Project description:Retrotransposition of endogenous retroviruses (ERVs) poses a substantial threat to genome stability. Transcriptional silencing of a subset of these parasitic elements in early mouse embryonic and germ cell development is dependent upon the lysine methyltransferase SETDB1, which deposits H3K9 trimethylation (H3K9me3) and the co-repressor KAP1, which binds SETDB1 when SUMOylated. Here we identified the transcription co-factor hnRNP K as a novel binding partner of the SETDB1/KAP1 complex in mouse embryonic stem cells (mESCs) and show that hnRNP K is required for ERV silencing. RNAi-mediated knockdown of hnRNP K led to depletion of H3K9me3 at ERVs, concomitant with de-repression of proviral reporter constructs and specific ERV subfamilies, as well as a cohort of germline-specific genes directly targeted by SETDB1. While hnRNP K recruitment to ERVs is dependent upon KAP1, SETDB1 binding at these elements requires hnRNP K. Furthermore, an intact SUMO conjugation pathway is necessary for SETDB1 recruitment to proviral chromatin and depletion of hnRNP K resulted in reduced SUMOylation at ERVs. Taken together, these findings reveal a novel regulatory hierarchy governing SETDB1 recruitment and in turn, transcriptional silencing in mESCs.
Project description:The transcription factor Oct4 plays a key regulatory role in the induction and maintenance of cellular pluripotency. With this paper, we show that ubiquitous and multifunctional poly(C) DNA/RNA-binding protein hnRNP-K occupies Oct4 (Pou5f1) enhancers in embryonic stem cells (ESCs) but is dispensable for the initiation, maintenance, and downregulation of Oct4 gene expression. Nevertheless, hnRNP-K has an essential cell-autonomous function in ESCs to maintain their proliferation and viability. To better understand mechanisms of hnRNP-K action in ESCs we have performed ChIP-seq analysis of genome-wide binding of hnRNP-K and identified several thousands of hnRNP-K target sites that are frequently co-occupied by pluripotency-related and common factors (Oct4, TBP, Sox2, Nanog, Otx2, etc.), as well as active histone marks. Furthermore, hnRNP-K localizes exclusively within open chromatin, implying its role in the onset and/or maintenance of this chromatin state.
Project description:In mouse embryonic stem cells (mESCs), the expression of provirus and endogenous retroelements is epigenetically repressed. Although many cellular factors involved in retroelement silencing have been identified, the complete molecular mechanism remains elusive. In this study, we performed a genome-wide CRISPR screen to advance our understanding of retroelement silencing in mESCs. The Moloney murine leukemia virus (MLV)-based retroviral vector MSCV-GFP, which is repressed by the SETDB1/TRIM28 pathway in mESCs, was used as a reporter provirus, and we identified more than 80 genes involved in this process. In particular, ATF7IP and the BAF complex components are linked with the repression of most of the SETDB1 targets. We characterized two factors, MORC2A and RESF1, of which RESF1 is a novel molecule in retroelement silencing. Although both factors are recruited to repress provirus, their roles in repression are different. MORC2A appears to function dependent on repressive epigenetic modifications, while RESF1 regulates repressive epigenetic modifications associated with SETDB1. Our genome-wide CRISPR screen cataloged genes which function at different levels in silencing of SETDB1-target retroelements and provides a useful resource for further molecular studies.
Project description:We used NEBNext Ultra Directional RNA Library Prep Kits to prepare RNA-seq libraries of total RNA from hnRNP A2/B1 and A1 depleted A549 cells. Pro-seq libraries were prepared from A549 cells using Illumina adapters hnRNP A2/B1 and A1 depleted A549 cells were generated by lentiviral infections of shRNA constructs. RNAs were isolated using Trizol.
Project description:Limited knowledge of the downstream targets of hnRNP A2/B1 has, however, precluded a clear understanding of their roles in cancer cell growth. To define the pathways in which this protein acts we have now carried out microarray experiments with total RNA from Colo16 epithelial cells transfected with an shRNA that markedly suppresses hnRNP A2/B1 expression. The microarray data identified 123 genes, among 22283 human gene probe sets, with altered expression levels in hnRNP A2/B1-depleted cells. Ontological analysis showed that many of these downstream targets are involved in regulation of the cell cycle and cell proliferation and that this group of proteins is significantly over-represented amongst the affected proteins. The changes detected in the microarray experiments were confirmed by real-time PCR for a subset of proliferation-related genes. Immunoprecipitation-RT-PCR demonstrated that hnRNP A2/B1 formed complexes with the transcripts of many of the verified downstream genes, suggesting that hnRNP A2/B1 contributes to the regulation of these genes.
Project description:Post-transcriptional regulatory networks are dependent on the interplay of many RNA-binding proteins having a major role in mRNA processing events in mammals. We have been interested in the concerted action of the two RNA-binding proteins hnRNP A1 and HuR, both stable components of immunoselected hnRNP complexes and having a major nuclear localization. Specifically, we present here the application of the RNA-immunoprecipitation (RIP)-Chip technology to identify a population of nuclear transcripts associated with hnRNP A1-RNPs as isolated from the nuclear extract of either HuR WT or HuR-depleted (KO) mouse embryonic fibroblast (MEF) cells. The outcome of this analysis was a list of target genes regulated via HuR for their association (either increased or reduced) with the nuclear hnRNP A1-RNP complexes. Real time PCR analysis was applied to validate a selected number of nuclear mRNA transcripts, as well as to identify pre-spliced transcripts (in addition to their mature mRNA counterpart) within the isolated nuclear hnRNP A1-RNPs. The differentially enriched mRNAs were found to belong to GO categories relevant to biological processes anticipated for hnRNP A1 and HuR (such as transport, transcription, translation, apoptosis and cell cycle) indicative of their concerted function in mRNA metabolism. Ribonucleoprotein Immunoprecipitation (RIP) using hnRNP A1 specific antibody was performed in nuclear extracts from HuR WT and HuR KO Mouse Embryonic Fibroblasts (MEFs). RNA isolated from these IPs together with nuclear RNA from the two cell types, was subjected to microarray analysis. Three biological replicates, representing three independent experiments, are available for each condition except in the case of nuclear RNA isolated from HuR WT MEFs that one replicate didn’t pass the quality control.
Project description:Post-transcriptional regulatory networks are dependent on the interplay of many RNA-binding proteins having a major role in mRNA processing events in mammals. We have been interested in the concerted action of the two RNA-binding proteins hnRNP A1 and HuR, both stable components of immunoselected hnRNP complexes and having a major nuclear localization. Specifically, we present here the application of the RNA-immunoprecipitation (RIP)-Chip technology to identify a population of nuclear transcripts associated with hnRNP A1-RNPs as isolated from the nuclear extract of either HuR WT or HuR-depleted (KO) mouse embryonic fibroblast (MEF) cells. The outcome of this analysis was a list of target genes regulated via HuR for their association (either increased or reduced) with the nuclear hnRNP A1-RNP complexes. Real time PCR analysis was applied to validate a selected number of nuclear mRNA transcripts, as well as to identify pre-spliced transcripts (in addition to their mature mRNA counterpart) within the isolated nuclear hnRNP A1-RNPs. The differentially enriched mRNAs were found to belong to GO categories relevant to biological processes anticipated for hnRNP A1 and HuR (such as transport, transcription, translation, apoptosis and cell cycle) indicative of their concerted function in mRNA metabolism.