UC Berkeley

As an essential safeguard against autoimmunity, apoptosis during negative selection of self-reactive T cell precursors is important in establishing a self-tolerant T cell repertoire capable of responding to a large array of foreign antigens. The fate of a thymocyte is imposed by signals through the T cell receptor (TCR). During T cell development, thymocytes expressing TCRs that strongly react to self-antigens in the thymus trigger apoptosis and die. The Nur77 family of orphan nuclear hormone receptors and the Bcl-2 family of proteins are important molecules implicated in thymocyte apoptosis and clonal deletion. Strong TCR signals induce the expression and translocation of Nur77 and Nor-1 from the nucleus to the mitochondria, where they bind Bcl-2 and expose Bcl-2’s pro-apoptotic, killer BH3 domain. Through extensive Bcl-2 mutagenesis and functional assays, we identify residues within Bcl-2 that are essential for Nur77/Nor-1 interaction. We find that the Bcl-2 mutants that interfere with this interaction do not affect normal Bcl-2 anti-apoptotic function, but lose the ability to mediate Nur77/Nor-1-initiated apoptosis. This study refines the molecular details of this interaction and may assist in generating a novel tool to study the significance of this interaction in vivo. The importance of the Bcl-2 BH3 domain was revealed in Bcl-2 BH3 transgenic mice (BH3* Tg) where the BH3 domain is mutated. Unlike mice with a T cell-specific transgenic expression of wild-type Bcl-2, BH3* Tg mice exhibited accelerated morbidity from multi-organ autoimmunity. To further understand what might cause autoimmunity in these mice, we identified a provisional ubiquitous autoantigen found in the antisera of BH3* Tg mice. This data provides the groundwork to further study the potential cause of autoimmune syndrome in these mice. The increase of an autoreactive T cell repertoire in BH3* Tg mice may reject tumor better since self-antigens are largely shared by tumors. However, we found that the presence of an increased autoreactive T cell repertoire in BH3* Tg mice exacerbates tumor growth and morbidity. In sum, this work advances our understanding of molecular mechanisms involved in T cell negative selection and offers insights into the etiology in autoimmunity pathology and potential use for cancer immunotherapy.