SUBCELLULAR REDISTRIBUTION OF COMPONENTS OF THE UBIQUITIN-PROTEASOME PATHWAY DURING LENS DIFFERENTIATION AND MATURATION

Authors: GIRAO, HENRIQUE - UNIVERSITY OF COIMBRA; PEREIRA, PAULO - UNIVERSITY OF COIMBRA; TAYLOR, ALLEN - TUFTS-HNRCA; SHANG, FU - TUFTS-HNRCA

Submitted to: Investigative Ophthalmology and Visual Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2004
Publication Date: 3/24/2005
Citation: Girao, H., Pereira, P., Taylor, A., Shang, F. 2005. Subcellular redistribution of components of the ubiquitin-proteasome pathway during lens differentiation and maturation. Investigative Ophthalmology and Visual Science. 46(4):1386-1392.

Interpretive Summary: Frozen sections of different regions of an adult cow lens were stained and analyzed using a fine laser beam to identify the presence and distribution of antigens beneath the cellular level. Western blotting was used to determine specificities of the antibodies used in this study. Ubiquitin is a polypeptide that latches onto cellular protein immediately before it is broken down. The analyzed sections of the adult cow lenses showed that ubiquitinn-activating enzyme (E1) and a ubiquitin-conjugating enzyme (Ubc1) were present both outside and inside the nucleus of the epithelial cells. While Ubc3 and ubiquitin conjugates were mostly confined to the nucleus and Ubc4/5 was localized in clusters in the vicinity of the nuclear membrane, 19S and 20S proteasome complexes were found in the area outside the nucleus. When the epithelial cells separated into fiber cells at the transition zone, all components of the ubiquitin-proteasome pathway, an intracellular protein degrading system, were primarily present in the nucleus, with the exception of Ubc4. The results show that during lens fiber separation and growth, the components of the ubiquitin-proteasome pathway are redistributed at subcellular levels. The changes in localization beneath the cellular level of these components, suggests that the ubiquitin-proteasome pathway may have distinct functions during different stages of lens fiber separation.

Technical Abstract: In order to evaluate the subcellular distribution of components of the ubiquitin-proteasome pathway in different regions of bovine lens, adult bovine lens cryosections were stained for immunofluorescence and analyzed by confocal microscopy. The specificities of the antibodies used in this study were determined by western blotting. Cryosections of bovine lenses show that E1 and Ubc1 were present in both the cytoplasm and the nucleus in epithelial cells, while Ubc3 and ubiquitin conjugates were mostly confined to the nucleus and Ubc4/5 was preferentially localized in clusters in the vicinity of the nuclear membrane. The 19S and 20S proteasome complexes were preferentially localized in the cytoplasm, particularly in the perinuclear region. When the epithelial cells differentiate into fiber cells at the transition zone, all components of UPP were primarily present in the nucleus, with the exception of Ubc4, which was associated with the nuclear membrane. The results show that during lens fiber differentiation and maturation, the components of the ubiquitin-proteasome pathway are redistributed at subcellular levels. The alterations in subcellular localization of these components suggest that the ubiquitin-proteasome pathway may have different functions during different stages of lens fiber differentiation.