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Molecular and Cellular Biology, July 2009, p. 3754-3769, Vol. 29, No. 13
0270-7306/09/$08.00+0 doi:10.1128/MCB.01836-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
The NF90-NF45 Complex Functions as a Negative Regulator in the MicroRNA Processing Pathway
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Shuji Sakamoto,1,2*
Kazuma Aoki,2,3
Takuma Higuchi,1
Hiroshi Todaka,1
Keiko Morisawa,1
Nobuyuki Tamaki,2,4
Etsuro Hatano,4
Atsuki Fukushima,5
Taketoshi Taniguchi,1 and
Yasutoshi Agata2,6
Laboratory of Molecular Biology, Science Research Center, Kochi Medical School, Kochi 783-8505, Japan,1 Horizontal Medical Research Organization, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan,2 Biological Information Research Center, National Institute of Advanced Industrial Science and Technology, Japan Biological Informatics Consortium, Tokyo, Japan,3 Department of Surgery, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan,4 Department of Ophthalmology, Kochi Medical School, Kochi 783-8505, Japan,5 Department of Immunology and Cell Biology, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan6
Received 2 December 2008/ Returned for modification 30 January 2009/ Accepted 17 April 2009
The positive regulatory machinery in the microRNA (miRNA) processing pathway is relatively well characterized, but negative regulation of the pathway is largely unknown. Here we show that a complex of nuclear factor 90 (NF90) and NF45 proteins functions as a negative regulator in miRNA biogenesis. Primary miRNA (pri-miRNA) processing into precursor miRNA (pre-miRNA) was inhibited by overexpression of the NF90 and NF45 proteins, and considerable amounts of pri-miRNAs accumulated in cells coexpressing NF90 and NF45. Treatment of cells overexpressing NF90 and NF45 with an RNA polymerase II inhibitor, 
-amanitin, did not reduce the amounts of pri-miRNAs, suggesting that the accumulation of pri-miRNAs is not due to transcriptional activation. In addition, the NF90 and NF45 complex was not found to interact with the Microprocessor complex, which is a processing factor of pri-miRNAs, but was found to bind endogenous pri-miRNAs. NF90-NF45 exhibited higher binding activity for pri-let-7a than pri-miR-21. Of note, depletion of NF90 caused a reduction of pri-let-7a and an increase of mature let-7a miRNA, which has a potent antiproliferative activity, and caused growth suppression of transformed cells. These findings suggest that the association of the NF90-NF45 complex with pri-miRNAs impairs access of the Microprocessor complex to the pri-miRNAs, resulting in a reduction of mature miRNA production.
* Corresponding author. Mailing address: Laboratory of Molecular Biology, Science Research Center, Kochi Medical School, Kochi 783-8505, Japan. Phone: 81-88-880-2767. Fax: 81-88-880-2431. E-mail: sshuji{at}kochi-u.ac.jp
Published ahead of print on 27 April 2009.
Supplemental material for this article may be found at http://mcb.asm.org/.
Molecular and Cellular Biology, July 2009, p. 3754-3769, Vol. 29, No. 13
0270-7306/09/$08.00+0 doi:10.1128/MCB.01836-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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