title: A mammalian homolog of the zebrafish transmembrane protein 2 (TMEM2) is the long-sought-after cell-surface hyaluronidase.
abstract: Hyaluronan (HA) is an extremely large polysaccharide (glycosaminoglycan) involved in many cellular functions. HA catabolism is thought to involve the initial cleavage of extracellular high-molecular-weight (HMW) HA into intermediate-size HA by an extracellular or cell-surface hyaluronidase, internalization of intermediate-size HA, and complete degradation into monosaccharides in lysosomes. Despite considerable research, the identity of the hyaluronidase responsible for the initial HA cleavage in the extracellular space remains elusive. HYAL1 and HYAL2 have properties more consistent with lysosomal hyaluronidases, whereas CEMIP/KIAA1199, a recently identified HA-binding molecule that has HA-degrading activity, requires the participation of the clathrin-coated pit pathway of live cells for HA degradation. Here we show that transmembrane protein 2 (TMEM2), a mammalian homolog of a protein playing a role in zebrafish endocardial cushion development, is a cell-surface hyaluronidase. Live immunostaining and surface biotinylation assays confirmed that mouse TMEM2 is expressed on the cell surface in a type II transmembrane topology. TMEM2 degraded HMW-HA into ∼5-kDa fragments but did not cleave chondroitin sulfate or dermatan sulfate, indicating its specificity to HA. The hyaluronidase activity of TMEM2 was Ca2+-dependent; the enzyme's pH optimum is around 6-7, and unlike CEMIP/KIAA1199, TMEM2 does not require the participation of live cells for its hyaluronidase activity. Moreover, TMEM2-expressing cells could eliminate HA immobilized on a glass surface in a contact-dependent manner. Together, these data suggest that TMEM2 is the long-sought-after hyaluronidase that cleaves extracellular HMW-HA into intermediate-size fragments before internalization and degradation in the lysosome.
authors.affiliation: From the Human Genetics Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California 92037 and.
authors.forename: Hayato
authors.initials: H
authors.lastname: Yamamoto
authors.affiliation: From the Human Genetics Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California 92037 and.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Tobisawa
authors.affiliation: From the Human Genetics Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California 92037 and.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Inubushi
authors.affiliation: From the Human Genetics Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California 92037 and.
authors.forename: Fumitoshi
authors.initials: F
authors.lastname: Irie
authors.affiliation: the Department of Urology, Hirosaki University Graduate School of Medicine, Hirosaki 036-8562, Japan.
authors.forename: Chikara
authors.initials: C
authors.lastname: Ohyama
authors.affiliation: From the Human Genetics Program, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California 92037 and yyamaguchi@sbpdiscovery.org.
authors.forename: Yu
authors.initials: Y
authors.lastname: Yamaguchi
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology* / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D006801:Humans; D006820:Hyaluronic Acid / Q000235:genetics / Q000378:metabolism*; D006821:Hyaluronoglucosaminidase / Q000096:biosynthesis* / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice
chemical_list: D008565:Membrane Proteins; C485807:Tmem2 protein, mouse; D006820:Hyaluronic Acid; D006821:Hyaluronoglucosaminidase; D002118:Calcium
keywords: CEMIP/KIAA1199; TMEM2; cell surface; glycosaminoglycan; hyaluronan; hyaluronidase; membrane function