In vitro localization of TIGR/MYOC in trabecular meshwork extracellular matrix and binding to fibronectin

Purpose: To determine whether trabecular meshwork-inducible glucocorticoid response/myocilin (TIGR/MYOC) protein associates with the extracellular matrix (ECM) of human trabecular meshwork (HTM) cells.

Methods: The extracellular localization of TIGR/MYOC was examined by immunofluorescence microscopy in HTM cultures treated with and without dexamethasone and ascorbate and in a transformed HTM cell line, TM-1, transiently transfected with TIGR/MYOC cDNA. Antibodies to TIGR/MYOC, fibronectin, laminin, type IV collagen, or thrombospondin were used to determine the extracellular localization of TIGR/MYOC. Solid phase binding assays using 125I-recombinant TIGR/MYOC and types I and IV collagens, fibronectin, and laminin were done to examine the association of TIGR/MYOC with these proteins and to identify a specific TIGR/MYOC binding site within fibronectin. The domains of fibronectin tested were the fibrin/collagen binding domain, the RGD domain, and the Heparin II (Hep II) domain.

Results: TIGR/MYOC colocalized with fibronectin, laminin, and type IV collagen, but not thrombospondin in both dexamethasone and dexamethasone/ascorbate-treated HTM cultures and in TM-1 cultures transfected with TIGR/MYOC cDNA. In solid phase binding assays, 125I-TIGR/MYOC bound fibronectin but not laminin or type IV collagen. Binding to fibronectin could be competed with excess TIGR/MYOC or fibronectin. Specific binding was found for the Hep II domain of fibronectin.

Conclusions: TIGR/MYOC can associate with components of the ECM via interactions with the Hep II domain of fibronectin. The interactions with the Hep II domain of fibronectin could alter cell-matrix interactions in the TM and provides an interesting lead to explore the role(s) of TIGR/MYOC in both steroid-induced and primary open angle glaucoma.