DETERGENT-RESISTANT MEMBRANE MICRODOMAINS FROM CACO-2 CELLS DO NOT CONTAIN CAVEOLIN

In this study we analyzed the relationship between detergent-resistant microdomains and caveolae in Caco-2 cells. Caveolin was not detected on Western blots or Northern blots or by immunoprecipitation in these cells, in contrast to A 431 cells. Triton X-100-resistant membranes fr om Caco-2 and A 431 cells showed the same morphological aspect by elec tron microscopy and peaked at the same isopycnic density on sucrose gr adients. Detergent-resistant microdomains from Caco-2 cells were enric hed in glycosyl phosphatidylinositol (GPI)-anchored proteins, in sucra se-isomaltase, an apical marker, and in most of the proteins found in caveolin-rich membranes such as src-like proteins, fimbrin, ezrin, and G(i) alpha. Caveolae-like structures were present in A 431 but absent from Caco-2 cells at the electron microscopic level. Detergent-resist ant microdomains from Caco-2 cells resemble caveolin-rich microdomains in their molecular composition but do not seem to derive from morphol ogically identified caveolae. Our results also indicate that caveolin is not necessary for sorting of GPI-Linked proteins to the apical memb rane of Caco-2 cells.