State Key Laboratory of Cancer Biology and Institute of Digestive Diseases, Xijing Hospital of Digestive Diseases, Xi'an, China.
PLoS One. 2011 Apr 18;6(4):e18409. doi: 10.1371/journal.pone.0018409.
MicroRNAs (miRNAs) are important regulators that play key roles in tumorigenesis and tumor progression. A previous report has shown that let-7 family members can act as tumor suppressors in many cancers. Through miRNA array, we found that let-7f was downregulated in the highly metastatic potential gastric cancer cell lines GC9811-P and SGC7901-M, when compared with their parental cell lines, GC9811 and SGC7901-NM; however, the mechanism was not clear. In this study, we investigate whether let-7f acts as a tumor suppressor to inhibit invasion and metastasis in gastric cancers.
METHODOLOGY/PRINCIPAL: Real-time PCR showed decreased levels of let-7f expression in metastatic gastric cancer tissues and cell lines that are potentially highly metastatic. Cell invasion and migration were significantly impaired in GC9811-P and SGC7901-M cell lines after transfection with let-7f-mimics. Nude mice with xenograft models of gastric cancer confirmed that let-7f could inhibit gastric cancer metastasis in vivo after transfection by the lentivirus pGCsil-GFP- let-7f. Luciferase reporter assays demonstrated that let-7f directly binds to the 3'UTR of MYH9, which codes for myosin IIA, and real-time PCR and Western blotting further indicated that let-7f downregulated the expression of myosin IIA at the mRNA and protein levels.
CONCLUSIONS/SIGNIFICANCE: Our study demonstrated that overexpression of let-7f in gastric cancer could inhibit invasion and migration of gastric cancer cells through directly targeting the tumor metastasis-associated gene MYH9. These data suggest that let-7f may be a novel therapeutic candidate for gastric cancer, given its ability to reduce cell invasion and metastasis.
微小 RNA（miRNAs）是重要的调控因子，在肿瘤发生和肿瘤进展中发挥关键作用。先前的研究表明，let-7 家族成员可以在许多癌症中作为肿瘤抑制因子发挥作用。通过 miRNA 阵列，我们发现与亲本细胞系 GC9811-NM 相比，高转移潜能的胃癌细胞系 GC9811-P 和 SGC7901-M 中 let-7f 的表达下调；然而，其机制尚不清楚。在本研究中，我们研究了 let-7f 是否作为肿瘤抑制因子抑制胃癌的侵袭和转移。
方法/原理：实时 PCR 显示转移性胃癌组织和高转移潜能的细胞系中 let-7f 表达水平降低。转染 let-7f 模拟物后，GC9811-P 和 SGC7901-M 细胞系的细胞侵袭和迁移能力显著受损。携带胃癌异种移植模型的裸鼠证实，转染慢病毒 pGCsil-GFP-let-7f 后，let-7f 可抑制体内胃癌转移。荧光素酶报告基因实验表明，let-7f 可直接结合编码肌球蛋白 IIA 的 MYH9 的 3'UTR，实时 PCR 和 Western blot 进一步表明，let-7f 在 mRNA 和蛋白水平下调肌球蛋白 IIA 的表达。
结论/意义：我们的研究表明，胃癌中 let-7f 的过表达可通过直接靶向肿瘤转移相关基因 MYH9 抑制胃癌细胞的侵袭和迁移。这些数据表明，鉴于 let-7f 降低细胞侵袭和转移的能力，它可能成为胃癌的一种新的治疗候选物。
