Toll-like Receptor-mediated Down-regulation of the Deubiquitinase Cylindromatosis ( CYLD) Protects Macrophages from Necroptosis in Wild-derived Mice

Background: Necroptosis is a regulated signaling pathway leading to necrotic cell death. Results: Genetic mapping identified that down-regulation of the deubiquitinase CYLD confers resistance to necroptosis in a wild-derived mouse strain. Conclusion: Different strains of inbred mice regulate cell death pathways using distinct mechanisms. Significance: Genetic diversity of wild-derived mice underlies phenotypic diversity, which can identify novel mechanisms of regulation in cell death signaling. Pathogen recognition by the innate immune system initiates the production of proinflammatory cytokines but can also lead to programmed host cell death. Necroptosis, a caspase-independent cell death pathway, can contribute to the host defense against pathogens or cause damage to host tissues. Receptor-interacting protein (RIP1) is a serine/threonine kinase that integrates inflammatory and necroptotic responses. To investigate the mechanisms of RIP1-mediated activation of immune cells, we established a genetic screen on the basis of RIP1-mediated necroptosis in wild-derived MOLF/EiJ mice, which diverged from classical laboratory mice over a million years ago. When compared with C57BL/6, MOLF/EiJ macrophages were resistant to RIP1-mediated necroptosis induced by Toll-like receptors. Using a forward genetic approach in a backcross panel of mice, we identified cylindromatosis (CYLD), a deubiquitinase known to act directly on RIP1 and promote necroptosis in TNF receptor signaling, as the gene conferring the trait. We demonstrate that CYLD is required for Toll-like receptor-induced necroptosis and describe a novel mechanism by which CYLD is down-regulated at the transcriptional level in MOLF/EiJ macrophages to confer protection from necroptosis.