MicroRNA Let-7f Inhibits Tumor Invasion and Metastasis by Targeting MYH9 in Human Gastric Cancer

BackgroundMicroRNAs (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/PrincipalReal-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/SignificanceOur 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.

背景：微小RNA(miRNAs)是一类重要的调控因子，在肿瘤发生与发展过程中发挥关键作用。既往研究表明，let-7家族成员在多种癌症中可作为肿瘤抑制因子。通过miRNA芯片分析，我们发现相较于亲本细胞系GC9811与SGC7901-NM，高转移潜能胃癌细胞系GC9811-P和SGC7901-M中let-7f的表达呈下调趋势，但具体调控机制尚不明确。本研究旨在探究let-7f是否可作为肿瘤抑制因子，抑制胃癌的侵袭与转移。
方法与主要结果：实时荧光定量PCR结果显示，在转移性胃癌组织及高转移潜能细胞系中，let-7f的表达水平显著降低。将let-7f模拟物转染至GC9811-P和SGC7901-M细胞系后，细胞的侵袭与迁移能力显著受损。裸小鼠胃癌异种移植模型实验证实，通过慢病毒pGCsil-GFP-let-7f转染后，let-7f可在体内抑制胃癌的转移。荧光素酶报告基因实验证实，let-7f可直接结合至编码肌球蛋白IIA的MYH9基因的3'非翻译区；实时荧光定量PCR与蛋白质免疫印迹实验进一步表明，let-7f可在mRNA与蛋白质水平下调肌球蛋白IIA的表达。
结论与意义：本研究证实，在胃癌中过表达let-7f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与迁移能力。鉴于let-7f可抑制细胞侵袭与转移，上述研究结果表明let-7f或可成为胃癌治疗的新型候选靶点。