MicroRNA-21 targets the tumor suppressor gene tropomyosin 1 (TPM1).
MicroRNAs are small noncoding RNA molecules that control expression of target genes. Our previous studies show that mir-21 is overexpressed in tumor tissues compared with the matched normal tissues. Moreover, suppression of mir-21 by antisense oligonucleotides inhibits tumor cell growth both in vitro and in vivo. However, it remains largely unclear as to how mir-21 affects tumor growth, because our understanding of mir-21 targets is limited. In this study, we performed two-dimensional differentiation in-gel electrophoresis of tumors treated with anti-mir-21 and identified the tumor suppressor tropomyosin 1 (TPM1) as a potential mir-21 target. In agreement with this, there is a putative mir-21 binding site at the 3'-untranslated region (3'-UTR) of TPM1 variants V1 and V5. Thus, we cloned the 3'-UTR of TPM1 into a luciferase reporter and found that although mir-21 down-regulated the luciferase activity, anti-mir-21 up-regulated it. Moreover, deletion of the mir-21 binding site abolished the effect of mir-21 on the luciferase activity, suggesting that this mir-21 binding site is critical. Western blot with the cloned TPM1-V1 plus the 3'-UTR indicated that TPM1 protein level was also regulated by mir-21, whereas real-time quantitative reverse transcription-PCR revealed no difference at the mRNA level, suggesting translational regulation. Finally, overexpression of TPM1 in breast cancer MCF-7 cells suppressed anchorage-independent growth. Thus, down-regulation of TPM1 by mir-21 may explain, at least in part, why suppression of mir-21 can inhibit tumor growth, further supporting the notion that mir-21 functions as an oncogene.
Zhu
Shuomin
S
Department of Medical Microbiology, Immunology, and Cell Biology, Southern Illinois University School of Medicine, Springfield, IL 62794, USA.
Si
Min-Liang
ML
Wu
Hailong
H
Mo
Yin-Yuan
YY
D020413:3' Untranslated Regions / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008156:Luciferases; D051379:Mice; D008819:Mice, Nude; D035683:MicroRNAs / Q000037:antagonists & inhibitors / Q000502:physiology*; D016376:Oligonucleotides, Antisense / Q000494:pharmacology*; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014335:Tropomyosin / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D014410:Tumor Stem Cell Assay
D020413:3' Untranslated Regions; D035683:MicroRNAs; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; C490775:TPM1 protein, human; C490774:Tpm1 protein, mouse; D014335:Tropomyosin; D008156:Luciferases