Periplakin Interactions with Lens Intermediate and Beaded Filaments

PURPOSE. The lens assembles two systems of intermediated filaments-vimentin intermediate filament IF) and highly divergent, lens-specific beaded filament (BF)-sequentially as epithelial cells differentiate into fiber cells. The goal of this study was to identify linker proteins that integrate the different lens IF into the biology of the lens fiber cells. METHODS. Antibodies to periplakin were used in coimmunoprecipitation studies to identify proteins that complex with BF and IF in detergent extracts of mouse lens. GST-periplakin fusion proteins were used to confirm coimmunoprecipitation results. Yeast two-hybrid analysis was used to establish direct linkage between periplakin and BF/IF proteins and to narrow down binding domains. Immunocytochemistry was used to establish spatial and temporal coexpression of periplakin and BF/IF. RESULTS. Periplakin is found complexed to BF and IF in the lens. The COOH terminus of periplakin was shown to have a strong affinity for the CP49 rod 2 domain but not its head or rod 1 domains. Low-level affinity was seen between the filensin rod domain and periplakin. Periplakin localization in lens overlapped with BF and IF. CONCLUSIONS. Despite divergence in primary sequence, predicted secondary structure, and filament structure, CP49 has conserved the capacity to bind a common IF linker protein, periplakin, and shares that binding capacity with the other major lens IF protein, vimentin. This suggests that mutations in periplakin have the potential to emulate the cataract seen in lenses with defective BF proteins. (Invest Ophthalmol Vis Sci. 2009; 50: 1283-1289) DOI:10.1167/iovs.08-2894