CELLULAR PHARMACOLOGY AND MOLECULAR-BIOLOGY OF THE TRABECULAR MESHWORK INDUCIBLE GLUCOCORTICOID RESPONSE GENE-PRODUCT

Studies of the effects of glucocorticoid (GC) and oxidative stress sti muli in differentiated cultures of human trabecular meshwork (HTM) cel ls have provided the rationale for our studies of a major new gene ter med TIGR (trabecular meshwork inducible GC response). The TIGR clone w as 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 i nduction 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 consider ed a candidate gene for outflow obstruction in glaucoma. Among the pro perties of TIGR cDNA were a signal sequence for secretion. several str uctural features for interactions with glycosaminoglycans and other gl ycoproteins and putative sites for cell surface interactions. In addit ion, the leucine zippers in the structure were related to TIGR-TIGR ol igomerization that was shown to occur with native and recombinant TIGR protein. The verification that TIGR was a major stress response prote in in HTM cells following hydrogen peroxide (or phorbol esters) exposu re provided a potential link between GC and oxidative mechanisms thoug ht to be involved in glaucoma pathogenesis. Pharmacological evaluation showed that basic fibroblast growth factory and transforming growth f actor beta decreased the GC induction of TIGR, and certain nonsteroida l anti-inflammatory drugs protected against both GC- and oxidation-ind uced stress responses in HTM cells. Our recent studies of TIGR's genom ic structure have shown motifs in the promoter region that suggest a b asis by which multiple hormonal:environmental stimuli call regulate TI GR 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 w ill be helpful in understanding the role of TIGR in different glaucoma syndromes.