Emerging evidence suggests that lineage-specifying transcription factors control the progression of pancreatic ductal adenocarcinoma (PDAC). We have discovered a transcription factor switching mechanism involving the poorly characterized orphan nuclear receptor HNF4G and the putative pioneer factor FOXA1, which drives PDAC progression. Using our unbiased protein interactome discovery approach, we identified HNF4A and HNF4G as reproducible, FOXA1-associated proteins, in both preclinical models and Whipple surgical samples. In the primary tumor context, we consistently find that the dominant transcription factor is HNF4G, where it functions as the driver. A molecular switch occurs in advanced disease, whereby HNF4G expression or activity decreases, unmasking FOXA1's transcriptional potential. Derepressed FOXA1 drives late-stage disease by orchestrating metastasis-specific enhancer-promoter loops to regulate the expression of metastatic genes. Overall survival is influenced by HNF4G and FOXA1 activity in primary tumor growth and in metastasis, respectively. We suggest that the existence of stage-dependent transcription factor activity, triggered by molecular compartmentalization, mediates the progression of PDAC.

Abstract Despite recent advances in the treatment of pancreatic adenocarcinoma (PDAC), the median survival remains <12 months. Patients typically present with late-stage disease and have limited treatment options. Therefore, there is an immediate need for the generation of new and innovative therapeutic targets. Little is known about the role of pioneer factors such as FOXA1 and their interaction partners in a PDAC context. Inspired by literature reports implicating FOXA1 and GATA5/GATA6 in regulating pancreatic cancer resistance and metastasis, our study hypothesised the possibility of an undiscovered nuclear receptor that works with FOXA1 (similar to Estrogen receptor in breast cancer). Using innovative ‘omic’ based approaches (RIME) developed in our laboratory 1 we discovered a nuclear receptor (NR) complex involving HNF4A and HNF4G in the classical sub-type of pancreatic cancer. Subsequently the interaction was independently validated in Whipple surgical biopsies from PDAC patients using ChIP-sequencing studies. Across multiple patient tumors (n=7) a binding overlap specifically between FOXA1 and HNF4G (3461 sites) was established. To investigate the therapeutic potential of HNF4G in the classical subtype of PDAC, we generated CRISPR deletions (KO) of HNF4G in the HPAF-II cells. HNF4G-KO cells were orthotopically implanted into the pancreas of NSG mice. A significant survival advantage of 12 days (<0.001) and reduced growth (<0.02) was observed in these mice compared to the controls. To better understand the impact of HNF4G-KO on gene expression, the orthotopic tumors were subjected to RNA-seq analyses. Gene set enrichment and pathway analysis revealed significantly down-regulated pathways to include EMT transition. TCGA data highlighted HNF4G amplification in 9% of PDAC patients with concomitant decreased progression free survival. These data point towards HNF4G being a therapeutically viable target for further exploration. Protein Arginine Methyl Transferase 1 (PRMT1) is a common interactor of both FOXA1 and HNF4G. Our study reveals a unique dependency of PRMT1 on the HNF4G-FOXA1 complex in PDAC biopsies. HNF4G-KO drastically reduces the chromatin binding of PRMT1, implicating them as functionally dependent. Treatment of HNF4G-KO cells with GSK3368715 (PRMT1 inhibitor) further sensitizes these cells and results in a significant survival advantage (10 days <0.02). We propose a model of HNF4G inhibition in combination with PRMT1 as a novel therapeutic opportunity to treat the classical sub-type of PDAC. Further, our study reveals a unique reliance of primary classical tumors on HNF4G. Although HNF4G appears to dominate FOXA1 functionality in the primary disease, FOXA1 remains instrumental in priming metastasis and enhancer reprograming. 1. Papachristou EK, Kishore K, Holding AN, Harvey K, Roumeliotis TI, Chilamakuri CSR, et al. A quantitative mass spectrometry-based approach to monitor the dynamics of endogenous chromatin-associated protein complexes. Nature Communications. 2018;9(1):2311. Citation Format: Shalini V. Rao, Lisa Young, Danya Cheeseman, Stephanie Mack, Jill Temple, Chandra Shekar Reddy Chilamakuri, Evangelia Papachristou, Catherina Pelicano, Amy Smith, Dominique-Laurent Couturier, Michael Gill, Duncan Jodrell Jodrell, Alasdair Russell, Igor Chernukhin, Jason Carroll. New insights into the role of FOXA1- HNF4 axis in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C076.

Acute stroke therapy and rehabilitation declined during the COVID-19 pandemic. We characterized changes in acute stroke disposition and readmissions during the pandemic.We used the California State Inpatient Database in this retrospective observational study of ischemic and hemorrhagic stroke. We compared discharge disposition across a pre-pandemic period (January 2019 to February 2020) to a pandemic period (March to December 2020) using cumulative incidence functions (CIF), and re-admission rates using chi-squared.There were 63,120 and 40,003 stroke hospitalizations in the pre-pandemic and pandemic periods, respectively. Pre-pandemic, the most common disposition was home [46%], followed by skilled nursing facility (SNF) [23%], and acute rehabilitation [13%]. During the pandemic, there were more home discharges [51%, subdistribution hazard ratio 1.17, 95% CI 1.15-1.19], decreased SNF discharges [17%, subdistribution hazard ratio 0.70, 95% CI 0.68-0.72], and acute rehabilitation discharges were unchanged [CIF, p<0.001]. Home discharges increased with increasing age, with an increase of 8.2% for those ≥85 years. SNF discharges decreased in a similar distribution by age. Thirty-day readmission rates were 12.7 per 100 hospitalizations pre-pandemic compared to 11.6 per 100 hospitalizations during the pandemic [p<0.001]. Home discharge readmission rates were unchanged between periods. Readmission rates for discharges to SNF (18.4 vs. 16.7 per 100 hospitalizations, p=0.003) and acute rehabilitation decreased (11.3 vs. 10.1 per 100 hospitalizations, p=0.034).During the pandemic a greater proportion of patients were discharged home, with no change in readmission rates. Research is needed to evaluate the impact on quality and financing of post-hospital stroke care.

Somatic DNA copy number variations (CNVs) are prevalent in cancer and can drive cancer progression, albeit with often uncharacterized roles in altering cell signaling states. Here, we integrate genomic and proteomic data for 5,598 tumor samples to identify CNVs leading to aberrant signal transduction. The resulting associations recapitulate known kinase-substrate relationships, and further network analysis prioritizes likely causal genes. Of the 303 significant associations we identify from the pan-tumor analysis, 43% are replicated in cancer cell lines, including 44 robust gene-phosphosite associations identified across multiple tumor types. Several predicted regulators of hippo signaling are experimentally validated. Using RNAi, CRISPR, and drug screening data, we find evidence of kinase addiction in cancer cell lines, identifying inhibitors for targeting of kinase-dependent cell lines. We propose copy number status of genes as a useful predictor of differential impact of kinase inhibition, a strategy that may be of use in the future for anticancer therapies.

Previously, we showed that 3% (31/1032)of asymptomatic healthcare workers (HCWs) from a large teaching hospital in Cambridge, UK, tested positive for SARS-CoV-2 in April 2020. About 15% (26/169) HCWs with symptoms of coronavirus disease 2019 (COVID-19) also tested positive for SARS-CoV-2 (Rivett et al., 2020). Here, we show that the proportion of both asymptomatic and symptomatic HCWs testing positive for SARS-CoV-2 rapidly declined to near-zero between 25th April and 24th May 2020, corresponding to a decline in patient admissions with COVID-19 during the ongoing UK ‘lockdown’. These data demonstrate how infection prevention and control measures including staff testing may help prevent hospitals from becoming independent ‘hubs’ of SARS-CoV-2 transmission, and illustrate how, with appropriate precautions, organizations in other sectors may be able to resume on-site work safely.

In metastatic cancer, the degree of heterogeneity of the tumor microenvironment (TME) and its molecular underpinnings remain largely unstudied. To characterize the tumor–immune interface at baseline and during neoadjuvant chemotherapy (NACT) in high-grade serous ovarian cancer (HGSOC), we performed immunogenomic analysis of treatment-naive and paired samples from before and after treatment with chemotherapy. In treatment-naive HGSOC, we found that immune-cell-excluded and inflammatory microenvironments coexist within the same individuals and within the same tumor sites, indicating ubiquitous variability in immune cell infiltration. Analysis of TME cell composition, DNA copy number, mutations and gene expression showed that immune cell exclusion was associated with amplification of Myc target genes and increased expression of canonical Wnt signaling in treatment-naive HGSOC. Following NACT, increased natural killer (NK) cell infiltration and oligoclonal expansion of T cells were detected. We demonstrate that the tumor–immune microenvironment of advanced HGSOC is intrinsically heterogeneous and that chemotherapy induces local immune activation, suggesting that chemotherapy can potentiate the immunogenicity of immune-excluded HGSOC tumors. Immunogenomic analyses of advanced high-grade serous ovarian cancer samples before and after neoadjuvant chemotherapy show that the tumor–immune microenvironment is intrinsically heterogeneous and that chemotherapy induces local immune activation.

Abstract Pancreatic ductal adenocarcinoma (PDAC) is characterized by desmoplasia, with macrophages as one of the most abundant, multifunctional immune cell populations in the tumor microenvironment (TME) and a major component of the immune infiltrate. To best improve clinical outcomes, consideration must be placed on targeted therapeutics that blunt heterotypic interactions between tumor cells and supporting cells within the TME. Here, we provide new insight into the dichotomous relationship between epithelial and mesenchymal phenotypes of PDAC cells in 3D culture. We report the ability of PDAC mesenchymal cells to form vascular mimicry-like structures in a 3D in vitro assay of invasion. Additionally, we demonstrate that macrophages have the ability to impart a proinvasive phenotype to PDAC cells when co-cultured in 3D, irrespective of EMT (epithelial-to-mesenchymal transition) status. To elucidate a mechanism for this macrophage-mediated proinvasive phenotype, we employed an unbiased, multi-omics approach. First, PDAC cell lines and primary macrophages were CTAP (cell-type specific labeling using amino acid precursors) labeled and admixed together for a prolonged period of time. To identify cell of origin of novel RNA and proteins, these mixed co-cultures were FACS sorted for downstream RNA-sequencing analysis or harvested in bulk for downstream proteome and secretome analysis. Preliminary integration of cell culture transcriptomes with CTAP-TMT (tandem mass tag) proteomes and secretomes implicates several key epithelial- and macrophage-derived signaling molecules as principal instructing signals for mediating the observed proinvasive phenotype. Blockade of this signaling axis, by inhibition of the signaling molecules or their receptors, disrupted the crosstalk between the two cell types and impaired the ability of macrophages to impart a proinvasive phenotype to PDAC cells. These preliminary preclinical data, recapitulated in vivo, suggest that targeting the TME of patients by using a staging regimen of chemokine inhibitor to disrupt tumor-macrophage cell interactions, followed with therapeutic modalities such as gemcitabine (and/or immunotherapy), would improve upon standard of care and inform future treatment options for PDAC in the clinic. Citation Format: Tony J. Wu, Oliver Cast, Danish Memon, Alejandro Jimenez-Sanchez, Anne Machel, Sebastian Kehrloesser, Michael B. Gill, Martin L. Miller. Identifying mechanisms of macrophage-mediated metastasis and therapy resistance in PDAC [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr C65.

Tumours are composed of an array of unique cancer cell clones along with many non-tumour cells such as immune cells, fibroblasts and endothelial cells, which make up the complex tumour microenvironment. To better understand the co-evolution of tumour clones and cells of the tumour microenvironment, we require tools to spatially resolve heterotypic cellular interactions at the single cell level. We present a novel protein-based barcoding technology termed nuclear tandem epitope protein (nTEP) barcoding, which can be designed to combinatorially encode and track dozens to hundreds of tumour clones in their spatial context within complex cellular mixtures using multiplexed antibody-based imaging. Here we provide proof-of-principle of nTEP barcoding and develop the technology, which relies on lentiviral - based stable expression of a nuclear-localised fluorophore that contains unique combinations of protein epitope tags that can be decoded by a limited set of antibodies. By generating a series of cell lines expressing unique nTEP barcodes, we were able to robustly identify and spatially deconvolve specific clones present within highly complex cell mixtures at the single cell level using state-of-the-art iterative indirect immunofluorescence imaging (4i). We define the utility of nTEP-barcoding as a powerful tool for visualising and resolving tumour heterogeneity at the cellular level, and envision its usage in mouse tumour models for understanding how tumour clones modulate and interact with stromal- and immune cells in cancer.

Abstract Optoacoustic imaging has the potential to monitor tumour neo-vascularization, essential for disease progression and also a target for therapy. While promising in some settings, anti-angiogenic therapy has yet to fulfil its promise and mechanisms of resistance are poorly understood. In breast cancer, for example, resistance has been linked to hormonal status, oxygen consumption and alternative mechanisms of neo-vasculogenesis, including vascular mimicry (VM). Here, we use two mouse xenograft models: estrogen-dependent MCF-7 and estrogen independent MDA-MB-231. We analyse their characteristics in vivo using Multispectral optoacoustic tomography (MSOT) to detect oxy- and deoxy- haemoglobin (Hb) during tumour growth. We also analysed their histological and biochemical characteristics for blood vessel density (CD31) and maturity (aSMA, PAS staining), tumour hypoxia (CAIX), angiogenesis, inflammation and VM. Anti-angiogenic therapy response was also tested using Bevacizumab (BV, 10 mg/Kg) in two cohorts. While MSOT reveals similar blood content in both tumours, estrogen-dependent MCF-7 tumours show higher blood oxygenation than estrogen-independent MDA-MB-231 (55.8±7.5 % vs. 45.6±5.1%, p=0.0008) with values similar to healthy tissue (55.8±7.5 % vs. 57.8±5.3%, p=0.917). Ex vivo histological analysis shows that while MDA-MB-231 tumours are more hypoxic compared to MCF-7, they have a higher blood vessel density, however, the vasculature of MCF-7 tumours is more mature (vessel wall thickness and aSMA coverage). Based on molecular biomarkers, MCF-7 presents a more pro-inflammatory endothelial-like response, marked by an increase of vascular endothelial growth factor (p<0.0001) of host origin (mVEGF), macrophage Nitric Oxide Sinthase (iNOS) and circulating NO, a mediator in inflammation and endothelial homeostasis (p=0.0031). VE-Cadherin of human origin is detectable in MDA-MB-231 tumours, which present CD31-absent blood vessels; together, these findings indicate presence of VM in MDA-MB-231 tumours. Interestingly, these 2 biological profiles respond differently to the anti-angiogenic drug BV: we observed a partial response in MDA-MB-231 tumours (CR=2/22, PR=3/22), but no effect in tumour size or survival was observed in MCF-7 tumours. While no change was observed in mVEGF upon BV treatment in any cohort, changes in optoacoustic signal of total Hb were observed in the MDA-MB-231 tumours after treatment. In conclusion, optoacoustic imaging delineates the vascular function of the blood vessel networks generated by angiogenesis and vascular mimicry respectively in our estrogen-dependent and estrogen-independent breast cancer xenografts. This study highlights the potential application of this technique in monitoring tumour vasculature development and in the future could be used to assess response to therapy. Citation Format: Isabel Quiros-Gonzalez, Michal Tomaszewski, Laura Ansel-Bollepalli, Sarah J. Aikten, Michael Gill, Sarah E. Bohndiek. Differences in optoacoustic signal reflect different characteristics of the vasculature and response to antiangiogenic therapy in breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4121.

BACKGROUND: Optoacoustic tomography (OT) of breast tumour oxygenation is a promising new technique, currently in clinical trials, which may help to determine disease stage and therapeutic response. However, the ability of OT to distinguish breast tumours displaying different vascular characteristics has yet to be established. The aim of the study is to prove OT as a sensitive technique for differentiating breast tumour models with manifestly different vasculatures. METHODS: Multispectral OT (MSOT) was performed in oestrogen-dependent (MCF-7) and oestrogen-independent (MDA-MB-231) orthotopic breast cancer xenografts. Total haemoglobin (THb) and oxygen saturation (SO2MSOT) were calculated. Pathological and biochemical evaluation of the tumour vascular phenotype was performed for validation. RESULTS: MCF-7 tumours show SO2 MSOT similar to healthy tissue in both rim and core, despite significantly lower THb in the core. MDA-MB-231 tumours show markedly lower SO2 MSOT with a significant rim-core disparity. Ex vivo analysis revealed that MCF-7 tumours contain fewer blood vessels (CD31+) that are more mature (CD31+/aSMA+) than MDA-MB-231. MCF-7 presented higher levels of stromal VEGF and iNOS, with increased NO serum levels. The vasculogenic process observed in MCF-7 was consistent with angiogenesis, while MDA-MB-231 appeared to rely more on vascular mimicry. CONCLUSIONS: OT is sensitive to differences in the vascular phenotypes of our breast cancer models.

Abstract The effect of chemotherapy on tumor heterogeneity and activation of the immune system in cancer is poorly understood. We present an unusual case of a patient with high-grade serous ovarian cancer, treated with multiple chemotherapy regimens, who exhibited spontaneous regression of some metastatic lesions with concomitant progression of other lesions during a treatment-free period. The primary tumor was resected before chemotherapy treatment started. After 5 years of chemotherapy without response, treatment was stopped, the patient transitioned to best supportive care and was followed clinically with regular CA125 biomarker evaluation. During the course of 2 years of clinical follow up, CA125 decreased and computerized tomography (CT) scans revealed one regressing (right upper quadrant), one stable (liver), and two progressing (spleen and vaginal cuff) metastases. Due to abdominal discomfort, metastases were simultaneously resected. We performed: a) CT scan-based radiomics to anlayze tumor heterogeneity, b) exome sequencing to identify somatic mutations, predict neoepitopes, and estimate neoepitope depletion, and c) immunofluorescence staining to analyze immune cell infiltration on the primary and four metastatic tumors. We found that chemotherapy increases tumor heterogeneity, and metastases that developed after multi-line chemotherapy have a higher somatic mutation rate, more neoepitopes, and mutations in immune recognition molecules compared to metastases that appeared earlier. The right upper quadrant regressing and the liver stable metastases were infiltrated by CD4+ and CD8+ T cells. The vaginal cuff progressing metastasis was characterized by immune cell exclusion, while the spleen progressing metastasis was infiltrated only by CD8+ T cells. Finally, we detected neoepitope depletion only in the right upper quadrant regressing metastasis, potentially indicating an active immunoediting process. These findings indicate that multiple distinct tumor immune microenvironments can co-exist within a single individual, evidencing potential clinical challenges for the appropriate application of immunotherapy and chemotherapy combinations to overcome tumor heterogeneity at the genetic and tumor-microenvironment levels. Citation Format: Alejandro Jiménez-Sánchez, Harini Veeraraghavan, Yanyun Li, Hebert Alberto Vargas, Michael B. Gill, Kay J. Park, Oliver Zivanovic, Jason Konner, Jacob Ricca, Dmitriy Zamarin, Carol Aghajanian, Jedd D. Wolchok, Taha Merghoub, Evis Sala, Alexandra Snyder, Martin L. Miller. Heterogeneous fates of metastatic lesions linked to immune escape in an ovarian cancer patient. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr B09.

We present an exceptional case of a patient with high-grade serous ovarian cancer, treated with multiple chemotherapy regimens, who exhibited regression of some metastatic lesions with concomitant progression of other lesions during a treatment-free period. Using immunogenomic approaches, we found that progressing metastases were characterized by immune cell exclusion, whereas regressing and stable metastases were infiltrated by CD8+ and CD4+ T cells and exhibited oligoclonal expansion of specific T cell subsets. We also detected CD8+ T cell reactivity against predicted neoepitopes after isolation of cells from a blood sample taken almost 3 years after the tumors were resected. These findings suggest that multiple distinct tumor immune microenvironments co-exist within a single individual and may explain in part the heterogeneous fates of metastatic lesions often observed in the clinic post-therapy. VIDEO ABSTRACT.

ABSTRACTEpstein-Barr virus (EBV) attachment to human CD21 on the B-cell surface initiates infection. Whether CD21 is a simple tether or conveys vital information to the cell interior for production of host factors that promote infection of primary B cells is controversial, as the cytoplasmic fragment of CD21 is short, though highly conserved. The ubiquity of CD21 on normal B cells, the diversity of this population, and the well-known resistance of primary B cells to gene transfer technologies have all impeded resolution of this question. To uncover the role(s) of the CD21 cytoplasmic domain during infection initiation, the full-length receptor (CD21 = CR), a mutant lacking the entire cytoplasmic tail (CT), and a control vector (NEO) were stably expressed in two pre-B-cell lines that lack endogenous receptor. Genome-wide transcriptional analysis demonstrated that stable CD21 surface expression alone (either CR or CT) produced multiple independent changes in gene expression, though both dramatically decreased class I melanoma-associated antigen (MAGE) family RNAs and upregulated genes associated with B-cell differentiation (e.g., C2TA, HLA-II, IL21R, MIC2, CD48, and PTPRCAP/CD45-associated protein). Temporal analysis spanning 72 h revealed that not only CR- but also CT-expressing lines initiated latency. In spite of this, the number and spectrum of transcripts altered in CR- compared with CT-bearing lines at 1 h after infection further diverged. Differential modulation of immediate early cellular transcripts (e.g., c-Jun and multiple histones), both novel and previously linked to CD21-initiated signaling, as well as distinct results from pathway analyses support a separate role for the cytoplasmic domain in initiation of intracellular signals.IMPORTANCEMembrane proteins that mediate virus attachment tether virus particles to the cell surface, initiating infection. In addition, upon virus interaction such proteins may transmit signals to the interior of the cell that support subsequent steps in the infection process. Here we show that expression of the Epstein-Barr virus B-cell attachment receptor, CD21, in B cells that lack this receptor results in significant changes in gene expression, both before and rapidly following EBV-CD21 interaction. These changes translate into major signaling pathway alterations that are predicted to support stable infection.

Qualitative researchers have developed and employed a variety of phenomenological methodologies to examine individuals' experiences. However, there is little guidance to help researchers choose between these variations to meet the specific needs of their studies. The purpose of this article is to illuminate the scope and value of phenomenology by developing a typology that classifies and contrasts five popular phenomenological methodologies. By explicating each methodology's differing assumptions, aims, and analytical steps, the article generates a series of guidelines to inform researchers' selections. Subsequent sections distinguish the family of phenomenological methodologies from other qualitative methodologies, such as narrative analysis and autoethnography. The article then identifies institutional work and organizational identity as topical bodies of research with particular research needs that phenomenology could address.

Paradoxically, the thymidine kinase (TK) encoded by Kaposi sarcoma-associated herpesvirus (KSHV) is an extremely inefficient nucleoside kinase, when compared to TKs from related herpesviruses. We now show that KSHV-TK, in contrast to HSV1-TK, associates with the actin cytoskeleton and induces extensive cell contraction followed by membrane blebbing. These dramatic changes in cell morphology depend on the auto-phosphorylation of tyrosines 65, 85 and 120 in the N-terminus of KSHV-TK. Phosphorylation of tyrosines 65/85 and 120 results in an interaction with Crk family proteins and the p85 regulatory subunit of PI3-Kinase, respectively. The interaction of Crk with KSHV-TK leads to tyrosine phoshorylation of this cellular adaptor. Auto-phosphorylation of KSHV-TK also induces a loss of FAK and paxillin from focal adhesions, resulting in activation of RhoA-ROCK signalling to myosin II and cell contraction. In the absence of FAK or paxillin, KSHV-TK has no effect on focal adhesion integrity or cell morphology. Our observations demonstrate that by acting as a tyrosine kinase, KSHV-TK modulates signalling and cell morphology.

The difficulty of eliminating herpesvirus carriage makes host entry a key target for infection control. However, its viral requirements are poorly defined. Murid herpesvirus-4 (MuHV-4) can potentially provide insights into gammaherpesvirus host entry. Upper respiratory tract infection requires the MuHV-4 thymidine kinase (TK) and ribonucleotide reductase large subunit (RNR-L), suggesting a need for increased nucleotide production. However, both TK and RNR-L are likely to be multifunctional. We therefore tested further the importance of nucleotide production by disrupting the MuHV-4 ribonucleotide reductase small subunit (RNR-S). This caused a similar attenuation to RNR-L disruption: despite reduced intra-host spread, invasive inoculations still established infection, whereas a non-invasive upper respiratory tract inoculation did so only at high dose. Histological analysis showed that RNR-S−, RNR-L−and TK−viruses all infected cells in the olfactory neuroepithelium but unlike wild-type virus then failed to spread. Thus captured host nucleotide metabolism enzymes, up to now defined mainly as important for alphaherpesvirus reactivation in neurons, also have a key role in gammaherpesvirus host entry. This seemed to reflect a requirement for lytic replication to occur in a terminally differentiated cell before a viable pool of latent genomes could be established.

Dendritic cells (DCs) play a central role in initiating immune responses. Some persistent viruses infect DCs and can disrupt their functions in vitro. However, these viruses remain strongly immunogenic in vivo. Thus what role DC infection plays in the pathogenesis of persistent infections is unclear. Here we show that a persistent, B cell-tropic gamma-herpesvirus, Murid Herpesvirus-4 (MuHV-4), infects DCs early after host entry, before it establishes a substantial infection of B cells. DC-specific virus marking by cre-lox recombination revealed that a significant fraction of the virus latent in B cells had passed through a DC, and a virus attenuated for replication in DCs was impaired in B cell colonization. In vitro MuHV-4 dramatically altered the DC cytoskeleton, suggesting that it manipulates DC migration and shape in order to spread. MuHV-4 therefore uses DCs to colonize B cells.

ABSTRACT Rotaviruses are a major cause of acute gastroenteritis in children worldwide. Early stages of rotavirus assembly in infected cells occur in viroplasms. Confocal microscopy demonstrated that viroplasms associate with lipids and proteins (perilipin A, ADRP) characteristic of lipid droplets (LDs). LD-associated proteins were also found to colocalize with viroplasms containing a rotaviral NSP5-enhanced green fluorescent protein (EGFP) fusion protein and with viroplasm-like structures in uninfected cells coexpressing viral NSP2 and NSP5. Close spatial proximity of NSP5-EGFP and cellular perilipin A was confirmed by fluorescence resonance energy transfer. Viroplasms appear to recruit LD components during the time course of rotavirus infection. NSP5-specific siRNA blocked association of perilipin A with NSP5 in viroplasms. Viral double-stranded RNA (dsRNA), NSP5, and perilipin A cosedimented in low-density gradient fractions of rotavirus-infected cell extracts. Chemical compounds interfering with LD formation (isoproterenol plus isobutylmethylxanthine; triacsin C) decreased the number of viroplasms and inhibited dsRNA replication and the production of infectious progeny virus; this effect correlated with significant protection of cells from virus-associated cytopathicity. Rotaviruses represent a genus of another virus family utilizing LD components for replication, pointing at novel therapeutic targets for these pathogens.

ABSTRACT Viral enzymes that process small molecules provide potential chemotherapeutic targets. A key constraint—the replicative potential of spontaneous enzyme mutants—has been hard to define with human gammaherpesviruses because of their narrow species tropisms. Here, we disrupted the murid herpesvirus 4 (MuHV-4) ORF61, which encodes its ribonucleotide reductase (RNR) large subunit. Mutant viruses showed delayed in vitro lytic replication, failed to establish infection via the upper respiratory tract, and replicated to only a very limited extent in the lower respiratory tract without reaching lymphoid tissue. RNR could therefore provide a good target for gammaherpesvirus chemotherapy.

Gammaherpesviruses infect at least 90 % of the world's population. Infection control is difficult, in part because some fundamental features of host colonization remain unknown, for example whether normal latency establishment requires viral lytic functions. Since human gammaherpesviruses have narrow species tropisms, answering such questions requires animal models. Murid herpesvirus-4 (MuHV-4) provides one of the most tractable. MuHV-4 genomes delivered to the lung or peritoneum persist without lytic replication. However, they fail to disseminate systemically, suggesting that the outcome is inoculation route-dependent. After upper respiratory tract inoculation, MuHV-4 infects mice without involving the lungs or peritoneum. We examined whether host entry by this less invasive route requires the viral thymidine kinase (TK), a gene classically essential for lytic replication in terminally differentiated cells. MuHV-4 TK knockouts delivered to the lung or peritoneum were attenuated but still reached lymphoid tissue. In contrast, TK knockouts delivered to the upper respiratory tract largely failed to establish a detectable infection. Therefore TK, and by implication lytic replication, is required for MuHV-4 to establish a significant infection by a non-invasive route.