MicroRNA-21 promotes cell transformation by targeting the programmed cell death 4 gene.
MicroRNAs (miRNAs) are small noncoding RNA molecules that negatively control expression of target genes in animals and plants. The microRNA-21 gene (mir-21) has been identified as the only miRNA commonly overexpressed in solid tumors of the lung, breast, stomach, prostate, colon, brain, head and neck, esophagus and pancreas. We initiated a screen to identify miR-21 target genes using a reporter assay and identified a potential miR-21 target in the 3'-UTR of the programmed cell death 4 (PDCD4) gene. We cloned the full-length 3'-UTR of human PDCD4 downstream of a reporter and found that mir-21 downregulated, whereas a modified antisense RNA to miR-21 upregulated reporter activity. Moreover, deletion of the putative miR-21-binding site (miRNA regulatory element, MRE) from the 3'-UTR of PDCD4, or mutations in the MRE abolished the ability of miR-21 to inhibit reporter activity, indicating that this MRE is a critical regulatory region. Western blotting showed that Pdcd4 protein levels were reduced by miR-21 in human and mouse cells, whereas quantitative real-time PCR revealed little difference at the mRNA level, suggesting translational regulation. Finally, overexpression of mir-21 in MCF-7 human breast cancer cells and mouse epidermal JB6 cells promoted soft agar colony formation by downregulating Pdcd4 protein levels. The demonstration that miR-21 promotes cell transformation supports the concept that mir-21 functions as an oncogene by a mechanism that involves translational repression of the tumor suppressor Pdcd4.
Lu
Z
Z
Department of Biochemistry and Molecular Biology, University of Louisville, Louisville, KY 40202, USA.
Liu
M
M
Stribinskis
V
V
Klinge
C M
CM
Ramos
K S
KS
Colburn
N H
NH
Li
Y
Y
D020413:3' Untranslated Regions; D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051379:Mice; D035683:MicroRNAs / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000737:chemistry; D010641:Phenotype; D014176:Protein Biosynthesis; D012313:RNA / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D014018:Tissue Distribution
D020413:3' Untranslated Regions; D051017:Apoptosis Regulatory Proteins; C524940:MIRN21 microRNA, human; D035683:MicroRNAs; D016376:Oligonucleotides, Antisense; C114487:PDCD4 protein, human; D016601:RNA-Binding Proteins; D012313:RNA