Transforming growth factor-beta (TGFβ) is a multifunctional cytokine with a well-established role in mammary gland development and both oncogenic and tumor-suppressive functions. The extracellular matrix (ECM) indirectly regulates TGFβ activity by acting as a storage compartment of latent-TGFβ, but how TGFβ 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 TGFβ signaling through the release of latent-TGFβ from the ECM storage compartment. Mammary glands in hepsin CRISPR knockout mice showed reduced TGFβ signaling and increased epithelial branching, accompanied by increased levels of fibronectin and latent-TGFβ1, while overexpression of hepsin in mammary tumors increased TGFβ signaling. Cell-free and cell-based experiments showed that hepsin is capable of direct proteolytic cleavage of fibronectin but not latent-TGFβ and, importantly, that the ability of hepsin to activate TGFβ signaling is dependent on fibronectin. Altogether, this study demonstrates a role for hepsin as a regulator of the TGFβ pathway in the mammary gland via a novel mechanism involving proteolytic downmodulation of fibronectin.

中文翻译：

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Hepsin 通过纤连蛋白蛋白水解调节 TGFβ 信号传导

转化生长因子-β (TGFβ) 是一种多功能细胞因子，在乳腺发育以及致癌和肿瘤抑制功能中具有公认的作用。细胞外基质 (ECM) 通过充当潜在 TGFβ 的储藏室间接调节 TGFβ 活性，但 TGFβ 如何通过蛋白水解机制从 ECM 释放仍然很大程度上未知。在这项研究中，我们证明 hepsin 是一种在 70% 的乳腺肿瘤中过度表达的 II 型跨膜蛋白酶，它通过从 ECM 储存室释放潜伏的 TGFβ 来促进经典的 TGFβ 信号传导。hepsin CRISPR敲除小鼠的乳腺显示TGFβ信号减少和上皮分支增加，伴随着纤连蛋白和潜伏TGFβ1水平的增加，而乳腺肿瘤中hepsin的过表达增加了TGFβ信号。无细胞和基于细胞的实验表明，hepsin 能够直接蛋白水解裂解纤连蛋白，但不能直接裂解潜在的 TGFβ，而且重要的是，hepsin 激活 TGFβ 信号传导的能力依赖于纤连蛋白。总而言之，这项研究通过涉及纤连蛋白的蛋白水解下调的新机制证明了 hepsin 作为乳腺中 TGFβ 通路的调节剂的作用。