Fas Ligand Expression in the Organ of Corti

We have previously demonstrated by FACS analysis and histochemistry that Fas ligand (FasL) increases on cochlear cell surfaces after immune response or stimulation with γ-interferon (IFN-γ). To determine whether the appearance of FasL on cochlear cell membranes is related to gene expression or to posttranslational events, cochlear cells were treated with IFN-γ. They were evaluated for FasL gene expression by real-time PCR and for FasL protein localization by confocal microscopy of permeabilized and immunolabeled cells. Real-time PCR analysis of cDNAs generated from unstimulated or IFN-γ-stimulated organ of Corti demonstrated no change in the transcription of the gene encoding FasL. In contrast, confocal microscopy revealed dramatic changes in the cellular distribution of FasL, consistent with movement from the endoplasmic reticulum to the cytoplasm and cell membrane. The results suggest that recruitment of preformed FasL from intracellular compartments, rather than its biosynthesis, is responsible for the increase in FasL on the cell surface following IFN-γ stimulation. This is similar to the response of cytotoxic T lymphocytes in which gene expression is not involved in FasL surface appearance. Presumably, the use of preformed FasL increases the rapidity of this response. FasL localization to the membrane may be involved in protecting the inner ear from autoimmunity or inflammation. Alternatively it may be related to cochlear cell death in response to inflammatory stress.