Interleukin-5 (IL-5) is a hematopoietic cytokine that is central to the pathophysiology of eosinophilic inflammation in atopy and asthma. Understanding mechanisms that extinguish IL-5 receptor (IL-5R)-induced inflammatory signals has importance for the development of novel approaches to modulate IL-5-mediated inflammation. The goal of this application is to define the molecular mechanisms controlling IL-5R internalization by the ubiquitin and proteasome degradation pathway. Our overall hypothesis is that IL-5-induced IL-5R internalization is regulated by two different mechanisms: the ubiquitin/proteasome degradation pathway and clathrin-mediated endocytosis. Aim 1. Test the hypothesis that proteasomes mediate internalization of the ligated IL-5R by first degrading the (c cytoplasmic domain. To determine if degradation of a portion of the (c cytoplasmic domain is the initiating signal for IL-5R internalization, various cytoplasmically truncated (c mutants will be examined for their ability to mediate proteasome-independent internalization of the ligated IL-5R. In addition, requirement for proteasome activity in (c internalization by the other (c engaging cytokines, IL-3 and GM-CSF, will be investigated. Aim 2. Test the hypothesis that the IL-5R is internalized by clathrin-mediated endocytosis and that internalization of the receptor occurs before proteasome degradation of the (c cytoplasmic domain. Two different approaches that inhibit clathrin-mediated endocytosis will be used to determine if the IL-5R is internalized by this mechanism and if IL-5-stimulated (c signaling and proteasome degradation occur after IL-5R internalization. Aim 3. Investigate the functional role and nature of (c ubiquitination in IL-5R internalization. The temperature sensitive ts20 cell line which has a temperature sensitive defect in ubiquitin conjugation, a (c mutant that is defective in all forms of ubiquitination, and dominant negative ubiquitin isoforms will be used to examine the role and nature of (c ubiquitination in IL-5R endocytosis. [unreadable] [unreadable]