Transferrin receptor 1 shedding by the pro-inflammatory iRhom-ADAM17 complex and ADAM10 regulates cellular iron uptake and ferroptosis.

Iron homeostasis is a tightly regulated mechanism, wherein the uptake, transport, storage and export of iron are stringently controlled. Dysregulation and excessive iron uptake lead to iron-dependent programmed cell death called ferroptosis, a promising future cancer therapy target. Cellular iron uptake is limited by the surface presence of membrane-bound transferrin receptor 1 (TfR1). Soluble TfR1 is used as a major clinical marker to differentiate anemia types. Here we identify iRhoms, the regulatory interactors of the surface protease ADAM17, as substrate platforms. They bind TfR1 and facilitate ADAM17-mediated proteolytic TfR1 release (TfR1 shedding). Thereby, the iRhom-ADAM17 complex regulates TfR1 surface levels. Notably, TfR1 preferentially binds to pro-inflammatory iRhom2 over iRhom1, with the cytosolic N terminus of iRhom serving as a critical binding determinant. By CRISPR-Cas9-based knockout and pharmacological inhibition in vitro, in human primary endothelial cells as well as in ex vivo human lung slices, we also demonstrate that TfR1 is a shared substrate of ADAM10 and ADAM17. Functionally, we found that ADAM17-dependent TfR1 shedding reduces excessive iron uptake. By live cell imaging, we identified TfR1 shedding as a protective mechanism against ferroptosis. Moreover, reduced TfR1 shedding correlaśtes with elevated serum iron levels in ADAM17-hypomorphic mice, highlighting its systemic relevance for patho(physiological) iron homeostasis. iRhom-ADAM17 complex and ADAM10-shed TfR1. Cellular iron uptake is facilitated by TfR1. TfR1 interacts with the substrate platform iRhom, which is a regulator of the protease ADAM17. The iRhom-ADAM17 complex and ADAM10 cleave TfR1, thereby releasing soluble TfR1. By this, iron overloaded is prevented. Therefore, ectodomain shedding of TfR1 is a protective mechanism to hinder ferroptosis.