title: Identification of CD109 as part of the TGF-beta receptor system in human keratinocytes.
abstract: We have previously reported that keratinocytes defective in glycosylphosphatidylinositol (GPI)-anchor biosynthesis display enhanced TGF-beta responses. These studies implicated the involvement of a 150 kDa GPI-anchored TGF-beta1 binding protein, r150, in modulating TGF-beta signaling. Here, we sought to determine the molecular identity of r150 by affinity purification and microsequencing. Our results identify r150 as CD109, a novel member of the alpha2-macroglobulin (alpha2M)/complement superfamily, whose function has remained obscure. In addition, we have identified a novel CD109 isoform that occurs in the human placenta but not keratinocytes. Biochemical studies show that r150 contains an internal thioester bond, a defining feature of the alpha2M/complement family. Loss and gain of function studies demonstrate that CD109 is a component of the TGF-beta receptor system, and a negative modulator of TGF-beta responses in keratinocytes, as implicated for r150. Our data suggest that CD109 can inhibit TGF-beta signaling independently of ligand sequestration and may exert its effect on TGF-beta signaling by direct modulation of receptor activity. Together, our results linking CD109 function to regulation of TGF-beta signaling suggest that CD109 plays a unique role in the regulation of isoform-specific TGF-beta signaling in keratinocytes.
authors.affiliation: Department of Surgery, McGill University, Montreal, Quebec, Canada.
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Finnson
authors.forename: Betty Y Y
authors.initials: BY
authors.lastname: Tam
authors.forename: Kai
authors.initials: K
authors.lastname: Liu
authors.forename: Anne
authors.initials: A
authors.lastname: Marcoux
authors.forename: Pierre
authors.initials: P
authors.lastname: Lepage
authors.forename: Stephane
authors.initials: S
authors.lastname: Roy
authors.forename: Albane A
authors.initials: AA
authors.lastname: Bizet
authors.forename: Anie
authors.initials: A
authors.lastname: Philip
mesh_terms: D015703:Antigens, CD / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D058851:GPI-Linked Proteins; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects / Q000502:physiology*; D009363:Neoplasm Proteins / Q000235:genetics / Q000502:physiology*; D018125:Receptors, Transforming Growth Factor beta / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D015703:Antigens, CD; C120523:CD109 protein, human; D058851:GPI-Linked Proteins; D009363:Neoplasm Proteins; D018125:Receptors, Transforming Growth Factor beta; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta