title: Essential role of endocytosis of the type II transmembrane serine protease TMPRSS6 in regulating its functionality.
abstract: The type II transmembrane serine protease TMPRSS6 (also known as matriptase-2) controls iron homeostasis through its negative regulation of expression of hepcidin, a key hormone involved in iron metabolism. Upstream of the hepcidin-regulated signaling pathway, TMPRSS6 cleaves its target substrate hemojuvelin (HJV) at the plasma membrane, but the dynamics of the cell-surface expression of the protease have not been addressed. Here, we report that TMPRSS6 undergoes constitutive internalization in transfected HEK293 cells and in two human hepatic cell lines, HepG2 and primary hepatocytes, both of which express TMPRSS6 endogenously. Cell surface-labeled TMPRSS6 was internalized and was detected in clathrin- and AP-2-positive vesicles via a dynamin-dependent pathway. The endocytosed TMPRSS6 next transited in early endosomes and then to lysosomes. Internalization of TMPRSS6 is dependent on specific residues within its N-terminal cytoplasmic domain, as site-directed mutagenesis of these residues abrogated internalization and maintained the enzyme at the cell surface. Cells coexpressing these mutants and HJV produced significantly decreased levels of hepcidin compared with wild-type TMPRSS6 due to the sustained cleavage of HJV at the cell surface by TMPRSS6 mutants. Our results underscore for the first time the importance of TMPRSS6 trafficking at the plasma membrane in the regulation of hepcidin expression, an event that is essential for iron homeostasis.
authors: Department of Pharmacology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4, Canada.
authors: François
authors: F
authors: Béliveau
authors: Department of Pharmacology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4, Canada.
authors: Cédric
authors: C
authors: Brulé
authors: Department of Pharmacology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4, Canada.
authors: Antoine
authors: A
authors: Désilets
authors: Departments of Medicine and Pharmacology & Therapeutics, McGill University Health Center Research Institute, McGill University, Montreal H3A 1A1, Canada.
authors: Brandon
authors: B
authors: Zimmerman
authors: Departments of Medicine and Pharmacology & Therapeutics, McGill University Health Center Research Institute, McGill University, Montreal H3A 1A1, Canada.
authors: Stéphane A
authors: SA
authors: Laporte
authors: Department of Pharmacology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4, Canada.
authors: Christine L
authors: CL
authors: Lavoie
authors: Department of Pharmacology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Québec J1H 5N4, Canada. Electronic address: richard.leduc@usherbrooke.ca.
authors: Richard
authors: R
authors: Leduc
mesh_terms: D023181:Antimicrobial Cationic Peptides / Q000096:biosynthesis / Q000235:genetics; D002462:Cell Membrane / Q000201:enzymology* / Q000235:genetics; D022163:Clathrin-Coated Vesicles / Q000201:enzymology / Q000235:genetics; D004705:Endocytosis / Q000502:physiology*; D058851:GPI-Linked Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D057809:HEK293 Cells; D000071020:Hemochromatosis Protein; D056945:Hep G2 Cells; D064451:Hepcidins; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007501:Iron / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*
chemical_list: D023181:Antimicrobial Cationic Peptides; D058851:GPI-Linked Proteins; C578702:HAMP protein, human; C481006:HJV protein, human; D000071020:Hemochromatosis Protein; D064451:Hepcidins; D008565:Membrane Proteins; D007501:Iron; D012697:Serine Endopeptidases; C504318:TMPRSS6 protein, human