This is a Building Interdiscplinary Research Teams (BIRT) revision application for RO1 AR44422 entitled "The Genetics of Rheumatoid Arthritis". The original application continues to support the discovery of disease susceptibility genes for rheumatoid arthritis. This has been extremely successful, now with over 30 confirmed risk loci, including the PTPN22 locus on chromosome 1. This revision application will support an entirely new line of investigation by the PI and focuses on developing a deeper understanding of the functional consequences of the PTPN22 R620W allelic variant, with a move toward the development of pharmacologic agents that can be utilized experimentally, and possibly therapeutically. This has necessarily catalyzed new scientific collaborations with investigators who bring biochemical and pharmacological expertise. Dr. Nunzio Bottini is widely recognized for his contributions to the genetic and biochemical characterization of PTPN22, and has developed reagents that will allow us to immediately embark on the proposed studies. Dr. Yousef Al-Abed is an experienced medicinal chemist with demonstrated success in developing small molecules that can modulate neuro-inflammatory pathways. Being at the same institution as the PI, Dr. Al-Abed has been acquainted with PI for many years, has frequently discussed potential projects, but the current proposal represents the first serious attempt at collaborative scientific activity. The idea and rationale for the proposed project was generated by the PI, but is ideally suited to bring together the complementary talents of these three investigators. Dr. Bottini is actively engaged in developing pharmacological modifiers directed at PTPN22, but using a completely different approach. Thus, this new proposal is an excellent vehicle for collaboration for all three investigators, and it is likely that additional projects will be catalyzed by these new scientific relationships. The current proposal as a key transitional move in the scientific career of the PI that will enable him to embrace more fully, and act upon, the scientific and practical implications of the new genetic findings that continue to emerge in human autoimmune disease. The proposal contains three specific aims. Specific aim 1: Based on existing information on the interaction between PTPN22 and the SH3 domain of Csk, we will develop a panel of small peptides to explore the structure function relationships of this interaction using an in vitro protein-protein binding assay. We will focus on inhibition of PTPN22 wild type (620R) containing P1 domain, and its interaction with the SH3 domain of Csk, thus mimicking the effects of the 620W risk allele. Specific aim 2: Based on the results in specific aim 1, we will develop small molecules (peptide mimotopes) that inhibit the interaction between the Csk SH3 domain the proline rich P1 SH3-binding domain on PTPN22. Specific aim 3.: We will utilize the reagents developed in specific aim 3 to examine the role of PTPN22-Csk interactions in T and B cell function, using both cell lines and normal peripheral blood cells. PUBLIC HEALTH RELEVANCE: This proposal will develop pharmaceutical inhibitors of an intracellular enzyme that is known to be directly involved in human autoimmune diseases, as well as in the immune defense against infection. These studies will provide insight into the mechanisms of these diseases, and may lead to new drug therapies for a variety of human disorders of the immune system.