MiR-24 tumor suppressor activity is regulated independent of p53 and through a target site polymorphism.
MicroRNAs (miRNAs) are predicted to regulate approximately 30% of all human genes; however, only a few miRNAs have been assigned their targets and specific functions. Here we demonstrate that miR-24, a ubiquitously expressed miRNA, has an anti-proliferative effect independent of p53 function. Cell lines with differential p53 status were used as a model to study the effects of miR-24 on cell proliferation, cell cycle control, gene regulation and cellular transformation. Overexpression of miR-24 in six different cell lines, independent of p53 function, inhibited cell proliferation and resulted in G2/S cell cycle arrest. MiR-24 over expression in cells with wt-p53 upregulated TP53 and p21 protein; however, in p53-null cells miR-24 still induced cell cycle arrest without the involvement of p21. We show that miR-24 regulates p53-independent cellular proliferation by regulating an S-phase enzyme, dihydrofolate reductase (DHFR) a target of the chemotherapeutic drug methotrexate (MTX). Of interest, we found that a miR-24 target site polymorphism in DHFR 3' UTR that results in loss of miR-24-function and high DHFR levels in the cell imparts a growth advantage to immortalized cells and induces neoplastic transformation. Of clinical significance, we found that miR-24 is deregulated in human colorectal cancer tumors and a subset of tumors has reduced levels of miR-24. A novel function for miR-24 as a p53-independent cell cycle inhibitory miRNA is proposed.
Mishra
Prasun J
PJ
Laboratory of Cancer Biology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, United States of America.
Song
Bo
B
Mishra
Pravin J
PJ
Wang
Yuan
Y
Humeniuk
Rita
R
Banerjee
Debabrata
D
Merlino
Glenn
G
Ju
Jingfang
J
Bertino
Joseph R
JR
D020413:3' Untranslated Regions / Q000235:genetics; D000818:Animals; D002448:Cell Adhesion / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D048430:Cell Shape / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D015536:Down-Regulation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D016195:G2 Phase / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008727:Methotrexate / Q000494:pharmacology; D051379:Mice; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D041681:NIH 3T3 Cells; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D016196:S Phase / Q000187:drug effects; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D020413:3' Untranslated Regions; D018797:Cell Cycle Proteins; C543845:MIRN24 microRNA, human; D035683:MicroRNAs; D016159:Tumor Suppressor Protein p53; D013762:Tetrahydrofolate Dehydrogenase; D008727:Methotrexate