Kimura T, Sakamoto H, Appella E, Siraganian R P
Laboratory of Immunology, NIDR, NCI, National Institutes of Health, Bethesda, Maryland 20892-1188, USA.
J Biol Chem. 1997 May 23;272(21):13991-6. doi: 10.1074/jbc.272.21.13991.
The SH2 domain-containing inositol-polyphosphate 5-phosphatase, SHIP, associates with FcgammaRIIB and negatively regulates both B-cell and mast cell function. We report here that SHIP was tyrosine-phosphorylated after high affinity IgE receptor (FcepsilonRI) aggregation in rat basophilic leukemia RBL-2H3 cells. The tyrosine phosphorylation of SHIP was an early event after receptor aggregation and was present in cells deficient in the protein-tyrosine kinase Syk. Furthermore it was not secondary to the increase of intracellular calcium or the activation of protein kinase C. SHIP was precipitated by immobilized phosphorylated synthetic peptides based on the immunoreceptor tyrosine-based activation motif (ITAM) of the beta but not the gamma subunit of the high affinity IgE receptor. Tyrosine phosphorylation of SHIP and its association with the tyrosine-phosphorylated beta subunit of FcepsilonRI could play an important role in down-regulating receptor-mediated signal transduction in mast cells. Thus, whereas the activation molecule Syk associates with the gamma subunit ITAM, the beta subunit ITAM binds the negative signaling molecule SHIP. Therefore, unlike B cells where the antigen receptor and coreceptors such as FcgammaRIIB or CD22 each recruits molecules with opposite effects, the FcepsilonRI contains subunits which recruit molecules that activate and inhibit signal transduction.
含SH2结构域的肌醇多磷酸5-磷酸酶SHIP与FcγRIIB结合，并对B细胞和肥大细胞功能起负调节作用。我们在此报告，在大鼠嗜碱性白血病RBL-2H3细胞中，高亲和力IgE受体（FcepsilonRI）聚集后SHIP发生酪氨酸磷酸化。SHIP的酪氨酸磷酸化是受体聚集后的早期事件，在缺乏蛋白酪氨酸激酶Syk的细胞中也存在。此外，它并非细胞内钙增加或蛋白激酶C激活的继发结果。基于高亲和力IgE受体β亚基而非γ亚基的免疫受体酪氨酸激活基序（ITAM）的固定化磷酸化合成肽可沉淀SHIP。SHIP的酪氨酸磷酸化及其与FcepsilonRI酪氨酸磷酸化β亚基的结合可能在下调肥大细胞中受体介导的信号转导中起重要作用。因此，激活分子Syk与γ亚基ITAM结合，而β亚基ITAM结合负信号分子SHIP。所以，与抗原受体和共受体（如FcγRIIB或CD22）各自招募具有相反作用分子的B细胞不同，FcepsilonRI包含招募激活和抑制信号转导分子的亚基。
