Normal and Pathological Regulation of DNA Damage Response to T-cell Receptor Gene Rearrangement (36.61)

Abstract

Abstract The T-cell receptor (TCR) is encoded by tandem arrays of variable (V), diversity (D), and joining (J) gene segments that are somatically rearranged during thymic development. During this process the RAG recombinase introduces transient DNA double strand breaks (DSBs) which are repaired by non-homologous end joining (NHEJ). Additionally, the DSBs are detected by components of the cellular DNA damage response (DDR) which bind to the chromatin within 1 megabase of the break forming foci. One component of DDR, Ataxia Telangiectasia mutated (ATM), plays a major role in activating downstream effectors involved in apoptosis, cell cycle arrest and DNA repair. ATM-deficiency is characterized by reduced rearrangement at the TCR-α locus in CD4/CD8 double positive (DP) thymocytes, high frequency of thymic lymphomas carrying translocations at the TCR-α locus, and increased frequency of TCR-β/TCR-γ trans-rearrangements. Since TCR-β, γ and δ recombination occurs in CD4/CD8 double negative (DN) cells, we examined the effect of ATM deficiency on these rearrangements. We found that rearrangement is impaired at the TCR-β, γ and δ loci. We also demonstrate increased frequency of TCR-β/TCR-γ trans-rearrangements in ATM deficient cells. Such trans-rearrangements may be the result of concurrent recombination at multiple TCR loci in DN cells. We are currently testing this hypothesis using combined immunofluorescence detection of DDR foci and fluorescent in situ hybridization of TCR loci.