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S. Diskin, N. Panjwani; Galectin-8 Promotes Cytoskeletal Rearrangement in Trabecular Meshwork Cells Through Activation of Rho Signaling. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2067.
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Cell-matrix interactions and the dynamics of cytoskeletal structure play a pivotal role in the normal function of the trabecular meshwork (TM) and in the maintenance of aqueous outflow facility. Recently, a carbohydrate-binding protein, galectin-8 (Gal-8), was shown to play a vital role in cell adhesion and cytoskeletal arrangement in nonocular cells. Here we demonstrate that Gal-8 promotes cell adhesion and Rho signaling in TM cells.
RT-PCR, Western blot and immunohistochemical analyses were used to assess Gal-8 expression in TM cell cultures and tissue. Countereceptors for Gal-8 were isolated by affinity chromatography of TM cell lysates on a GST-Gal-8-conjugated Sepharose column, and were identified by MALDI-TOF. To study the role of Gal-8 in cell adhesion, the wells of cell culture plates were coated with Gal-8 and TM cells were added to each well. After 4 hr incubation, the cells were fixed and stained with either GIEMSA or phalloidin. Cell spreading assays on Gal-8 coated wells were performed in the presence and absence of a Rho-kinase inhibitor, Y27632.
The results indicated that Gal-8 is expressed in TM cell cultures as well as in TM tissue. Integrins ß1,α3,α5 and αv were identified as major countereceptors of Gal-8 in TM cells. A competing sugar, ß-lactose, but not a non-competing sugar, sucrose, abolished the binding of Gal-8 to the integrins. This indicated that Gal-8 interacts with its integrin counterreceptors via a carbohydrate-based recognition. Interestingly, TM cells adhered to and spread on Gal-8 coated wells but not on Gal-1 or Gal-3 coated wells. Again, the adhesion of TM cells to Gal-8 coated wells was abolished by ß-lactose but not sucrose. An anti-ß1 integrin antibody inhibited the adhesion of TM cells to Gal-8 coated wells. Cell spreading on Gal-8 was associated with: (i) formation of stress fibers that was inhibited by the Rho-kinase inhibitor, Y27632, and (ii) accumulation of phosphorylated myosin light chain.
Gal-8 may play a role in the regulation of aqueous outflow facility by influencing TM cell adhesion and the Rho signaling pathway.
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