Indik Z K, Park J G, Pan X Q, Schreiber A D
Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia.
Blood. 1995 Mar 1;85(5):1175-80.
The transmission of extracellular signals to cellular targets by many noncatalytic surface receptors is dependent on interaction between cytoplasmic protein tyrosine kinases (PTKs) and tyrosine-containing sequences in the cytoplasmic domain of the receptor or an associated subunit. Isoforms of each of the three classes of the noncatalytic Fc gamma receptors, Fc gamma RI, Fc gamma RII, and Fc gamma RIII, are able to transmit a phagocytic signal in transfected COS-1 cells. Both Fc gamma RI and Fc gamma RIIIA require the gamma subunit for this signaling event. The protein tyrosine kinase Syk dramatically enhances phagocytosis mediated by both these receptors and increases the number of cells able to mediate phagocytosis. Two gamma chain cytoplasmic YXXL sequences are required for this effect. The action of Syk is less pronounced on the phagocytic Fc gamma RII receptor, Fc gamma RIIA, which does not require the gamma chain for phagocytosis. However, Syk allows phagocytosis by the nonphagocytic Fc gamma RII receptor Fc gamma RIIB2, which contains only a single YXXL sequence, when an additional tyrosine-containing sequence, YMTL, is introduced. These studies indicate that the efficiency of phagocytosis is markedly enhanced by the presence of a specific protein tyrosine kinase.
许多非催化性表面受体将细胞外信号传递至细胞靶点，这依赖于细胞质蛋白酪氨酸激酶（PTK）与受体或相关亚基细胞质结构域中含酪氨酸序列之间的相互作用。三类非催化性Fcγ受体（FcγRI、FcγRII和FcγRIII）的各亚型都能够在转染的COS-1细胞中传递吞噬信号。FcγRI和FcγRIIIA在这一信号传导事件中都需要γ亚基。蛋白酪氨酸激酶Syk显著增强了这两种受体介导的吞噬作用，并增加了能够介导吞噬作用的细胞数量。这一效应需要两个γ链细胞质YXXL序列。Syk对吞噬性FcγRII受体FcγRIIA的作用不太明显，该受体在吞噬作用中不需要γ链。然而，当引入一个额外的含酪氨酸序列YMTL时，Syk可使仅含有单个YXXL序列的非吞噬性FcγRII受体FcγRIIB2发生吞噬作用。这些研究表明，特定蛋白酪氨酸激酶的存在可显著提高吞噬作用的效率。
