Pathological mutations reveal the key role of the cytosolic iRhom2 N-terminus for phosphorylation-independent 14-3-3 interaction and ADAM17 binding, stability, and activity

Abstract

The protease ADAM17 plays an important role in inflammation and cancer and is regulated by iRhom2. Mutations in the cytosolic N-terminus of human iRhom2 cause tylosis with oesophageal cancer (TOC). In mice, partial deletion of the N-terminus results in a curly hair phenotype (cub). These pathological consequences are consistent with our findings that iRhom2 is highly expressed in keratinocytes and in oesophageal cancer. Cub and TOC are associated with hyperactivation of ADAM17-dependent EGFR signalling. However, the underlying molecular mechanisms are not understood. We have identified a regulatory site, encompassing all known TOC mutations, whose disruption increases constitutive ADAM17 activity. The larger cub deletion also includes the TOC site and thus also promotes increased constitutive ADAM17 activity. Furthermore, the cub mutation, but not the TOC mutation, causes severe reductions in stimulated shedding, binding and stability of ADAM17, suggesting the presence of additional regulatory sites in the N-terminus of iRhom2. Overall, this study contrasts the TOC and cub mutations, illustrates their different molecular consequences and reveals important key functions of the iRhom2 N-terminus in regulating ADAM17.