Sun Jianmin, Pedersen Malin, Rönnstrand Lars
Experimental Clinical Chemistry, Department of Laboratory Medicine, Malmö University Hospital, Lund University, SE-205 02 Malmö, Sweden.
Experimental Clinical Chemistry, Department of Laboratory Medicine, Malmö University Hospital, Lund University, SE-205 02 Malmö, Sweden.
J Biol Chem. 2008 Oct 10;283(41):27444-27451. doi: 10.1074/jbc.M709703200. Epub 2008 Aug 11.
The stem cell factor receptor/c-Kit plays an important physiological role in hematopoiesis, melanogenesis, and gametogenesis. It has also been implicated in numerous human malignancies. Signal transduction pathways shown to be of importance for c-Kit-mediated transformation include the phosphoinositide 3-kinase (PI3K)/Akt pathway. We have previously shown that two alternative splice forms of c-Kit, denoted GNNK(-) and GNNK(+), mediate distinctively different signals. In this study, we found that in the hematopoietic cell line Ba/F3, GNNK(-) c-Kit mediates a substantially stronger activation of PI3K/Akt than GNNK(+) c-Kit. This difference in signaling was shown to be dependent on the association of the scaffolding protein Gab2 with c-Kit, and Src-mediated phosphorylation of Gab2 was shown to be to be independent of the direct association of PI3K with c-Kit. Furthermore, proliferation and survival of Ba/F3 cells expressing a mutant of c-Kit that fails to bind to PI3K directly were slightly decreased compared with wild-type c-Kit-expressing cells. Using small interfering RNA technology, we further verified a role of Gab2 in inducing activation of PI3K/Akt downstream of c-Kit. To summarize, we show that PI3K activation by c-Kit is both splice form-dependent and cell type-specific. Furthermore, activation of PI3K by c-Kit is dependent both on the direct PI3K-binding site in c-Kit and on the phosphorylation of Gab2. The fact that c-Kit has been found mutated in numerous human malignancies, including acute myeloid leukemia, and that Gab2 is often overexpressed in acute myeloid leukemia suggests a potential role of Gab2-mediated PI3K activation in transformation.
干细胞因子受体/c-Kit在造血、黑色素生成和配子发生过程中发挥着重要的生理作用。它也与多种人类恶性肿瘤有关。已证明对c-Kit介导的转化具有重要意义的信号转导途径包括磷酸肌醇3-激酶（PI3K）/Akt途径。我们之前已经表明，c-Kit的两种可变剪接形式，即GNNK(-)和GNNK(+)，介导明显不同的信号。在本研究中，我们发现，在造血细胞系Ba/F3中，GNNK(-) c-Kit介导的PI3K/Akt激活比GNNK(+) c-Kit强得多。这种信号差异被证明依赖于支架蛋白Gab2与c-Kit的结合，并且Src介导的Gab2磷酸化被证明独立于PI3K与c-Kit的直接结合。此外，与表达野生型c-Kit的细胞相比，表达不能直接与PI3K结合的c-Kit突变体的Ba/F3细胞的增殖和存活略有下降。使用小干扰RNA技术，我们进一步验证了Gab2在诱导c-Kit下游PI3K/Akt激活中的作用。总之，我们表明c-Kit对PI3K的激活既依赖于剪接形式，又具有细胞类型特异性。此外，c-Kit对PI3K的激活既依赖于c-Kit中的直接PI3K结合位点，也依赖于Gab2的磷酸化。c-Kit在包括急性髓性白血病在内的多种人类恶性肿瘤中被发现发生突变，并且Gab2在急性髓性白血病中经常过度表达，这一事实表明Gab2介导的PI3K激活在转化过程中具有潜在作用。
