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. 2008 Jul 3;454(7200):56-61.
doi: 10.1038/nature07086. Epub 2008 Jun 11.

SMAD proteins control DROSHA-mediated microRNA maturation

Brandi N Davis  1 , Aaron C Hilyard, Giorgio Lagna, Akiko Hata
Affiliations

SMAD proteins control DROSHA-mediated microRNA maturation

Brandi N Davis et al. Nature. .

Abstract

MicroRNAs (miRNAs) are small non-coding RNAs that participate in the spatiotemporal regulation of messenger RNA and protein synthesis. Aberrant miRNA expression leads to developmental abnormalities and diseases, such as cardiovascular disorders and cancer; however, the stimuli and processes regulating miRNA biogenesis are largely unknown. The transforming growth factor beta (TGF-beta) and bone morphogenetic protein (BMP) family of growth factors orchestrates fundamental biological processes in development and in the homeostasis of adult tissues, including the vasculature. Here we show that induction of a contractile phenotype in human vascular smooth muscle cells by TGF-beta and BMPs is mediated by miR-21. miR-21 downregulates PDCD4 (programmed cell death 4), which in turn acts as a negative regulator of smooth muscle contractile genes. Surprisingly, TGF-beta and BMP signalling promotes a rapid increase in expression of mature miR-21 through a post-transcriptional step, promoting the processing of primary transcripts of miR-21 (pri-miR-21) into precursor miR-21 (pre-miR-21) by the DROSHA (also known as RNASEN) complex. TGF-beta- and BMP-specific SMAD signal transducers are recruited to pri-miR-21 in a complex with the RNA helicase p68 (also known as DDX5), a component of the DROSHA microprocessor complex. The shared cofactor SMAD4 is not required for this process. Thus, regulation of miRNA biogenesis by ligand-specific SMAD proteins is critical for control of the vascular smooth muscle cell phenotype and potentially for SMAD4-independent responses mediated by the TGF-beta and BMP signalling pathways.

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Figures

Figure 1
Figure 1. miR-21 is critical for the modulation of the VSMC phenotype by BMP
a, The level of expression of miRNAs normalized to U6 small nuclear RNA (snRNA) in PASMCs treated with BMP4 for 24 h (*P < 0.05, n = 4). b, PASMCs transfected with antisense RNA oligonucleotides against different miRNAs or GFP (control). After BMP4 treatment (48 h), cells were stained with anti-SMA antibody (green) and 4,6-diamidino-2-phenylindole (DAPI; blue). c, PASMCs were infected with an adenovirus carrying CMV-driven GFP (control; Ad-GFP), miR-21 (Ad-miR-21) or miR-125b (Ad-miR-125b). The SMA mRNA level was measured after BMP4 treatment (48 h) (*P < 0.05, n = 4). d, 10T1/2 cells were transfected with vector (mock) or a human PDCD4 cDNA construct, followed by BMP4 treatment (24 h). Expression of Sma, calponin, Sm22α, Id3 or human PDCD4 relative to GAPDH mRNA is shown (*P < 0.001, n = 3). e, PASMCs transfected with control siRNA (Control-siRNA) or siRNA for PDCD4 (PDCD4-siRNA). Relative mRNA expression is shown as in d. Error bars represent s.e.m.
Figure 2
Figure 2. Post-transcriptional regulation of miR-21 biosynthesis by TGF-β
a, Expression of mature miR-21 and miR-199a normalized to U6 snRNA in PASMCs stimulated with BMP4 or TGF-β (24 h; *P < 0.05; n = 3). b, Time course of pri-miR-21, pre-miR-21 or mature miR-21 expression in PASMCs on stimulation with BMP4 (upper panel) or TGF-β (lower panel). c, PASMCs pretreated with α-amanitin were stimulated with BMP4 (5 h). Expression of pri-miR-21, pre-miR-21 and mature miR-21 or ID1 is shown (*P < 0.05; n = 3). d, Relative expression of pri-miR-21, pre-miR-21 and mature miR-21 derived from increasing amounts of human miR-21 expression construct (pCMV-miR-21) transfected into 10T1/2 cells (*P < 0.05; n = 3). Error bars represent s.e.m.
Figure 3
Figure 3. Interaction of SMADs with p68, a component of the DROSHA complex
a, PASMCs were transfected with control siRNA (Control-siRNA) or a mixture of siRNAs for SMAD1 and SMAD5 (SMAD-siRNA). After BMP4 treatment (2 h), the expression of pri-miR-21, pre-miR-21 and mature miR-21 was compared (top panel). As controls, expression of ID3, SMAD1, SMAD5 and SMA is shown (bottom panel). NS, not significant (P > 0.05). b, PASMCs were transfected with control siRNA (Control-siRNA) or siRNAs for p68 (p68-siRNA). Expression of pri-miR-21, pre-miR-21 and mature miR-21 was examined after BMP4 treatment (2 h) (*P < 0.05; n = 3). c, Nuclear extracts prepared from PASMCs treated with BMP4 (2 h) and subjected to immunoprecipitation with anti-p68, anti-DROSHA antibody, or non-specific IgG (control), followed by immunostaining with anti-SMAD1/5, anti-p68 or anti-DROSHA antibody. Nuclear extracts were immunostained with anti-lamin A/C antibody (control). IB, immunoblot; error bars represent s.e.m.
Figure 4
Figure 4. Association of SMADs with pri-miRNA promotes processing by DROSHA
a, Cos7 cells transfected with pCMV-miR-21 and Flag–SMAD1, Flag–SMAD3 or Flag–SMAD2, followed by BMP4 or TGF-β treatment (2 h). RNA-ChIP performed with anti-Flag antibody or non-specific IgG (control), followed by PCR amplification with miR-21 primers (*P < 0.05, compared to no treatment; n = 4). IP, immunoprecipitation. b, After treatment of PASMCs with BMP4 or TGF-β (1 h), endogenous SMAD1/SMAD5, SMAD2/ SMAD3, p68 or DROSHA were immunoprecipitated and subjected to PCR analysis with miR-21, miR-199a or miR-214 primers. As controls, RNA samples untreated with reverse transcriptase (–RT) or immunoprecipitated with non-specific IgG (IgG) were subjected to PCR (*P < 0.05 compared to none; n = 4). c, In vitro pri-miRNA processing assay performed by incubating pri-miR-21 substrate with the nuclear extracts prepared from Cos7 cells treated with vehicle, BMP4 or TGF-β (2 h). nt, nucleotide; error bars represent s.e.m.
Figure 5
Figure 5. SMAD4-independent mechanism of maturation of pri-miRNA
a, Level of expression of pri-miR-21, pre-miR-21 and mature miR-21 or SMAD4 after treatment with BMP4 (2 h) in PASMCs transfected with control siRNA (Control-siRNA) or SMAD4 siRNA (SMAD4-siRNA). b, Level of expression of pri-miR-21, pre-miR-21 and mature miR-21 or PAI-1 in human SMAD4-negative breast carcinoma MDA-MB-468 cells stimulated with TGF-β (0.5 h) (*P < 0.05; n = 3). c, MDA-MB-468 cells were treated with TGF-β (1 h) before RNA-ChIP. Endogenous proteins were precipitated with anti-SMAD1/SMAD5, anti-SMAD2/SMAD3 or anti-DROSHA antibodies, followed by PCR analysis with a miR-21 primer (*P < 0.05, compared to none; n = 3). d, MDA-MB-468 cells were infected with adenovirus carrying dominant-negative type I TGF-β receptor (dnALK5), an inhibitor of TGF-β signalling, before TGF-β treatment (1 h). The amount of pri-miR-21, pre-miR-21 and mature miR-21 was examined (*P < 0.05, compared to none; n = 3). Error bars represent s.e.m.
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