Usp14 knock down disrupts ubiquitin homeostasis unveiling the functional wiring of proteostatic, bioenergetic and DNA damage response modules

Age-related physiological changes are primarily caused by the gradual accumulation of damaged biomolecules combined with the progressive deterioration of cellular stress responses, which then leads to systemic decline of organismal homeostasis. As cells are composed of complex protein 3D structures and machineries, organisms have developed quality control systems, namely the proteostasis network (PN), to limit loss of proteostasis, a major hallmark of aging. As part of the PN, deubiquitinase enzymes (DUBs) regulate cellular responses to proteotoxicity by controlling selective spatiotemporal protein turnover. DUBs reverse ubiquitin signaling and modulate, among other processes, ubiquitin homeostasis. In particular, Usp14 reversibly associates with the proteasome and regulates protein degradation at three distinct checkpoints, namely ubiquitin recognition, initiation of substrate translocation and ubiquitin recycling. Here, we investigated the in vivo molecular alterations that occur following Usp14 knockdown (KD) in Drosophila melanogaster . We found that Usp14 KD-mediated disruption of ubiquitin homeostasis results in graded proteostatic, mitostatic, and metabolic tissue adaptations. Interestingly, Usp14 KD also led to the accumulation of DNA damage, which activated DNA damage response mechanisms depending on the extent of Usp14 KD. These findings further highlight the Usp14’s pivotal role in modulating proteome and genome stability.