Project description:Nuclear pore complexes (NPCs) are the central apparatus of nucleocytoplasmic transport. Disease-specific alterations of NPCs contribute to the pathogenesis of many cancers; however, the roles of NPCs in glioblastoma (GBM) are unknown. In this study, we report genomic amplification of NUP107, a component of NPCs, in GBM and show that NUP107 is overexpressed simultaneously with MDM2, a critical E3 ligase that mediates p53 degradation. Depletion of NUP107 inhibits the growth of GBM cell lines through p53 protein stabilization. Mechanistically, NPCs establish a p53 degradation platform via an export pathway coupled with 26S proteasome tethering. NUP107 is the keystone for NPC assembly; the loss of NUP107 affects the integrity of the NPC structure, and thus the proportion of 26S proteasome in the vicinity of nuclear pores significantly decreases. Together, our findings establish roles of NPCs in transport surveillance and provide insights into p53 inactivation in GBM.
Project description:We found that in addition to promoters, multiple Nups bind enhancers and insulators in the Drosophila genome. We identified a functional role for Nup98 in mediating enhancer-promoter looping at ecdysone-inducible genes. These genes were found to be stably associated with nuclear pores before and after activation. Interestingly, although changing the levels of Nup98 disrupted induced enhancer-promoter contact, it did not affect transcriptional activation. Instead, loss of Nup98-mediated enhancer-promoter contact affected the primed response to subsequent transcriptional activation or transcriptional memory. In support of the enhancer-looping role, we found Nup98 to gain and retain physical interactions with several architectural proteins upon stimulation with ecdysone.
Project description:Nuclear pores are essential pathways for nuclear-cytoplasmic transport of molecules. Whether and how cells change nuclear pores to alter nuclear transport and cellular function is unknown. Here, we show that heart muscle cells (cardiomyocytes) undergo a 63% decrease in nuclear pore numbers during differentiation, which alters their response to extracellular signals. This maturation-associated decline in nuclear pore numbers per nucleus is associated with lower nuclear levels and import of Mitogen-activated Protein Kinase (MAPK) signaling proteins. Experimental reduction of nuclear pore numbers decreased nuclear import of MAPK signaling proteins. In a mouse model of high blood pressure, reduction of cardiomyocyte nuclear pore numbers reduced adverse heart remodeling and gene regulation, which reduced progression to lethal heart failure. The observed decrease in nuclear pore numbers in cardiomyocyte differentiation and resulting functional changes suggest a paradigm by which terminally differentiated cells could permanently alter their handling of information flux across the nuclear envelope and, with that, their behavior.
Project description:Transcription hinders replication fork progression and stability, and the Mec1/ATR checkpoint protects fork integrity. Examining checkpoint-dependent mechanisms controlling fork stability, we find that fork reversal or dormant origin firing owing to checkpoint defects are rescued in checkpoint mutants lacking THO, TREX-2 or inner basket nucleoporins. Gene gating tethers transcribed genes to the nuclear periphery and is counteracted by checkpoint kinases through phosphorylation of nucleoporins such as Mlp1. Checkpoint mutants fail to detach transcribed genes from nuclear pores, thus generating topological impediments for incoming forks. Releasing this topological complexity by introducing a double-strand break between a fork and a transcribed unit prevents fork collapse. Mlp1 mutants mimicking constitutive checkpoint-dependent phosphorylation also alleviate checkpoint defects. We propose that the checkpoint assists fork progression and stability at transcribed genes by phosphorylating key nucleoporins and counteracting gene gating, thus neutralizing the topological tension generated at nuclear pore gated genes.
Project description:Cancer-relevant signalling pathways rely on bidirectional nucleocytoplasmic transport events through the nuclear pore complex (NPC). However, mechanisms by which individual NPC components (Nups) participate in the regulation of these pathways remain poorly understood. We discovered by integrating large scale proteomics, polysome fractionation and a focused RNAi approach that Nup155 controls mRNA translation of p21 (CDKN1A), a key mediator of the p53 response. The underlying mechanism involves transcriptional regulation of the putative tRNA and rRNA methyltransferase FTSJ1 by Nup155. Furthermore, we observed that Nup155 and FTSJ1 are p53 repression targets and accordingly found a correlation between the p53 status, Nup155 and FTSJ1 expression in murine and human hepatocellular carcinoma (HCC). Our data suggest an unanticipated regulatory network linking translational control by and repression of a structural NPC component modulating the p53 pathway through its effectors.
Project description:Piwi in a complex with Piwi-interacting RNAs (piRNAs) triggers transcriptional silencing of Transposable Elements (TEs) in Drosophila ovaries, thus ensuring genome stability. To do this, Piwi must scan the nascent transcripts of genes and TEs for complementarity to piRNAs. The mechanism of this scanning is currently unknown. Here we report the DamID-seq mapping of multiple Piwi-interacting chromosomal domains in somatic cells of Drosophila ovaries. These domains significantly overlap with genomic regions tethered to Nuclear Pore Complexes (NPCs). Accordingly, Piwi was coimmunoprecipitated with the component of NPCs Elys and with the Xmas-2 subunit of RNA transcription and export complex, known to interact with NPCs. However, only a small Piwi fraction has transient access to DNA at nuclear pores. Importantly, although 36%of protein-coding genes overlap with Piwi-interacting domains and RNA-immunoprecipitation results demonstrate promiscuous Piwi binding to numerous genic and TE nuclear transcripts, according to available data Piwi does not silence these genes, likely due to the absence of perfect base-pairing between piRNAs and their transcripts.
Project description:Transport of macromolecules through the nuclear envelope (NE) is mediated by nuclear pore complexes (NPCs) consisting of nucleoporins (Nups). Elys/Mel-28 is the Nup that binds and connects the decondensing chromatin with the reassembled NPCs at the end of mitosis. Whether Elys links chromatin with the NE during interphase is unknown. Using DamID-seq, we identified Elys binding sites in Drosophila late embryos and divided them into those associated with nucleoplasmic or NPC-linked Elys. These Elys binding sites are located within active or inactive chromatin, respectively. Strikingly, Elys knockdown in S2 cells results in peripheral chromatin displacement from the NE, in decondensation of NE-attached chromatin, and in derepression of genes within. It also leads to slightly more compact active chromatin regions. Our findings indicate that NPC-linked Elys, together with the nuclear lamina, anchors peripheral chromatin to the NE, whereas nucleoplasmic Elys decompacts active chromatin.
Project description:Transport of macromolecules through the nuclear envelope (NE) is mediated by nuclear pore complexes (NPCs) consisting of nucleoporins (Nups). Elys/Mel-28 is the Nup that binds and connects the decondensing chromatin with the reassembled NPCs at the end of mitosis. Whether Elys links chromatin with the NE during interphase is unknown. Using DamID-seq, we identified Elys binding sites in Drosophila late embryos and divided them into those associated with nucleoplasmic or with NPC-linked Elys. These Elys binding sites are located within active or inactive chromatin, respectively. Strikingly, Elys knockdown in S2 cells results in peripheral chromatin displacement from the NE, in decondensation of NE-attached chromatin, and in derepression of genes within. It also leads to slightly more compact active chromatin regions. Our findings indicate that NPC-linked Elys, together with the nuclear lamina, anchors peripheral chromatin to the NE, whereas nucleoplasmic Elys decompacts active chromatin.