Hepsin regulates TGFβ signaling via fibronectin proteolysis

Abstract

Transforming growth factor-beta (TGFb) is a multifunctional cyto-kine with a well-established role in mammary gland development and both oncogenic and tumor-suppressive functions. The extra-cellular matrix (ECM) indirectly regulates TGFb activity by acting as a storage compartment of latent-TGFb, but how TGFb is released from the ECM via proteolytic mechanisms remains largely unknown. In this study, we demonstrate that hepsin, a type II transmembrane protease overexpressed in 70% of breast tumors, promotes canonical TGFb signaling through the release of latent-TGFb from the ECM storage compartment. Mammary glands in hepsin CRISPR knockout mice showed reduced TGFb signaling and increased epithelial branching, accompanied by increased levels of fibronectin and latent-TGFb1, while overexpression of hepsin in mammary tumors increased TGFb signaling. Cell-free and cell-based experiments showed that hepsin is capable of direct prote-olytic cleavage of fibronectin but not latent-TGFb and, importantly, that the ability of hepsin to activate TGFb signaling is dependent on fibronectin. Altogether, this study demonstrates a role for hepsin as a regulator of the TGFb pathway in the mammary gland via a novel mechanism involving proteolytic downmodulation of fibronectin.