title: Myxoma viral serpin, Serp-1, inhibits human monocyte adhesion through regulation of actin-binding protein filamin B.
abstract: Serp-1 is a secreted myxoma viral serine protease inhibitor (serpin) with proven, highly effective, anti-inflammatory defensive activity during host cell infection, as well as potent immunomodulatory activity in a wide range of animal disease models. Serp-1 binds urokinase-type plasminogen activator (uPA) and the tissue-type PA, plasmin, and factor Xa, requiring uPA receptor (uPAR) for anti-inflammatory activity. To define Serp-1-mediated effects on inflammatory cell activation, we examined the association of Serp-1 with monocytes and T cells, effects on cellular migration, and the role of uPAR-linked integrins and actin-binding proteins in Serp-1 cellular responses. Our results show that Serp-1 associates directly with activated monocytes and T lymphocytes, in part through interaction with uPAR (P<0.001). Serp-1, but not mammalian serpin PA inhibitor-1 (PAI-1), attenuated cellular adhesion to the extracellular matrix. Serp-1 and PAI-1 reduced human monocyte and T cell adhesion (P<0.001) and migration across endothelial monolayers in vitro (P<0.001) and into mouse ascites in vivo (P<0.001). Serp-1 and an inactive Serp-1 mutant Serp-1(SAA) bound equally to human monocytes and T cells, but a highly proinflammatory mutant, Serp-1(Ala(6)), bound less well to monocytes. Serp-1 treatment of monocytes increased expression of filamin B actin-binding protein and reduced CD18 (beta-integrin) expression (P<0.001) in a uPAR-dependent response. Filamin colocalized and co-immunoprecipitated with uPAR, and short interference RNA knock-down of filamin blocked Serp-1 inhibition of monocyte adhesion. We report here that the highly potent, anti-inflammatory activity of Serp-1 is mediated through modification of uPAR-linked beta-integrin and filamin in monocytes, identifying this interaction as a central regulatory axis for inflammation.
authors.affiliation: Vascular Biology Research Group, Robarts Research Institute, University of Western Ontario, London, Ontario, Canada.
authors.forename: Kasinath
authors.initials: K
authors.lastname: Viswanathan
authors.forename: Jakob
authors.initials: J
authors.lastname: Richardson
authors.forename: Babajide
authors.initials: B
authors.lastname: Togonu-Bickersteth
authors.forename: Erbin
authors.initials: E
authors.lastname: Dai
authors.forename: Liying
authors.initials: L
authors.lastname: Liu
authors.forename: Pracha
authors.initials: P
authors.lastname: Vatsya
authors.forename: Yun-ming
authors.initials: YM
authors.lastname: Sun
authors.forename: Jeff
authors.initials: J
authors.lastname: Yu
authors.forename: Ganesh
authors.initials: G
authors.lastname: Munuswamy-Ramanujam
authors.forename: Henry
authors.initials: H
authors.lastname: Baker
authors.forename: Alexandra R
authors.initials: AR
authors.lastname: Lucas
mesh_terms: D002448:Cell Adhesion; D003285:Contractile Proteins / Q000378:metabolism*; D064448:Filamins; D006801:Humans; D007249:Inflammation; D039641:Integrin beta Chains / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism*; D009000:Monocytes / Q000166:cytology*; D009233:Myxoma virus / Q000472:pathogenicity*; D011485:Protein Binding / Q000276:immunology; D015843:Serpins / Q000502:physiology*; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism; D014764:Viral Proteins / Q000502:physiology*
chemical_list: D003285:Contractile Proteins; D064448:Filamins; D039641:Integrin beta Chains; D008840:Microfilament Proteins; D015843:Serpins; D014764:Viral Proteins; D014568:Urokinase-Type Plasminogen Activator