Signal transducing molecules and glycosyl-phosphatidylinositol-linked proteins form a caveolin-rich insoluble complex in MDCK cells

阅读量：

作者：

M Sargiacomo，M Sudol，ZhaoLan Tang and Michael P. Lisanti

展开

摘要：

GPI-linked protein molecules become Triton-insoluble during polarized sorting to the apical cell surface of epithelial cells. These insoluble complexes, enriched in cholesterol, glycolipids, and GPI-linked proteins, have been isolated by flotation on sucrose density gradients and are thought to contain the putative GPI-sorting machinery. As the cellular origin and molecular protein components of this complex remain unknown, we have begun to characterize these low-density insoluble complexes isolated from MDCK cells. We find that these complexes, which represent 0.4-0.8% of the plasma membrane, ultrastructurally resemble caveolae and are over 150-fold enriched in a model GPI-anchored protein and caveolin, a caveolar marker protein. However, they exclude many other plasma membrane associated molecules and organellespecific marker enzymes, suggesting that they represent microdomains of the plasma membrane. In addition to caveolin, these insoluble complexes contain a subset of hydrophobic plasma membrane proteins and cytoplasmically-oriented signaling molecules, including: (a) GTP-binding proteins--both small and heterotrimeric; (b) annexin II--an apical calcium-regulated phospholipid binding protein with a demonstrated role in exocytic fusion events; (c) c-Yes--an apically localized member of the Src family of non-receptor type protein-tyrosine kinases; and (d) an unidentified serine-kinase activity. As we demonstrate that caveolin is both a transmembrane molecule and a major phospho-acceptor component of these complexes, we propose that caveolin could function as a transmembrane adaptor molecule that couples luminal GPI-linked proteins with cytoplasmically oriented signaling molecules during GPI-membrane trafficking or GPI-mediated signal transduction events. In addition, our results have implications for understanding v-Src transformation and the actions of cholera and pertussis toxins on hetero-trimeric G proteins.

展开

关键词：

Animals Dogs Rats Fibroblasts Cell Line Cell Membrane GTP-Binding Proteins src-Family Kinases Glycosylphosphatidylinositols Membrane Glycoproteins