Department of Surgical Oncology, First Affiliated Hospital, China Medical University, 110001 Shenyang, People's Republic of China.
Dig Dis Sci. 2012 Mar;57(3):650-9. doi: 10.1007/s10620-011-1922-5. Epub 2011 Sep 29.
Chemokine receptors are now known to play an important role in cancer growth and metastasis. However, there is little information regarding chemokine expression in gastric cancer. In this study, we examined CXCL12 expression in gastric cancer and also evaluated whether the down-regulation of CXCL12 is due to aberrant methylation of the gene.
CXCL12 expression was examined using real-time reverse-transcription polymerase chain reaction (RT-PCR), immunofluorescence, flow cytometry, and immunohistochemistry, and the methylation status of the gene was evaluated by methylation-specific PCR (MSP) in normal gastric and gastric cancer cell lines and 35 primary gastric carcinomas and corresponding nonmalignant gastric tissues.
The down-regulation of CXCL12 was observed in gastric cancer cell lines and primary gastric carcinomas, while decreased expression of CXCL12 protein was significantly associated with lymph node metastasis and histological grade. And this down-regulation was found to be in accordance with aberrant methylation of the gene. Hypermethylation of the gene was observed in 65.7% (23 of 35) of the primary gastric carcinomas, while it was found in only 11.4% (4/35) of the corresponding nonmalignant tissues. Furthermore, CXCL12 expression was restored in gastric cancer cell lines after treatment with the demethylating agent, 5-aza-2'-deoxycytidine (5-Aza-dC), and demethylation of the highly metastatic cells SGC-7901 induced invasion suppression of the cells. For two CXCL12 receptors, CXCR4 and CXCR7, the mRNA levels remained almost unchanged with the 5-Aza-dC treatment.
Collectively, our results suggest that the aberrant methylation of CXCL12 frequently occurs in the down-regulation of CXCL12 in gastric cancers and that it may play a role in the metastasis of gastric cancer.
趋化因子受体在肿瘤生长和转移中起着重要作用，这一点已得到证实。然而，关于趋化因子在胃癌中的表达情况，目前信息较少。在本研究中，我们检测了趋化因子 CXCL12 在胃癌中的表达情况，并评估了 CXCL12 的下调是否归因于基因的异常甲基化。
使用实时逆转录聚合酶链反应（RT-PCR）、免疫荧光、流式细胞术和免疫组化检测 CXCL12 的表达情况，并用甲基化特异性 PCR（MSP）检测基因的甲基化状态，检测对象包括正常胃组织和胃癌细胞系以及 35 例原发性胃癌及其相应的非恶性胃组织。
在胃癌细胞系和原发性胃癌中观察到 CXCL12 的下调，而 CXCL12 蛋白表达的降低与淋巴结转移和组织学分级显著相关。这种下调与基因的异常甲基化相一致。在 35 例原发性胃癌中，有 65.7%（23/35）存在基因的高甲基化，而在相应的非恶性组织中，只有 11.4%（4/35）存在基因的高甲基化。此外，在用去甲基化剂 5-氮杂-2′-脱氧胞苷（5-Aza-dC）处理后，胃癌细胞系中 CXCL12 的表达得到恢复，并且高度转移性细胞 SGC-7901 的去甲基化诱导了细胞侵袭抑制。对于两个 CXCL12 受体 CXCR4 和 CXCR7，5-Aza-dC 处理后其 mRNA 水平几乎没有变化。
总的来说，我们的研究结果表明，CXCL12 的异常甲基化在胃癌中 CXCL12 的下调中经常发生，并且可能在胃癌的转移中发挥作用。
