J Biol Chem:CXCR4介导信号通路研究新进展

趋化因子受体CXCR4介导的信号通路在细胞增殖和迁移中起着重要的作用，但是受体具体的调节机制依旧不是完全清晰。健康科学研究所04级博士生潘恒同学在客座教授范国煌指导下，发现免疫因子cyclophilin A(cypa)能够和CXCR4结合，并且对其下游具有一系列影响。

首先发现在稳定表达CXCR4的HEK293细胞中，CXCR4能和cypa免疫共沉淀，CXCR4-N端和CXCR4-C端的GST融合蛋白都能和纯化的cypa蛋白结合，而当切掉CXCR4的C端，受体和cypa在细胞内的结合则明显受到了抑制，这表明CXCR4受体C端对于二者在细胞内的结合至关重要。实验首次发现CXCR4的配体CXCL12能够引起cypa磷酸化和核转移，以及cypa和transportin1结合。当用RNAi下调transportin1能够阻断CXCL12引起的cypa的核转移，证明transportin1介导了cypa的进核。另外，还发现cypa还能和异质核蛋白hnRNP A2结合，并且hnRNP A2能够在细胞被CXCR4激活以后出核，而当用RNAi下调cypa，CXCR4介导的hnRNP A2出核则被抑制。更进一步，CXCR4引起的ERK1/2的激活能够在用RNAi下调cypa，或过表达cypa的一个异构酶活性缺失突变体，或用免疫抑制药物cyclosporine A和sanglifehrin A预处理的情况下被削弱。在下调cypa了或者用CsA预处理后，由CXCL12激活的稳表达CXCR4的HEK293细胞和Jurkat细胞的细胞迁移也被抑制。相关内容已发表在《生物化学杂志》（JBC）上。（来源：健康科学研究所）

生物谷推荐原始出处：

（J Biol Chem.），Vol. 283, Issue 1, 623-637，Heng Pan，Guo-Huang Fan）

Cyclophilin A Is Required for CXCR4-mediated Nuclear Export of Heterogeneous Nuclear Ribonucleoprotein A2, Activation and Nuclear Translocation of ERK1/2, and Chemotactic Cell Migration

Heng Pan, Cherry Luo, Runsheng Li, Aimin Qiao, Li Zhang, Marjelo Mines, Alfred M. Nyanda, Jingwu Zhang, and Guo-Huang Fan

The chemokine receptor CXCR4-mediated signaling cascades play an important role in cell proliferation and migration, but the underlying mechanisms by which the receptor signaling is regulated remain incompletely understood. Here, we demonstrate that CXCR4 was co-immunoprecipitated with cyclophilin A (CyPA) from the lysate of HEK293 cells stably expressing CXCR4. Although both the glutathione S-transferase-CXCR4 N- and C-terminal fusion proteins were associated with the purified CyPA, truncation of the C-terminal domain of CXCR4 robustly inhibited the receptor co-immunoprecipitation with CyPA in intact cells, thereby suggesting a critical role of the receptor C terminus in this interaction. Ligand stimulation of CXCR4 induced CyPA phosphorylation and nuclear translocation, both of which were inhibited by truncation of the C-terminal domain of CXCR4. CyPA was associated with transportin 1, and knockdown of transportin 1 by RNA interference (RNAi) blocked CXCL12-induced nuclear translocation of CyPA, thereby suggesting a transportin 1-mediated nuclear import of CyPA. CyPA formed a complex with heterogeneous nuclear ribonucleoprotein (hnRNP) A2, which underwent nuclear export in response to activation of CXCR4. Interestingly, the CXCR4-mediated nuclear export of hnRNP A2 was blocked by RNAi of CyPA. Moreover, CXCR4-evoked activation of extracellular signal-regulated kinase 1/2 (ERK1/2) was attenuated by CyPA RNAi, by overexpression of a PPIase-deficient mutant of CyPA (CyPA-R55A), and by pretreatment of the immunosuppressive drugs, cyclosporine A and sanglifehrin A. Finally, CXCL12-induced chemotaxis of HEK293 cells stably expressing CXCR4 or Jurkat T cells was inhibited by CyPA RNAi or CsA treatment.