Human Molecular Genetics Advance Access originally published online on July 10, 2009
Human Molecular Genetics 2009 18(19):3673-3683; doi:10.1093/hmg/ddp315
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Matriptase-2 mutations in iron-refractory iron deficiency anemia patients provide new insights into protease activation mechanisms
1 Departamento de Bioquímica y Biología Molecular, Facultad de Medicina, Instituto Universitario de Oncología, Universidad de Oviedo, 33006 Oviedo, Spain, 2 European Molecular Biology Laboratory, 69117 Heidelberg, Germany, 3 Departamento de Hematología and 4 Departamento de Genética, Hospital de la Santa Creu i Sant Pau, 08025 Barcelona, Spain and 5 Servicio de Hematología, Complejo Hospitalario de Toledo, 45005 Toledo, Spain
* To whom correspondence should be addressed. Tel: +34 985104201; Fax: +34 985103564; Email: clo{at}uniovi.es
Received May 26, 2009; Accepted July 7, 2009
Mutations leading to abrogation of matriptase-2 proteolytic activity in humans are associated with an iron-refractory iron deficiency anemia (IRIDA) due to elevated hepcidin levels. Here we describe two novel heterozygous mutations within the matriptase-2 (TMPRSS6) gene of monozygotic twin girls exhibiting an IRIDA phenotype. The first is the frameshift mutation (P686fs) caused by the insertion of the four nucleotides CCCC in exon 16 (2172_2173insCCCC) that is predicted to terminate translation before the catalytic serine. The second mutation is the di-nucleotide substitution c.467C>A and c.468C>T in exon 3 that causes the missense mutation A118D in the SEA domain of the extracellular stem region of matriptase-2. Functional analysis of both variant matriptase-2 proteases has revealed that they lead to ineffective suppression of hepcidin transcription. We also demonstrate that the A118D SEA domain mutation causes an intra-molecular structural imbalance that impairs matriptase-2 activation. Collectively, these results extend the pattern of TMPRSS6 mutations associated with IRIDA and functionally demonstrate that mutations affecting protease regions other than the catalytic domain may have a profound impact in the regulatory role of matriptase-2 during iron deficiency.