Experimental Clinical Chemistry, Department of Laboratory Medicine, Wallenberg Laboratory, Lund University, Skåne University Hospital, 20502 Malmö, Sweden.
Cell Signal. 2013 Sep;25(9):1852-60. doi: 10.1016/j.cellsig.2013.05.016. Epub 2013 May 21.
Type III receptor tyrosine kinases (RTKs), FLT3 and c-Kit play important roles in a variety of cellular processes. A number of SH2-domain containing proteins interact with FLT3 and c-Kit and regulate downstream signaling. The SH2-domain containing non-receptor protein tyrosine kinase CSK is mainly studied in the context of regulating Src family kinases. Here we present an additional role of this kinase in RTK signaling. We show that CSK interacts with FLT3 and c-Kit in a phosphorylation dependent manner. This interaction is facilitated through the SH2-domain of CSK. Under basal conditions CSK is mainly localized throughout the cytosolic compartment but upon ligand stimulation it is recruited to the inner side of cell membrane. CSK association did not alter receptor ubiquitination or phosphorylation but disrupted downstream signaling. Selective depletion of CSK using siRNA, or inhibition with CSK inhibitor, led to increased phosphorylation of Akt and Erk, but not p38, upon FLT3 ligand (FL) stimulation. Stem cell factor (SCF)-mediated Akt and Erk activation was also elevated by CSK inhibition. However, siRNA mediated CSK knockdown increased SCF stimulated Akt phosphorylation but decreased Erk phosphorylation. CSK depletion also significantly increased both FL- and SCF-induced SHC, Gab2 and SHP2 phosphorylation. Furthermore, CSK depletion contributed to oncogenic FLT3- and c-Kit-mediated cell proliferation, but not to cell survival. Thus, the results indicate that CSK association with type III RTKs, FLT3 and c-Kit can have differential impact on receptor downstream signaling.
III 型受体酪氨酸激酶（RTKs）、FLT3 和 c-Kit 在多种细胞过程中发挥重要作用。许多含有 SH2 结构域的蛋白质与 FLT3 和 c-Kit 相互作用并调节下游信号转导。含有 SH2 结构域的非受体酪氨酸激酶 CSK 主要在调节 Src 家族激酶的背景下进行研究。在这里，我们提出了该激酶在 RTK 信号转导中的另一个作用。我们表明，CSK 以依赖于磷酸化的方式与 FLT3 和 c-Kit 相互作用。这种相互作用是通过 CSK 的 SH2 结构域促进的。在基础条件下，CSK 主要定位于整个细胞质区室，但在配体刺激下，它被募集到细胞膜的内侧。CSK 结合不会改变受体泛素化或磷酸化，但会破坏下游信号转导。使用 siRNA 进行 CSK 选择性耗竭，或用 CSK 抑制剂抑制，导致在 FLT3 配体（FL）刺激下 Akt 和 Erk 的磷酸化增加，但 p38 没有增加。CSK 抑制也导致干细胞因子（SCF）介导的 Akt 和 Erk 激活增加。然而，siRNA 介导的 CSK 敲低增加了 SCF 刺激的 Akt 磷酸化，但降低了 Erk 磷酸化。CSK 耗竭还显著增加了 FL 和 SCF 诱导的 SHC、Gab2 和 SHP2 的磷酸化。此外，CSK 耗竭有助于致癌性 FLT3 和 c-Kit 介导的细胞增殖，但对细胞存活没有影响。因此，结果表明，CSK 与 III 型 RTKs、FLT3 和 c-Kit 的结合对受体下游信号转导可能有不同的影响。
