Butyrate enhances the synthesis of interphotoreceptor retinoid-binding protein (IRBP) by Y-79 human retinoblastoma cells.

The synthesis and secretion of interphotoreceptor retinoid-binding protein (IRBP) from Y-79 human retinoblastoma cells was investigated using immunocytochemistry and SDS-polyacrylamide gel electrophoresis. Indirect immunofluorescence of cells growing in monolayer culture for 11 and 13 days showed no significant IRBP staining although by SDS-polyacrylamide gel electrophoresis, a small amount of IRBP was detected in the culture medium, suggesting synthesis and extracellular secretion. Butyrate (2mM) treatment of cells starting on the eighth day of culture resulted in a dramatic increase of IRBP fluorescence 3-5 days after treatment. Treatment of cells in all conditions with 1 microM monensin for 3 h showed concentration of IRBP in the Golgi apparatus of about 10-20% of cells as proved by a double immunofluorescent technique, employing anti-IRBP antibody and wheat-germ agglutinin. Incubation of cells with either radiolabeled amino acids or glucosamine followed by analysis of cell cytosol and culture medium by SDS-polyacrylamide gel electrophoresis also confirmed that 1) IRBP is synthesized by the Y-79 cells and secreted into the medium and 2) its production is markedly increased by butyrate treatment. The enhancement of IRBP synthesis by butyrate suggests biochemical differentiation of Y-79 cells possibly into photoreceptor-like cells and offers a new system for studying the properties of this unique retinoid-binding protein and of factors that control its synthesis and secretion.