miR-192 Regulates dihydrofolate reductase and cellular proliferation through the p53-microRNA circuit.
OBJECTIVE
The purpose of this study is to investigate the molecular mechanism of miR-192 in colon cancer.


METHODS
Human colon cancer cell lines with different p53 status were used as our model system to study the effect of miR-192 on cell proliferation, cell cycle control, and mechanism of regulation.


RESULTS
Our results show that one of the key miR-192 target genes is dihydrofolate reductase (DHFR). miR-192 affects cellular proliferation through the p53-miRNA circuit. Western immunoblot analyses indicated that the expression of DHFR was significantly decreased by miR-192. Further investigation revealed that such suppression was due to translational arrest rather than mRNA degradation. More profound inhibition of cellular proliferation was observed by ectopic expression of miR-192 in colon cancer cell lines containing wild-type p53 than cells containing mutant p53. Thus, the effect of miR-192 on cellular proliferation is mainly p53 dependent. Overexpression of miR-192 triggered both G1 and G2 arrest in HCT-116 (wt-p53) cells but not in HCT-116 (null-p53) cells. The cell cycle checkpoint control genes p53 and p21 were highly overexpressed in cells that overexpressed miR-192. Endogenous miR-192 expression was increased in HCT-116 (wt-p53) and RKO (wt-p53) cells treated with methotrexate, which caused an induction of p53 expression. Chromatin immunoprecipitation-quantitative reverse transcription-PCR analysis revealed that the p53 protein interacted with the miR-192 promoter sequence.


CONCLUSIONS
These results indicate that miR-192 may be another miRNA candidate that is involved in the p53 tumor suppressor network with significant effect on cell cycle control and cell proliferation.
Song
Bo
B
Translational Research Laboratory, Department of Pathology, Stony Brook University Medical Center, Stony Brook, New York 11794-8691, USA.
Wang
Yuan
Y
Kudo
Kenji
K
Gavin
Elaine J
EJ
Xi
Yaguang
Y
Ju
Jingfang
J
D002453:Cell Cycle; D049109:Cell Proliferation; D015971:Gene Expression Regulation, Enzymologic; D045325:HCT116 Cells; D019073:HT29 Cells; D006801:Humans; D008727:Methotrexate / Q000494:pharmacology; D035683:MicroRNAs / Q000502:physiology*; D011401:Promoter Regions, Genetic; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*
D035683:MicroRNAs; D016159:Tumor Suppressor Protein p53; D013762:Tetrahydrofolate Dehydrogenase; D008727:Methotrexate