Proteome of WT and Usp30KO cytotoxic T lymphocytes

Recent work in immunometabolism has emphasised the role of mitochondria in both the innate and adaptive immune system. Mitochondria are important in T cell development and differentiation, but less is known about their role in CD8+ effector T cells (CTLs). We found that CTLs that lack the mitochondrial deubiquitinase USP30 undergo promiscuous mitophagy, destroying most of the cellular mitochondria. Surprisingly, this results in a markedly diminished killing capacity, while motility, signalling and secretion remain intact. This study uses quantitative DIA proteomics to measure the impact of USP30 deficiency on the global proteome of IL-2 maintained, 4.5 h TCR retriggered and 4.5 h TCR retriggered + cycloheximide CTL. Unexpectedly, inhibition of mitochondrial translation, through genetic or pharmacologic methods, was the mechanism by which CTL killing was impaired. Reduced mitochondrial translation triggered attenuated cytosolic translation which precluded replenishment of secreted effector molecules thereby limiting the capacity of CTLs to serially kill multiple targets. Thus, mitochondria emerge as a previously unappreciated homeostatic regulator of protein translation required for serial CTL killing.