Membrane rafts are small plasma membrane domains that contain high levels of cholesterol and sphingolipids. They have been implicated in processes as diverse as signal transduction, endocytosis and cholesterol trafficking. Traditional methods for the biochemical preparation of lipid rafts involve the extraction of membranes with nonionic detergents followed by the separation of a low-density, detergent-resistant membrane fraction on density gradients. Because of concerns regarding the possible introduction of artifacts through the use of detergents, several methods were developed for the isolation of lipid rafts that do not involve detergent extraction. / In this study, we compared three different biochemical methodologies of membrane rafts preparation from purified rat liver PM. Only detergent-resistant membranes (DRMs) fulfill the requirements of membrane rafts. We subsequently found using the low dose of EGF (1 ug/100 g BW); the content of EGFR in PM-DRMs did not changed significantly following EGF administration. When a higher dose of EGF (5 ug/100 g BW) is administrated we observed a rapid and almost complete disappearance of EGFR (around 80%) from both PM and DRMs fractions. Interestingly, following the administration of a low or high dose of EGF, the pool of EGFR in the PM-DRMs fraction becomes highly Tyr-phosphorylated. In accordance with the higher level of EGFR Tyr-Phosphorylation, EGF induced an augmented recruitment of Grb2 and Shc proteins to PM-DRMs compared with whole PM. / Furthermore neither high nor low dose of EGF affects the caveolin content in DRMs and PM. These observations suggest that EGFR located in DRM are competent for signaling and non-caveolae PM rafts are involved in the compartmentalization and presumably internalization of the EGFR.

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