title: Tissue transglutaminase localization and activity regulation in the extracellular matrix of articular cartilage.
abstract: Tissue transglutaminase (tTG) catalyzes a Ca2+-dependent transglutaminase (TGase) activity which cross-links proteins and stabilizes many tissues [C.S. Greenberg et al. FASEB J. 5 (1991) 3071]. Because cartilage is subjected to great stress in vivo, an enzyme that strengthens and stabilizes tissue could play an integral role in maintaining cartilage integrity. The purpose of this study was to determine if active tTG is present in the extracellular matrix (ECM) of adult human osteoarthritic articular cartilage. Using a TGase activity assay along with immunolabeling for tTG of cartilage sections, TGase activity and tTG immunoreactivity were localized in the ECM in cartilage sections, predominantly in the superficial layer. Previous in vitro studies have demonstrated that the Mg-GTP complex inhibits the TGase activity of tTG [T.S. Lai et al. J. Biol. Chem. 273 (1998) 1776]. To investigate the in situ regulation of the TGase activity of tTG, a TGase activity assay was done with a dose response of GTP, measuring incorporation of fluorescein cadaverine. TGase activity was inhibited by GTP in a similar manner as in vitro. These results not only confirm tTG presence in the ECM. but also indicate tTG as the major TGase activity of the ECM. Secondly, the study provides a possible mechanism by which extracellular tTG is regulated in vivo.
authors.affiliation: Department of Medicine, Thurston Arthritis Research Center, University of North Carolina, Chapel Hill 27599-7280, USA.
authors.forename: Brett T
authors.initials: BT
authors.lastname: Summey
authors.forename: Ronald D
authors.initials: RD
authors.lastname: Graff
authors.forename: Thung-Sheng
authors.initials: TS
authors.lastname: Lai
authors.forename: Charles S
authors.initials: CS
authors.lastname: Greenberg
authors.forename: Greta M
authors.initials: GM
authors.lastname: Lee
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000368:Aged; D015153:Blotting, Western; D002358:Cartilage, Articular / Q000737:chemistry / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D005109:Extracellular Matrix / Q000201:enzymology*; D026122:Factor XIIIa / Q000032:analysis; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006801:Humans; D008875:Middle Aged; D011503:Transglutaminases / Q000032:analysis / Q000378:metabolism*
chemical_list: D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D026122:Factor XIIIa; D011503:Transglutaminases