TY - JOUR

T1 - SPINT2 (HAI-2) missense variants identified in congenital sodium diarrhea/tufting enteropathy affect the ability of HAI-2 to inhibit prostasin but not matriptase

AU - Holt-Danborg, Lasse

AU - Vodopiutz, Julia

AU - Nonboe, Annika W

AU - De Laffolie, Jan

AU - Skovbjerg, Signe

AU - Wolters, Victorien M

AU - Müller, Thomas

AU - Hetzer, Benjamin

AU - Querfurt, Alexander

AU - Zimmer, Klaus-Peter

AU - Jensen, Jan K

AU - Entenmann, Andreas

AU - Heinz-Erian, Peter

AU - Vogel, Lotte K

AU - Janecke, Andreas R

PY - 2019

Y1 - 2019

N2 - The syndromic form of congenital sodium diarrhea (SCSD) is caused by bi-allelic mutations in SPINT2, which encodes a Kunitz type serine protease inhibitor (HAI-2). We report three novel SCSD patients, two novel SPINT2 mutations, and review published cases. The most common findings in SCSD patients were choanal atresia (20/34), and keratitis of infantile onset (26/34). Characteristic epithelial tufts on intestinal histology were reported in 13/34 patients. Of 13 different SPINT2 variants identified in SCSD, four are missense variants and localize to the second Kunitz domain (KD2) of HAI-2. HAI-2 has been implicated in the regulation of the activities of several serine proteases including prostasin and matriptase, which are both important for epithelial barrier formation. No patient with bi-allelic stop mutations was identified, suggesting that at least one SPINT2 allele encoding a protein with residual HAI-2 function is necessary for survival. We show that the SCSD-associated HAI-2 variants p.Phe161Val, p.Tyr163Cys, and p.Gly168Ser all display decreased ability to inhibit prostasin-catalyzed cleavage. However, the SCSD-associated HAI-2 variants inhibited matriptase as efficiently as the wild-type HAI-2. Homology modeling indicated limited solvent exposure of the mutated amino acids, suggesting that they induce misfolding of KD2. This suggests that prostasin needs to engage with an exosite motif located on KD2 in addition to the binding loop (Cys47/Arg48) located on the first Kunitz domain in order to inhibit prostasin. In conclusion our data suggests that SCSD is caused by lack of inhibition of prostasin or a similar protease in the secretory pathway or on the plasma membrane.

AB - The syndromic form of congenital sodium diarrhea (SCSD) is caused by bi-allelic mutations in SPINT2, which encodes a Kunitz type serine protease inhibitor (HAI-2). We report three novel SCSD patients, two novel SPINT2 mutations, and review published cases. The most common findings in SCSD patients were choanal atresia (20/34), and keratitis of infantile onset (26/34). Characteristic epithelial tufts on intestinal histology were reported in 13/34 patients. Of 13 different SPINT2 variants identified in SCSD, four are missense variants and localize to the second Kunitz domain (KD2) of HAI-2. HAI-2 has been implicated in the regulation of the activities of several serine proteases including prostasin and matriptase, which are both important for epithelial barrier formation. No patient with bi-allelic stop mutations was identified, suggesting that at least one SPINT2 allele encoding a protein with residual HAI-2 function is necessary for survival. We show that the SCSD-associated HAI-2 variants p.Phe161Val, p.Tyr163Cys, and p.Gly168Ser all display decreased ability to inhibit prostasin-catalyzed cleavage. However, the SCSD-associated HAI-2 variants inhibited matriptase as efficiently as the wild-type HAI-2. Homology modeling indicated limited solvent exposure of the mutated amino acids, suggesting that they induce misfolding of KD2. This suggests that prostasin needs to engage with an exosite motif located on KD2 in addition to the binding loop (Cys47/Arg48) located on the first Kunitz domain in order to inhibit prostasin. In conclusion our data suggests that SCSD is caused by lack of inhibition of prostasin or a similar protease in the secretory pathway or on the plasma membrane.

U2 - 10.1093/hmg/ddy394

DO - 10.1093/hmg/ddy394

M3 - Journal article

C2 - 30445423

VL - 28

SP - 828

EP - 841

JO - Human Molecular Genetics

JF - Human Molecular Genetics

SN - 0964-6906

IS - 5

ER -