Fan Guo-Huang, Lapierre Lynne A, Goldenring James R, Richmond Ann
Department of Veterans Affairs, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
Blood. 2003 Mar 15;101(6):2115-24. doi: 10.1182/blood-2002-07-1965. Epub 2002 Oct 31.
Intracellular trafficking of chemokine receptors plays an important role in fine-tuning the functional responses of neutrophils and lymphocytes in the inflammatory process and HIV infection. Although many chemokine receptors internalize through clathrin-coated pits, regulation of the receptor trafficking is not fully understood. The present study demonstrated that CXCR2 was colocalized with transferrin and low-density lipoprotein (LDL) after agonist treatment for different periods of time, suggesting 2 intracellular trafficking pathways for this receptor. CXCR2 was colocalized with Rab5 and Rab11a, which are localized in early and recycling endosomes, respectively, in response to agonist stimulation for a short period of time, suggesting a recycling pathway for the receptor trafficking. However, overexpression of a dominant-negative Rab5-S34N mutant significantly attenuated CXCR2 sequestration. The internalized CXCR2 was recycled back to the cell surface after removal of the agonist and recovery of the cells, but receptor recycling was inhibited by overexpression of a dominant-negative Rab11a-S25N mutant. After prolonged (4-hour) agonist treatment, CXCR2 exhibited significantly increased colocalization with Rab7, which is localized in late endosomes. The colocalization of CXCR2 with LDL and LAMP-1 suggests that CXCR2 is targeted to lysosomes for degradation after prolonged ligand treatment. However, the colocalization of CXCR2 with Lamp1 was blocked by the overexpression of a dominant-negative Rab7-T22N mutant. In cells overexpressing Rab7-T22N, CXCR2 was retained in the Rab5- and Rab11a-positive endosomes after prolonged (4-hour) agonist treatment. Our data suggest that the intracellular trafficking of CXCR2 is differentially regulated by Rab proteins.
趋化因子受体的细胞内运输在炎症过程和HIV感染中对中性粒细胞和淋巴细胞功能反应的微调中起着重要作用。尽管许多趋化因子受体通过网格蛋白包被小窝内化，但受体运输的调控尚未完全明确。本研究表明，在激动剂处理不同时间段后，CXCR2与转铁蛋白和低密度脂蛋白（LDL）共定位，提示该受体存在两条细胞内运输途径。短时间激动剂刺激后，CXCR2分别与定位于早期内体和再循环内体的Rab5和Rab11a共定位，提示受体运输的再循环途径。然而，显性负性Rab5 - S34N突变体的过表达显著减弱了CXCR2的隔离。去除激动剂并使细胞恢复后，内化的CXCR2会再循环回到细胞表面，但显性负性Rab11a - S25N突变体的过表达抑制了受体再循环。长时间（4小时）激动剂处理后，CXCR2与定位于晚期内体的Rab7的共定位显著增加。CXCR2与LDL和LAMP - 1的共定位提示，长时间配体处理后CXCR2靶向溶酶体进行降解。然而，显性负性Rab7 - T22N突变体的过表达阻断了CXCR2与Lamp1的共定位。在过表达Rab7 - T22N的细胞中，长时间（4小时）激动剂处理后CXCR2保留在Rab5和Rab11a阳性内体中。我们的数据表明，Rab蛋白对CXCR2的细胞内运输进行差异调控。
