The High‐Affinity Immunoglobulin‐E Receptor (FceRI) is Endocytosed by an AP‐2/Clathrin‐Independent, Dynamin‐Dependent Mechanism

G Fattakhova, M Masilamani, F Borrego, AM Gilfillan… - Traffic, 2006 - Wiley Online Library
G Fattakhova, M Masilamani, F Borrego, AM Gilfillan, DD Metcalfe, JE Coligan
Traffic, 2006Wiley Online Library
Aggregation of the high‐affinity immunoglobulin E (IgE) receptor (FcɛRI), expressed on
mast cells and basophils, initiates the immediate hypersensitivity reaction. Aggregated
FcɛRI has been reported to rapidly migrate to lipid rafts in RBL‐2H3 cells. We confirmed that
aggregated FcɛRI is found in the lipid raft fractions of cellular lysates. Furthermore, we show
that the cross‐linked FcɛRI remains associated with detergent‐resistant structures upon
internalization. Previous morphological studies have reported that aggregated FcɛRI is …
Aggregation of the high‐affinity immunoglobulin E (IgE) receptor (FcɛRI), expressed on mast cells and basophils, initiates the immediate hypersensitivity reaction. Aggregated FcɛRI has been reported to rapidly migrate to lipid rafts in RBL‐2H3 cells. We confirmed that aggregated FcɛRI is found in the lipid raft fractions of cellular lysates. Furthermore, we show that the cross‐linked FcɛRI remains associated with detergent‐resistant structures upon internalization. Previous morphological studies have reported that aggregated FcɛRI is endocytosed via clathrin‐coated pits, which in general are not lipid raft associated. To address this apparent discrepancy, we employed siRNA to suppress expression of components of the clathrin‐mediated internalization machinery, namely, clathrin heavy chain, and the AP‐2 (α‐adaptin or µ2‐subunit). Transferrin receptor (TfR) is endocytosed by a clathrin‐mediated process and, as expected, each transfected siRNA caused a two to threefold elevation of TfR surface expression and almost completely inhibited its endocytosis. In contrast, there was no effect on surface expression levels of FcɛRI nor on the endocytosis of the dinitrophenyl‐human serum albumin (DNP‐HSA)/IgE/FcɛRI complex. On the contrary, internalization of DNP‐HSA/IgE/FcɛRI was inhibited by overexpression of a dominant‐negative dynamin mutant. We conclude that internalization of cross‐linked FcɛRI does not require the AP‐2/clathrin complex but is dynamin‐dependent and may be lipid raft mediated.
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