Jiang Kun, Zhong Bin, Gilvary Danielle L, Corliss Brian C, Vivier Eric, Hong-Geller Elizabeth, Wei Sheng, Djeu Julie Y
Immunology Program, H. Lee Moffitt Cancer Center, Department of Interdisciplinary Oncology, University of South Florida College of Medicine, Tampa, FL 33612, USA.
J Immunol. 2002 Apr 1;168(7):3155-64. doi: 10.4049/jimmunol.168.7.3155.
Emerging evidence suggests that NK-activatory receptors use KARAP/DAP12, CD3zeta, and FcepsilonRIgamma adaptors that contain immunoreceptor tyrosine-based activatory motifs to mediate NK direct lysis of tumor cells via Syk tyrosine kinase. NK cells may also use DAP10 to drive natural cytotoxicity through phosphoinositide 3-kinase (PI3K). In contrast to our recently identified PI3K pathway controlling NK cytotoxicity, the signaling mechanism by which Syk associates with downstream effectors to drive NK lytic function has not been clearly defined. In NK92 cells, which express DAP12 but little DAP10/NKG2D, we now show that Syk acts upstream of PI3K, subsequently leading to the specific signaling of the PI3K-->Rac1-->PAK1-->mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase-->ERK cascade that we earlier described. Tumor cell ligation stimulated DAP12 tyrosine phosphorylation and its association with Syk in NK92 cells; Syk tyrosine phosphorylation and activation were also observed. Inhibition of Syk function by kinase-deficient Syk or piceatannol blocked target cell-induced PI3K, Rac1, PAK1, mitogen-activated protein/ERK kinase, and ERK activation, perforin movement, as well as NK cytotoxicity, indicating that Syk is upstream of all these signaling events. Confirming that Syk does not act downstream of PI3K, constitutively active PI3K reactivated all the downstream effectors as well as NK cytotoxicity suppressed in Syk-impaired NK cells. Our results are the first report documenting the instrumental role of Syk in control of PI3K-dependent natural cytotoxicity.
新出现的证据表明，NK细胞激活受体利用含有基于免疫受体酪氨酸的激活基序的KARAP/DAP12、CD3ζ和FcepsilonRIγ衔接蛋白，通过Syk酪氨酸激酶介导NK细胞对肿瘤细胞的直接裂解。NK细胞也可能利用DAP10通过磷酸肌醇3激酶（PI3K）驱动自然细胞毒性。与我们最近确定的控制NK细胞毒性的PI3K途径相反，Syk与下游效应器结合以驱动NK细胞裂解功能的信号传导机制尚未明确界定。在表达DAP12但几乎不表达DAP10/NKG2D的NK92细胞中，我们现在表明Syk在PI3K的上游起作用，随后导致我们先前描述的PI3K→Rac1→PAK1→丝裂原活化蛋白/细胞外信号调节激酶（ERK）激酶→ERK级联的特异性信号传导。肿瘤细胞连接刺激了NK92细胞中DAP12的酪氨酸磷酸化及其与Syk的结合；也观察到了Syk的酪氨酸磷酸化和激活。用激酶缺陷型Syk或白藜芦醇抑制Syk功能可阻断靶细胞诱导的PI3K、Rac1、PAK1、丝裂原活化蛋白/ERK激酶和ERK激活、穿孔素移动以及NK细胞毒性，表明Syk在所有这些信号事件的上游。证实Syk不在PI3K的下游起作用，组成型活性PI3K重新激活了所有下游效应器以及在Syk受损的NK细胞中被抑制的NK细胞毒性。我们的结果是第一份记录Syk在控制PI3K依赖性自然细胞毒性中的重要作用的报告。
