A highly conserved luminal ER exit motif in the pseudoproteases iRhom1 and iRhom2 is indispensable for TNF������ and EGF receptor ligand release

Membrane-tethered signalling proteins such as TNF������ and many EGF receptor ligands undergo shedding by the metalloproteinase ADAM17 to get released. The pseudoproteases iRhom1 and iRhom2 are important for the ER exit and activity of ADAM17. Yet, their structural requirements to promote ER exit remained unexplored. Utilising in silico and in vitro methods, we here map the conserved iRhom homology domain (IRHD) and provide insights into its structure and function. We identified a highly conserved motif within the IRHD, which is indispensable for the ER exit of iRhoms and termed it CERES (conserved ER exit sequence). Strikingly, single point mutations in CERES abrogate the ER exit without disrupting other iRhom functions. We confirmed the physiological significance of CERES by inactivating it in mice which abrogates ADAM17-mediated shedding ex vivo and in vivo. This demonstrates a crucial role of CERES in the ADAM17-dependent release of various growth factor and cytokine signals.