Sai Jiqing, Raman Dayanidhi, Liu Yuxin, Wikswo John, Richmond Ann
Department of Cancer Biology, School of Medicine, Vanderbilt University, Nashville, Tennessee 37232, USA.
J Biol Chem. 2008 Sep 26;283(39):26538-47. doi: 10.1074/jbc.M805611200. Epub 2008 Jul 28.
The requirement for phosphatidylinositol 3-kinase (PI3K) in the establishment of cell polarity and motility in a number of cell types has recently come into question. In this study, we demonstrate that inhibition of PI3K by wortmannin in neutrophil-like differentiated HL60 cells expressing CXCR2 resulted in reduced cell motility but normal chemotaxis in response to a gradient of CXCL8. However, wortmannin inhibition of PI3K did impair the ability of cells to re-orient their polarity and respond quickly to a change in the direction of the CXCL8 gradient. We hypothesized that Src-regulated ELMO-Dock2-Rac2 activation mediates chemotaxis in the absence of PI3K activity. Inhibition of Src with the small molecule inhibitor, PP2, or inhibition of Dock2 by shRNA knockdown confirmed the functional role of Src and Dock2 in regulating chemotaxis when PI3K was inhibited. Moreover, neutrophils isolated from bone marrow of hck(-/-)fgr(-/-)lyn(-/-) mice exhibited much more severe inhibition of chemotaxis when PI3K was blocked with wortmannin as compared with neutrophils isolated from bone marrow of wild-type mice. Thus, PI3K and Src-ELMO-Dock2 pathways work in parallel to activate Rac2 and modulate chemotaxis in response to a CXCL8 gradient in neutrophils.
磷脂酰肌醇3激酶（PI3K）在多种细胞类型中建立细胞极性和运动性方面的必要性最近受到质疑。在本研究中，我们证明，渥曼青霉素对表达CXCR2的中性粒细胞样分化HL60细胞中PI3K的抑制作用导致细胞运动性降低，但对CXCL8梯度的趋化性正常。然而，渥曼青霉素对PI3K的抑制作用确实损害了细胞重新定向其极性并对CXCL8梯度方向变化快速做出反应的能力。我们推测，Src调节的ELMO-Dock2-Rac2激活在没有PI3K活性的情况下介导趋化作用。用小分子抑制剂PP2抑制Src或通过shRNA敲低抑制Dock2证实了Src和Dock2在PI3K被抑制时调节趋化作用的功能作用。此外，与从野生型小鼠骨髓中分离的中性粒细胞相比，用渥曼青霉素阻断PI3K时，从hck(-/-)fgr(-/-)lyn(-/-)小鼠骨髓中分离的中性粒细胞趋化作用受到更严重的抑制。因此，PI3K和Src-ELMO-Dock2途径平行发挥作用，激活Rac2并调节中性粒细胞对CXCL8梯度的趋化作用。
