FILENSIN IS PROTEOLYTICALLY PROCESSED DURING LENS FIBER CELL-DIFFERENTIATION BY MULTIPLE INDEPENDENT PATHWAYS

Filensin is a lens-specific intermediate filament protein, expressed i n the lens fiber cells but not the lens epithelium. Using antibodies t o filensin and the other lens intermediate filament proteins, vimentin and CP49, the codistribution of filensin with CP49 and independence o f this network from the vimentin network was confirmed. Monoclonal and polyclonal antibodies to peptides and specific subdomains of filensin were used to follow changes in tbe subcellular distribution of filens in during bovine lens fiber cell differentiation. Filensin is shown to be extensively processed during lens fiber cell differentiation to gi ve protein fragments derived from distinct protein domains, one corres ponding to the N-terminal non-alpha-helical/and rod domain and the oth er to the C-terminal non-alpha-helical tail domain. Immunoblotting ana lysis using anti-filensin peptide polyclonal antibodies suggested that the two fragment sets arose separately. Residues 331 to 430 in filens in have been identified as an important region in the processing pathw ay(s). Our results clarify previous confusion in the literature regard ing the processing of filensin which arose because of the similar rela tive electrophoretic mobilities by sodium dodecyl sulfate polyacrylami de gel electrophoresis (SDS-PAGE) of the different fragment sets. The predicted secondary structure characteristics of the different domains of filensin suggests different functions for the two fragment sets to give filensin a dual role in the lens. This suggestion is supported b y the subtly different subcellular distributions in the peripheral and mature fiber cells of the two filensin fragment sets.