Screening and modulation of extracellular signals by mucous barrier. Serum glycosylphosphatidylinositol phospholipase D (GPI-PLD) releases protective mucous barrier from oral mucosa.

BACKGROUND: Performance of mucosal epithelial barrier is modified by numerous agents that exert effects on mucin- Mucin Binding Protein (MBP) complex. The aim ofthe studies described was to determine the nature of the damage or modification of oral mucous barrier by the short-term exposure to ethanol.
METHODS: Culture of rat buccal mucosa in the presence of ethanol and [3H]-labeled proline and palmitate revealed substantial decrease in MBP synthesis and the release of MBPto the medium. The radioscanning of the samples prepared from the culture medium and the apical epithelial membranes subjected to SDS-PAGE and western blotting disclosed that the released, water soluble 97kDa MBP glycopeptide was labeled with proline and palmitate. When the experiments were conducted in the presence of 5mM EDTA, the GPI-PLD inhibitor, the majority of radiolabeled MBP remained in the membrane-bound form and was extractable with Triton X- 114. The results on the purified GPI-linked MBP degradation by serum enzyme, by the saliva containing serum transudate, and the suppression of the process by inclusion of GPI-PLD-specific inhibitor support our contention that membrane MBP is released to medium by GPI-PLD-like activity.
RESULTS: The release of MBP from apical epithelial surfaces was induced by depletion of mucin and the presence of serum-derived GPI-PLD in the tissue homogenate. Strong likelihood exists that under in situ conditions ethanol-induced transudation of serum to saliva provides the vehicle for the transfer of GPI-PLD activity to salivary contents. Defacement of the oral surfaces from mucous barrier signals prospect of lumenal agent influence on the unprotected epithelial exterior, and allows ingression of microbes and untoward acting substances into the organism.