Department of Gastroenterological Surgery, Graduate School of Medical Science, Kumamoto University, Kumamoto, Japan.
PLoS One. 2013 Nov 28;8(11):e81839. doi: 10.1371/journal.pone.0081839. eCollection 2013.
Bmi1 is overexpressed in a variety of human cancers including gastrointestinal cancer. The high expression level of Bmi1 protein is associated with poor prognosis of gastrointestinal cancer patients. On the other hand, tumor-associated macrophages (TAMs) contribute to tumor growth, invasion, and metastasis by producing various mediators in the tumor microenvironment. The aim of this study was to investigate TAM-mediated regulation of Bmi1 expression in gastrointestinal cancer. The relationship between TAMs and Bmi1 expression was analyzed by immunohistochemistry and quantitative real-time PCR (qRT-PCR), and results showed a positive correlation with tumor-infiltrating macrophages (CD68 and CD163) and Bmi1 expression in cancer cells. Co-culture with TAMs triggered Bmi1 expression in cancer cell lines and enhanced sphere formation ability. miRNA microarray analysis of a gastric cancer cell line co-cultured with macrophages was conducted, and using in silico methods to analyze the results, we identified miR-30e* as a potential regulator of Bmi1 expression. Luciferase assays using miR-30e* mimic revealed that Bmi1 was a direct target for miR-30e* by interactions with the putative miR-30e* binding sites in the Bmi1 3' untranslated region. qRT-PCR analysis of resected cancer specimens showed that miR-30e* expression was downregulated in tumor regions compared with non-tumor regions, and Bmi1 expression was inversely correlated with miR-30e* expression in gastric cancer tissues, but not in colon cancer tissues. Our findings suggest that TAMs may cause increased Bmi1 expression through miR-30e* suppression, leading to tumor progression. The suppression of Bmi1 expression mediated by TAMs may thus represent a possible strategy as the treatment of gastrointestinal cancer.
Bmi1 在多种人类癌症中过表达，包括胃肠道癌。Bmi1 蛋白的高表达水平与胃肠道癌患者的预后不良相关。另一方面，肿瘤相关巨噬细胞（TAMs）通过在肿瘤微环境中产生各种介质促进肿瘤生长、侵袭和转移。本研究旨在探讨 TAM 介导的胃肠道癌中 Bmi1 表达的调节。通过免疫组织化学和定量实时 PCR（qRT-PCR）分析 TAMs 与 Bmi1 表达之间的关系，结果显示与肿瘤浸润巨噬细胞（CD68 和 CD163）和癌细胞中的 Bmi1 表达呈正相关。与 TAMs 共培养可触发癌细胞系中 Bmi1 的表达，并增强球体形成能力。对与巨噬细胞共培养的胃癌细胞系进行 miRNA 微阵列分析，并通过计算方法分析结果，我们鉴定出 miR-30e* 是 Bmi1 表达的潜在调节因子。使用 miR-30e* 模拟物进行的荧光素酶测定显示，Bmi1 是 miR-30e* 的直接靶标，通过与 Bmi1 3'非翻译区中推定的 miR-30e* 结合位点相互作用。对切除的癌症标本进行 qRT-PCR 分析显示，与非肿瘤区域相比，肿瘤区域中 miR-30e* 的表达下调，并且在胃癌组织中 Bmi1 表达与 miR-30e* 表达呈负相关，但在结肠癌组织中则不相关。我们的研究结果表明，TAMs 可能通过抑制 miR-30e* 导致 Bmi1 表达增加，从而促进肿瘤进展。TAMs 介导的 Bmi1 表达抑制可能是治疗胃肠道癌的一种潜在策略。
