Cellular Pharmacology and molecular Biology of the Trabecular Meshwork Inducible glucocorticoid Response Gene Product

Abstract

Studies of the effects of glucocorticoid (GC) and oxidative stress stimuli in differentiated cultures of human trabecular meshwork (HTM) cells have provided the rationale for our studies of a major new gene termed TIGR (trabecular meshwork inducible GC response). The TIGR clone was isolated by differential library screening using selection criteria based on the induction pattern of a new protein/glycoprotein found in HTM cultures after prolonged but not brief exposure to GCs. This GC induction patter matched the time course and dose response required for intraocular pressure elevation in patients receiving corticosteroids. The very large, progressive induction of TIGR combined with specific structural features of its cDNA suggested that TIGR should be considered a candidate gene for outflow obstruction in glaucoma. Among the properties of TIGR cDNA were a signal sequence for secretion, several structural features for interactions with glycosaminoglycans and other glycoproteins and putative sites for cell surface interactions. In addition, the leucine zippers in the structure were related to TIGR-TIGR oligomerization that was shown to occur with native and recombinant TIGR protein. The verification that TIGR was a major stress response protein in HTM cells following hydrogen peroxide (or phorbol esters) exposure provided a potential link between GC and oxidative mechanisms thought to be involved in glaucoma pathogenesis. Pharmacological evaluation showed that basic fíbroblast growth factory and transforming growth factor β decreased the GC induction of TIGR, and certain nonsteroidal anti-inflammatory drugs protected against both GC- and oxidation-induced stress responses in HTM cells. Our recent studies of TIGR’s genomic structure have shown motifs in the promoter region that suggest a basis by which multiple hormonal/environmental stimuli can regulate TIGR production and by which putative genetic alterations could lead to an overexpression of the protein. Further application of cell biology/biochemistry, molecular biology, genetic and histological approaches will be helpful in understanding the role of TIGR in different glaucoma syndromes.

Gene Structure and Properties of TIGR, an Olfactomedin-related Glycoprotein Cloned from Glucocorticoid-induced Trabecular Meshwork Cells

“…The 66-kDa form of TIGR might be retained in the meshwork due to predicted interactions with other extracellular matrix molecules. An in vivo role for TIGR (and its potential effect in obstructing outflow) is reinforced by recent findings of increased TIGR gene products in DEX-treated organ culture and glaucoma eyes (43). DISCUSSION In this paper, we have shown that the induction of the TIGR gene expression in TM cells by prolonged DEX treatment results in high levels of new extracellular proteins.…”

“…It also has a consensus HA binding sequence Arg-Arg-Gly-Gln-Cys-Pro-Ser-Thre-Arg (at aa 181-189) that resembles the consensus motif B(X 7 )B, in which B is a basic aa and X is any aa (25). The cDNA also contains the GAG initiation sites Asp-Gln-Ser-Gly (at aa [42][43][44][45] and Ser-Gly-Glu-Gly (at aa 238 -241) sequences that match consensus motifs Asp-Xss-Ser-Gly and Ser-Gly-Xaa-Gly described for proteoglycans (26,27). Other important features of the molecule include clusters of two and seven leucine zippers and an olfactomedin homology domain of 178 aa at the carboxyl terminus that is considered in greater detail later.…”

Regulation of human myocilin/TIGR gene transcription in trabecular meshwork cells and astrocytes: role of upstream stimulatory factor

“…MYOC/TIGR was originally isolated from cultured human TM cells expressing this protein in high amounts following long-term treatment with dexamethasone and, independently, from normal human retina (Fauss et al 1993;Nguyen et al 1993;Kubota et al 1997;Polansky et al 1997). In addition to TM and retina, MYOC/TIGR is expressed in other ocular tissues such as the cornea, sclera, ciliary body, iris and optic nerve head (Adam et al 1997;Ortego et al 1997;Tomarev et al 1998;Karali et al 2000).…”

Toward a Functional Annotation of the Human Genome Using Artificial Transcription Factors

“…Another group consists of annexin A3, se20-4 tumor antigen, and myocilin (Table 1). Annexin is an inhibitor of phospholipase A2 (PLA-2) (Oh et al 2000); se20-4 tumor antigen is the nucleolar TGF-␤1 target protein (Ozbun et al 2001); and myocilin is a trabecular meshwork-inducible glucocorticoid response protein (Polansky et al 1997). As TGF-␤1 and glucocorticoid attenuate IL1-␤-induced PLA2 elevation (Muhl et al 1992), these three genes might be common downstream targets of TGF-␤ or glucocorticoid signaling.…”