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BACKGROUND {\&} AIMS RNase H2 is a holoenzyme,composed of 3 subunits (ribonuclease H2 subunits A,B,and C),that cleaves RNA:DNA hybrids and removes mis-incorporated ribonucleotides from genomic DNA through ribonucleotide excision repair. Ribonucleotide incorporation by eukaryotic DNA polymerases occurs during every round of genome duplication and produces the most frequent type of naturally occurring DNA lesion. We investigated whether intestinal epithelial proliferation requires RNase H2 function and whether RNase H2 activity is disrupted during intestinal carcinogenesis. METHODS We generated mice with epithelial-specific deletion of ribonuclease H2 subunit B (H2b$\Delta$IEC) and mice that also had deletion of tumor-suppressor protein p53 (H2b/p53$\Delta$IEC); we compared phenotypes with those of littermate H2bfl/fl or H2b/p53fl/fl (control) mice at young and old ages. Intestinal tissues were collected and analyzed by histology. We isolated epithelial cells,generated intestinal organoids,and performed RNA sequence analyses. Mutation signatures of spontaneous tumors from H2b/p53$\Delta$IEC mice were characterized by exome sequencing. We collected colorectal tumor specimens from 467 patients,measured levels of ribonuclease H2 subunit B,and associated these with patient survival times and transcriptome data. RESULTS The H2b$\Delta$IEC mice had DNA damage to intestinal epithelial cells and proliferative exhaustion of the intestinal stem cell compartment compared with controls and H2b/p53$\Delta$IEC mice. However,H2b/p53$\Delta$IEC mice spontaneously developed small intestine and colon carcinomas. DNA from these tumors contained T{\textgreater}G base substitutions at GTG trinucleotides. Analyses of transcriptomes of human colorectal tumors associated lower levels of RNase H2 with shorter survival times. CONCLUSIONS In analyses of mice with disruption of the ribonuclease H2 subunit B gene and colorectal tumors from patients,we provide evidence that RNase H2 functions as a colorectal tumor suppressor. H2b/p53$\Delta$IEC mice can be used to study the roles of RNase H2 in tissue-specific carcinogenesis. View Publication

mAbs constitute an important biological tool for influenza virus haemagglutinin (HA) epitope mapping through the generation of escape mutants,which could provide insights into immune evasion mechanisms and may benefit the future development of vaccines. Several influenza A (H1N1) pandemic 2009 (pdm09) HA escape mutants have been recently described. However,the HA antigenic sites of the previous seasonal A/Brisbane/59/2007 (H1N1) (Bris07) virus remain poorly documented. Here,we produced mAbs against pdm09 and Bris07 HA proteins expressed in human HEK293 cells. Escape mutants were generated using mAbs that exhibited HA inhibition and neutralizing activities. The resulting epitope mapping of the pdm09 HA protein revealed 11 escape mutations including three that were previously described (G172E,N173D and K256E) and eight novel ones (T89R,F128L,G157E,K180E,A212E,R269K,N311T and G478E). Among the six HA mutations that were part of predicted antigenic sites (Ca1,Ca2,Cb,Sa or Sb),three (G172E,N173D and K180E) were within the Sa site. Eight escape mutations (H54N,N55D,N55K,L60H,N203D,A231T,V314I and K464E) were obtained for Bris07 HA,and all but one (N203D,Sb site) were outside the predicted antigenic sites. Our results suggest that the Sa antigenic site is immunodominant in pdm09 HA,whereas the N203D mutation (Sb site),present in three different Bris07 escape mutants,appears as the immunodominant epitope in that strain. The fact that some mutations were not part of predicted antigenic sites reinforces the necessity of further characterizing the HA of additional H1N1 strains. View Publication

Erythropoietin (Epo) is a cytokine that binds and activates an Epo receptor (EpoR) expressed on the surface of erythroid progenitor cells to promote erythropoiesis. While early studies suggested EpoR transcripts were expressed exclusively in the erythroid compartment,low-level EpoR transcripts were detected in nonhematopoietic tissues and tumor cell lines using sensitive RT-PCR methods. However due to the widespread use of nonspecific anti-EpoR antibodies there are conflicting data on EpoR protein expression. In tumor cell lines and normal human tissues examined with a specific and sensitive monoclonal antibody to human EpoR (A82),little/no EpoR protein was detected and it was not functional. In contrast,EpoR protein was reportedly detectable in a breast tumor cell line (MCF-7) and breast cancer tissues with an anti-EpoR polyclonal antibody (M-20),and functional responses to rHuEpo were reported with MCF-7 cells. In another study,a functional response was reported with the lung tumor cell line (NCI-H838) at physiological levels of rHuEpo. However,the specificity of M-20 is in question and the absence of appropriate negative controls raise questions about possible false-positive effects. Here we show that with A82,no EpoR protein was detectable in normal human and matching cancer tissues from breast,lung,colon,ovary and skin with little/no EpoR in MCF-7 and most other breast and lung tumor cell lines. We show further that M-20 provides false positive staining with tissues and it binds to a non-EpoR protein that migrates at the same size as EpoR with MCF-7 lysates. EpoR protein was detectable with NCI-H838 cells,but no rHuEpo-induced phosphorylation of AKT,STAT3,pS6RP or STAT5 was observed suggesting the EpoR was not functional. Taken together these results raise questions about the hypothesis that most tumors express high levels of functional EpoR protein. View Publication

Epstein-Barr Virus latent membrane protein-1 (LMP1) interacts with the SUMO-conjugating enzyme Ubc9,which induces protein sumoylation and may contribute to LMP1-mediated oncogenesis. After analyzing human lymphoma tissues and EBV-positive cell lines,we now document a strong correlation between LMP1 and sumo-1/2/3 or SUMO-1/2/3 levels,and show that LMP1-induced sumo expression requires the activation of NF-kappaB signaling through CTAR1 and CTAR2. Together,these results point to a second mechanism by which LMP1 dysregulates sumoylation processes and adds EBV-associated lymphomas to the list of malignancies associated with increased SUMO expression. View Publication

Epstein-Barr virus (EBV) is associated with the development of malignant lymphomas and lymphoproliferative disorders in immunocompromised individuals. The LMP2A protein of EBV is thought to play a central role in this process by allowing the virus to persist in latently infected B lymphocytes. We have demonstrated that LMP2A,when expressed in B cells of transgenic mice,allows normal B-cell developmental checkpoints to be bypassed. To identify cellular genes targeted by LMP2A that are involved in this process,we have utilized DNA microarrays to compare gene transcription in B cells from wild-type versus LMP2A transgenic mice. In B cells from LMP2A transgenic mice,we observed decreased expression of many genes associated with normal B-cell development as well as reduced levels of the transcription factors that regulate their expression. In particular,expression of the transcription factor E2A was down-regulated in bone marrow and splenic B cells. Furthermore,E2A activity was inhibited in these cells as determined by decreased DNA binding and reduced expression of its target genes,including the transcription factors early B-cell factor and Pax-5. Expression of two E2A inhibitors,Id2 and SCL,was up-regulated in splenic B cells expressing LMP2A,suggesting a possible mechanism for E2A inhibition. These results indicate that LMP2A deregulates transcription factor expression and activity in developing B cells,and this likely allows for a bypass of normal signaling events required for proper B-cell development. The ability of LMP2A to interfere with B-cell transcription factor regulation has important implications regarding its role in EBV latency. View Publication

Epstein-Barr Virus (EBV) is associated with numerous cancers including B cell lymphomas. In vitro,EBV transforms primary B cells into immortalized Lymphoblastoid Cell Lines (LCLs) which serves as a model to study the role of viral proteins in EBV malignancies. EBV induced cellular transformation is driven by viral proteins including EBV-Nuclear Antigens (EBNAs). EBNA-LP is important for the transformation of naïve but not memory B cells. While EBNA-LP was thought to promote gene activation by EBNA2,EBNA-LP Knockout (LPKO) virus-infected cells express EBNA2-activated cellular genes efficiently. Therefore,a gap in knowledge exists as to what roles EBNA-LP plays in naïve B cell transformation. We developed a trans-complementation assay wherein transfection with wild-type EBNA-LP rescues the transformation of peripheral blood- and cord blood-derived naïve B cells by LPKO virus. Despite EBNA-LP phosphorylation sites being important in EBNA2 co-activation; neither phospho-mutant nor phospho-mimetic EBNA-LP was defective in rescuing naïve B cell outgrowth. However,we identified conserved leucine-rich motifs in EBNA-LP that were required for transformation of adult naïve and cord blood B cells. Because cellular PPAR-g coactivator (PGC) proteins use leucine-rich motifs to engage transcription factors including YY1,a key regulator of DNA looping and metabolism,we examined the role of EBNA-LP in engaging transcription factors. We found a significant overlap between EBNA-LP and YY1 in ChIP-Seq data. By Cut&Run,YY1 peaks unique to WT compared to LPKO LCLs occur at more highly expressed genes. Moreover,Cas9 knockout of YY1 in primary B cells prior to EBV infection indicated YY1 to be important for EBV-mediated transformation. We confirmed EBNA-LP and YY1 biochemical association in LCLs by endogenous co-immunoprecipitation and found that the EBNA-LP leucine-rich motifs were required for YY1 interaction in LCLs. We propose that EBNA-LP engages YY1 through conserved leucine-rich motifs to promote EBV transformation of naïve B cells. Author summaryEpstein-Barr Virus (EBV) is associated with various B cell lymphomas,particularly in immunosuppressed individuals. In the absence of a functional immune system,viral latency proteins,including EBV Nuclear Antigens (EBNAs) act as oncoproteins to promote tumorigenesis. EBNA-LP is one of the first viral proteins produced after infection and is important for the transformation of naïve B cells. However,the roles of EBNA-LP during infection are largely undefined. In this study,developed an assay in which the role of wild type and mutant EBNA-LP could be investigated in the context of primary naïve B cells infected with an EBNA-LP Knockout virus. Using this assay,we identified highly conserved leucine-rich motifs within EBNA-LP that are important for transformation of EBV-infected naïve B cells. These conserved motifs associate with the cellular transcription factor YY1,an important transcriptional regulator in B cell development and in many cancers,that we now show is essential for outgrowth of EBV infected B cells. Our study provides further insights into the mechanisms by which EBV transforms naïve B cells. View Publication

Endoplasmic reticulum (ER) stress occurs during early embryonic development. The aim of this study is to determine whether ER stress occurs during human embryonic stem cell differentiation induced by retinoic acid (RA). H9 human embryonic stem cells were subjected to RA treatment for up to 29. days to induce differentiation. HEK293 cells were treated with RA as a control. The results demonstrate that several ER stress-responsive genes are differentially regulated in H9 and HEK293 cells in response to 5. days of RA treatment. GRP78/Bip was upregulated in H9 cells but downregulated in HEK293 cells. eIF2?? was downregulated in H9 cells but not in HEK293 cells. Phosphorylation of eIF2?? was downregulated in H9 cells but upregulated in HEK293 cells. XBP-1 was downregulated immediately after RA treatment in H9 cells,but its downregulation was much slower in HEK293 cells. Additionally,two ER-resident E3 ubiquitin ligases,gp78 and Hrd1,were both upregulated in H9 cells following 5. days of exposure to RA. Moreover,the protein Bcl2 was undetectable in H9 cells and H9-derived cells but was expressed in HEK293 cells,and it expression in the two types of cells was unaltered by RA treatment. In H9 cells treated with RA for 29. days,GRP78/Bip,XBP-1 and Bcl2 were all upregulated. These results suggest that ER stress is involved in H9 cell differentiation induced by RA. ?? 2011 Elsevier Inc. View Publication

The gut microbiome contributes to inflammatory bowel disease (IBD),in which bacteria can be present within the epithelium. Epithelial barrier function is decreased in IBD,and dysfunctional epithelial mitochondria and endoplasmic reticulum (ER) stress have been individually associated with IBD. We therefore hypothesized that the combination of ER and mitochondrial stresses significantly disrupt epithelial barrier function. Here,we treated human colonic biopsies,epithelial colonoids,and epithelial cells with an uncoupler of oxidative phosphorylation,dinitrophenol (DNP),with or without the ER stressor tunicamycin and assessed epithelial barrier function by monitoring internalization and translocation of commensal bacteria. We also examined barrier function and colitis in mice exposed to dextran sodium sulfate (DSS) or DNP and co-treated with DAPK6,an inhibitor of death-associated protein kinase 1 (DAPK1). Contrary to our hypothesis,induction of ER stress (i.e. the unfolded protein response) protected against decreased barrier function caused by the disruption of mitochondrial function. ER stress did not prevent DNP-driven uptake of bacteria; rather,specific mobilization of the ATF6 arm of ER stress and recruitment of DAPK1 resulted in enhanced autophagic killing (xenophagy) of bacteria. Of note,epithelia with a Crohn's disease-susceptibility mutation in the autophagy gene ATG16L1 exhibited less xenophagy. Systemic delivery of the DAPK1 inhibitor DAPK6 increased bacterial translocation in DSS- or DNP-treated mice. We conclude that promoting ER stress-ATF6-DAPK1 signaling in transporting enterocytes counters the transcellular passage of bacteria evoked by dysfunctional mitochondria,thereby reducing the potential for metabolic stress to reactivate or perpetuate inflammation. View Publication

Protein glycosylation provides proteomic diversity in regulating protein localization,stability,and activity; it remains largely unknown whether the sugar moiety contributes to immunosuppression. In the study of immune receptor glycosylation,we showed that EGF induces programmed death ligand 1 (PD-L1) and receptor programmed cell death protein 1 (PD-1) interaction,requiring beta$-1,3-N-acetylglucosaminyl transferase (B3GNT3) expression in triple-negative breast cancer. Downregulation of B3GNT3 enhances cytotoxic T cell-mediated anti-tumor immunity. A monoclonal antibody targeting glycosylated PD-L1 (gPD-L1) blocks PD-L1/PD-1 interaction and promotes PD-L1 internalization and degradation. In addition to immune reactivation,drug-conjugated gPD-L1 antibody induces a potent cell-killing effect as well as a bystander-killing effect on adjacent cancer cells lacking PD-L1 expression without any detectable toxicity. Our work suggests targeting protein glycosylation as a potential strategy to enhance immune checkpoint therapy. View Publication

Mechanisms determining intrinsic differentiation bias inherent to human pluripotent stem cells (hPSCs) toward cardiogenic fate remain elusive. We evaluated the interplay between ErbB4 and EGFR in determining cardiac differentiation in vitro as these receptor tyrosine kinases (RTKs) are key to heart and brain development in vivo. Our results demonstrate that during cardiac differentiation,cell fate biases exist in hPSCs due to cardiac/neuroectoderm divergence post cardiac mesoderm stage. Stage-specific up-regulation of EGFR in concert with persistent Wnt3a signaling post cardiac mesoderm favors commitment towards neural progenitor cells (NPCs). Inhibition of EGFR abrogates these effects with enhanced (textgreater2-fold) cardiac differentiation efficiencies by increasing proliferation of Nkx2-5 expressing cardiac progenitors while reducing proliferation of Sox2 expressing NPCs. Forced overexpression of ErbB4 rescued cardiac commitment by augmenting Wnt11 signaling. Convergence between EGFR/ErbB4 and canonical/non-canonical Wnt signaling determines cardiogenic fate in hPSCs. This article is protected by copyright. All rights reserved. View Publication

Activation of ErbB4 receptor signaling is instrumental in heart development,lack of which results in embryonic lethality. However,mechanism governing its intracellular signaling remains elusive. Using human pluripotent stem cells,we show that ErbB4 is critical for cardiogenesis whereby its genetic knockdown results in loss of cardiomyocytes. Phospho-proteome profiling and Western blot studies attribute this loss to inactivation of p38$\$ isoform which physically interacts with NKx2.5 and GATA4 transcription factors. Post-cardiomyocyte formation p38$\$/NKx2.5 downregulation is followed by p38$\$/MEF2c upregulation suggesting stage-specific developmental roles of p38 MAPK isoforms. Knockdown of p38$\$ similarly disrupts cardiomyocyte formation in spite of the presence of NKx2.5. Cell fractionation and NKx2.5 phosphorylation studies suggest inhibition of ErbB4-p38$\$ hinders NKx2.5 nuclear translocation during early cardiogenesis. This study reveals a novel pathway that directly links ErbB4 and p38$\$ the transcriptional machinery of NKx2.5-GATA4 complex which is critical for cardiomyocyte formation during mammalian heart development. View Publication

In this study,we investigated the effect of intracerebroventricular administration of ERK and p38 specific inhibitors,U0126 and PD169316,respectively,on learning and memory deficits induced by amyloid beta (Aβ) in rats. To investigate the effects of these compounds on learning and memory,we performed Morris water maze (MWM) test. U0126 and/or PD169316 improved spatial learning in MWM in Aβ-injected rats,20 days after Aβ-injection. To determine the mechanisms of action of U0126 and PD169316,we studies their effect on some intracellular signaling pathways such as Ca(+)/cAMP-response element binding protein (CREB),c-fos,and transcription factors that regulate mitochondrial biogenesis. Based on our data,CREB and c-fos levels decreased 7 days after Aβ-injection,while U0126 and/or PD169316 pretreatments significantly increased these levels. Moreover,U0126 and PD169316 activated peroxisome proliferator-activated receptor gamma coactivator-1a,nuclear respiratory factor 1,and mitochondrial transcription factor A,7 days after Aβ-injection. Surprisingly,these factors were returned to vehicle level,20 days after Aβ-injection. Our findings reinforce the potential neuroprotective effect of these inhibitors against the Aβ toxicity. View Publication