Department of Cell Biology and Medical Genetics, Molecular Medicine and Cancer Research Center, Chongqing Medical University, No. 1, Medical College Road, 400016 Chongqing, China.
J Cancer Res Clin Oncol. 2010 Jul;136(7):1023-8. doi: 10.1007/s00432-009-0747-5. Epub 2009 Dec 22.
Down-regulation of let-7 microRNA (miRNA) plays an important role in the pathogenesis of lung cancer. k-Ras and c-Myc, two key oncogenes in lung cancer, have been found to be targeted by let-7 in vitro. However, the in vivo relevance of these findings is unknown. The aim of the present study is to determine the effect of let-7a, a member of let-7 family, on the growth of lung cancer in vivo and to investigate whether let-7-induced suppression of k-Ras and c-Myc is involved in lung cancer.
A549-let-7a cell line and A549-control cell line, two stable transfected cell lines over-expressing let-7a and the control miRNA, were established and preserved in our lab. A549, A549-control, and A549-let-7a cells were injected subcutaneously into nude mice, respectively. After 30 days, the mice were killed; the xenografts were excised and weighed. The expression of let-7a in tumor xenografts was assessed by real-time reverse transcription-PCR (RT-PCR). The expression of k-Ras and c-Myc in xenografts were determined by western blot and immunohistochemistry detection.
Real-time RT-PCR showed the expression of let-7a was increased significantly in A549-let-7a cells-injected group, compared with A549-control cells-injected group and A549 cells-injected group (P < 0.01). In the xenografts of A549-let-7a cells-injected group, a significant depression in tumor weight (P < 0.05) and significant decrease of k-Ras and c-Myc protein were observed (P < 0.01), compared to A549 cells-injected group and A549-control cells-injected group.
Overexpression of let-7a can inhibit the growth of lung cancer transplanted subcutaneously in nude mice by suppression of k-Ras and c-Myc.
下调 let-7 微 RNA（miRNA）在肺癌发病机制中起着重要作用。体外研究发现，肺癌中的两个关键癌基因 k-Ras 和 c-Myc 可被 let-7 靶向。然而，这些发现的体内相关性尚不清楚。本研究旨在确定 let-7a，let-7 家族的一个成员，对体内肺癌生长的影响，并研究 let-7 诱导的 k-Ras 和 c-Myc 抑制是否参与肺癌。
我们实验室建立并保存了稳定转染 let-7a 和对照 miRNA 的 A549-let-7a 细胞系和 A549-对照细胞系。将 A549、A549-对照和 A549-let-7a 细胞分别皮下注射入裸鼠，30 天后处死小鼠，切除移植瘤并称重。实时逆转录-PCR（RT-PCR）评估肿瘤移植瘤中 let-7a 的表达。Western blot 和免疫组化检测检测移植瘤中 k-Ras 和 c-Myc 的表达。
实时 RT-PCR 显示，与 A549-对照细胞系和 A549 细胞系注射组相比，A549-let-7a 细胞系注射组中 let-7a 的表达显著增加（P <0.01）。在 A549-let-7a 细胞系注射组的移植瘤中，肿瘤重量明显降低（P <0.05），k-Ras 和 c-Myc 蛋白明显减少（P <0.01），与 A549 细胞系和 A549-对照细胞系注射组相比。
过表达 let-7a 可通过抑制 k-Ras 和 c-Myc 抑制裸鼠皮下移植肺癌的生长。
