Division of Oncology, Abramson Research Center, Children's Hospital of Philadelphia, ARC-907A, 3615 Civic Center Blvd, Philadelphia, Pennsylvania 19104-4399, USA.
Mol Cancer. 2009 Dec 22;8:126. doi: 10.1186/1476-4598-8-126.
CXCR4, the receptor for the chemokine stromal-derived factor 1 (SDF-1), has been shown to mediate many of the processes essential for cancer progression such as tumor cell proliferation, metastasis, and angiogenesis. To understand the role of CXCR4 in the biology of neuroblastoma, a disease that presents with wide spread metastases in over 50% of patients, we screened ten patient derived-neuroblastoma cell-lines for basal CXCR4 expression and sought to identify characteristics that correlate with tumor cell phenotype.
All cell lines expressed CXCR4 mRNA at variable levels, that correlated well with three distinct classes of CXCR4 surface expression (low, moderate, or high) as defined by flow cytometry. Analysis of the kinetics of CXCR4 surface expression on moderate and high expressing cell lines showed a time-dependent down-regulation of the receptor that directly correlated with cell confluency, and was independent of SDF1. Cell lysates showed the presence of multiple CXCR4 isoforms with three major species of approximately 87, 67 and 55 kDa associating with high surface expression, and two distinct species of 45 and 38 kDa correlating with low to null surface expression. Western blot analysis of CXCR4 immunoprecipitates showed that the 87 and 67 kDa forms were ubiquitinated, while the others were not. Finally, treatment of cells with a proteasome inhibitor resulted in down regulation of CXCR4 surface expression.
Taken together, these data show that regulation of CXCR4 surface expression in neuroblastoma cells can occur independently of SDF-1 contribution arguing against an autocrine mechanism. Additionally these data suggest that post-translational modifications of CXCR4, in part through direct ubiquitination, can influence trafficking of CXCR4 to the surface of neuroblastoma cells in a ligand-independent manner.
趋化因子受体 4（CXCR4）是趋化因子基质衍生因子 1（SDF-1）的受体，已被证明介导许多对癌症进展至关重要的过程，如肿瘤细胞增殖、转移和血管生成。为了了解 CXCR4 在神经母细胞瘤生物学中的作用，这种疾病在超过 50%的患者中出现广泛转移，我们筛选了十个患者来源的神经母细胞瘤细胞系，以检测基础 CXCR4 表达，并试图确定与肿瘤细胞表型相关的特征。
所有细胞系均以可变水平表达 CXCR4 mRNA，这与通过流式细胞术定义的三种不同的 CXCR4 表面表达（低、中或高）很好地相关。对中表达和高表达细胞系中 CXCR4 表面表达的动力学分析表明，受体存在时间依赖性下调，这与细胞汇合直接相关，且独立于 SDF1。细胞裂解物显示存在多种 CXCR4 同工型，其中三种主要的约 87、67 和 55 kDa 与高表面表达相关，两种不同的约 45 和 38 kDa 与低至无表面表达相关。CXCR4 免疫沉淀的 Western blot 分析表明，87 和 67 kDa 形式被泛素化，而其他形式则没有。最后，用蛋白酶体抑制剂处理细胞导致 CXCR4 表面表达下调。
综上所述，这些数据表明，神经母细胞瘤细胞中 CXCR4 表面表达的调节可以独立于 SDF-1 的贡献发生，这表明不存在自分泌机制。此外，这些数据表明，CXCR4 的翻译后修饰，部分通过直接泛素化，可以以配体非依赖的方式影响 CXCR4 向神经母细胞瘤细胞表面的转运。
