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Here, we describe the Ago2-miRNA-co-IP assay designed to quantify an active pool of specific miRNAs induced by TGF-β1 in human bronchial epithelial CFBE41o- cells. This assay provides functional information on the recruitment of miRNA to the RNA induced silencing complex, quantified by qRT-PCR using specific miRNA primers and TaqMan hydrolysis probes.
Micro(mi)RNAs are short, non-coding RNAs that mediate the RNA interference (RNAi) by post-transcriptional mechanisms. Specific miRNAs are recruited to the cytoplasmic RNA induced silencing complex (RISC). Argonaute2 (Ago2), an essential component of RISC, facilitates binding of miRNA to the target-site on mRNA, followed by cleaving the miRNA-mRNA duplex with its endonuclease activity. RNAi is mediated by a specific pool of miRNAs recruited to RISC, and thus is referred to as the functional pool. The cellular levels of many miRNAs are affected by the cytokine Transforming Growth Factor-β1 (TGF-β1). However, little is known about whether the TGF-β1 affects the functional pools of these miRNAs. The Ago2-miRNA-co-IP assay, discussed in this manuscript, is designed to examine effects of TGF-β1 on the recruitment of miRNAs to RISC and it helps to determine whether changes in the cellular miRNA levels correlate with changes in the RISC-associated, functional pools. The general principles of the assay are as follows. Cultured cells treated with TGF-β1 or vehicle control are lysed and the endogenous Ago2 is immunoprecipitated with immobilized anti-Ago2 antibody, and the active miRNAs complexed with Ago2 are isolated with a RISC immunoprecipitation (RIP) assay kit. The miRNAs are identified with quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) using miRNA-specific stem-looped primers during reverse transcription, followed by PCR using miRNA-specific forward and reverse primers, and TaqMan hydrolysis probes.
Transforming Growth Factor-β1 (TGF-β1) is a multifunctional cytokine that can change the expression of many micro(mi)RNAs1,2,3. The total cellular level of a particular miRNA does not correlate with its inhibitory potential because only a specific fraction of the miRNA is incorporated into RNA induced silencing complex (RISC) to perform RNA interference (RNAi)3. Only up to 10% of each miRNA is RISC-associated and participates in RNAi4,5. Next, the RNAi process involves binding of the RISC-associated miRNA to the target mRNA recognition sequence(s)6. The RISC association is influenced by the availability of the target mRNA and the miRNA complementarity to the binding site, usually present at 3’ untranslated region (UTR) of the mRNA4. The Argonaute2-miRNA-co-immunoprecipitation (Ago2-miRNA-co-IP) assay, described in this manuscript, is designed to examine the effect of TGF-β1 on the recruitment of specific miRNAs to RISC by detecting differences in the RISC-associated miRNAs after TGF-β1 treatment, compared to the vehicle control. Examining the RISC-associated functional pool of a specific miRNA is much more informative about the miRNA effects than examining the total cellular level of the miRNA. RISC consists of proteins that scan the binding site on the target mRNA and cleave the miRNA-mRNA duplex. Argonaute2 (Ago2) is the main component of RISC. Out of the five Ago isoforms (Ago1-Ago5), Ago2 is the only one that has endonuclease activity and participates in RNAi in human cells7,8,9,10. The Ago2-miRNA-RISC complex is the functional unit for miRNA-mediated post-transcriptional mRNA repression11. The Ago2-associated miRNA represents the native state of miRNA in response to intracellular or extracellular signaling. Thus, immunoprecipitation of the endogenous Ago2 provides an excellent opportunity to detect the active, RISC-associated fraction of a specific miRNA as well as the functional assessment of its targets. This assay is superior to the pull-down of endogenous target mRNA with biotinylated miRNA mimics because of unpredictable efficiency of the cellular uptake of biotinylated nucleic acid molecules and their off-target effects.
The Ago2-miRNA-co-IP assay, discussed in this manuscript, was optimized to determine the effects of TGF-β1 on RISC recruitment of miRNAs in immortalized human bronchial epithelial CFBE41o- cells3. Components of the RIP assay kit were used to perform Ago2-miRNA-co-IP assay with modifications in the protocol provided by the manufacturer. A separation method was used to isolate small and large RNA, in which small RNA was used to quantify miRNA with the help of quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) using miRNA-specific stem-looped primers during reverse transcription, followed by PCR using miRNA-specific forward and reverse primers, and TaqMan hydrolysis probes.
1. Preparation before experiment
2. Immunoprecipitation of Ago2
3. RNA Isolation
4. Quantification of miRNA by quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR)
We have previously shown that TGF-β1 increased the total cellular levels of miR-145-5p, miR-143-5p, and miR-154-5p miRNAs in CFBE41o- cells3. Next, we employed the Ago2-miRNA-co-IP assay to elucidate the functional effects of TGF-β1 on these miRNAs. The RISC recruitment of miR-145-5p, miR-143-5p, and miR-154-5p was studied in CFBE41o- cells stably expressing the wild type (WT)-cystic fibrosis transmembrane conductance regulator (CFTR) or mutant CFTR with the deletion of phenylalanin...
The Ago2-miRNA-co-IP assay is designed to investigate the active pool of miRNAs in response to TGF-β1 treatment. The active or RISC-associated miRNAs are important to understand their inhibitory potential for the target mRNA4. Panshin et al. recently showed that the immunoprecipitation efficiency of Ago2 and miRNAs may depend on the protocol16. There are several differences between the protocol here and the above published data. The protocol here was optimized for CFBE...
The authors declare that, they have no competing financial interest, and they have nothing to disclose.
We thank John Wakefield from Tranzyme, Inc. (Birmingham, AL) who generated the CFBE41o- cells, and J.P. Clancy from the CFFT who provided the cells. This research was funded by the National Institutes of Health grants R01HL144539 and R56HL127202 (to A.S.-U.), and the Cystic Fibrosis Foundation grant SWIATE18G0.
Name | Company | Catalog Number | Comments |
100 mM dNTPs (with dTTPs) | Applied Biosystems | 4366596 | |
10x Reverse Transcription Buffer (RT Buffer) | Applied Biosystems | 4366596 | |
2-propanol | Fisher BioReagents | BP2618-1 | |
2x Laemmli Sample Buffer | Bio-Rad | 1610737 | |
7300 Real Time PCR System | Applied Biosystems | 4345240 | |
Anti-Ago2 antibody (anti-EIF2C2), mouse monoclonal against human Ago2 | Medical & Biological Laboratories Co. Ltd | RN003M | |
Bovine Albumin Fraction V (7.5% solution) | Thermo Scientific | 15260037 | |
Collagen I (Purecol-Type I Bovie collagen solution) | Advanced Biometrix | 50005-100mL | |
DL-Dithiothreitol (DTT) | Sigma | 646563-.5ML | |
DTT | Sigma-Aldrich | 646563 | |
Ethanol | Deacon Laboratories | 64175 | |
Fetal Bovine Serum | ATLANTA Biologicals | S10350 | |
Goat Anti-Mouse IgG | Bio-Rad | 1706516 | |
L-glutamine (200 mM Solution; 29.20 mg/mL) | Corning | 25-005-Cl | |
Mini cell scrapers United Biosystems | Thermo Fisher | MCS-200 | |
Minimal Essential Medium | Thermo Fisher Scientific | 11095-080 | |
miRNA specific stem looped RT primers | Applied Biosystems | 4427975 | |
Mouse IgG2 control | Dako, Glostrup, Denmark | A0424 | |
MultiScribe Reverse Transcriptase, 50 U/µL | Applied Biosystems | 4366596 | |
Nano Drop ND-1000 Spectrophotometer | NanoDrop Technologies, Inc. | E112352 | |
Nuclease-free water | Ambion | AM9937 | |
Opti-MEM (1x) Reduced Serum Medium | Gibco by Life Technologies | 11058-021 | |
PBS | Gibco | 14190250 | |
Penicillin-streptomycin, Sterile | Sigma-Aldrich | P0781 | |
Pierce Protease Inhibitor Tablets, EDTA-Free | Thermo Scientific | A32955 | |
Protein G agarose beads (Pierce Protein G Plus Agarose) | Thermo Scientific | 22851 | |
Puromycin | InvivoGen | ant-pr-1 | |
RiboCluster Profiler RIP-Assay Kit for microRNA | Medical & Biological Laboratories Co. Ltd | RN1005 | |
RNase Inhibitor, 20 U/µL | Applied Biosystems | 4366596 | |
TaqMan 2x Universal PCR master mix without AmpErase UNG | Applied Biosystems | 4427975 | |
TaqMan miRNA single tube Assay (20x) containing miRNA specific forward/reverse primers and probe | Applied Biosystems | 4427975 (assay ID #002278, #002146, and #000477) | |
TGF-beta1 | Sigma | T1654 | |
Transwell filters (24 mm) | Corning Life Sciences Plastic | 3412 | |
Veriti 96 Well Thermal Cycler (Model:9902) | Applied Biosystems | 4375786 |
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