Loss of Matriptase Suppression Underlies Spint1 Mutation-Associated Ichthyosis and Postnatal Lethality

Abstract

Hepatocyte growth factor activator inhibitor-1 (HAI)-1 is an epithelial Kunitz-type transmembrane serine protease inhibitor that is encoded by the SPINT1 gene. HAI-1 displays potent inhibitory activity toward a large number of trypsin-like serine proteases. HAI-1 was recently shown to play an essential role in postnatal epithelial homeostasis. Thus, Spint1-deficient mice were found to display severe growth retardation and are unable to survive beyond postnatal day 16. The mice present histologically with overt hyperkeratosis of the forestomach, hyperkeratosis and acanthosis of the epidermis, and hypotrichosis associated with abnormal cuticle development. In this study, we show that loss of inhibition of a proteolytic pathway that is dependent on the type II transmembrane serine protease, matriptase, underlies the detrimental effects of postnatal Spint1 deficiency. Matriptase and HAI-1 precisely co-localize in all tissues that are affected by the Spint1 disruption. Spint1-deficient mice that have low matriptase levels, caused by a hypomorphic mutation in the St14 gene that encodes matriptase, not only survived the neonatal period but were healthy and displayed normal long-term survival. Furthermore, a detailed histological analysis of neonatal, young adult, as well as aged mice did not reveal any abnormalities in Spint1-deficent mice that have low matriptase levels. This study identifies matriptase suppression as an essential function of HAI-1 in postnatal tissue homeostasis. Trypsin-like serine proteases constitute a large family of secreted and membrane-bound proteolytic enzymes that operate in the pericellular environment to facilitate embryonic development tissue homeostasis, tissue remodeling, and tissue repair. These enzymes are synthesized as inactive precursors, or zymogens, that are converted to their catalytically active form by endoproteolytic cleavage within a highly conserved activation site. This activation step is irreversible, and proteolysis is terminated by specific macromolecular protease inhibitors that bind directly to the active site of their cognate proteases. 1-3Inhibition of trypsin-like serine proteases is mediated by a large number of serine protease inhibitors belonging to one of three structurally and functionally distinct families: serpin-type inhibitors, Kazal-type inhibitors, and Kunitztype inhibitors.1-3 Hepatocyte growth factor activator-1 (HAI-1) is a recently discovered membrane-associated Kunitz-type serine protease inhibitor. This peculiar serine protease inhibitor, which is structurally distinct from other previously described Kunitz-type inhibitors, is a type I transmembrane glycoprotein that consists of an N-terminal MANEC-domain followed by two extracellular Kunitztype inhibitory domains that are separated by a single low-density lipoprotein receptor type a repeat, and a C-terminal transmembrane/cytoplasmic tail domain. 4 -8 HAI-1 is widely expressed in embryonic and extra-embryonic epithelia of the developing embryo, as well as in simple, stratified and pseudo-stratif...

Membrane-Bound Serine Protease Inhibitor HAI-1 Is Required for Maintenance of Intestinal Epithelial Integrity

“…6,7 In mouse skin, HAI-1/SPINT1 interacts with matriptase to play a central role in regulated keratinization of the epidermis. 8,9 The participation of HAI-1/SPINT1 in the maintenance of epidermal integrity in zebrafish was also demonstrated. 13 Even in neoplastic cells, short hairpin RNA knockdown of HAI-1/ SPINT1 induced epithelial to mesenchymal transition in certain human epithelial cancer cell lines with enhanced metastatic colonization capability.…”

Hepatocyte Growth Factor Activator Inhibitor Type 1 Maintains the Assembly of Keratin into Desmosomes in Keratinocytes by Regulating Protease-Activated Receptor 2–Dependent p38 Signaling

“…PAR-2 is activated by serine proteases, such as trypsin, factor Xa, KLKs 4, 5, 6, and 14, and tryptase, as well as membrane-anchored trypsin-like serine proteases, such as matriptase, prostasin, TMPRSS2, hepsin, and human airway trypsin-like protease. 17,27,43e46 Considering the established role of HAI-1 as a regulator of transmembrane trypsin-like serine protease activities, 17,24 it is possible to speculate that HAI-1 is a key regulatory molecule that controls PAR-2 activity and, hence, is critical in maintaining epidermal integrity. The current study provided evidence for this hypothesis.…”

“…17,27,30 The evidence suggested that the most important cognate protease of HAI-1 in keratinocytes is matriptase. 24 Therefore, we hypothesized that the activity of matriptase was enhanced because of insufficient HAI-1, which eventually led to PAR-2 activation in HAI KD HaCaT cells. To test this hypothesis, we examined cellular expression of matriptase and its activity in culture supernatants of HaCaT cells.…”

“…22 Moreover, hair cuticle formation was severely impaired. 22 More important, these skin pathologies caused by HAI-1 deficiency were totally abrogated in the matriptase hypomorphic mice, 24 indicating that HAI-1 is a critical regulator of matriptase in the skin. Matriptase is also known to activate other serine proteases, such as prostasin and KLK-5.…”

Selective Inhibition of Prostasin in Human Enterocytes by the Integral Membrane Kunitz-Type Serine Protease Inhibitor HAI-2

“…An in vivo functional link between these two membrane-bound serine proteases and the two Kunitz inhibitors has also been observed in several animal studies. In the mouse and/or zebra fish, epidermal, placental or embryonic defects associated with genetic ablation of HAI-1 or HAI-2 can be rescued by simultaneous deletion or suppression of matriptase or prostasin [12][13][14][15][16].…”