title: Neuropeptide Y is a physiological substrate of fibroblast activation protein: Enzyme kinetics in blood plasma and expression of Y2R and Y5R in human liver cirrhosis and hepatocellular carcinoma.
abstract: Fibroblast activation protein (FAP) is a dipeptidyl peptidase (DPP) and endopeptidase that is weakly expressed in normal adult human tissues but is greatly up-regulated in activated mesenchymal cells of tumors and chronically injured tissue. The identities and locations of target substrates of FAP are poorly defined, in contrast to the related protease DPP4. This study is the first to characterize the physiological substrate repertoire of the DPP activity of endogenous FAP present in plasma. Four substrates, neuropeptide Y (NPY), peptide YY, B-type natriuretic peptide and substance P, were analyzed by mass spectrometry following proteolysis in human or mouse plasma, and by in vivo localization in human liver tissues with cirrhosis and hepatocellular carcinoma (HCC). NPY was the most efficiently cleaved substrate of both human and mouse FAP, whereas all four peptides were efficiently cleaved by endogenous DPP4, indicating that the in vivo degradomes of FAP and DPP4 differ. All detectable DPP-specific proteolysis and C-terminal processing of these neuropeptides was attributable to FAP and DPP4, and plasma kallikrein, respectively, highlighting their combined physiological significance in the regulation of these neuropeptides. In cirrhotic liver and HCC, NPY and its receptor Y2R, but not Y5R, were increased in hepatocytes near the parenchymal-stromal interface where there is an opportunity to interact with FAP expressed on nearby activated mesenchymal cells in the stroma. These novel findings provide insights into the substrate specificity of FAP, which differs greatly from DPP4, and reveal a potential function for FAP in neuropeptide regulation within liver and cancer biology.
authors.affiliation: Centenary Institute of Cancer Medicine and Cell Biology, Sydney Medical School, The University of Sydney, NSW 2006, Australia.
authors.forename: Pok Fai
authors.initials: PF
authors.lastname: Wong
authors.affiliation: Centenary Institute of Cancer Medicine and Cell Biology, Sydney Medical School, The University of Sydney, NSW 2006, Australia.
authors.forename: Margaret G
authors.initials: MG
authors.lastname: Gall
authors.affiliation: Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, MA 02111, USA.
authors.forename: William W
authors.initials: WW
authors.lastname: Bachovchin
authors.affiliation: Centenary Institute of Cancer Medicine and Cell Biology, Sydney Medical School, The University of Sydney, NSW 2006, Australia.
authors.forename: Geoffrey W
authors.initials: GW
authors.lastname: McCaughan
authors.affiliation: Centenary Institute of Cancer Medicine and Cell Biology, Sydney Medical School, The University of Sydney, NSW 2006, Australia.
authors.forename: Fiona M
authors.initials: FM
authors.lastname: Keane
authors.affiliation: Centenary Institute of Cancer Medicine and Cell Biology, Sydney Medical School, The University of Sydney, NSW 2006, Australia. Electronic address: m.gorrell@centenary.usyd.edu.au.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Gorrell
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D016022:Case-Control Studies; D018819:Dipeptidyl Peptidase 4 / Q000097:blood; D010450:Endopeptidases; D018093:Gelatinases / Q000737:chemistry* / Q000502:physiology; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008103:Liver Cirrhosis / Q000378:metabolism*; D008113:Liver Neoplasms / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000502:physiology; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009478:Neuropeptide Y / Q000737:chemistry*; D011480:Protease Inhibitors / Q000737:chemistry; D059748:Proteolysis; D017476:Receptors, Neuropeptide Y / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000502:physiology; D013045:Species Specificity; D013379:Substrate Specificity; D000099167:Fibroblast Activation Protein Alpha
chemical_list: D018819:Dipeptidyl Peptidase 4; D010450:Endopeptidases; D018093:Gelatinases; D008565:Membrane Proteins; D009478:Neuropeptide Y; D011480:Protease Inhibitors; D017476:Receptors, Neuropeptide Y; D012697:Serine Endopeptidases; D000099167:Fibroblast Activation Protein Alpha; C095889:neuropeptide Y2 receptor; C100568:neuropeptide Y5 receptor; C042807:DPP4 protein, human
keywords: Cancer; Dipeptidyl peptidase; Fibroblast activation protein; Kallikrein; Liver disease; Protease substrates