title: How Soluble GARP Enhances TGFβ Activation.
abstract: GARP (glycoprotein A repetitions predominant) is a cell surface receptor on regulatory T-lymphocytes, platelets, hepatic stellate cells and certain cancer cells. Its described function is the binding and accommodation of latent TGFβ (transforming growth factor), before the activation and release of the mature cytokine. For regulatory T cells it was shown that a knockdown of GARP or a treatment with blocking antibodies dramatically decreases their immune suppressive capacity. This confirms a fundamental role of GARP in the basic function of regulatory T cells. Prerequisites postulated for physiological GARP function include membrane anchorage of GARP, disulfide bridges between the propeptide of TGFβ and GARP and connection of this propeptide to αvβ6 or αvβ8 integrins of target cells during mechanical TGFβ release. Other studies indicate the existence of soluble GARP complexes and a functionality of soluble GARP alone. In order to clarify the underlying molecular mechanism, we expressed and purified recombinant TGFβ and a soluble variant of GARP. Surprisingly, soluble GARP and TGFβ formed stable non-covalent complexes in addition to disulfide-coupled complexes, depending on the redox conditions of the microenvironment. We also show that soluble GARP alone and the two variants of complexes mediate different levels of TGFβ activity. TGFβ activation is enhanced by the non-covalent GARP-TGFβ complex already at low (nanomolar) concentrations, at which GARP alone does not show any effect. This supports the idea of soluble GARP acting as immune modulator in vivo.
authors.affiliation: Cell and Matrix Biology, Institute of Zoology, JGU Mainz, Mainz, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Fridrich
authors.affiliation: University Hospital Mainz, Dermatology, Mainz, Germany.
authors.forename: Susanne A
authors.initials: SA
authors.lastname: Hahn
authors.affiliation: Cell and Matrix Biology, Institute of Zoology, JGU Mainz, Mainz, Germany.
authors.forename: Marion
authors.initials: M
authors.lastname: Linzmaier
authors.affiliation: Cell and Matrix Biology, Institute of Zoology, JGU Mainz, Mainz, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Felten
authors.affiliation: University Hospital Mainz, 3rd medical center, Mainz, Germany.
authors.forename: Jenny
authors.initials: J
authors.lastname: Zwarg
authors.affiliation: University Hospital Mainz, 3rd medical center, Mainz, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Lennerz
authors.affiliation: University Hospital Mainz, Dermatology, Mainz, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Tuettenberg
authors.affiliation: Cell and Matrix Biology, Institute of Zoology, JGU Mainz, Mainz, Germany.
authors.forename: Walter
authors.initials: W
authors.lastname: Stöcker
mesh_terms: D049109:Cell Proliferation; D002942:Circular Dichroism; D003001:Cloning, Molecular; D057809:HEK293 Cells; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: C087215:LRRC32 protein, human; D008565:Membrane Proteins; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta