Myocilin from COS-1 cells binds specifically to NIH3T3 cells

Myocilin gene is directly linked to the most common form of glaucoma. The gene product is secreted into aqueous humor and is thought to be involved in the regulation of intraocular pressure. Most of the mutant myocilin proteins accumulate in cultured cells and are not secreted. In this study, through staining experiments of various cell lines, we demonstrated that secreted myocilin could bind to a particular cell surface to exert its function. Myocilin secreted by COS-1 cells was able to bind specifically to the surface of NIH3T3 cells. The binding of myocilin was dependent on the cell density. These results suggest that myocilin recognizes a specific cell and exerts its effect upon binding to the cell surface. Introduction Glaucoma is a progressive blinding disease that is characterized by the gradual loss of vision due to optic neuropathy and retinal ganglion cell death, and is the second largest cause of bilateral blindness in the world. It is speculated that there are an estimated 70 million glaucoma patients worldwide and thus, it is one of the most prevalent vision disorders that require immediate attention (Quigley, 1996). The relationship of the mechanism of onset with various factors, such as a mutation in the gene and the environment, has been extensively examined. However, little is known about the underlying pathological mechanism. Myocilin was originally identified as trabecular meshwork inducible glucocorticoid response gene (TIGR) (Polansky et al., 1997). Mutations in the myocilin gene were found in 3-4% of patients with primary open angle glaucoma (POAG), the most common form of glaucoma (Stone et al., 1997), and in a subset of families with autosomal dominant juvenile-onset open angle glaucoma (OAG) and adult-onset OAG (Fingert et al., 1999, 2002). It has been shown that the myocilin knockout mouse and the transgenic mouse expressing a high level of wild-type myocilin in the angle tissue do not exhibit the glaucoma phenotype (Kim et al., 2001; Gould et al., 2004). Therefore, it is surmised that the change in myocilin expression level is not responsible for the onset of glaucoma. Senatorov et al. (2006) reported that the OAG-like phenotype was induced in mouse expressing a specific mutant myocilin. The above findings support the idea that specific mutant myocilins are responsible for the onset of various glaucoma. Myocilin is ubiquitously distributed in various locations, including non-ocular tissues and organs, and strongly expressed in various components of the eye, namely, aqueous humor, sclera, iris, cornea, lens, ciliary body, optic nerve, retina, and trabecular meshwork (Kubota et al., 1997; Polansky et al., 1997; Nguyen et al., 1998; Karali et al., 2000; Noda et al., 2000; Rao et al., 2000; Clark et al., 2001; Fautsch and Johnson, 2001; Ricard et al., 2001; Russell et al., 2001; Tamm, 2002). Myocilin is a glycoprotein composed of 504 amino acids and has a molecular Myocilin from COS-1 cells binds specifically to NIH3T3 cells