Division of Hematology-Oncology, Department of Pediatrics, University of Southern California Keck School of Medicine and Developmental Therapeutics Program, Childrens Hospital, P.O. Box 27367, Los Angeles, CA 90027-0367, USA.
Proc Natl Acad Sci U S A. 2010 Feb 16;107(7):2902-7. doi: 10.1073/pnas.0909086107. Epub 2010 Jan 29.
We provide unprecedented genetic and biochemical evidence that the antiapoptotic transcription factor STAT3 serves as a substrate for SYK tyrosine kinase both in vitro and in vivo. Induction of SYK in an ecdysone-inducible mammalian expression system results in STAT3 activation, as documented by tyrosine phosphorylation and nuclear translocation of STAT3, as well as amplified expression of several STAT3 target genes. STAT3 activation after oxidative stress (OS) is strongly diminished in DT40 chicken B-lineage lymphoma cells rendered SYK-deficient by targeted disruption of the syk gene. Introduction of a wild-type, C-terminal or N-terminal SH2 domain-mutated, but not a kinase domain-mutated, syk gene into SYK-deficient DT40 cells restores OS-induced enhancement of STAT-3 activity. Thus, SYK plays an important and indispensable role in OS-induced STAT3 activation and its catalytic SH1 domain is critical for this previously unknown regulatory function. These results provide evidence for the existence of a novel mode of cytokine-independent cross-talk that operates between SYK and STAT3 pathways and regulates apoptosis during OS. We further provide experimental evidence that SYK is capable of associating with and phosphorylating STAT3 in human B-lineage leukemia/lymphoma cells challenged with OS. In agreement with a prerequisite role of SYK in OS-induced STAT3 activation, OS does not induce tyrosine phosphorylation of STAT3 in SYK-deficient human proB leukemia cells. Notably, inhibition of SYK with a small molecule drug candidate prevents OS-induced activation of STAT3 and overcomes the resistance of human B-lineage leukemia/lymphoma cells to OS-induced apoptosis.
我们提供了前所未有的遗传和生化证据，表明抗凋亡转录因子 STAT3 既是体外又是体内 SYK 酪氨酸激酶的底物。在蜕皮激素诱导的哺乳动物表达系统中诱导 SYK，可导致 STAT3 的激活，这可通过 STAT3 的酪氨酸磷酸化和核转位以及几个 STAT3 靶基因的扩增表达来证明。在用靶向敲除 syk 基因使 SYK 缺陷的 DT40 鸡 B 细胞淋巴瘤细胞中，氧化应激（OS）后 STAT3 的激活大大减弱。将野生型、C 末端或 N 末端 SH2 结构域突变但激酶结构域不变的 syk 基因导入 SYK 缺陷的 DT40 细胞中，可恢复 OS 诱导的 STAT-3 活性增强。因此，SYK 在 OS 诱导的 STAT3 激活中发挥重要且不可或缺的作用，其催化 SH1 结构域对于这种以前未知的调节功能至关重要。这些结果为 SYK 和 STAT3 途径之间存在的一种新型细胞因子非依赖性串扰模式提供了证据，并调节 OS 期间的细胞凋亡。我们进一步提供了实验证据，表明在受到 OS 挑战的人类 B 细胞白血病/淋巴瘤细胞中，SYK 能够与 STAT3 结合并磷酸化 STAT3。与 SYK 在 OS 诱导的 STAT3 激活中的必需作用一致，OS 不会诱导 SYK 缺陷的人类前 B 白血病细胞中 STAT3 的酪氨酸磷酸化。值得注意的是，用小分子药物候选物抑制 SYK 可防止 OS 诱导的 STAT3 激活，并克服人类 B 细胞白血病/淋巴瘤细胞对 OS 诱导的凋亡的抗性。
