title: Activity-modulating monoclonal antibodies to the human serine protease HtrA3 provide novel insights into regulating HtrA proteolytic activities.
abstract: Mammalian HtrA (high temperature requirement factor A) proteases, comprising 4 multi-domain members HtrA1-4, play important roles in a number of normal cellular processes as well as pathological conditions such as cancer, arthritis, neurodegenerative diseases and pregnancy disorders. However, how HtrA activities are regulated is not well understood, and to date no inhibitors specific to individual HtrA proteins have been identified. Here we investigated five HtrA3 monoclonal antibodies (mAbs) that we have previously produced, and demonstrated that two of them regulated HtrA3 activity in an opposing fashion: one inhibited while the other stimulated. The inhibitory mAb also blocked HtrA3 activity in trophoblast cells and enhanced migration and invasion, confirming its potential in vivo utility. To understand how the binding of these mAbs modulated HtrA3 protease activity, their epitopes were visualized in relation to a 3-dimensional HtrA3 homology model. This model suggests that the inhibitory HtrA3 mAb blocks substrate access to the protease catalytic site, whereas the stimulatory mAb may bind to the PDZ domain alone or in combination with the N-terminal and protease domains. Since HtrA1, HtrA3 and HtrA4 share identical domain organization, our results establish important foundations for developing potential therapeutics to target these HtrA proteins specifically for the treatment of a number of diseases, including cancer and pregnancy disorders.
authors.affiliation: MIMR-PHI Institute of Medical Research, Clayton, Victoria, Australia; Monash University, Clayton, Victoria, Australia.
authors.forename: Harmeet
authors.initials: H
authors.lastname: Singh
authors.affiliation: ACRF Rational Drug Discovery Centre, St Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia.
authors.forename: Tracy L
authors.initials: TL
authors.lastname: Nero
authors.affiliation: MIMR-PHI Institute of Medical Research, Clayton, Victoria, Australia; Monash University, Clayton, Victoria, Australia.
authors.forename: Yao
authors.initials: Y
authors.lastname: Wang
authors.affiliation: ACRF Rational Drug Discovery Centre, St Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia; Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, the University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Parker
authors.affiliation: MIMR-PHI Institute of Medical Research, Clayton, Victoria, Australia; Monash University, Clayton, Victoria, Australia.
authors.forename: Guiying
authors.initials: G
authors.lastname: Nie
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D002460:Cell Line; D002465:Cell Movement / Q000187:drug effects* / Q000502:physiology; D000939:Epitopes; D005260:Female; D006801:Humans; D011247:Pregnancy; D012697:Serine Endopeptidases / Q000276:immunology*; D014327:Trophoblasts / Q000187:drug effects* / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; C474013:HTRA3 protein, human; D012697:Serine Endopeptidases