Raft-partitioning of the ubiquitin ligases Cbl and Nedd4 upon IgE-triggered cell signaling.
The high affinity receptor for IgE, FcepsilonRI on mast cells and basophils plays an essential role in immunological defense. Upon multivalent antigen binding, FcepsilonRI becomes phoshorylated by the protein-tyrosine kinase Lyn, as a result of receptor clustering in lipid rafts. FcepsilonRI has been shown to be ubiquitinated. Ubiquitination can lead to degradation by proteasomes, but it can also act as a sorting signal to internalize proteins destined to the endosomal/lysosomal pathway. We have analyzed whether FcepsilonRI ubiquitination takes place within rafts. We report biochemical and imaging evidence in rat basoleukemia cells for the presence of ubiquitinated FcepsilonRI in clustered rafts upon receptor activation. Moreover, we demonstrated that the ubiquitin ligases Cbl and Nedd4 colocalize with FcepsilonRI patches and showed that both ligases become associated with lipid rafts after activation of IgE signaling. Because Cbl is known to interact with the FcepsilonRI signaling complex, ubiquitination is likely to be an important parameter regulating IgE-triggered signaling occurring in rafts.
Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 110, D-01307 Dresden, Germany. Frank.Lafont@biochem.unige.ch
F
F
Lafont
K
K
Simons
D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D056827:Endosomal Sorting Complexes Required for Transport; D007073:Immunoglobulin E / Q000378:metabolism / Q000494:pharmacology; D008025:Ligases / Q000235:genetics / Q000378:metabolism*; D021962:Membrane Microdomains / Q000378:metabolism*; D000075702:Nedd4 Ubiquitin Protein Ligases; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D050721:Proto-Oncogene Proteins c-cbl; D051381:Rats; D017455:Receptors, IgE / Q000378:metabolism*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases
D002135:Calcium-Binding Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D011518:Proto-Oncogene Proteins; D017455:Receptors, IgE; D025801:Ubiquitin; D007073:Immunoglobulin E; C000618479:NEDD4L protein, rat; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618484:Nedd4 protein, rat; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D008025:Ligases