M6A-seq data analysis of control and PCIF1 knockdown transcriptome
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ABSTRACT: 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: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: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: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: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:We analyzed m6A distribution by m6A MeRIP in otder to determine the effect of PCIF1 KO over m6A distribution in human melanoma cells
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: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: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:N6-methyladenosine (m6A) is a widespread internal RNA modification whose function is poorly understood. Here we report that m6A residues within the 5'UTR promote a novel form of cap-independent translation which is mediated through an interaction between m6A residues and the translation initiation factor, eIF3. We performed m6A profiling in cells subjected to heat shock stress and observed increased 5'UTR methylation after heat shock. For these studies, we used single-nucleotide resolution m6A mapping (miCLIP), which enables the detection of m6A residues separately from m6Am residues. Thus, the goal of these experiments was to identify m6A residues which are increased in the 5'UTR after heat shock stress.