Molecular Mechanisms Governing Matriptase

Abstract

Matriptase, a type II transmembrane serine protease, and its cognate inhibitor hepatocyte growth factor activator inhibitor-1 (HAI-1) is broadly expressed by epithelial and carcinoma cells. The critical interaction between matriptase and HAI-1 are essential for placenta development, epithelial integrity, and epidermal functions. Deregulation of matriptase has been implicated in cancer development and progression. It is thought that the proteolytic activity of matriptase is how this protease participates in these physiological and pathological functions. Since searching for the physiological substrates of matriptase has not been completely successful due to the rapid inhibition by HAI-1, to elucidate the molecular regulatory mechanisms of matriptase becomes the best alternative option to understand its function. Therefore, in this dissertation, I elucidated and revealed the biochemical and cellular details of matriptase autoactivation as well as the alternative inhibitory mechanism. Although matriptase autoactivation can be induced by a variety of structurally unrelated stimuli in a loose cell-type specific manner, they all share some common features including tight coupling with HAI-1 inhibition on the cell surface, which indicates the existence of core autoactivation machinery. Based on this concept, cell-free and intact-cell autoactivation activation systems have been set up to study the molecular mechanisms governing matriptase autoactivation. Among all the chemical and physical factors that could alter the autoactivation, acids seem to be the most likely factor capable of conducting activation as a rapid onset, fast kinetics, in the magnitude of activation ever seen. This could further imply the role of matriptase under acidic pathological conditions, such as in a tumor microenvironment. In the last part of the dissertation, three blood-borne serpin type serine protease inhibitors from human breast milk have been characterized as the alternative mechanisms for matriptase inhibition. This suggests an alternative inhibitory mechanism that may be used physiologically in tissues with low or no HAI-1, such as in hematopoietic cells. Altogether, the dissertation provides insights into the regulatory mechanisms of matriptase. Those insights can be applied to the functional study of matriptase, especially to facilitate the search of its substrates, in the future.