Messika E J, Avni O, Gallily R, Yefenof E, Baniyash M
Lautenberg Center for General and Tumor Immunology, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
J Immunol. 1995 Jun 15;154(12):6563-70.
CR3 is a member of the beta 2 integrin family which functions as a bidirectional signaling receptor. The CR3 is composed of the alpha (CD11b) and beta (CD18) subunits, which contain a short intracytoplasmic domain devoid of catalytic activity. It was therefore postulated that CR3 is associated with intracellular molecules that link it to the cytoplasmic signal transduction apparatus. However, no direct association between such molecules and CR3 have been identified so far. We searched for CR3 co-associated molecules that might regulate the function of this receptor. For this purpose CR3 was immunoprecipitated from radiolabeled bone marrow macrophages using a combination of anti-CD11b and anti-CD18 mAbs. Two-dimensional isoelectric focusing analysis of the immunoprecipitates revealed the two CR3 subunits and an additional 16-kDa protein with an apparent isoelectric point of 5.1. This protein, designated p16/5.1, was intracellular, monomeric, nonglycosylated and noncovalently associated with CR3 but not with CR4. CR3-associated p16/5.1 was also detected in four of six macrophage lines as well as in thymic large macrophages, all of which express cell-surface CR3. We suggest that p16/5.1 may be involved in CR3-mediated function.
CR3是β2整合素家族的成员，作为双向信号受体发挥作用。CR3由α（CD11b）和β（CD18）亚基组成，这两个亚基含有一个缺乏催化活性的短胞质内结构域。因此推测CR3与将其连接到细胞质信号转导装置的细胞内分子相关。然而，到目前为止尚未鉴定出此类分子与CR3之间的直接关联。我们寻找了可能调节该受体功能的与CR3共同相关的分子。为此，使用抗CD11b和抗CD18单克隆抗体的组合从放射性标记的骨髓巨噬细胞中免疫沉淀CR3。对免疫沉淀物进行二维等电聚焦分析，发现了两个CR3亚基以及另一种表观等电点为5.1的16 kDa蛋白质。这种蛋白质命名为p16/5.1，位于细胞内，为单体，非糖基化，与CR3非共价结合，但与CR4不结合。在六个巨噬细胞系中的四个以及胸腺大巨噬细胞中也检测到了与CR3相关的p16/5.1，所有这些细胞都表达细胞表面CR3。我们认为p16/5.1可能参与CR3介导的功能。
