Binding of Candida albicans enolase to plasmin(ogen) results in enhanced invasion of human brain microvascular endothelial cells

1 Division of Hematology–Oncology, Mailstop 57, Childrens Hospital Los Angeles, Los Angeles, CA 90027, USA 2 Division of Infectious Diseases, Johns Hopkins University School of Medicine, Baltimore, MD, USA 3,4 Division of Infectious Diseases 3 and Department of Surgery 4 , Childrens Hospital Los Angeles, Los Angeles, CA 90027, USA Correspondence Ambrose Y. Jong ajong{at}chla.usc.edu Received August 28, 2002 Accepted December 6, 2002 Infection by the human opportunistic fungal pathogen Candida albicans has been increasing over recent years. In an attempt to understand the molecular mechanism of Candida invasion across host tissues, the relationship of C. albicans enolase to human plasminogen/plasmin was investigated. C. albicans enolase is a cell-surface protein and an immunodominant antigen in infected patients’ sera. Plasminogen is an abundant plasma protein. Several lines of evidence support the binding of C. albicans enolase to human plasminogen. Firstly, it was found that various Candida strains were able to bind to plasminogen and its active form, plasmin. Secondly, recombinant Candida enolase was retained in a nickel-chelating affinity column matrix that can bind 125 I-labelled plasminogen or plasmin in a dose-dependent manner. Plasmin(ogen)-specific inhibitors, such as -aminocaproic acid and aprotinin, can effectively block plasmin-binding activity. Thirdly, as with many plasminogen receptors, binding of Candida enolase to plasmin(ogen) is lysine-dependent, whereas little inhibition occurred with arginine, aspartate and glutamate. Fourthly, immobilized enolase enhanced plasminogen's affinity for streptokinase at least tenfold, as demonstrated by its activation of plasmin activity. To elucidate the biological significance of this result, it was demonstrated that the plasmin(ogen)-bound Candida cells were able to induce fibrinolysis activity in a matrix-gel assay. Furthermore, plasmin-bound Candida cells had an increased ability to cross an in vitro blood–brain barrier system. The results given here indicate that Candida enolase is a plasminogen- and plasmin-binding protein and that the interaction of C. albicans enolase with the plasminogen system may contribute to invasion of the tissue barrier. These authors contributed equally to this work. Abbreviations: EACA, -aminocaproic acid; ECM, extracellular matrix; HBMEC, human brain microvascular endothelial cells; Ni-NTA, nickel nitrilotriacetic acid; SAP, secreted aspartyl proteinase; TEER, transendoth