PROJECT SUMMARY The Sts proteins (Sts-1 and -2) negatively regulate signaling pathways within cells of the mammalian immune system. Mice lacking Sts expression (Sts-/-) are profoundly resistant to infection by clinically relevant fungal and bacterial pathogens, including Candida albicans, Francisella tularensis, and Staphylococcus aureus. Resistance is associated with rapid pathogen clearance and reduced inflammation. We recently identified a novel, functionally relevant, phosphodiesterase (PDE) enzyme activity of Sts-1. We hypothesize that this unprecedented activity plays a key role in regulating immune cell signaling pathways. To fulfill our long-term goal of developing novel therapies for infectious diseases, the objective of this proposal is to elucidate the signaling role of the Sts-1 PDE domain and identify molecular determinants of its function. Guided by strong preliminary data, we will test our hypothesis and accomplish our overall objective by pursuing the following two specific aims: 1) Elucidate the role of the Sts PDE domain in negatively regulating immune cell signaling pathways; and 2) Identify the substrate, and define the molecular determinants of function of the Sts PDE domain. In the first aim, we will utilize cell- and animal-based models to evaluate Sts-1 PDE domain function. In the second aim, we will use both a targeted, kinetics-based approach and global metabolomics to define Sts-1 PDE domain substrate breadth and specificity. In addition, we will determine the mechanism and molecular features that define the enzyme’s function. The proposed studies are innovative because they focus on a newly discovered enzyme domain that has previously not been characterized. The proposed research is significant because it is expected to substantially expand our understanding of the role of the Sts proteins in regulating immune cell responses. As therapeutic down-modulation of Sts function is expected to increase resistance to select microbial pathogens, we aim to exploit the results of these studies to develop new anti-microbial therapies that target the Sts-1 PDE domain.

PROJECT NARRATIVE The Sts phosphatases negatively regulate signaling pathways within cells of the immune system, and mice lacking Sts expression are profoundly resistant to infection by different microbial pathogens. Recently, we discovered a novel phosphodiesterase enzyme activity associated with the Sts proteins, and in this proposal we aim to characterize its functional significance and biochemical activity. This work is relevant to public health because elucidation of the role that this enzyme activity plays in immune signaling pathways will increase our understanding of immune regulation and may lead to the development of new treatments for infectious diseases.