Role of the polycystic kidney disease domain in matriptase chaperone activity and localization of hepatocyte growth factor activator inhibitor‐1

Abstract

Hepatocyte growth factor activator inhibitor-1 (HAI-1, also known as SPINT1) is an inhibitor of matriptase, a type-2 transmembrane protease widely expressed in epithelial cells. HAI-1 also functions as a chaperone to maintain the processing and localization of matriptase required for epithelial integrity. However, mechanisms underpinning the chaperone function remain to be elucidated. Here, we show that the first Kunitz domain (KD1) and the adjacent polycystic kidney disease (PKD) domain-like internal domain of HAI-1 are essential for the chaperone function. In HEK293T cells, which do not express endogenous HAI-1 or matriptase, forced matriptase overexpression was unsuccessful unless sufficient HAI-1 was co-expressed. Among mutant HAI-1 constructs, HAI-1 with inactivation mutation in KD1 (HAI-1mKD1) or HAI-1 lacking the PKD domain (HAI-1dPKD) was unable to support matriptase expression, and neither mutant formed a complex with activated matriptase. Matriptase did not localize to the cell surface when co-expressed with HAI-1dPKD. Moreover, HAI-1dPKD accumulated in the cytoplasm of HEK293T and HaCaT cells rather than localizing to the cell surface, presumably due to misfolding as judged by altered antibody recognition. On the other hand, activationlocked and activity-incompetent matriptase were stable and readily overexpressed and localized to the cell surface without HAI-1. Therefore, the observed matriptase instability was caused by its own catalytic activity in the absence of inhibitory HAI-1. The matriptase chaperone function of HAI-1 is thus mediated primarily by the inhibition of undesired intracellular matriptase activity, and the PKD domain is essential for the proper folding and trafficking of inhibitory HAI-1 and its chaperone function.

Understanding HAIs: Ally proteins in the fight against cancer

“…likely involved in conformational changes of matripdescribed by Yamashita et al [12] as altered antibody recognition.…”

“…To explain the poorly understood connection between HAIs and the presence of matriptase protein in cells, HAIs have been proposed to affect cellular transport of matriptase along the secretory pathway [ 9 , 10 ], to chaperone [ 7 , 8 , 11 ], and to stabilize matriptase protein expression [ 8 ]. In the present issue of The FEBS Journal , the study by Yamashita, et al [ 12 ] successfully gives us new insight into this phenomenon by describing a ‘chaperone‐like function’ of HAI‐1.…”

“…Research into these matters is necessary and may hold the key to curing epithelial‐derived cancer. We thank Yamashita et al [ 12 ] for being bold enough to embark on this journey.…”

“…Both matriptase and HAI‐1 are known to have several conformational forms [14,15] and the HAIs are likely involved in conformational changes of matriptase, described by Yamashita et al [12] as altered antibody recognition.…”

Pharmacological impact of microRNAs in head and neck squamous cell carcinoma: Prevailing insights on molecular pathways, diagnosis, and nanomedicine treatment

“…Met is constituted of numerous structural elements, namely, the semaphorin (SEMA), the protein tyrosine kinase motif (PTKM), and the juxtamembrane (JM-operational motif), which adheres to its receptor, i.e ., hepatocyte growth factor (HGF) ( Faiella et al, 2022 ; Raj et al, 2022 ). Most of the HGF in HNSCC is expressed by tumor-associated fibroblasts (TAFs) in the tumor microenvironment as an ineffective proenzyme that must be enzymatically degraded by the cell surface protease, matriptase ( Yamashita et al, 2022 ). Coupling of MET to HGF promotes upregulation of the enzymatic efficiency of tyrosine kinase, namely, Y1235, Y1234, and Y1230, MET dimerization, and intracellular phosphorylation, leading to cellular expansion, migration, and longevity ( Zhang et al, 2018 ).…”