. I have undertaken two independent, but related, lines of investigation to address this question. One project sought to elucidate the regulation of the ARTEMIS nuclease during V(D)J recombination. I examined the molecular mechanisms underlying tumorigenesis caused by an Artemis hypomorphic disease allele and identified that the ARTEMIS C-terminus suppresses tumorigenesis associated with misrepair of DNA DSBs generated during V(D)J recombination. My findings raise the possibility that particular defects in ARTEMIS that result in partial loss of function, can predispose to lymphoma, but not complete immunodeficiency. The second project focused on determining the interplay between the ARTEMIS and MRE11 nuclease in facilitating normal and aberrant V(D)J rearrangements. My results indicate that mutation of the MRE11 complex prevents tumorigenesis associated with aberrant end joining of V(D)J loci, an in turn, implicates the MRE11 complex in promoting tumorigenesis associated with DNA damage. Both projects have led to a greater understanding of the mechanisms underlying human lymphoma caused by impaired ARTEMIS nuclease activity, and additionally, identified the MRE11 complex as a possible chemotherapeutic target for improved treatment for lymphoid malignancies.