Effect of PCIF1 knockdown on gene exppression in HeLa S3 cells
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ABSTRACT: We previously identified PCIF1 (Phosphorylated CTD Interacting Factor 1) as a novel phosphorylated C-terminal domain (CTD) of RNA polymerase II. We also recently identified PCIF1 as a new cap-specific adenine N6 methyltransferase (CAPAM) responsible for creating N6, 2’-O-dimethyladenosine (m6Am) at the 5’-end of mRNAs. However, it remains unclear how PCIF1 regulates gene expression. To identify genes whose expression levels are affected by PCIF1 knockdown in human cultured cells, we performed gene expression profiling by microarray analysis.
Project description:The 5' end of eukaryotic mRNAs is protected by the m7G-cap structure. The transcription start site nucleotide is ribose methylated (Nm) in many eukaryotes, while an adenosine at this position is further methylated at the N6 position (m6A) by the mammalian Phosphorylated CTD-interacting Factor 1 (PCIF1) to generate m6Am. Here we show that while loss of cap-specific m6Am in mice does not affect viability or fertility, the Pcif1 mutants display reduced body-weight. Transcriptome analyses of mutant mouse tissues support a role for the cap-specific m6Am modification in stabilizing transcripts. In contrast, the Drosophila Pcif1 is catalytically-dead, but like its mammalian counterpart it retains the ability to associate with the Ser5-phosphorylated CTD of RNA pol II. Finally, we show that the Trypanosoma Pcif1 is an m6Am methylase that contributes to the N6,N6,2?-O-trimethyladenosine (m62Am) in the hypermethylated cap4 structure of Trypanosomatids. Thus, PCIF1 has evolved to function in catalytic and non-catalytic roles.
Project description:mRNAs are regulated by nucleotide modifications that influence their cellular fate. Two of the most abundant modified nucleotides are N6-methyladenosine (m6A), found within mRNAs, and N6,2′-O-dimethyladenosine (m6Am), which is found at the first transcribed nucleotide. Distinguishing these modifications in mapping studies has been difficult. Here, we identify and biochemically characterize PCIF1, the methyltransferase that generates m6Am. We find that PCIF1 binds and is dependent on the m7G cap. By depleting PCIF1, we generated transcriptome-wide maps that distinguish m6Am and m6A. We find that m6A and m6Am misannotations arise from mRNA isoforms with alternative transcription start sites (TSSs). These isoforms contain m6Am that maps to “internal” sites, increasing the likelihood of misannotation. We find that depleting PCIF1 does not substantially affect mRNA translation but is associated with reduced stability of a subset of m6Am-annotated mRNAs. The discovery of PCIF1 and our accurate mapping technique will facilitate future studies to characterize m6Am’s function.
Project description:T cell-based cancer immunotherapies have revolutionized cancer treatment, yet durable responses remain elusive. Here, we report that PCIF1, an RNA N6, 2’-O-dimethyladenosine (m6Am) methyltransferase, negatively regulates CD8+ T cell anti-tumor responses. Whole-body or T cell-specific Pcif1 knockout (KO) significantly reduces tumor growth in mice. Single-cell RNA sequencing reveals heightened tumor-infiltrating cytotoxic CD8+ T cells in Pcif1-deficient mice. Mechanistically, proteomic and m6Am-sequencing analyses pinpoint that Pcif1 KO elevates crucial m6Am-modified targets, specifically ferroptosis suppressor genes (Fth1, Slc3a2), and T cell activation gene Cd69, imparting resistance to ferroptosis and enhancing CD8+ T cell activation. Of note, Pcif1-deficient mice with tumors exhibit enhanced responses to anti-PD-1 immunotherapy, and Pcif1 KO CAR T cells demonstrate improved tumor control. Clinically, cancer patients with low PCIF1 expression in T cells exhibit enhanced responses to immunotherapies. These findings suggest that PCIF1 suppresses CD8+ T cell activation and targeting PCIF1 as a promising strategy to boost anti-tumor immunity.
Project description:N6-methyladenosine (m6A), a major modification of messenger RNAs (mRNAs), plays critical roles in RNA metabolism and function. In addition to the internal m6A, N6, 2'-O-dimethyladenosine (m6Am) is present at the transcription start nucleotide of capped mRNAs in vertebrates. However, its biogenesis and functional role remain elusive. Using a reverse genetics approach, we identified PCIF1, a factor that interacts with the serine-5-phosphorylated carboxyl-terminal domain of RNA polymerase II, as a cap-specific adenosine methyltransferase (CAPAM) responsible for N6-methylation of m6Am. The crystal structure of CAPAM in complex with substrates revealed the molecular basis of cap-specific m6A formation. A transcriptome-wide analysis revealed that N6-methylation of m6Am promotes the translation of capped mRNAs. Thus, a cap-specific m6A writer promotes translation of mRNAs starting from m6Am.
Project description:To identify m6Am genes that are responsible for HIV inhibition, m6Am-exo-seq was performed in control, PCIF1 KO T cells, and cells infected with HIV.
Project description:Purpose: To identify the in vivo RNA targets of PCIF1, we performed meRIP experiments for PCIF1 KD and control cells using an anti-m6A antibody. We envisioned that the cap-specific PCIF1 should selectively alter the m6Am modification at the 5-terminal region of transcripts. Indeed, we observed a reduction of modification peaks at the 5’-end but not the 3’-UTR regions of mRNA upon PCIF1 KD.
Project description:To identify m6Am genes that are responsible for HIV inhibition, MeRIP-seq was performed in control and PCIF1 KO T cells infected with HIV.
Project description:Various methylases and demethylases catalyze methylation and demethylation of N6-methyladenosine (m6A) and N6,2?-O-dimethyladenosine (m6Am) but precise methylomes uniquely mediated by each methylase/demethylase are still lacking. Here, we developed m6A-Crosslinking-Exonuclease-sequencing (m6ACE-seq) to map m6A and m6Am at transcriptome-wide single-base-resolution. m6ACE-seq's ability to quantify relative differences in methylation levels across samples enabled the generation of a comprehensive atlas of distinct methylomes uniquely mediated by every individual known methylase/demethylase. We determined METTL16 to indirectly impact manifold methylation targets beyond its consensus target motif, and highlighted the importance of precision in mapping PCIF1-dependent m6Am. Rather than reverse RNA methylation, we found that both ALKBH5 and FTO demethylases instead maintain their regulated sites in an unmethylated steady-state. In FTO's absence, anomalous m6Am disrupts snRNA interaction with nuclear export machinery, potentially causing aberrant pre-mRNA splicing events. We propose a model whereby RNA demethylases ensure normal RNA metabolism by suppressing disruptive RNA methylation in the nucleus.
Project description:N6,2'-O-dimethyladenosine (m6Am) is a critical and reversible RNA modification that plays a significant role in regulating RNA stability and gene expression. However, the lack of precise tools for manipulating m6Am modifications on specific transcripts has hindered the ability to elucidate the relationship between m6Am-modified transcripts and their phenotypic outcomes. Here, we present a CRISPR-Cas13d-based tool for the targeted installation of m6Am modifications on specific RNA transcripts. This tool is engineered by fusing a catalytically inactive variant of RfxCas13d (dCasRx) with the m6Am methyltransferase PCIF1. The dCasRx-PCIF1 fusion protein enables precise methylation of target m6Am-modified RNAs. We demonstrate that INSTALLER can effectively install m6Am modifications on GAPDH and ACTB RNAs, significantly enhancing their stability. MTD keywords Human, HEK293T cells MTD sample_processing_protocol Protein extraction and tryptic digestion. Cell lysates were lysed in lysis buffer (RPIA) supplemented with protease inhibitors and phosphatase inhibitors for 30 min. Then they were sonicated by grinding instrument at 4 ℃ and centrifuged at 12000 rpm for 15 min to remove the tissue debris. The protein in supernatants were collected and measured by using BCA protein assay. Next, 20 mM Tris (2-chloroethyl) phosphate (TCEP) was added to the protein solution to react at 60℃ for 1 h. After that, 200 mM Chloroacetamide (CAA) was added to the mixture and react at room temperature for 30 min in darkness. After the reaction, ice-cold acetone was used to precipitate the protein at -20℃ for 4 h. The pellet was air-dried and then resuspended in 150 μl 0.1M ABB. Protein samples underwent trypsin digestion (enzyme-to-substrate ratio of 1:25 at 37 ℃for 16 hours) followed by desalting through sola HRP cartridges and vacuum- dried by Speed Vac. Nano-LC-MS/MS analysis. Peptide samples were analyzed by an EASY-nLC 1200 LC system coupled with Orbitrap mass spectrometry (Thermo Fisher). The column was C18 nano-capillary analytical column (25 cm*75 mm, 1.9 μm). Peptides were re-dissolved in mobile phase A (Water/CAN/formic acid, 98/2/0.1, v/v). The gradient was 0-5 min, 5-10% B; 5-55 min, 10-28% B; 55-58 min, 28-40% B,58-63 min, 40-95% B; 63-75 min; 95% B with flow rate of 350 nL/min. Mass spectrometry was operated under a data independent acquisition mode (DIA). The m/z range was 350 to 1500 Da in MS1 with the resolution of 60,000. The automatic gain control (ACG) was set as 3e6. The maximal ion injection time was 50 ms. MS2 acquisition was higher energy collision dissociation (HCD) with the collision energy of 30 eV. The resolution was 30,000, with loop count set to: 25, MSX count set to: 1, isolation window set to: 8.3m/z, fixed maximum mass set to: 200m/z, respectively.
Project description:N6-methyladenosine (m6A) is the most abundant modified base in eukaryotic mRNA and has been linked to diverse effects on mRNA fate and function. Current m6A mapping approaches rely on immunoprecipitation of m6A-containing RNA fragments to identify regions of transcripts that contain m6A. This approach localizes m6A residues to 100-200 nt-long regions of transcripts. The precise position of m6A in mRNAs cannot be identified on a transcriptome-wide level because there are no chemical methods to distinguish between m6A and adenosine. Here we show that anti-m6A antibodies can induce specific mutational signatures at m6A residues after ultraviolet light-induced antibody-RNA crosslinking and reverse transcription. Similarly, we find these antibodies induce mutational signatures at N6, 2’-O-dimethyladenosine (m6Am), a nucleotide found at the first encoded position of certain mRNAs. Using these mutational signatures, we map m6A and m6Am at single-nucleotide resolution in human and mouse mRNA and identify snoRNAs as a novel class of m6A-containing ncRNAs. UV-crosslinking and immunoprecipitation with m6A-specific antibodies was used to map m6A and m6Am in cellular RNA with single nucleotide resolution.