The let-7a microRNA protects from growth of lung carcinoma by suppression of k-Ras and c-Myc in nude mice.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
Overexpression of let-7a can inhibit the growth of lung cancer transplanted subcutaneously in nude mice by suppression of k-Ras and c-Myc.
He
Xiao-Yan
XY
Department of Cell Biology and Medical Genetics, Molecular Medicine and Cancer Research Center, Chongqing Medical University, No. 1, Medical College Road, 400016 Chongqing, China.
Chen
Jun-xia
JX
Zhang
Zheng
Z
Li
Chun-lei
CL
Peng
Qiong-le
QL
Peng
Hui-min
HM
D000818:Animals; D015153:Blotting, Western; D015536:Down-Regulation; D007150:Immunohistochemistry; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D051379:Mice; D008819:Mice, Nude; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D009374:Neoplasms, Experimental / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D035683:MicroRNAs; D016271:Proto-Oncogene Proteins c-myc; C542687:mirnlet7 microRNA, mouse; C495971:Hras protein, mouse; D016283:Proto-Oncogene Proteins p21(ras)