Biology subjects

Lehner, P. J.

Publications and source records attributed to Lehner, P. J..

26 records · Page 2Linked to original sources

bioRxiv2019

A trimeric Rab7 GEF controls NPC1-dependent lysosomal cholesterol export

Cholesterol import in mammalian cells is mediated by the LDL receptor pathway. Here, using an endogenous cholesterol reporter in a genome-wide CRISPR screen we identify >70 genes involved in LDL-cholesterol import. We characterise C18orf8 as a core component of the mammalian Mon1-Ccz1 guanidine exchange factor (GEF) for Rab7, required for complex stability and function. C18orf8-deficient cells lack Rab7 activation and show severe defects in late endosome morphology and endosomal LDL trafficking, resulting in cellular cholesterol deficiency. Unexpectedly, free cholesterol accumulates within swollen lysosomes, suggesting a critical additional defect in lysosomal cholesterol export. We find that active Rab7 interacts with the NPC1 cholesterol transporter and licenses lysosomal cholesterol export. This process is abolished in C18orf8-, Ccz1- and Mon1A/B-deficient cells and restored by a constitutively active Rab7. The trimeric Mon1-Ccz1-C18orf8 (MCC) GEF therefore plays a central role in cellular cholesterol homeostasis coordinating Rab7 activation, endosomal LDL trafficking and NPC1-dependent lysosomal cholesterol export.

cell biology↗

bioRxiv2019

Antagonism of PP2A is an independent and conserved function of HIV-1 Vif and causes cell cycle arrest

The seminal description of cellular restriction factor APOBEC3G and its antagonism by HIV-1 Vif has underpinned two decades of research on the host-virus interaction. As well as APOBEC3G and its homologues, however, we have recently discovered that Vif is also able to degrade the PPP2R5 family of regulatory subunits of key cellular phosphatase PP2A (PPP2R5A-E) (Greenwood et al., 2016; Naamati et al., 2019). We now identify amino acid polymorphisms at positions 31 and 128 of HIV-1 Vif which selectively regulate the degradation of PPP2R5 family proteins. These residues covary across HIV-1 viruses in vivo, favouring depletion of PPP2R5A-E. Through analysis of point mutants and naturally occurring Vif variants, we further show that degradation of PPP2R5 family subunits is both necessary and sufficient for Vif-dependent G2/M cell cycle arrest. Antagonism of PP2A by HIV-1 Vif is therefore independent of APOBEC3 family proteins, and regulates cell cycle progression in HIV-infected cells.

microbiology↗

bioRxiv2019

Interferon-responsive genes are targeted during the establishment of human cytomegalovirus latency

Human cytomegalovirus (HCMV) latency is an active process which remodels the latently infected cell to optimise latent carriage and reactivation. This is achieved, in part, through the expression of viral genes, including the G-protein coupled receptor US28. Here, we use an unbiased proteomic screen to assess changes in host proteins induced by US28, revealing that interferon-inducible genes are downregulated by US28. We validate that MHC Class II and two PYHIN proteins, MNDA and IFI16, are downregulated during experimental latency in primary human CD14+ monocytes. We find that IFI16 is targeted rapidly during the establishment of latency in a US28-dependent manner, but only in undifferentiated myeloid cells, a natural site of latent carriage. Finally, by overexpressing IFI16, we show that IFI16 can activate the viral major immediate early promoter and immediate early gene expression during latency via NF-{kappa}B, a function which explains why downregulation of IFI16 during latency is advantageous for the virus.\n\nImportanceHuman cytomegalovirus (HCMV) is a ubiquitous herpesvirus which infects 50-100% of humans worldwide. HCMV causes a lifelong subclinical infection in immunocompetent individuals, but is a serious cause of mortality and morbidity in the immunocompromised and in neonates. In particular, reactivation of HCMV in the transplant setting is a major cause of transplant failure and related disease. Therefore, a molecular understanding of HCMV latency and reactivation could provide insights into potential ways to target the latent viral reservoir in at-risk patient populations.

microbiology↗

bioRxiv2019

Integrative functional genomics decodes herpes simplex virus 1

Since the genome of herpes simplex virus 1 (HSV-1) was first sequenced more than 30 years ago, its predicted 80 genes have been intensively studied. Here, we unravel the complete viral transcriptome and translatome during lytic infection with base-pair resolution by computational integration of multi-omics data. We identified a total of 201 viral transcripts and 284 open reading frames (ORFs) including all known and 46 novel large ORFs. Multiple transcript isoforms expressed from individual gene loci explain translation of the vast majority of novel viral ORFs as well as N-terminal extensions (NTEs) and truncations thereof. We show that key viral regulators and structural proteins possess NTEs, which initiate from non-canonical start codons and govern subcellular protein localization and packaging. We validated a novel non-canonical large spliced ORF in the ICP0 locus and identified a 93 aa ORF overlapping ICP34.5 that is thus also deleted in the FDA-approved oncolytic virus Imlygic. Finally, we extend the current nomenclature to include all novel viral gene products. Taken together, this work provides a valuable resource for future functional studies, vaccine design and oncolytic therapies.

microbiology↗

bioRxiv2018

The sterol-responsive RNF145 E3 ubiquitin ligase mediates the degradation of HMG-CoA reductase together with gp78 and Hrd1

HMG-CoA reductase (HMGCR), the rate-limiting enzyme of the cholesterol biosynthetic pathway and the therapeutic target of statins, is post-transcriptionally regulated by sterol-accelerated degradation. Under cholesterol-replete conditions, HMGCR is ubiquitinated and degraded, but the identity of the E3 ubiquitin ligase(s) responsible for mammalian HMGCR turnover remains controversial. Using systematic, unbiased CRISPR/Cas9 genome-wide screens with a sterol-sensitive endogenous HMGCR reporter, we comprehensively map the E3 ligase landscape required for sterol-accelerated HMGCR degradation. We find that RNF145 and gp78, independently co-ordinate HMGCR ubiquitination and degradation. RNF145, a sterol-responsive ER-resident E3 ligase, is unstable but accumulates following sterol depletion. Sterol addition triggers RNF145 recruitment to HMGCR and Insig-1, promoting HMGCR ubiquitination and proteasome-mediated degradation. In the absence of both RNF145 and gp78, Hrd1, a third UBE2G2-dependent ligase partially regulates HMGCR activity. Our findings reveal a critical role for the sterol-responsive RNF145 in HMGCR regulation and elucidate the complexity of sterol-accelerated HMGCR degradation.

cell biology↗

bioRxiv2018

Functional proteomic atlas of HIV-infection inprimary human CD4+ T cells

Viruses manipulate host cells to enhance their replication, and the identification of host factors targeted by viruses has led to key insights in both viral pathogenesis and cellular physiology. We previously described global changes in cellular protein levels during human immunodeficiency virus (HIV) infection using transformed CEM-T4 T cells as a model. In this study, we develop an HIV reporter virus displaying a streptavidin-binding affinity tag at the surface of infected cells, allowing facile one-step selection with streptavidin-conjugated magnetic beads. We use this system to obtain pure populations of HIV-infected primary human CD4+ T cells for detailed proteomic analysis, including quantitation of >9,000 proteins across 4 different donors, and temporal profiling during T cell activation. Remarkably, amongst 650 cellular proteins significantly perturbed during HIV infection of primary T cells (q<0.05), almost 50% are regulated directly or indirectly by the viral accessory proteins Vpr, Vif, Nef and Vpu. The remainder have not been previously characterised, but include novel Vif-dependent targets FMR1 and DPH7, and 192 targets not identified and/or regulated in T cell lines, such as AIRD5A and PTPN22. We therefore provide a high-coverage functional proteomic atlas of HIV infection, and a mechanistic account of HIV-dependent changes in its natural target cell.

microbiology↗

bioRxiv2018

Vpr drives massive cellular proteome remodelling in HIV-1 infection

Viral infection causes global remodelling of the cellular proteome. We previously mapped the temporal changes in abundance of thousands of proteins in HIV-1 infected cells (Greenwood & Matheson, 2016). While a small proportion of these changes were attributable to specific HIV-1 accessory proteins, most were unexplained. Here, we use complementary unbiased mass spectrometry-based approaches to demonstrate that a single viral protein, Vpr, is both necessary and sufficient to cause the vast majority of these changes. This global protein regulation requires substrate binding and degradation via DCAF1, but is mostly independent of Vpr-mediated cell cycle arrest. Combined approaches of pulsed-Stable Isotope Labelling with Amino Acids in Cell Culture (pulsed-SILAC) and immunoprecipitation-mass spectrometry (IP-MS) identified at least 38 such cellular proteins directly targeted for degradation by Vpr. Thus, whilst other HIV-1 accessory proteins downregulate a small number of host factors, Vpr degrades multiple protein targets, causing systems-level remodelling of the cellular proteome.\n\nImpact statementHIV infection causes massive changes to the cellular proteome and a single HIV protein, Vpr, is necessary and sufficient to drive almost all these changes by degrading multiple host proteins.

microbiology↗

bioRxiv2017

Neuropathic mutations in MORC2 perturb GHKL ATPase dimerization dynamics and epigenetic silencing by multiple structural mechanisms

Missense mutations in MORC2 cause neuropathies including spinal muscular atrophy and Charcot-Marie-Tooth disease. We recently identified MORC2 as an effector of epigenetic silencing by the HUSH complex. Here we report the biochemical and cellular activities of MORC2 variants, alongside crystal structures of wild-type and neuropathic forms of a human MORC2 fragment comprising the GHKL-type ATPase module and CW-type zinc finger. This fragment dimerizes upon binding ATP and contains a hinged, functionally critical coiled coil insertion absent in other GHKL ATPases. We find that dimerization and DNA binding of the MORC2 ATPase module transduce HUSH-dependent silencing. Disease mutations change the dynamics of dimerization by distinct structural mechanisms: destabilizing the ATPase-CW module, trapping the ATP lid or perturbing the dimer interface. These defects lead to modulation of HUSH function, thus providing a molecular basis for understanding MORC2-associated neuropathies.

biochemistry↗