Abstract
Abstract: :
Purpose: To investigate the role of the ubiquitin–proteasome pathway in controlling lens cell proliferation and differentiation. Methods: bFGF–induced lens cell proliferation and differentiation was monitored in rat lens epithelial explants by BrdU incorporation, expression of crystallins and other differentiation markers. Lactacystin was used as a proteasome–specific inhibitor to study the role of proteasome in controlling the proliferation and differentiation process. Results: Explants treated with bFGF initially underwent enhanced proliferation as indicated by BrdU incorporation and multilayering of the epithelial cells, and then withdrawal from cell cycle as indicated by diminished BrdU incorporation. After 7 days treatment with bFGF, Lens epithelial explants displayed characteristics of lens fibers, including expression of large quantities of crystallins, MIP26, CP49 and filensin. Addition of the lactacystin to the medium at the same time as bFGF (Day 0) prohibited or delayed bFGF–induced cell proliferation and differentiation as indicated by reduced BrdU incorporation, decreased expression of beta– and gamma–crystallins, MIP26, CP49 and filensin. If lactacystin was added to the medium at day 4 of bFGF treatment, when the cells stopped proliferation, it still decreased the production of beta–crystallins and CP49. Conclusions: The data show that the ubiquitin–proteasome pathway is required for lens cell proliferation and differentiation. It appears that the ubiquitin–proteasome pathway is not only required at the proliferative stages of the differentiation process, it is also required for the expression of fiber–specific proteins. Disruption of the function of this proteolytic pathway may cause abnormal lens development, such as delayed differentiation and maturation of lens fibers.
Keywords: proliferation • proteolysis • cataract