Krystal G W, DeBerry C S, Linnekin D, Litz J
Department of Medicine, Medical College of Virginia Commonwealth University, McGuire Veterans Affairs Medical Center, Richmond 23249, USA.
Cancer Res. 1998 Oct 15;58(20):4660-6.
At least 70% of small cell lung cancers (SCLCs) express the Kit receptor tyrosine kinase and its ligand, stem cell factor (SCF). In an effort to define the signal transduction pathways activated by Kit in SCLC, we focused on Src family kinases and, in particular, Lck, a Src-related tyrosine kinase that is expressed in hemopoietic cells and certain tumors, including SCLC. SCF treatment of the H526 cell line induced a physical association between Kit and Lck that, in vitro, was dependent on phosphorylation of the juxtamembrane domain of Kit. Stimulation of Kit with recombinant SCF resulted in a rapid 3-6-fold increase in the specific activity of Lck, which was similar in magnitude to the activation of Lck resulting from the cross-linking of the T-cell receptor complex of Jurkat cells. Lck activity peaked by 5 min after SCF addition, and the elevated activity persisted for at least 30 min in the presence of SCF, with kinetics similar to the activation of mitogen-activated protein kinase. PP1, an inhibitor of Src family kinases with selectivity for Lck, completely inhibited SCF-mediated growth but had little effect on insulin-like growth factor-I-mediated growth. PP1 antagonized both SCF-mediated proliferation and inhibition of apoptosis. PP1 had no effect on Kit kinase activity but was shown to block total Lck activity by at least 90% by immune complex kinase assay. Low levels of Src, Hck, and Yes were also expressed in the H526 cell line; only Yes showed a consistent increase in specific activity, which was also inhibited by PP1 following SCF treatment. These data demonstrate that, in the H526 SCLC cell line, Lck and, possibly, Yes are downstream of Kit in a signal transduction pathway; the inhibition by PP1 of SCF-mediated proliferation and inhibition of apoptosis suggests that Src family kinases are intermediates in the signaling pathways that regulate these processes.
至少70%的小细胞肺癌（SCLCs）表达Kit受体酪氨酸激酶及其配体干细胞因子（SCF）。为了确定SCLC中由Kit激活的信号转导途径，我们聚焦于Src家族激酶，尤其是Lck，一种与Src相关的酪氨酸激酶，在造血细胞和某些肿瘤（包括SCLC）中表达。用SCF处理H526细胞系可诱导Kit与Lck发生物理结合，在体外，这种结合依赖于Kit近膜结构域的磷酸化。用重组SCF刺激Kit导致Lck的比活性迅速增加3至6倍，其幅度与Jurkat细胞T细胞受体复合物交联导致的Lck激活相似。添加SCF后5分钟Lck活性达到峰值，在有SCF存在的情况下，升高的活性持续至少30分钟，其动力学与丝裂原活化蛋白激酶的激活相似。PP1是一种对Lck具有选择性的Src家族激酶抑制剂，它完全抑制SCF介导的生长，但对胰岛素样生长因子-I介导的生长几乎没有影响。PP1拮抗SCF介导的增殖和对细胞凋亡的抑制。PP1对Kit激酶活性没有影响，但通过免疫复合物激酶测定显示它能将总Lck活性至少阻断90%。H526细胞系中也表达低水平的Src、Hck和Yes；只有Yes的比活性持续增加，在SCF处理后也被PP1抑制。这些数据表明，在H526 SCLC细胞系中，Lck以及可能的Yes在信号转导途径中位于Kit的下游；PP1对SCF介导的增殖和细胞凋亡抑制的抑制作用表明，Src家族激酶是调节这些过程的信号通路中的中间体。
