Activation of macrophage-stimulating protein by human airway trypsin-like protease.

Macrophage-stimulating protein (MSP) circulates as a proform protein and requires proteolytic processing for activation. Respiratory ciliated cells express the MSP receptor, recepteur d'origine nantais (RON), at the apical surface, which reportedly has an important role in ciliary function. Like RON, human airway trypsin-like protease (HAT) is also expressed at the apical surface of ciliated cells. Here we show that HAT cleaves proMSP at the physiological activation site, Arg483-Val484. MSP processed by HAT could induce chemotactic responses and morphological changes of peritoneal macrophages. In human respiratory epithelial cells, knock down of HAT expression reduced proMSP processing and RON autophosphorylation. We suggest that HAT is important for MSP-RON signaling in the respiratory tract.