Abstract
Loss of either hepatocyte growth factor activator inhibitor (HAI)-1 or -2 is associated with embryonic lethality in mice, which can be rescued by the simultaneous inactivation of the membrane-anchored serine protease, matriptase, thereby demonstrating that a matriptase-dependent proteolytic pathway is a critical developmental target for both protease inhibitors. Here, we performed a genetic epistasis analysis to identify additional components of this pathway by generating mice with combined deficiency in either HAI-1 or HAI-2, along with genes encoding developmentally co-expressed candidate matriptase targets, and screening for the rescue of embryonic development. Hypomorphic mutations in Prss8, encoding the GPI-anchored serine protease, prostasin (CAP1, PRSS8), restored placentation and normal development of HAI-1–deficient embryos and prevented early embryonic lethality, mid-gestation lethality due to placental labyrinth failure, and neural tube defects in HAI-2–deficient embryos. Inactivation of genes encoding c-Met, protease-activated receptor-2 (PAR-2), or the epithelial sodium channel (ENaC) alpha subunit all failed to rescue embryonic lethality, suggesting that deregulated matriptase-prostasin activity causes developmental failure independent of aberrant c-Met and PAR-2 signaling or impaired epithelial sodium transport. Furthermore, phenotypic analysis of PAR-1 and matriptase double-deficient embryos suggests that the protease may not be critical for focal proteolytic activation of PAR-2 during neural tube closure. Paradoxically, although matriptase auto-activates and is a well-established upstream epidermal activator of prostasin, biochemical analysis of matriptase- and prostasin-deficient placental tissues revealed a requirement of prostasin for conversion of the matriptase zymogen to active matriptase, whereas prostasin zymogen activation was matriptase-independent.
Highlights
Studies conducted within the past two decades have uncovered a large family of membrane-anchored serine proteases that regulates vertebrate development, tissue homeostasis, and tissue repair by providing focal proteolysis essential for cytokine and growth factor maturation, extracellular matrix remodeling, signaling receptor activation, receptor shedding, regulation of ion channel activity, and more
We show that two of these membrane-anchored serine proteases, prostasin and matriptase, constitute a single proteolytic signaling cascade that is active at multiple stages of development
We show that failure to precisely regulate the enzymatic activity of both prostasin and matriptase by two developmentally coexpressed transmembrane serine protease inhibitors, hepatocyte growth factor activator inhibitor-1 and -2, causes an array of developmental defects, including clefting of the embryonic ectoderm, lack of placental labyrinth formation, and inability to close the neural tube
Summary
Studies conducted within the past two decades have uncovered a large family of membrane-anchored serine proteases that regulates vertebrate development, tissue homeostasis, and tissue repair by providing focal proteolysis essential for cytokine and growth factor maturation, extracellular matrix remodeling, signaling receptor activation, receptor shedding, regulation of ion channel activity, and more (reviewed in [1,2,3]) Individual members of this family regulate both vertebrate development and postnatal tissue homeostasis, including auditory and vestibular system development [4,5,6], differentiation of stratified epithelia [7,8], loss of epithelial tight junction function [9,10], failure to activate digestive enzymes [11], thyroid hormone availability [4], sodium and water homeostasis [12,13,14], iron homeostasis [15,16], and fertility [17,18]. In the human and mouse epidermis, matriptase appears to function as part of a proteolytic cascade in which it acts upstream of the GPI-anchored serine protease prostasin (CAP1/PRSS8), most likely by directly activat-
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