Jin Hua, Wang Jean Y J
Division of Biological Sciences, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA 92093-0820, USA.
Mol Biol Cell. 2007 Oct;18(10):4143-54. doi: 10.1091/mbc.e07-01-0085. Epub 2007 Aug 8.
The nonreceptor Abl tyrosine kinase stimulates F-actin microspikes and membrane ruffles in response to adhesion and growth factor signals. We show here that induced dimerization of Abl-FKBP, but not the kinase-defective AblKD-FKBP, inhibits cell spreading on fibronectin. Conversely, knockdown of cellular Abl by shRNA stimulates cell spreading. The Abl kinase inhibitor, imatinib, also stimulates cell spreading and its effect is overridden by the imatinib-resistant AblT315I. Expression of Abl but not AbkKD in Abl/Arg-deficient cells again inhibits spreading. Furthermore, Abl inhibits spreading of cells that express the activated Rac, RacV12, correlating with RacV12 localization to dorsal membrane protrusions. Ectopic expression of CrkII, a Rac activator that is inactivated by Abl-mediated tyrosine phosphorylation, antagonizes Abl-mediated dorsal membrane localization of RacV12. Ectopic expression of a dynamin-2 mutant, previously shown to induce Rac-GTP localization to the dorsal membrane, abolishes the stimulatory effect of imatinib on cell spreading. These results suggest that Abl tyrosine kinase, through CrkII phosphorylation and in collaboration with dynamin-2 can regulate the partitioning of Rac-GTP to favor dorsal ruffles during cell spreading. The Abl-dependent dorsal membrane localization of activated Rac explains its positive role in ruffling and negative role in cell spreading and migration.
非受体Abl酪氨酸激酶响应黏附及生长因子信号刺激F-肌动蛋白微刺和膜皱褶。我们在此表明，诱导Abl-FKBP二聚化，而非激酶缺陷型AblKD-FKBP二聚化，会抑制细胞在纤连蛋白上的铺展。相反，用短发夹RNA敲低细胞内的Abl会刺激细胞铺展。Abl激酶抑制剂伊马替尼也会刺激细胞铺展，而其耐药型AblT315I可消除该作用。在Abl/Arg缺陷型细胞中表达Abl而非AbkKD同样会抑制铺展。此外，Abl抑制表达活化型Rac即RacV12的细胞铺展，这与RacV12定位于背侧膜突起相关。CrkII是一种被Abl介导的酪氨酸磷酸化失活的Rac激活剂，其异位表达可拮抗Abl介导的RacV12背侧膜定位。一种此前显示可诱导Rac-GTP定位于背侧膜的发动蛋白-2突变体的异位表达，消除了伊马替尼对细胞铺展的刺激作用。这些结果表明，Abl酪氨酸激酶通过CrkII磷酸化并与发动蛋白-2协同作用，可在细胞铺展过程中调节Rac-GTP的分配，以促进背侧皱褶形成。活化型Rac依赖Abl的背侧膜定位解释了其在皱褶形成中的正向作用以及在细胞铺展和迁移中的负向作用。
