M1-linked ubiquitination facilitates stress responses during sterile-induced inflammation Anna Aalto1, Gabriela Martínez-Chacón1, Nadezhda Tsyganova1, Joose Kreutzer2, Pasi Kallio2, Meike Broemer3, Annika Meinander1 1. Faculty of Science and Engineering, Cell Biology, Åbo Akademi University, BioCity, Turku, Finland 2. Faculty of Medicine and Health Technology, BioMediTech, Tampere University, Finland 3. German Center for Neurodegenerative Diseases (DZNE), Sigmund-Freud-Str. 27, 53127, Bonn, Germany. M1-linked ubiquitination plays a key role in regulation of inflammatory NF-κB signalling and is important for clearance of pathogenic infection in Drosophila melanogaster. M1-linked ubiquitin (M1-Ub) chains are assembled by the linear ubiquitin E3 ligase (LUBEL) in flies. Here, we have studied the role of LUBEL in sterile inflammation induced by different types of cellular stresses. We have found that LUBEL catalyses formation of M1-Ub chains in response to hypoxic, oxidative and mechanic stress conditions. LUBEL is important for flies to survive low oxygen conditions and paraquat-induced oxidative stress. This protective action seems to be driven by stress-induced activation of the NF-κB transcription factor Relish via the IMD pathway. In addition to LUBEL, the intracellular mediators of Relish activation, including the Drosophila inhibitor of apoptosis (IAP) DIAP2, the IκB kinase γ (IKKγ) Kenny and the initiator caspase Dredd, but not the pattern-recognition receptor PGRP-LCx, are required for the sterile inflammatory and survival responses to such cell stress. Finally, we show that the stress-induced upregulation of M1-Ub chains in response to hypoxia, oxidative and mechanical stress is induced also in mammalian cells. Taken together, our results suggest that M1-Ub chains are important for NF-κB signalling in sterile inflammation induced by stress conditions often observed in chronic inflammatory diseases and cancer.