The transmembrane serine protease (TMPRSS3) mutated in deafness DFNB8/10 activates the epithelial sodium channel (ENaC) in vitro

Abstract

TMPRSS3 encodes a transmembrane serine protease that contains both LDLRA and SRCR domains and is mutated in non-syndromic autosomal recessive deafness (DFNB8/10). To study its function, we cloned the mouse ortholog which maps to Mmu17, which is structurally similar to the human gene and encodes a polypeptide with 88% identity to the human protein. RT-PCR and RNA in situ hybridization on rat and mouse cochlea revealed that Tmprss3 is expressed in the spiral ganglion, the cells supporting the organ of Corti and the stria vascularis. RT-PCR on mouse tissues showed expression in the thymus, stomach, testis and E19 embryos. Transient expression of wild-type or tagged TMPRSS3 protein showed a primary localization in the endoplasmic reticulum. The epithelial amiloride-sensitive sodium channel (ENaC), which is expressed in many sodium-reabsorbing tissues including the inner ear and is regulated by membrane-bound channel activating serine proteases (CAPs), is a potential substrate of TMPRSS3. In the Xenopus oocyte expression system, proteolytic processing of TMPRSS3 was associated with increased ENaC mediated currents. In contrast, 6 TMPRSS3 mutants (D103G, R109W, C194F, W251C, P404L, C407R) causing deafness and a mutant in the catalytic triad of TMPRSS3 (S401A), failed to undergo proteolytic cleavage and activate ENaC. These data indicate that important signaling pathways in the inner ear are controlled by proteolytic cleavage and suggest: (i) the existence of an auto-catalytic processing by which TMPRSS3 would become active, and (ii) that ENaC could be a substrate of TMPRSS3 in the inner ear.

Human DESC1 serine protease confers tumorigenic properties to MDCK cells and it is upregulated in tumours of different origin

“…However, DESC1 was spontaneously released from the GST probably as a consequence of an autocatalytic processing during the course of the different assays ( Figure 1A). This effect has been described for other TTSPs such as matriptase (Takeuchi et al, 1999), matriptase-2 (Velasco et al, 2002), matriptase-3 , TMPRSS2 (Afar et al, 2001) and TMPRSS3 (Guipponi et al, 2002).…”

“…Although the specific role of most of these enzymes remains unresolved, available information indicates that the TTSP are involved in a variety of key biological functions. Thus, matriptase is an essential enzyme for postnatal survival, epidermal barrier function, hair follicle development and thymic homeostasis in mice (List et al, 2002; HAT (human airway trypsin-like protease) has been proposed to play a role in host immune defence (Yamaoka et al, 1998); corin regulates blood pressure by activating the cardiac hormone pro-ANP (Yan et al, 2000); and TMPRSS3 has been suggested to be involved in inner ear development (Guipponi et al, 2002). Likewise, the role of the TTSP in tumour growth, cancer invasion and metastasis processes are being increasingly documented for proteases such as matriptase (List et al, 2005), matriptase-2 (Velasco et al, 2002) and hepsin (Hobson et al, 2004;Klezovitch et al, 2004).…”

Activation of Epithelial Sodium Channels by Mouse Channel Activating Proteases (mCAP) Expressed in Xenopus Oocytes Requires Catalytic Activity of mCAP3 and mCAP2 but not mCAP1

“…Seven mutations have been identified in TMPRSS3 in patients with nonsyndromic autosomal recessive deafness (DFNB8/10) (22,23). An alignment between mTMPRSS3 and mCAP2 revealed that all except one of the aa that were found to be mutated in TMPRSS3 and to confer deafness were identical between the two proteases (the remaining aa was a conservative substitution).…”

“…The mutants D86G, R103W, C181L, R202L, W237C, P388C, and Y391R (Figure 2A) correspond to the TMPRSS3 mutants D103G, R109W, C194F, R216L, W251C, P404L, and C407R (22,23).…”

“…Seven mutations were identified in TMPRSS3, a homolog of mCAP2 (TMPRSS4) (38% identity, 53% homology at the protein level), in patients with nonsyndromic autosomal recessive deafness (DFNB8/10) (22,23). In the Xenopus oocyte expression system, TMPRSS3 was cleaved and able to increase ENaCmediated currents.…”