Lafont F, Simons K
Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 110, D-01307 Dresden, Germany.
Proc Natl Acad Sci U S A. 2001 Mar 13;98(6):3180-4. doi: 10.1073/pnas.051003498.
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.
肥大细胞和嗜碱性粒细胞上的IgE高亲和力受体FcepsilonRI在免疫防御中起重要作用。多价抗原结合后，由于受体在脂筏中聚集，FcepsilonRI被蛋白酪氨酸激酶Lyn磷酸化。FcepsilonRI已被证明会发生泛素化。泛素化可导致蛋白酶体降解，但它也可作为一种分选信号，使注定进入内体/溶酶体途径的蛋白质内化。我们分析了FcepsilonRI泛素化是否在脂筏内发生。我们报告了大鼠嗜碱性白血病细胞中的生化和成像证据，表明受体激活后聚集的脂筏中存在泛素化的FcepsilonRI。此外，我们证明泛素连接酶Cbl和Nedd4与FcepsilonRI斑块共定位，并表明在IgE信号激活后，这两种连接酶都与脂筏相关。由于已知Cbl与FcepsilonRI信号复合物相互作用，泛素化可能是调节脂筏中IgE触发信号的一个重要参数。
