iRhoms are related to a family of intramembrane serine proteinases called rhomboids but lack proteolytic activity. In mammals, there are two iRhoms, iRhom1 and iRhom2, which have similar domain structures and overlapping specificities as well as distinctive functions. These catalytically inactive rhomboids are essential regulators for the maturation and trafficking of the disintegrin metalloprotease ADAM17 from the endoplasmic reticulum to the cell surface, and are required for the cleavage and release of a variety of membrane-associated proteins, including the IL-6 receptor, L-selectin, TNF, and EGFR ligands. iRhom2-dependent regulation of ADAM17 function has been recently implicated in the development and progression of several autoimmune diseases including rheumatoid arthritis, lupus nephritis, as well as hemophilic arthropathy. In this review, we discuss our current understanding of iRhom biology, their implications in autoimmune pathologies, and their potential as therapeutic targets.
K E Y W O R D Sa disintegrin and metalloprotease 17 (ADAM17), epidermal growth factor receptor (EGFR), inactive rhomboid 1 (iRHOM1), inactive rhomboid 2 (iRHOM2), rhomboid 5 homolog 1 (RHBDF1), rhomboid 5 homolog 2 (RHBDF2), tumor necrosis factor (TNF) 1 L-selectin from leukocytes and has key roles in their recruitment to sites of inflammation. 10 Moreover, ADAM17 has a wide range of different substrates, 11 including the IL-6 receptor (IL6R), which has important roles in IL6R-dependent pathologies such as multiple myeloma, prostate cancer, and RA. 12,13 The rhomboid 5 homolog proteins iRhom1 and iRhom2 (also known as RHBDF1 and RHBDF2) are proteolytically inactive members of the rhomboid family and act as key regulators of ADAM17-dependent