Lentiviral gene therapy with IGF2-tagged GAA normalizes the skeletal muscle proteome in murine Pompe disease.

Pompe disease is a lysosomal storage disorder caused by deficiency of acid alpha-glucosidase (GAA), resulting in glycogen accumulation with profound pathology in skeletal muscle. We recently developed an optimized form of lentiviral gene therapy for Pompe disease in which a codon-optimized version of the GAA transgene (LV-GAAco) was fused to an insulin-like growth factor 2 (IGF2) peptide (LV-IGF2.GAAco), to promote cellular uptake via the cation-independent mannose-6-phosphate/IGF2 receptor. Lentiviral gene therapy with LV-IGF2.GAAco showed superior efficacy in heart, skeletal muscle, and brain of Gaa -/- mice compared to gene therapy with untagged LV-GAAco. Here, we used quantitative mass spectrometry using TMT labeling to analyze the muscle proteome and the response to gene therapy in Gaa -/- mice. We found that muscle of Gaa -/- mice displayed altered levels of proteins including those with functions in the CLEAR signaling pathway, autophagy, cytoplasmic glycogen metabolism, calcium homeostasis, redox signaling, mitochondrial function, fatty acid transport, muscle contraction, cytoskeletal organization, phagosome maturation, and inflammation. Gene therapy with LV-GAAco resulted in partial correction of the muscle proteome, while gene therapy with LV-IGF2.GAAco resulted in a near-complete restoration to wild type levels without inducing extra proteomic changes, supporting clinical development of lentiviral gene therapy for Pompe disease. SIGNIFICANCE: Lysosomal glycogen accumulation is the primary cause of Pompe disease, and leads to a cascade of pathological events in cardiac and skeletal muscle and in the central nervous system. In this study, we identified the proteomic changes that are caused by Pompe disease in skeletal muscle of a mouse model. We showed that lentiviral gene therapy with LV-IGF2.GAAco nearly completely corrects disease-associated proteomic changes. This study supports the future clinical development of lentiviral gene therapy with LV-IGF2.GAAco as a new treatment option for Pompe disease.

Distinct proteomic profiles in prefrontal subareas of elderly major depressive disorder and bipolar disorder patients.

We investigated for the first time the proteomic profiles both in the dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC) of major depressive disorder (MDD) and bipolar disorder (BD) patients. Cryostat sections of DLPFC and ACC of MDD and BD patients with their respective well-matched controls were used for study. Proteins were quantified by tandem mass tag and high-performance liquid chromatography-mass spectrometry system. Gene Ontology terms and functional cluster alteration were analyzed through bioinformatic analysis. Over 3000 proteins were accurately quantified, with more than 100 protein expressions identified as significantly changed in these two brain areas of MDD and BD patients as compared to their respective controls. These include OGDH, SDHA and COX5B in the DLPFC in MDD patients; PFN1, HSP90AA1 and PDCD6IP in the ACC of MDD patients; DBN1, DBNL and MYH9 in the DLPFC in BD patients. Impressively, depending on brain area and distinct diseases, the most notable change we found in the DLPFC of MDD was 'suppressed energy metabolism'; in the ACC of MDD it was 'suppressed tissue remodeling and suppressed immune response'; and in the DLPFC of BD it was differentiated 'suppressed tissue remodeling and suppressed neuronal projection'. In summary, there are distinct proteomic changes in different brain areas of the same mood disorder, and in the same brain area between MDD and BD patients, which strengthens the distinct pathogeneses and thus treatment targets.

Comparison of the PU.1 transcriptional regulome and interactome in human and mouse inflammatory dendritic cells.

Dendritic cells (DCs) are key immune modulators and are able to mount immune responses or tolerance. DC differentiation and activation imply a plethora of molecular and cellular responses, including transcriptional changes. PU.1 is a highly expressed transcription factor in DCs and coordinates relevant aspects of DC biology. Due to their role as immune regulators, DCs pose as a promising immunotherapy tool. However, some of their functional features, such as survival, activation, or migration, are compromised due to the limitations to simulate in vitro the physiologic DC differentiation process. A better knowledge of transcriptional programs would allow the identification of potential targets for manipulation with the aim of obtaining "qualified" DCs for immunotherapy purposes. Most of the current knowledge regarding DC biology derives from studies using mouse models, which not always find a parallel in human. In the present study, we dissect the PU.1 transcriptional regulome and interactome in mouse and human DCs, in the steady state or LPS activated. The PU.1 transcriptional regulome was identified by performing PU.1 chromatin immunoprecipitation followed by high-throughput sequencing and pairing these data with RNAsequencing data. The PU.1 interactome was identified by performing PU.1 immunoprecipitation followed by mass spectrometry analysis. Our results portray PU.1 as a pivotal factor that plays an important role in the regulation of genes required for proper DC activation and function, and assures the repression of nonlineage genes. The interspecies differences between human and mouse DCs are surprisingly substantial, highlighting the need to study the biology of human DCs.

DNA damage-induced replication stress results in PA200-proteasome-mediated degradation of acetylated histones.

Histone acetylation influences protein interactions and chromatin accessibility and plays an important role in the regulation of transcription, replication, and DNA repair. Conversely, DNA damage affects these crucial cellular processes and induces changes in histone acetylation. However, a comprehensive overview of the effects of DNA damage on the histone acetylation landscape is currently lacking. To quantify changes in histone acetylation, we developed an unbiased quantitative mass spectrometry analysis on affinity-purified acetylated histone peptides, generated by differential parallel proteolysis. We identify a large number of histone acetylation sites and observe an overall reduction of acetylated histone residues in response to DNA damage, indicative of a histone-wide loss of acetyl modifications. This decrease is mainly caused by DNA damage-induced replication stress coupled to specific proteasome-dependent loss of acetylated histones. Strikingly, this degradation of acetylated histones is independent of ubiquitylation but requires the PA200-proteasome activator, a complex that specifically targets acetylated histones for degradation. The uncovered replication stress-induced degradation of acetylated histones represents an important chromatin-modifying response to cope with replication stress.

Improvement of ubiquitylation site detection by Orbitrap mass spectrometry.

Ubiquitylation is an important posttranslational protein modification that is involved in many cellular events. Immunopurification of peptides containing a K-ε-diglycine (diGly) remnant as a mark of ubiquitylation combined with mass spectrometric detection has resulted in an explosion of the number of identified ubiquitylation sites. Here, we present several significant improvements to this workflow, including fast, offline and crude high pH reverse-phase fractionation of tryptic peptides into only three fractions with simultaneous desalting prior to immunopurification and better control of the peptide fragmentation settings in the Orbitrap HCD cell. In addition, more efficient sample cleanup using a filter plug to retain the antibody beads results in a higher specificity for diGly peptides and less non-specific binding. These relatively simple modifications of the protocol result in the routine detection of over 23,000 diGly peptides from HeLa cells upon proteasome inhibition. The efficacy of this strategy is shown for lysates of both non-labeled and SILAC labeled cell lines. Furthermore, we demonstrate that this strategy is useful for the in-depth analysis of the endogenous, unstimulated ubiquitinome of in vivo samples such as mouse brain tissue. This study presents a valuable addition to the toolbox for ubiquitylation site analysis to uncover the deep ubiquitinome. SIGNIFICANCE: A K-ε-diglycine (diGly) mark on peptides after tryptic digestion of proteins indicates a site of ubiquitylation, a posttranslational modification involved in a wide range of cellular processes. Here, we report several improvements to methods for the isolation and detection of diGly peptides from complex biological mixtures such as cell lysates and brain tissue. This adapted method is robust, reproducible and outperforms previously published methods in terms of number of modified peptide identifications from a single sample. In-depth analysis of the ubiquitinome using mass spectrometry will lead to a better understanding of the roles of protein ubiquitylation in cellular events.

Sp1/Sp3 transcription factors regulate hallmarks of megakaryocyte maturation and platelet formation and function.

Sp1 and Sp3 belong to the specificity proteins (Sp)/Krüppel-like transcription factor family. They are closely related, ubiquitously expressed, and recognize G-rich DNA motifs. They are thought to regulate generic processes such as cell-cycle and growth control, metabolic pathways, and apoptosis. Ablation of Sp1 or Sp3 in mice is lethal, and combined haploinsufficiency results in hematopoietic defects during the fetal stages. Here, we show that in adult mice, conditional pan-hematopoietic (Mx1-Cre) ablation of either Sp1 or Sp3 has minimal impact on hematopoiesis, whereas the simultaneous loss of Sp1 and Sp3 results in severe macrothrombocytopenia. This occurs in a cell-autonomous manner as shown by megakaryocyte-specific (Pf4-Cre) double-knockout mice. We employed flow cytometry, cell culture, and electron microscopy and show that although megakaryocyte numbers are normal in bone marrow and spleen, they display a less compact demarcation membrane system and a striking inability to form proplatelets. Through megakaryocyte transcriptomics and platelet proteomics, we identified several cytoskeleton-related proteins and downstream effector kinases, including Mylk, that were downregulated upon Sp1/Sp3 depletion, providing an explanation for the observed defects in megakaryopoiesis. Supporting this notion, selective Mylk inhibition by ML7 affected proplatelet formation and stabilization and resulted in defective ITAM receptor-mediated platelet aggregation.

Global quantitative proteomics reveals novel factors in the ecdysone signaling pathway in Drosophila melanogaster.

The ecdysone signaling pathway plays a major role in various developmental transitions in insects. Recent advances in the understanding of ecdysone action have relied to a large extent on the application of molecular genetic tools in Drosophila. Here, we used a comprehensive quantitative SILAC MS-based approach to study the global, dynamic proteome of a Drosophila cell line to investigate how hormonal signals are transduced into specific cellular responses. Global proteome data after ecdysone treatment after various time points were then integrated with transcriptome data. We observed a substantial overlap in terms of affected targets between the dynamic proteome and transcriptome, although there were some clear differences in timing effects. Also, downregulation of several specific mRNAs did not always correlate with downregulation of their corresponding protein counterparts, and in some cases there was no correlation between transcriptome and proteome dynamics whatsoever. In addition, we performed a comprehensive interactome analysis of EcR, the major target of ecdysone. Proteins copurified with EcR include factors involved in transcription, chromatin remodeling, ecdysone signaling, ecdysone biosynthesis, and other signaling pathways. Novel ecdysone-responsive proteins identified in this study might link previously unknown proteins to the ecdysone signaling pathway and might be novel targets for developmental studies. To our knowledge, this is the first time that ecdysone signaling is studied by global quantitative proteomics. All MS data have been deposited in the ProteomeXchange with identifier PXD001455 (http://proteomecentral.proteomexchange.org/dataset/PXD001455).

A novel complex, RUNX1-MYEF2, represses hematopoietic genes in erythroid cells.

RUNX1 is known to be an essential transcription factor for generating hematopoietic stem cells (HSC), but much less is known about its role in the downstream process of hematopoietic differentiation. RUNX1 has been shown to be part of a large transcription factor complex, together with LDB1, GATA1, TAL1, and ETO2 (N. Meier et al., Development 133:4913-4923, 2006) in erythroid cells. We used a tagging strategy to show that RUNX1 interacts with two novel protein partners, LSD1 and MYEF2, in erythroid cells. MYEF2 is bound in undifferentiated cells and is lost upon differentiation, whereas LSD1 is bound in differentiated cells. Chromatin immunoprecipitation followed by sequencing (ChIP-seq) and microarray expression analysis were used to show that RUNX1 binds approximately 9,000 target sites in erythroid cells and is primarily active in the undifferentiated state. Functional analysis shows that a subset of the target genes is suppressed by RUNX1 via the newly identified partner MYEF2. Knockdown of Myef2 expression in developing zebrafish results in a reduced number of HSC.

Genome-wide DNA methylation profiling of non-small cell lung carcinomas.

BACKGROUND: Non-small cell lung carcinoma (NSCLC) is a complex malignancy that owing to its heterogeneity and poor prognosis poses many challenges to diagnosis, prognosis and patient treatment. DNA methylation is an important mechanism of epigenetic regulation involved in normal development and cancer. It is a very stable and specific modification and therefore in principle a very suitable marker for epigenetic phenotyping of tumors. Here we present a genome-wide DNA methylation analysis of NSCLC samples and paired lung tissues, where we combine MethylCap and next generation sequencing (MethylCap-seq) to provide comprehensive DNA methylation maps of the tumor and paired lung samples. The MethylCap-seq data were validated by bisulfite sequencing and methyl-specific polymerase chain reaction of selected regions. RESULTS: Analysis of the MethylCap-seq data revealed a strong positive correlation between replicate experiments and between paired tumor/lung samples. We identified 57 differentially methylated regions (DMRs) present in all NSCLC tumors analyzed by MethylCap-seq. While hypomethylated DMRs did not correlate to any particular functional category of genes, the hypermethylated DMRs were strongly associated with genes encoding transcriptional regulators. Furthermore, subtelomeric regions and satellite repeats were hypomethylated in the NSCLC samples. We also identified DMRs that were specific to two of the major subtypes of NSCLC, adenocarcinomas and squamous cell carcinomas. CONCLUSIONS: Collectively, we provide a resource containing genome-wide DNA methylation maps of NSCLC and their paired lung tissues, and comprehensive lists of known and novel DMRs and associated genes in NSCLC.

Sox2 cooperates with Chd7 to regulate genes that are mutated in human syndromes.

The HMG-box transcription factor Sox2 plays a role throughout neurogenesis and also acts at other stages of development, as illustrated by the multiple organs affected in the anophthalmia syndrome caused by SOX2 mutations. Here we combined proteomic and genomic approaches to characterize gene regulation by Sox2 in neural stem cells. Chd7, a chromatin remodeling ATPase associated with CHARGE syndrome, was identified as a Sox2 transcriptional cofactor. Sox2 and Chd7 physically interact, have overlapping genome-wide binding sites and regulate a set of common target genes including Jag1, Gli3 and Mycn, genes mutated in Alagille, Pallister-Hall and Feingold syndromes, which show malformations also associated with SOX2 anophthalmia syndrome or CHARGE syndrome. Regulation of disease-associated genes by a Sox2-Chd7 complex provides a plausible explanation for several malformations associated with SOX2 anophthalmia syndrome or CHARGE syndrome. Indeed, we found that Chd7-haploinsufficient embryos showed severely reduced expression of Jag1 in the developing inner ear.

A systems approach to analyze transcription factors in mammalian cells.

Transcription factors (TFs) play a central role in the development of multicellular organisms. The sequential actions of critical TFs direct cells to adopt defined differentiation pathways leading to functional, fully differentiated tissues. Here, we describe a generic experimental pipeline that integrates biochemistry, genetics and next generation sequencing with bioinformatics to characterize TF complexes composition, function and target genes at a genome-wide scale. We show an application of this experimental pipeline which aims to unravel the molecular events taking place during hematopoietic cell differentiation.

Cell-specific occupancy of an extended repertoire of CREM and CREB binding loci in male germ cells.

BACKGROUND: CREB and CREM are closely related factors that regulate transcription in response to various stress, metabolic and developmental signals. The CREMτ activator isoform is selectively expressed in haploid spermatids and plays an essential role in murine spermiogenesis. RESULTS: We have used chromatin immunoprecipitation coupled to sequencing (ChIP-seq) to map CREM and CREB target loci in round spermatids from adult mouse testis and spermatogonia derived GC1-spg cells respectively. We identify more than 9000 genomic loci most of which are cell-specifically occupied. Despite the fact that round spermatids correspond to a highly specialised differentiated state, our results show that they have a remarkably accessible chromatin environment as CREM occupies more than 6700 target loci corresponding not only to the promoters of genes selectively expressed in spermiogenesis, but also of genes involved in functions specific to other cell types. The expression of only a small subset of these target genes are affected in the round spermatids of CREM knockout animals. We also identify a set of intergenic binding loci some of which are associated with H3K4 trimethylation and elongating RNA polymerase II suggesting the existence of novel CREB and CREM regulated transcripts. CONCLUSIONS: We demonstrate that CREM and CREB occupy a large number of promoters in highly cell specific manner. This is the first study of CREM target promoters directly in a physiologically relevant tissue in vivo and represents the most comprehensive experimental analysis of CREB/CREM regulatory potential to date.

The genome-wide dynamics of the binding of Ldb1 complexes during erythroid differentiation.

One of the complexes formed by the hematopoietic transcription factor Gata1 is a complex with the Ldb1 (LIM domain-binding protein 1) and Tal1 proteins. It is known to be important for the development and differentiation of the erythroid cell lineage and is thought to be implicated in long-range interactions. Here, the dynamics of the composition of the complex-in particular, the binding of the negative regulators Eto2 and Mtgr1-are studied, in the context of their genome-wide targets. This shows that the complex acts almost exclusively as an activator, binding a very specific combination of sequences, with a positioning relative to transcription start site, depending on the type of the core promoter. The activation is accompanied by a net decrease in the relative binding of Eto2 and Mtgr1. A Chromosome Conformation Capture sequencing (3C-seq) assay also shows that the binding of the Ldb1 complex marks genomic interaction sites in vivo. This establishes the Ldb1 complex as a positive regulator of the final steps of erythroid differentiation that acts through the shedding of negative regulators and the active interaction between regulatory sequences.

High-resolution identification of balanced and complex chromosomal rearrangements by 4C technology.

Balanced chromosomal rearrangements can cause disease, but techniques for their rapid and accurate identification are missing. Here we demonstrate that chromatin conformation capture on chip (4C) technology can be used to screen large genomic regions for balanced and complex inversions and translocations at high resolution. The 4C technique can be used to detect breakpoints also in repetitive DNA sequences as it uniquely relies on capturing genomic fragments across the breakpoint. Using 4C, we uncovered LMO3 as a potentially leukemogenic translocation partner of TRB@. We developed multiplex 4C to simultaneously screen for translocation partners of multiple selected loci. We identified unsuspected translocations and complex rearrangements. Furthermore, using 4C we detected translocations even in small subpopulations of cells. This strategy opens avenues for the rapid fine-mapping of cytogenetically identified translocations and inversions, and the efficient screening for balanced rearrangements near candidate loci, even when rearrangements exist only in subpopulations of cells.