Grant: Discovery Grants Program - Individual

All organs and tissues possess a framework of connective tissue, which provides them with structure and serves as mechanical support. Connective tissues also provide routes for diffusion of nutrients and oxygen from the blood, and participate in the regeneration of all organs following injury. Fibroblasts are a major cellular component of connective tissues. These cells play pivotal roles in the maintenance and regeneration of all organs. Fibroblasts respond to multiple cytokines and growth factors in their environment. In intact organs, fibroblast responses to transforming growth factor-ß1 (TGF-ß1) result in modulation of extracellular matrix protein production by these cells, which helps maintain organ structure. When an organ gets damaged, TGF-ß1 promotes the transition of fibroblasts into myofibroblasts, a process essential for tissue repair. Thus, fibroblast responses to TGF-ß1 are key for organ maintenance and repair in all organisms. Three receptors for TGF-ß are known in mammals. The TGF-ß receptors type I (TßRI) and type II(TßRII) activate several signaling cascades in response to this cytokine. Cells regulate TGF-ß receptor activity by internalizing these receptors (i.e. endocytosis), which can be followed by recycling to the plasma membrane, or by degradation. Our overall, LONG-TERM OBJECTIVE is to elucidate how TGF-ß receptor signaling is modulated. Significantly, and in spite of its importance, a critical gap still exists in understanding the regulatory mechanisms of TßRII, and the role that TßRII-binding proteins play in endocytosis, trafficking and, ultimately, signalling through this receptor. For example, although TßRII was first cloned two decades ago, no systematic, large-scale proteomic profiling if its interacting proteins has ever been reported. Our working HYPOTHESIS for the current proposal is that Rac1 and TßRII-interacting proteins regulate signaling of this receptor by modulating its specific endocytic and trafficking pathways towards either recycling or degradation. To test this hypothesis, we will address the following SHORT-TERM AIMS: (1) To determine the mechanisms of TßRII regulation by Rac1, and (2) To identify TßRII-interacting proteins involved in TßRII internalization and trafficking, through proteomic profiling approaches. Our studies will provide insight into the regulation of a signaling pathway that is fundamental for development, function and repair in multicellular organisms, from mammals to invertebrates. In addition, this research will contribute to the training of several graduate and undergraduate students, who will have the opportunity to learn state-of-the-art experimental approaches in biological research, including the use of genetically modified mice, complemented with studies on cultured cells to understand relevant molecular mechanisms, and proteomic profiling.