| TRIM2 belongs to the tripartite motif (TRIM) protein family and can function as an E3-ubiquitin ligase. However, the protein substrates for TRIM2 are still largely unknown. Identification ofTRIM2-interacting partners will help us to understand the biological roles of this newly identified ubiquitin ligase. Using yeast-two hybrid screening and other biochemical methods, we have identified Tyro3 as an interacting protein partner for TRIM2. We have also shown that TRIM2 promotes the poly-ubiquitination of Tyro3, suggesting that TRIM2 is a specific ubiquitin ligase for Tyro3. Given that Tyr03 and its family members (Axl and Mertk) play essential roles in innate immunity, we propose that TRIM2 could be important for regulating the activity ofTyro3 in this biological system.;To test this hypothesis, the Trim2 knockout mice generated in our lab were used to determine the function ofTRIM2 in the regulation of innate immunity. Using an established bone marrow-derived dendritic cell (BMDC) culture system, it was found that loss of TRIM2 resulted in a hyperactive inflammatory response. We demonstrated that upon LPS treatment, Trim2-/- BMDCs upregulate co-stimulatory marker expression and increase secretion of the pro-inflammatory cytokines TNFalpha, IL-6 and IL-12 compared to wild-type controls. Intracellular staining indicates Tyro3 is localized to punctate vesicles in the cytoplasm of Trim2-/- BMDCs whereas it is diffuse in wild-type cells, suggesting TRIM2 has a role in endosome transport. Moreover, we have also found that resident peritoneal macrophages have impaired phagocytic function. Taken together, this research demonstrates that TRIM2 is a novel regulator of the innate immune response which could be mediated through regulation of Tyro3 receptor recycling. |
