The NF90-NF45 Complex Functions as a Negative Regulator in the MicroRNA Processing Pathway

Abstract

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 primiRNAs, 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.MicroRNAs (miRNAs) constitute a class of noncoding small RNAs that function as repressors for eukaryotic gene regulation by binding to the 3Ј untranslated regions of target mRNAs (2). This binding causes mRNA cleavage or translational inhibition of the mRNA, depending upon the degree of complementarity. The lengths of miRNAs are 21 to 23 nucleotides (nt), and over 500 miRNAs have been discovered in mammals. miRNAs regulate the expression of a large number of genes (38) that are involved in cell proliferation, apoptosis, hematopoietic differentiation, viral infection, and tumorigenesis (4,5,7,22,26,32,39,45).In mammals, miRNA genes are transcribed by RNA polymerase II as primary miRNAs (pri-miRNAs) (36). These primiRNAs are processed into precursor miRNAs (pre-miRNAs) by the Microprocessor complex (8,13,20,31,33). Another complex comprised of exportin-5 and RanGTP transports the pre-miRNAs from the nucleus to the cytoplasm (3, 40, 58). In the cytoplasm, Dicer, a cytoplasmic RNase III enzyme, cleaves the pre-miRNAs to approximate 22-nt mature miRNA duplexes with 2-nt 3Ј overhangs (14,24,28). One strand of the duplex is incorporated into the RNA-induced silencing complex (12,19,29,41,51). The single strand of RNA guides the RNA-induced silencing complex to the target mRNA with sequence complementarity, which leads either to mRNA cleavage or to translational repression (12,24,41,44).The Microprocessor complex, which cleaves pri-miRNA to pre-miRNA during miRNA biogenesis, is comprised of a nuclear RNase III enzyme, Drosha, and its cofactor, DGCR8 (8,13,20). In addition to the Microprocessor complex, excessively expressed Drosha forms ...

TGFβ1 Promotes Gemcitabine Resistance through Regulating the LncRNA-LET/NF90/miR-145 Signaling Axis in Bladder Cancer

“…In addition to regulating the expression of different genes post-transcriptionally, NF90 also takes part in miRNA biogenesis. As a competitor for the association of the microprocessor complex with pri-miRNAs, NF90 usually inhibits miRNA production (27,41,42). We found that lncRNA-LET depletion resulted in elevated level of NF90 which in turn blocks miR-145 biogenesis by competitively binding to pri-miR-145 specifically.…”

ALS-associated mutations in TDP-43 increase its stability and promote TDP-43 complexes with FUS/TLS

“…The overlapping components between epitope-tagged Drosha (38) and TDP-43 (in this study) strongly suggest that TDP-43 is involved in microRNA biogenesis. Indeed, NF45/NF90 has been shown to complex with pre-miRNAs, and this association reduces the generation of mature miRNAs (49). In addition, adenosine deaminases (ADARs), found to bind to TDP-43 in our proteomic study, are known to influence microRNA processing through their editing activities (50).…”

Regulation of let-7 and its target oncogenes (Review)

“…The NF90-NF45 complex may thus inhibit the processing of pri-miRNA by the DGCR8-Drosha complex. NF90-NF45 also showed a higher binding affinity for pri-let-7a-1 than for pri-miR-21 (33).…”