DESCRIPTION (provided by applicant): Twenty million Americans suffer from autoimmune diseases, and organ transplant recipients have significant rates of graft loss and experience considerable ill effects from current immunosuppression. This project addresses these major unmet needs by focusing on key post-translational events at the N-terminus of Foxp3, a transcription factor that regulates the development and function of T-regulatory (Treg) cells. Tregs are central to regulation of immune responses, but much of the information about these cells is highly descriptive, and their proposed therapeutic manipulation is mainly envisaged as involving adoptive cellular therapy, despite major reservations about that approach. Our work will extend our biochemical studies of Foxp3, and explore the detailed mechanisms by which acetylation of Foxp3 can optimally be pharmacologically regulated, and will also assess the efficacy of targeting class IIA/Mef2 protein/protein interactions. Aim 1 will determine the efficay of targeting of individual class IIa HDAC versus individual class I HDAC enzymes. Our previous work has shown that deletion of the gene encoding the class IIa HDAC, HDAC9, could enhance Treg function in vitro and in vivo, leading to the questions of can this be usefully translated int targeting of HDAC9 protein, and what about the roles of the other class IIa HDAC enzymes in Treg cells? Accordingly, we will determine 1.1) biology and effects of pharmacologic targeting the class IIa HDAC enzyme, HDAC7, in Treg vs. conventional T-effector (Teff) cells; and 1.2) biology and effects of pharmacologic targeting the class IIa HDAC enzyme, HDAC9, in Treg vs. conventional T-effector (Teff) cells. Aim 2 will determine the roles of class IIa HDAC/Mef2 interactions in Treg biology. Class IIa HDACs control expression of the transcription factor, Mef2, and our data indicate that Mef2 protein can bind to the Foxp3 promoter and also co-associate with Foxp3 protein. Accordingly, we will determine 2.1) the importance of Mef2/Foxp3 DNA and Mef2/Foxp3 protein/protein interactions in Tregs; 2.2) the consequences on Treg (and Teff) cells of conditional deletion of individual Mef2 genes; and 2.3) the therapeutic value of pharmacologic targeting of class IIa HDAC/Mef2 protein/protein interactions. As a result of these studies, and * how and why targeting of Mef2/class IIa HDACs in Tregs can usefully promote Treg-dependent functions in vivo. Our work will generate new insights and likely identify first-in-class molecules for subsequent optimization and evaluation in clinical trials of autoimmunity and Tx rejection.