PrPC Undergoes Basal to Apical Transcytosis in Polarized Epithelial MDCK Cells

The Prion Protein (PrP) is an ubiquitously expressed glycosylated membrane protein attached to the external leaflet of the plasma membrane via a glycosylphosphatidylinositol anchor (GPI). While the misfolded PrPSc scrapie isoform is the infectious agent of prion disease, the cellular isoform (PrPC) is an enigmatic protein with unclear function. Of interest, PrP localization in polarized MDCK cells is controversial and its mechanism of trafficking is not clear. Here we investigated PrP traffic in MDCK cells polarized on filters and in three-dimensional MDCK cysts, a more physiological model of polarized epithelia. We found that, unlike other GPI-anchored proteins (GPI-APs), PrP undergoes basolateral-to-apical transcytosis in fully polarized MDCK cells. Following this event full-length PrP and its cleavage fragments are segregated in different domains of the plasma membrane in polarized cells in both 2D and 3D cultures.朊蛋白（Prion Protein，PrP）是一种普遍表达的糖基化膜蛋白，通过糖基磷脂酰肌醇锚定（glycosylphosphatidylinositol anchor，GPI）结合于质膜外小叶。错误折叠的PrPSc瘙痒病亚型是朊病毒病的感染因子，而细胞型朊蛋白（PrPC）则是一种功能尚不明确的神秘蛋白。值得关注的是，PrP在极化MDCK细胞中的定位存在争议，其运输机制也尚未阐明。本研究针对在滤膜上培养的极化MDCK细胞以及更具生理代表性的极化上皮三维MDCK细胞囊泡模型中的PrP运输过程进行了探究。研究发现，与其他糖基磷脂酰肌醇锚定蛋白（GPI-anchored proteins，GPI-APs）不同，PrP在完全极化的MDCK细胞中会发生基侧膜到顶膜的转胞吞作用。该过程完成后，全长PrP及其裂解片段会在二维及三维培养的极化细胞中，被分隔至质膜的不同结构域。