Huber M, Helgason C D, Damen J E, Liu L, Humphries R K, Krystal G
Terry Fox Laboratory, British Columbia Cancer Agency, Vancouver, BC, Canada V5Z 1L3.
Proc Natl Acad Sci U S A. 1998 Sep 15;95(19):11330-5. doi: 10.1073/pnas.95.19.11330.
To clarify the role that the src homology 2-containing inositol phosphatase (SHIP) plays in mast cell degranulation, the gene for SHIP was disrupted by homologous recombination in embryonic stem cells. Bone-marrow-derived mast cells from SHIP+/+, +/-, and -/- F2 littermates were compared. SHIP-/- mast cells were found to be far more prone to degranulation, after the crosslinking of IgE preloaded cells, than SHIP+/- or +/+ cells. Intriguingly, IgE alone also stimulated massive degranulation in SHIP-/- but not in +/+ mast cells. This degranulation with IgE alone, which may be due to low levels of IgE aggregates, correlated with a higher and more sustained intracellular calcium level than that observed with SHIP+/+ cells and was dependent upon the entry of extracellular calcium. Immunoprecipitation studies revealed that the addition of IgE alone to normal mast cells stimulates multiple cascades, which are prevented from progressing to degranulation by SHIP. PI 3-kinase inhibitor studies suggested that IgE-induced activation of PI 3-kinase is upstream of the entry of extracellular calcium and that SHIP restricts this entry by hydrolyzing phosphatidylinositol 3,4, 5-trisphosphate. These results show the critical role that SHIP plays in setting the threshold for degranulation and that SHIP directly modulates a "positive-acting" receptor.
为阐明含src同源2结构域的肌醇磷酸酶（SHIP）在肥大细胞脱颗粒中所起的作用，通过胚胎干细胞中的同源重组破坏了SHIP基因。对SHIP+/+、+/-和-/- F2同窝仔畜来源的骨髓肥大细胞进行了比较。结果发现，在预先加载IgE的细胞发生交联后，SHIP-/-肥大细胞比SHIP+/-或+/+细胞更容易发生脱颗粒。有趣的是，单独的IgE也能刺激SHIP-/-肥大细胞发生大量脱颗粒，但不能刺激+/+肥大细胞。这种单独由IgE引起的脱颗粒可能是由于低水平的IgE聚集体，与SHIP+/+细胞相比，其细胞内钙水平更高且更持久，并且依赖于细胞外钙的进入。免疫沉淀研究表明，向正常肥大细胞单独添加IgE会刺激多个级联反应，而SHIP可阻止这些反应发展为脱颗粒。PI 3激酶抑制剂研究表明，IgE诱导的PI 3激酶激活在细胞外钙进入的上游，并且SHIP通过水解磷脂酰肌醇3,4,5-三磷酸来限制这种进入。这些结果表明SHIP在设定脱颗粒阈值方面起着关键作用，并且SHIP直接调节一种“正性作用”受体。
