Polygenic risk scores indicates genetic overlap between peripheral pain syndromes and chronic postsurgical pain

Chronic postsurgical pain (CPSP) is a debilitating chronic pain condition that has a substantial effect on quality of life. CPSP shows considerable clinical overlap with different chronic peripheral pain syndromes, suggesting a shared aetiology. This study aims to assess the genetic overlap between different chronic pain syndromes and CPSP, providing relevant biological context for potential chronic pain markers of CPSP. To analyse the genetic overlap between CPSP and chronic peripheral pain syndromes, recent GWAS studies were combined for polygenic risk scores (PRS) analysis, using a cohort of CPSP patients as starting point. Biological contextualisation of genetic marker, overlap between CPSP and chronic pain syndromes, was assessed through Gene Ontology (GO), using Pathway Scoring Algorithm (PASCAL) and REVIGO. PRS analyses suggest a significant genetic overlap between CPSP and 3 chronic pain disorders: chronic widespread pain (CWP, p value threshold = 0.003, R2 0.06, p = 0.003), rheumatoid arthritis (RA, p value threshold = 0.0177, R2 = 0.04, p = 0.017) and possibly sciatica (p value threshold = 0.00025, R2 = 0.03, p = 0.045). Whereas no significant genetic overlap was found with cluster headache and migraine, the outcome for osteoarthritis (OA) was inconsistent between the cohorts. This is likely related to cohort composition, as repeated random reallocation of patients' nullified CPSP/OA outcome variation between the discovery and replication cohorts. GO analyses suggested an aetiological involvement of genetic markers that control neurological signalling (specifically sodium channels) and inflammatory response. The current study reaffirms the impact of sample size, cohort composition and open data accessibility on the unbiased identification of genetic overlap across disorders. In conclusion, this study is the first to report genetic overlap between regulatory processes implicated in CPSP and chronic peripheral pain syndromes. Interaction between neurological signalling and inflammatory response may explain the genetic overlap between CPSP, CWP and RA. Enhanced understanding of mechanisms underlying chronification of pain will aid the development of new therapeutic strategies for CPSP with sodium channel biochemistry as a potential candidate.

A Membranome-Centered Approach Defines Novel Biomarkers for Cellular Subtypes in the Intervertebral Disc

OBJECTIVE

Lack of specific marker-sets prohibits definition and functional distinction of cellular subtypes in the intervertebral disc (IVD), such as those from the annulus fibrosus (AF) and the nucleus pulposus (NP).

DESIGN

We recently generated immortalized cell lines from human NP and AF tissues; these comprise a set of functionally distinct clonal subtypes. Whole transcriptome analyses were performed of 12 phenotypically distinct clonal cell lines (4× NP-Responder, 4× NP-nonResponder, 2× AF-Sheet forming, and 2× AF-nonSheet forming). Data sets were filtered for membrane-associated marker genes and compared to literature.

RESULTS

Comparison of our immortal cell lines to published primary NP, AF, and articular chondrocytes (AC) transcriptome datasets revealed preservation of AF and NP phenotypes. NP-specific membrane-associated genes were defined by comparison to AF cells in both the primary dataset (46 genes) and immortal cell-lines (161 genes). Definition of AF-specific membrane-associated genes yielded 125 primary AF cell and 92 immortal cell-line markers. Overlap between primary and immortal NP cells yielded high-confidence NP-specific marker genes for NP-R (CLDN11, TMEFF2, CA12, ANXA2, CD44) and NP-nR (EFNA1, NETO2, SLC2A1). Overlap between AF and immortal AF subtypes yielded specific markers for AF-S (COLEC12, LPAR1) and AF-nS (CHIC1).

CONCLUSIONS

The current study provides a reference platform for preclinical evaluation of novel membrane-associated cell type-specific markers in the IVD. Future research will focus on their biological relevance for IVD function in development, homeostasis, and degenerate conditions.

The Interplay Between Reproductive Tract Microbiota and Immunological System in Human Reproduction

In the last decade, the microbiota, i.e., combined populations of microorganisms living inside and on the surface of the human body, has increasingly attracted attention of researchers in the medical field. Indeed, since the completion of the Human Microbiome Project, insight and interest in the role of microbiota in health and disease, also through study of its combined genomes, the microbiome, has been steadily expanding. One less explored field of microbiome research has been the female reproductive tract. Research mainly from the past decade suggests that microbial communities residing in the reproductive tract represent a large proportion of the female microbial network and appear to be involved in reproductive failure and pregnancy complications. Microbiome research is facing technological and methodological challenges, as detection techniques and analysis methods are far from being standardized. A further hurdle is understanding the complex host-microbiota interaction and the confounding effect of a multitude of constitutional and environmental factors. A key regulator of this interaction is the maternal immune system that, during the peri-conceptional stage and even more so during pregnancy, undergoes considerable modulation. This review aims to summarize the current literature on reproductive tract microbiota describing the composition of microbiota in different anatomical locations (vagina, cervix, endometrium, and placenta). We also discuss putative mechanisms of interaction between such microbial communities and various aspects of the immune system, with a focus on the characteristic immunological changes during normal pregnancy. Furthermore, we discuss how abnormal microbiota composition, “dysbiosis,” is linked to a spectrum of clinical disorders related to the female reproductive system and how the maternal immune system is involved. Finally, based on the data presented in this review, the future perspectives in diagnostic approaches, research directions and therapeutic opportunities are explored.

Quantitative analysis of ChIP-seq data uncovers dynamic and sustained H3K4me3 and H3K27me3 modulation in cancer cells under hypoxia

Background

A comprehensive assessment of the epigenetic dynamics in cancer cells is the key to understanding the molecular mechanisms underlying cancer and to improving cancer diagnostics, prognostics and treatment. By combining genome-wide ChIP-seq epigenomics and microarray transcriptomics, we studied the effects of oxygen deprivation and subsequent reoxygenation on histone 3 trimethylation of lysine 4 (H3K4me3) and lysine 27 (H3K27me3) in a breast cancer cell line, serving as a model for abnormal oxygenation in solid tumors. A priori, epigenetic markings and gene expression levels not only are expected to vary greatly between hypoxic and normoxic conditions, but also display a large degree of heterogeneity across the cell population. Where traditionally ChIP-seq data are often treated as dichotomous data, the model and experiment here necessitate a quantitative, data-driven analysis of both datasets.

Results

We first identified genomic regions with sustained epigenetic markings, which provided a sample-specific reference enabling quantitative ChIP-seq data analysis. Sustained H3K27me3 marking was located around centromeres and intergenic regions, while sustained H3K4me3 marking is associated with genes involved in RNA binding, translation and protein transport and localization. Dynamic marking with both H3K4me3 and H3K27me3 (hypoxia-induced bivalency) was found in CpG-rich regions at loci encoding factors that control developmental processes, congruent with observations in embryonic stem cells.

Conclusions

In silico-identified epigenetically sustained and dynamic genomic regions were confirmed through ChIP-PCR in vitro, and obtained results are corroborated by published data and current insights regarding epigenetic regulation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13072-016-0090-4) contains supplementary material, which is available to authorized users.

Hypoxia increases genome-wide bivalent epigenetic marking by specific gain of H3K27me3

Background

Trimethylation at histone H3 lysine 4 (H3K4me3) and lysine 27 (H3K27me3) controls gene activity during development and differentiation. Whether H3K4me3 and H3K27me3 changes dynamically in response to altered microenvironmental conditions, including low-oxygen conditions commonly present in solid tumors, is relatively unknown. Demethylation of H3K4me3 and H3K27me3 is mediated by oxygen and 2-oxoglutarate dioxygenases enzymes, suggesting that oxygen deprivation (hypoxia) may influence histone trimethylation. Using the MCF7 breast epithelial adenocarcinoma cell model, we have determined the relationship between epigenomic and transcriptomic reprogramming as a function of fluctuating oxygen tension.

Results

We find that in MCF7, H3K4me3 and H3K27me3 marks rapidly increase at specific locations throughout the genome and are largely reversed upon reoxygenation. Whereas dynamic changes are relatively highest for H3K27me3 marking under hypoxic conditions, H3K4me3 occupation is identified as the defining epigenetic marker of transcriptional control. In agreement with the global increase of H3K27 trimethylation, we provide direct evidence that the histone H3K27me3 demethylase KDM6B/JMJD3 is inactivated by limited oxygen. In situ immunohistochemical analysis confirms a marked rise of histone trimethylation in hypoxic tumor areas. Acquisition of H3K27me3 at H3K4me3-marked loci results in a striking increase in “bivalent” epigenetic marking. Hypoxia-induced bivalency substantially overlaps with embryonal stem cell-associated genic bivalency and is retained at numerous loci upon reoxygenation. Transcriptional activity is selectively and progressively dampened at bivalently marked loci upon repeated exposure to hypoxia, indicating that this subset of genes uniquely maintains the potential for epigenetic regulation by KDM activity.

Conclusions

These data suggest that dynamic regulation of the epigenetic state within the tumor environment may have important consequences for tumor plasticity and biology.

Electronic supplementary material

The online version of this article (doi:10.1186/s13072-016-0086-0) contains supplementary material, which is available to authorized users.

EGR1 controls divergent cellular responses of distinctive nucleus pulposus cell types

Background

Immediate early genes (IEGs) encode transcription factors which serve as first line response modules to altered conditions and mediate appropriate cell responses. The immediate early response gene EGR1 is involved in physiological adaptation of numerous different cell types. We have previously shown a role for EGR1 in controlling processes supporting chondrogenic differentiation. We recently established a unique set of phenotypically distinct cell lines from the human nucleus pulposus (NP). Extensive characterization showed that these NP cellular subtypes represented progenitor-like cell types and more functionally mature cells.

Methods

To further understanding of cellular heterogeneity in the NP, we analyzed the response of these cell subtypes to anabolic and catabolic factors. Here, we test the hypothesis that physiological responses of distinct NP cell types are mediated by EGR1 and reflect specification of cell function using an RNA interference-based experimental approach.

Results

We show that distinct NP cell types rapidly induce EGR1 exposure to either growth factors or inflammatory cytokines. In addition, we show that mRNA profiles induced in response to anabolic or catabolic conditions are cell type specific: the more mature NP cell type produced a strong and more specialized transcriptional response to IL-1β than the NP progenitor cells and aspects of this response were controlled by EGR1.

Conclusions

Our current findings provide important substantiation of differential functionality among NP cellular subtypes. Additionally, the data shows that early transcriptional programming initiated by EGR1 is essentially restrained by the cells’ epigenome as it was determined during development and differentiation. These studies begin to define functional distinctions among cells of the NP and will ultimately contribute to defining functional phenotypes within the adult intervertebral disc.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-016-0979-x) contains supplementary material, which is available to authorized users.

Novel Immortal Cell Lines Support Cellular Heterogeneity in the Human Annulus Fibrosus

Introduction

Loss of annulus fibrosus (AF) integrity predisposes to disc herniation and is associated with IVD degeneration. Successful implementation of biomedical intervention therapy requires in-depth knowledge of IVD cell biology. We recently generated unique clonal human nucleus pulposus (NP) cell lines. Recurring functional cellular phenotypes from independent donors provided pivotal evidence for cell heterogeneity in the mature human NP. In this study we aimed to generate and characterize immortal cell lines for the human AF from matched donors.

Methods

Non-degenerate healthy disc material was obtained as surplus surgical material. AF cells were immortalized by simian virus Large T antigen (SV40LTAg) and human telomerase (hTERT) expression. Early passage cells and immortalized cell clones were characterized based on marker gene expression under standardized culturing and in the presence of Transforming Growth factor β (TGFβ).

Results

The AF-specific expression signature included COL1A1, COL5A1, COL12A1, SFRP2 and was largely maintained in immortal AF cell lines. Remarkably, TGFβ induced rapid 3D sheet formation in a subgroup of AF clones. This phenotype was associated with inherent differences in Procollagen type I processing and maturation, and correlated with differential mRNA expression of Prolyl 4-hydroxylase alpha polypeptide 1 and 3 (P4HA1,3) and Lysyl oxidase (LOX) between clones and differential P4HA3 protein expression between AF cells in histological sections.

Conclusion

We report for the first time the generation of representative human AF cell lines. Gene expression profile analysis and functional comparison of AF clones revealed variation between immortalized cells and suggests phenotypic heterogeneity in the human AF. Future characterization of AF cellular (sub-)populations aims to combine identification of additional specific AF marker genes and their biological relevance. Ultimately this knowledge will contribute to clinical application of cell-based technology in IVD repair.

Novel immortal human cell lines reveal subpopulations in the nucleus pulposus

Introduction

Relatively little is known about cellular subpopulations in the mature nucleus pulposus (NP). Detailed understanding of the ontogenetic, cellular and molecular characteristics of functional intervertebral disc (IVD) cell populations is pivotal to the successful development of cell replacement therapies and IVD regeneration. In this study, we aimed to investigate whether phenotypically distinct clonal cell lines representing different subpopulations in the human NP could be generated using immortalization strategies.

Methods

Nondegenerate healthy disc material (age range, 8 to 15 years) was obtained as surplus surgical material. Early passage NP monolayer cell cultures were initially characterized using a recently established NP marker set. NP cells were immortalized by simian virus 40 large T antigen (SV40LTag) and human telomerase reverse transcriptase expression. Immortalized cells were clonally expanded and characterized based on collagen type I, collagen type II, α1 (COL2A1), and SRY-box 9 (SOX9) protein expression profiles, as well as on expression of a subset of established in vivo NP cell lineage markers.

Results

A total of 54 immortal clones were generated. Profiling of a set of novel NP markers (CD24, CA12, PAX1, PTN, FOXF1 and KRT19 mRNA) in a representative set of subclones substantiated successful immortalization of multiple cellular subpopulations from primary isolates and confirmed their NP origin and/or phenotype. We were able to identify two predominant clonal NP subtypes based on their morphological characteristics and their ability to induce SOX9 and COL2A1 under conventional differentiation conditions. In addition, cluster of differentiation 24 (CD24)–negative NP responder clones formed spheroid structures in various culture systems, suggesting the preservation of a more immature phenotype compared to CD24-positive nonresponder clones.

Conclusions

Here we report the generation of clonal NP cell lines from nondegenerate human IVD tissue and present a detailed characterization of NP cellular subpopulations. Differential cell surface marker expression and divergent responses to differentiation conditions suggest that the NP subtypes may correspond to distinct maturation stages and represent distinct NP cell subpopulations. Hence, we provide evidence that the immortalization strategy that we applied is capable of detecting cell heterogeneity in the NP. Our cell lines yield novel insights into NP biology and provide promising new tools for studies of IVD development, cell function and disease.

The immediate early gene product EGR1 and polycomb group proteins interact in epigenetic programming during chondrogenesis

Initiation of and progression through chondrogenesis is driven by changes in the cellular microenvironment. At the onset of chondrogenesis, resting mesenchymal stem cells are mobilized in vivo and a complex, step-wise chondrogenic differentiation program is initiated. Differentiation requires coordinated transcriptomic reprogramming and increased progenitor proliferation; both processes require chromatin remodeling. The nature of early molecular responses that relay differentiation signals to chromatin is poorly understood. We here show that immediate early genes are rapidly and transiently induced in response to differentiation stimuli in vitro. Functional ablation of the immediate early factor EGR1 severely deregulates expression of key chondrogenic control genes at the onset of differentiation. In addition, differentiating cells accumulate DNA damage, activate a DNA damage response and undergo a cell cycle arrest and prevent differentiation associated hyper-proliferation. Failed differentiation in the absence of EGR1 affects global acetylation and terminates in overall histone hypermethylation. We report novel molecular connections between EGR1 and Polycomb Group function: Polycomb associated histone H3 lysine27 trimethylation (H3K27me3) blocks chromatin access of EGR1. In addition, EGR1 ablation results in abnormal Ezh2 and Bmi1 expression. Consistent with this functional interaction, we identify a number of co-regulated targets genes in a chondrogenic gene network. We here describe an important role for EGR1 in early chondrogenic epigenetic programming to accommodate early gene-environment interactions in chondrogenesis.

MK3 controls Polycomb target gene expression via negative feedback on ERK

Background

Gene-environment interactions are mediated by epigenetic mechanisms. Polycomb Group proteins constitute part of an epigenetic cellular transcriptional memory system that is subject to dynamic modulation during differentiation. Molecular insight in processes that control dynamic chromatin association and dissociation of Polycomb repressive complexes during and beyond development is limited. We recently showed that MK3 interacts with Polycomb repressive complex 1 (PRC1). The functional relevance of this interaction, however, remained poorly understood. MK3 is activated downstream of mitogen- and stress-activated protein kinases (M/SAPKs), all of which fulfill crucial roles during development. We here use activation of the immediate-early response gene ATF3, a bona fide PRC1 target gene, as a model to study how MK3 and its effector kinases MAPK/ERK and SAPK/P38 are involved in regulation of PRC1-dependent ATF3 transcription.

Results

Our current data show that mitogenic signaling through ERK, P38 and MK3 regulates ATF3 expression by PRC1/chromatin dissociation and epigenetic modulation. Mitogenic stimulation results in transient P38-dependent H3S28 phosphorylation and ERK-driven PRC1/chromatin dissociation at PRC1 targets. H3S28 phosphorylation by itself appears not sufficient to induce PRC1/chromatin dissociation, nor ATF3 transcription, as inhibition of MEK/ERK signaling blocks BMI1/chromatin dissociation and ATF3 expression, despite induced H3S28 phosphorylation. In addition, we establish that concomitant loss of local H3K27me3 promoter marking is not required for ATF3 activation. We identify pERK as a novel signaling-induced binding partner of PRC1, and provide evidence that MK3 controls ATF3 expression in cultured cells via negative regulatory feedback on M/SAPKs. Dramatically increased ectopic wing vein formation in the absence of Drosophila MK in a Drosophila ERK gain-of-function wing vein patterning model, supports the existence of MK-mediated negative feedback regulation on pERK.

Conclusion

We here identify and characterize important actors in a PRC1-dependent epigenetic signal/response mechanism, some of which appear to be nonspecific global responses, whereas others provide modular specificity. Our findings provide novel insight into a Polycomb-mediated epigenetic mechanism that dynamically controls gene transcription and support a direct link between PRC1 and cellular responses to changes in the microenvironment.

Mapping of lamin A- and progerin-interacting genome regions

Mutations in the A-type lamins A and C, two major components of the nuclear lamina, cause a large group of phenotypically diverse diseases collectively referred to as laminopathies. These conditions often involve defects in chromatin organization. However, it is unclear whether A-type lamins interact with chromatin in vivo and whether aberrant chromatin–lamin interactions contribute to disease. Here, we have used an unbiased approach to comparatively map genome-wide interactions of gene promoters with lamin A and progerin, the mutated lamin A isoform responsible for the premature aging disorder Hutchinson–Gilford progeria syndrome (HGPS) in mouse cardiac myoytes and embryonic fibroblasts. We find that lamin A-associated genes are predominantly transcriptionally silent and that loss of lamin association leads to the relocation of peripherally localized genes, but not necessarily to their activation. We demonstrate that progerin induces global changes in chromatin organization by enhancing interactions with a specific subset of genes in addition to the identified lamin A-associated genes. These observations demonstrate disease-related changes in higher order genome organization in HGPS and provide novel insights into the role of lamin–chromatin interactions in chromatin organization.

Post-natal myogenic and adipogenic developmental: defects and metabolic impairment upon loss of A-type lamins

A-type lamins are a major component of the nuclear lamina. Mutations in the LMNA gene, which encodes the A-type lamins A and C, cause a set of phenotypically diverse diseases collectively called laminopathies. While adult LMNA null mice show various symptoms typically associated with laminopathies, the effect of loss of lamin A/C on early post-natal development is poorly understood. Here we developed a novel LMNA null mouse (LMNA(GT-/-)) based on genetrap technology and analyzed its early post-natal development. We detect LMNA transcripts in heart, the outflow tract, dorsal aorta, liver and somites during early embryonic development. Loss of A-type lamins results in severe growth retardation and developmental defects of the heart, including impaired myocyte hypertrophy, skeletal muscle hypotrophy, decreased amounts of subcutaneous adipose tissue and impaired ex vivo adipogenic differentiation. These defects cause death at 2 to 3 weeks post partum associated with muscle weakness and metabolic complications, but without the occurrence of dilated cardiomyopathy or an obvious progeroid phenotype. Our results indicate that defective early post-natal development critically contributes to the disease phenotypes in adult laminopathies.

Activation of NF-κB/p65 facilitates early chondrogenic differentiation during endochondral ossification

BACKGROUND

NF-κB/p65 has been reported to be involved in regulation of chondrogenic differentiation. However, its function in relation to key chondrogenic factor Sox9 and onset of chondrogenesis during endochondral ossification is poorly understood. We hypothesized that the early onset of chondrogenic differentiation is initiated by transient NF-κB/p65 signaling.

METHODOLOGY/PRINCIPAL FINDINGS

The role of NF-κB/p65 in early chondrogenesis was investigated in different in vitro, ex vivo and in vivo endochondral models: ATDC5 cells, hBMSCs, chicken periosteal explants and growth plates of 6 weeks old mice. NF-κB/p65 activation was manipulated using pharmacological inhibitors, RNAi and activating agents. Gene expression and protein expression analysis, and (immuno)histochemical stainings were employed to determine the role of NF-κB/p65 in the chondrogenic phase of endochondral development. Our data show that chondrogenic differentiation is facilitated by early transient activation of NF-κB/p65. NF-κB/p65-mediated signaling determines early expression of Sox9 and facilitates the subsequent chondrogenic differentiation programming by signaling through key chondrogenic pathways.

CONCLUSIONS/SIGNIFICANCE

The presented data demonstrate that NF-κB/p65 signaling, as well as its intensity and timing, represents one of the transcriptional regulatory mechanisms of the chondrogenic developmental program of chondroprogenitor cells during endochondral ossification. Importantly, these results provide novel possibilities to improve the success of cartilage and bone regenerative techniques.

Inhibition of cyclooxygenase-2 impacts chondrocyte hypertrophic differentiation during endochondral ossification

Skeletogenesis and bone fracture healing involve endochondral ossification, a process during which cartilaginous primordia are gradually replaced by bone tissue. In line with a role for cyclooxygenase-2 (COX-2) in the endochondral ossification process, non-steroidal anti-inflammatory drugs (NSAIDs) were reported to negatively affect bone fracture healing due to impaired osteogenesis. However, a role for COX-2 activity in the chondrogenic phase of endochondral ossification has not been addressed before. We show that COX-2 activity fulfils an important regulatory function in chondrocyte hypertrophic differentiation. Our data reveal essential cross-talk between COX-2 and bone morphogenic protein-2 (BMP-2) during chondrocyte hypertrophic differentiation. BMP-2 mediated chondrocyte hypertrophy is associated with increased COX-2 expression and pharmacological inhibition of COX-2 activity by NSAIDs (e.g., Celecoxib) decreases hypertrophic differentiation in various chondrogenic models in vitro and in vivo, while leaving early chondrogenic development unaltered. Our findings demonstrate that COX-2 activity is a novel factor partaking in chondrocyte hypertrophy in the context of endochondral ossification and these observations provide a novel etiological perspective on the adverse effects of NSAIDs on bone fracture healing and have important implications for the use of NSAIDs during endochondral skeletal development.

Genetic modification of the mouse: general technology - pronuclear and blastocyst injection

Introduction of germ line mutations in mice via genetic engineering involves alterations of the structure and characteristics of genes. These alterations are mostly introduced via molecular genetic technology either in embryonal stem cells or in one-cell stage embryos. This chapter describes classic biotechnological methods used to generate mice from modified pre-implantation embryos.

Mapping of protein- and chromatin-interactions at the nuclear lamina

The nuclear envelope and the lamina define the nuclear periphery and are implicated in many nuclear processes including chromatin organization, transcription and DNA replication. Mutations in lamin A proteins, major components of the lamina, interfere with these functions and cause a set of phenotypically diverse diseases referred to as laminopathies. The phenotypic diversity of laminopathies is thought to be the result of alterations in specific protein- and chromatin interactions due to lamin A mutations. Systematic identification of lamin A-protein and -chromatin interactions will be critical to uncover the molecular etiology of laminopathies. Here we summarize and critically discuss recent technology to analyze lamina-protein and-chromatin interactions.

Identification of differential protein interactors of lamin A and progerin

The nuclear lamina is an interconnected meshwork of intermediate filament proteins underlying the nuclear envelope. The lamina is an important regulator of nuclear structural integrity as well as nuclear processes, including transcription, DNA replication and chromatin remodeling. The major components of the lamina are A- and B-type lamins. Mutations in lamins impair lamina functions and cause a set of highly tissue-specific diseases collectively referred to as laminopathies. The phenotypic diversity amongst laminopathies is hypothesized to be caused by mutations affecting specific protein interactions, possibly in a tissue-specific manner. Current technologies to identify interaction partners of lamin A and its mutants are hampered by the insoluble nature of lamina components. To overcome the limitations of current technologies, we developed and applied a novel, unbiased approach to identify lamin A-interacting proteins. This approach involves expression of the high-affinity OneSTrEP-tag, precipitation of lamin-protein complexes after reversible protein cross-linking and subsequent protein identification by mass spectrometry. We used this approach to identify in mouse embryonic fibroblasts and cardiac myocyte NklTAg cell lines proteins that interact with lamin A and its mutant isoform progerin, which causes the premature aging disorder Hutchinson-Gilford progeria syndrome (HGPS). We identified a total of 313 lamina-interacting proteins, including several novel lamin A interactors, and we characterize a set of 35 proteins which preferentially interact with lamin A or progerin.

The unfolded protein response protects human tumor cells during hypoxia through regulation of the autophagy genes MAP1LC3B and ATG5

Tumor hypoxia is a common microenvironmental factor that adversely influences tumor phenotype and treatment response. Cellular adaptation to hypoxia occurs through multiple mechanisms, including activation of the unfolded protein response (UPR). Recent reports have indicated that hypoxia activates a lysosomal degradation pathway known as autophagy, and here we show that the UPR enhances the capacity of hypoxic tumor cells to carry out autophagy, and that this promotes their survival. In several human cancer cell lines, hypoxia increased transcription of the essential autophagy genes microtubule-associated protein 1 light chain 3beta (MAP1LC3B) and autophagy-related gene 5 (ATG5) through the transcription factors ATF4 and CHOP, respectively, which are regulated by PKR-like ER kinase (PERK, also known as EIF2AK3). MAP1LC3B and ATG5 are not required for initiation of autophagy but mediate phagophore expansion and autophagosome formation. We observed that transcriptional induction of MAP1LC3B replenished MAP1LC3B protein that was turned over during extensive hypoxia-induced autophagy. Correspondingly, cells deficient in PERK signaling failed to transcriptionally induce MAP1LC3B and became rapidly depleted of MAP1LC3B protein during hypoxia. Consistent with these data, autophagy and MAP1LC3B induction occurred preferentially in hypoxic regions of human tumor xenografts. Furthermore, pharmacological inhibition of autophagy sensitized human tumor cells to hypoxia, reduced the fraction of viable hypoxic tumor cells, and sensitized xenografted human tumors to irradiation. Our data therefore demonstrate that the UPR is an important mediator of the hypoxic tumor microenvironment and that it contributes to resistance to treatment through its ability to facilitate autophagy.

Talking to chromatin: post-translational modulation of polycomb group function

Polycomb Group proteins are important epigenetic regulators of gene expression. Epigenetic control by polycomb Group proteins involves intrinsic as well as associated enzymatic activities. Polycomb target genes change with cellular context, lineage commitment and differentiation status, revealing dynamic regulation of polycomb function. It is currently unclear how this dynamic modulation is controlled and how signaling affects polycomb-mediated epigenetic processes at the molecular level. Experimental evidence on regulation of polycomb function by post-translational mechanisms is steadily emerging: Polycomb Group proteins are targeted for ubiquitylation, sumoylation and phosphorylation. In addition, specific Polycomb Group proteins modify other (chromatin) associated proteins via similar post-translational modifications. Such modifications affect protein function by affecting protein stability, protein-protein interactions and enzymatic activities. Here, we review current insights in covalent modification of Polycomb Group proteins in the context of protein function and present a tentative view of integrated signaling to chromatin in the context of phosphorylation. Clearly, the available literature reveals just the tip of the iceberg, and exact molecular mechanisms in, and the biological relevance of post-translational regulation of polycomb function await further elucidation. Our understanding of causes and consequences of post-translational modification of polycomb proteins will gain significantly from in vivo validation experiments. Impaired polycomb function has important repercussions for stem cell function, development and disease. Ultimately, increased understanding of signaling to chromatin and the mechanisms involved in epigenetic remodeling will contribute to the development of therapeutic interventions in cell fate decisions in development and disease.

PPARgamma inhibits NF-kappaB-dependent transcriptional activation in skeletal muscle

Skeletal muscle pathology associated with a chronic inflammatory disease state (e.g., skeletal muscle atrophy and insulin resistance) is a potential consequence of chronic activation of NF-kappaB. It has been demonstrated that peroxisome proliferator-activated receptors (PPARs) can exert anti-inflammatory effects by interfering with transcriptional regulation of inflammatory responses. The goal of the present study, therefore, was to evaluate whether PPAR activation affects cytokine-induced NF-kappaB activity in skeletal muscle. Using C(2)C(12) myotubes as an in vitro model of myofibers, we demonstrate that PPAR, and specifically PPARgamma, activation potently inhibits inflammatory mediator-induced NF-kappaB transcriptional activity in a time- and dose-dependent manner. Furthermore, PPARgamma activation by rosiglitazone strongly suppresses cytokine-induced transcript levels of the NF-kappaB-dependent genes intracellular adhesion molecule 1 (ICAM-1) and CXCL1 (KC), the murine homolog of IL-8, in myotubes. To verify whether muscular NF-kappaB activity in human subjects is suppressed by PPARgamma activation, we examined the effect of 8 wk of rosiglitazone treatment on muscular gene expression of ICAM-1 and IL-8 in type 2 diabetes mellitus patients. In these subjects, we observed a trend toward decreased basal expression of ICAM-1 mRNA levels. Subsequent analyses in cultured myotubes revealed that the anti-inflammatory effect of PPARgamma activation is not due to decreased RelA translocation to the nucleus or reduced RelA DNA binding. These findings demonstrate that muscle-specific inhibition of NF-kappaB activation may be an interesting therapeutic avenue for treatment of several inflammation-associated skeletal muscle abnormalities.

A novel in vivo model to study endochondral bone formation; HIF-1alpha activation and BMP expression

Numerous growth and transcription factors have been implicated in endochondral bone formation of the growth plate. Many of these factors are up-regulated during hypoxia and downstream of Hypoxia-Inducible Factor (HIF)-1alpha activation. However, the specific function of these factors, in the context of oxygenation and metabolic adaptation during adult periosteal endochondral bone formation, is largely unknown. Here, we studied HIF-1alpha and the possible roles of (HIF-1alpha related) growth and transcription factors in a recently developed in vivo model for adult periosteal endochondral bone formation. At different phases of periosteal endochondral bone formation, mRNA levels of Transforming Growth Factor (TGF)-beta1, Bone Morphogenetic Proteins (BMP)-2, -4, and -7, Indian Hedgehog (Ihh), Parathyroid Hormone-related Protein (PTHrP), Sox9, Runx2, HIF-1alpha, Vascular Endothelial Growth Factor (VEGF), periostin (POSTN), and Glyceraldehyde-3-Phophate Dehydrogenase (GAPDH) were evaluated with RT-real time-PCR. Also protein levels of TGF-beta1, BMP-2, -4, and -7, HIF-1alpha, and POSTN were examined. During the chondrogenic phase, the expression of Sox9, Ihh, and HIF-1alpha was significantly up-regulated. TGF-beta1 mRNA levels were rather constant, and the mRNA levels of BMPs were significantly lower. Immunohistochemical detection of corresponding gene products, however, revealed the presence of the proteins of TGF-beta1, BMP-2, -4, and -7, HIF-1alpha, and POSTN within the chondrocytes during chondrogenesis. This discrepancy in gene expression between mRNA and protein level for TGF-beta1 and the different BMPs is indicative of post-transcriptional regulation of protein synthesis. HIF-1alpha activation and up-regulation of GAPDH support a hypoxia-induced metabolic shift during periosteal chondrogenesis. Our model recapitulates essential steps in osteochondrogenesis and provides a new experimental system to study and ultimately control tissue regeneration in the adult organism.

Gene expression during acute and prolonged hypoxia is regulated by distinct mechanisms of translational control

Hypoxia has recently been shown to activate the endoplasmic reticulum kinase PERK, leading to phosphorylation of eIF2alpha and inhibition of mRNA translation initiation. Using a quantitative assay, we show that this inhibition exhibits a biphasic response mediated through two distinct pathways. The first occurs rapidly, reaching a maximum at 1-2 h and is due to phosphorylation of eIF2alpha. Continued hypoxic exposure activates a second, eIF2alpha-independent pathway that maintains repression of translation. This phase is characterized by disruption of eIF4F and sequestration of eIF4E by its inhibitor 4E-BP1 and transporter 4E-T. Quantitative RT-PCR analysis of polysomal RNA indicates that the translation efficiency of individual genes varies widely during hypoxia. Furthermore, the translation efficiency of individual genes is dynamic, changing dramatically during hypoxic exposure due to the initial phosphorylation and subsequent dephosphorylation of eIF2alpha. Together, our data indicate that acute and prolonged hypoxia regulates mRNA translation through distinct mechanisms, each with important contributions to hypoxic gene expression.

TP53 overexpression in recurrent endometrial carcinoma

OBJECTIVE

To study alterations within the p53 pathway in relation to the development of recurrent stage I endometrioid endometrial carcinoma.

METHODS

Paraffin-embedded tumor tissue of both primary and recurrent tumors from 44 patients with and 44 without recurrence was used for immunohistochemical analysis of TP53, hMdm2, P21(Waf1/Cip1) and M30. DNA was extracted, and mutation analysis of p53 (exon 5-8, 11) was performed by direct sequencing.

RESULTS

TP53 overexpression was significantly associated with recurrent disease: Odds Ratio 3.8 (95% CI: 1.5-9.8). Overexpression of TP53 was associated with lower staining indices (SI:0-9) of both hMdm2 and P21 in tumors of patients with recurrence, compared to controls: 2.0 +/- 0.4 vs. 4.0 +/- 0.8 and 1.9 +/- 0.8 vs. 3.6 +/- 0.8, respectively. Eight p53 missense mutations were identified in six patients with recurrence and two controls. One nonsense mutation was found in a patient with recurrence and one deletion in a control patient. Only a minority of TP53 overexpression cases could be explained by the presence of these p53 mutations.

CONCLUSION

TP53 overexpression was significantly predictive for recurrent endometrial carcinoma, and mostly not correlated with p53 mutations. Concomitant low hMdm2 and P21(Waf1/Cip1) expression in tumors with overexpressed TP53 suggests a dysfunctional TP53-P21(Waf1/Cip1) pathway.

A-type lamins are essential for TGF-β1 induced PP2A to dephosphorylate transcription factors

Diseases caused by mutations in lamins A and C (laminopathies) suggest a crucial role for A-type lamins in different cellular processes. Laminopathies mostly affect tissues of mesenchymal origin. As transforming growth factor-beta1 (TGF-beta1) signalling impinges on the retinoblastoma protein (pRB) and SMADs, we tested the hypothesis that lamins modulate cellular responses to TGF-beta1 signalling, via the regulation of these transcription factors in mesenchymal cells. Here, we report that A-type lamins are essential for the inhibition of fibroblast proliferation by TGF-beta1. TGF-beta1 dephosphorylated pRB through PP2A, both of which, we show, are associated with lamin A/C. In addition, lamin A/C modulates the effect of TGF-beta1 on collagen production, a marker of mesenchymal differentiation. Our findings implicate lamin A/C in control of gene activity downstream of TGF-beta1, via nuclear phosphatases such as PP2A. This biological function provides a novel explanation for the observed mesenchymal dysfunction in laminopathies.

MAPKAP Kinase 3pK Phosphorylates and Regulates Chromatin Association of the Polycomb Group Protein Bmi1

Polycomb group (PcG) proteins form chromatin-associated, transcriptionally repressive complexes, which are critically involved in the control of cell proliferation and differentiation. Although the mechanisms involved in PcG-mediated repression are beginning to unravel, little is known about the regulation of PcG function. We showed previously that PcG complexes are phosphorylated in vivo, which regulates their association with chromatin. The nature of the responsible PcG kinases remained unknown. Here we present the novel finding that the PcG protein Bmi1 is phosphorylated by 3pK (MAPKAP kinase 3), a convergence point downstream of activated ERK and p38 signaling pathways and implicated in differentiation and developmental processes. We identified 3pK as an interaction partner of PcG proteins, in vitro and in vivo, by yeast two-hybrid interaction and co-immunoprecipitation, respectively. Activation or overexpression of 3pK resulted in phosphorylation of Bmi1 and other PcG members and their dissociation from chromatin. Phosphorylation and subsequent chromatin dissociation of PcG complexes were expected to result in de-repression of targets. One such reported Bmi1 target is the Cdkn2a/INK4A locus. Cells overexpressing 3pK showed PcG complex/chromatin dissociation and concomitant de-repression of p14(ARF), which was encoded by the Cdkn2a/INK4A locus. Thus, 3pK is a candidate regulator of phosphorylation-dependent PcG/chromatin interaction. We speculate that phosphorylation may not only affect chromatin association but, in addition, the function of individual complex members. Our findings linked for the first time MAPK signaling pathways to the Polycomb transcriptional memory system. This suggests a novel mechanism by which a silenced gene status can be modulated and implicates PcG-mediated repression as a dynamically controlled process.

Rnf2 (Ring1b) deficiency causes gastrulation arrest and cell cycle inhibition

The highly homologous Rnf2 (Ring1b) and Ring1 (Ring1a) proteins were identified as in vivo interactors of the Polycomb Group (PcG) protein Bmi1. Functional ablation of Rnf2 results in gastrulation arrest, in contrast to relatively mild phenotypes in most other PcG gene null mutants belonging to the same functional group, among which is Ring1. Developmental defects occur in both embryonic and extraembryonic tissues during gastrulation. The early lethal phenotype is reminiscent of that of the PcG-gene knockouts Eed and Ezh2, which belong to a separate functional PcG group and PcG protein complex. This finding indicates that these biochemically distinct PcG complexes are both required during early mouse development. In contrast to the strong skeletal transformation in Ring1 hemizygous mice, hemizygocity for Rnf2 does not affect vertebral identity. However, it does aggravate the cerebellar phenotype in a Bmi1 null-mutant background. Together, these results suggest that Rnf2 or Ring1-containing PcG complexes have minimal functional redundancy in specific tissues, despite overlap in expression patterns. We show that the early developmental arrest in Rnf2-null embryos is partially bypassed by genetic inactivation of the Cdkn2a (Ink4aARF) locus. Importantly, this finding implicates Polycomb-mediated repression of the Cdkn2a locus in early murine development.

Abnormal function of astroglia lacking Abr and Bcr RacGAPs

Experiments in cultured cells have implicated the molecular switch Rac in a wide variety of cellular functions. Here we demonstrate that the simultaneous disruption of two negative regulators of Rac, Abr and Bcr, in mice leads to specific abnormalities in postnatal cerebellar development. Mutants exhibit granule cell ectopia concomitant with foliation defects. We provide evidence that this phenotype is causally related to functional and structural abnormalities of glial cells. Bergmann glial processes are abnormal and GFAP-positive astroglia were aberrantly present on the pial surface. Older Abr;Bcr-deficient mice show spontaneous mid-brain glial hypertrophy, which can further be markedly enhanced by kainic acid. Double null mutant astroglia are hyper-responsive to stimulation with epidermal growth factor and lipopolysaccharide and exhibit constitutively increased phosphorylation of p38 mitogen-activated protein kinase, which is regulated by Rac. These combined data demonstrate a prominent role for Abr and Bcr in the regulation of glial cell morphology and reactivity, and consequently in granule cell migration during postnatal cerebellar development in mammals.

The Bcr N-terminal oligomerization domain contributes to the full oncogenicity of P190 Bcr/Abl in transgenic mice

The Bcr/Abl P190 oncoprotein is responsible for the development of Philadelphia-chromosome positive acute lymphoblastic leukemia (ALL). The Bcr moiety in Bcr/Abl activates the Abl tyrosine kinase, an ingredient essential for the transforming capability of Bcr/Abl. Residues 1-63 of Bcr form an N-terminal oligomerization domain and are key to Abl activation in vitro. Mice transgenic for P190 BCR/ABL reproducibly develop an aggressive B-lineage lymphoblastic leukemia/lymphoma. Here we test the hypothesis that residues 1-63 of Bcr have a major in vivo contribution to the oncogenicity of Bcr/Abl P190 by the generation of mice transgenic for an N-terminal deleted form of P190. We find that although the transgene is expressed in the bone marrow of mice at an early age, the incidence of leukemogenesis is greatly diminished as compared to mice transgenic for non-mutated P190 Bcr/Abl. Sporadic hematological malignancies which did develop showed decreased levels of phosphotyrosine as compared to those of wild-type P190 transgenics, although Ras was activated. These results demonstrate that the Bcr oligomerization domain contributes to the oncogenicity of Bcr/Abl in vivo.

Reduced oncogenicity of p190 Bcr/Abl F-actin-binding domain mutants

The deregulated Bcr/Abl tyrosine kinase is responsible for the development of Philadelphia (Ph)-positive leukemia in humans. To investigate the significance of the C-terminal Abl actin-binding domain within Bcr/Abl p190 in the development of leukemia/lymphoma in vivo, mutant p190 DNA constructs were used to generate transgenic mice. Eight founder and progeny mice of 5 different lines were monitored for leukemogenesis. Latency was markedly increased and occurrence decreased in the p190 del C lines as compared with nonmutated p190 BCR/ABL transgenics. Western blot analysis of involved hematologic tissues of the p190 del C transgenics with end-stage disease showed high-level expression of the transgene and tyrosine phosphorylation of Cbl and Hef1/Cas, proteins previously shown to be affected by Bcr/Abl. These results show that the actin-binding domain of Abl enhances leukemia development but does not appear to be an absolute requirement for leukemogenesis.

Chromatin-association of the Polycomb group protein BMI1 is cell cycle-regulated and correlates with its phosphorylation status

The human proto-oncogene Bmi1 is a member of the mammalian Polycomb Group (Pc-G) genes. The subnuclear distribution of the BMI1 protein was studied in several primary human and tumor-derived cell lines using immunohistochemical and biochemical methods. In primary and tumor cells, nuclear BMI1 shows a fine-grain distribution over chromatin, usually dense in interphase nuclei and significantly weaker along mitotic chromosomes. In addition, BMI1 preferentially associates with several distinct heterochromatic domains in tumor cell lines. In both primary and tumor cell lines a marked cell cycle-regulation of Pc-G-chromatin interaction is observed: nuclear BMI1-staining dissipates in late S phase and is re-established early in G(1)-phase. Chromatin-association of BMI1 inversely correlates with its phosphorylation status in a cell cycle-dependent fashion: at G(1)/S, hypophosphorylated BMI1 is specifically retained in the chromatin-associated nuclear protein fraction, whereas during G(2)/M, phosphorylated BMI1 is not chromatin-bound. Our findings indicate a strict cell cycle-controlled regulation of Pc-G complex-chromatin association and provide molecular tools for improving our understanding of Pc-G complex regulation and function in mammalian cells.

Bmi-1 collaborates with c-Myc in tumorigenesis by inhibiting c-Myc-induced apoptosis via INK4a/ARF

The bmi-1 and myc oncogenes collaborate strongly in murine lymphomagenesis, but the basis for this collaboration was not understood. We recently identified the ink4a-ARF tumor suppressor locus as a critical downstream target of the Polycomb-group transcriptional repressor Bmi-1. Others have shown that part of Myc's ability to induce apoptosis depends on induction of p19arf. Here we demonstrate that down-regulation of ink4a-ARF by Bmi-1 underlies its ability to cooperate with Myc in tumorigenesis. Heterozygosity for bmi-1 inhibits lymphomagenesis in Emu-myc mice by enhancing c-Myc-induced apoptosis. We observe increased apoptosis in bmi-1(-/-) lymphoid organs, which can be rescued by deletion of ink4a-ARF or overexpression of bcl2. Furthermore, Bmi-1 collaborates with Myc in enhancing proliferation and transformation of primary embryo fibroblasts (MEFs) in an ink4a-ARF dependent manner, by prohibiting Myc-mediated induction of p19arf and apoptosis. We observe strong collaboration between the Emu-myc transgene and heterozygosity for ink4a-ARF, which is accompanied by loss of the wild-type ink4a-ARF allele and formation of highly aggressive B-cell lymphomas. Together, these results reinforce the critical role of Bmi-1 as a dose-dependent regulator of ink4a-ARF, which on its turn acts to prevent tumorigenesis on activation of oncogenes such as c-myc.

Abnormal stress response and increased fighting behavior in mice lacking the bcr gene product

The in vivo function of proteins which regulate activity of the GTPase Rac is largely unknown. Here we establish that mice lacking bcr, a known GTPase activating protein for Rac, exhibit a defect in the regulation of both hormonal and behavioral stress responses. Bcr null mutants demonstrate prolonged elevation of plasma glucocorticoids and increased fighting in males in response to physiological and social stress, respectively. Combined biochemical and behavioral data indicate that bcr is involved in mediating the cellular effects of glucocorticoids, specifically down-regulation of the stress-activated hippocampal hypothalamic-pituitary-adrenal axis.

Interaction of mouse polycomb-group (Pc-G) proteins Enx1 and Enx2 with Eed: indication for separate Pc-G complexes

The Polycomb group (Pc-G) constitutes an important, functionally conserved group of proteins, required to stably maintain inactive homeobox genes repressed during development. Drosophila extra sex combs (esc) and its mammalian homolog embryonic ectoderm development (eed) are special Pc-G members, in that they are required early during development when Pc-G repression is initiated, a process that is still poorly understood. To get insight in the molecular function of Eed, we searched for Eed-interacting proteins, using the yeast two-hybrid method. Here we describe the specific in vivo binding of Eed to Enx1 and Enx2, two mammalian homologs of the essential Drosophila Pc-G gene Enhancer-of-zeste [E(z)]. No direct biochemical interactions were found between Eed/Enx and a previously characterized mouse Pc-G protein complex, containing several mouse Pc-G proteins including mouse polyhomeotic (Mph1). This suggests that different Pc-G complexes with distinct functions may exist. However, partial colocalization of Enx1 and Mph1 to subnuclear domains may point to more transient interactions between these complexes, in support of a bridging role for Enx1.

Bcr/Abl associated leukemogenesis in bcr null mutant mice

The BCR gene contributes to Philadelphia-positive leukemogenesis via a number of discrete mechanisms, one of which may be through interaction of its normal gene product with the Bcr/Abl oncoprotein. In the current study this hypothesis was tested in vivo by introducing a Bcr/Abl P190 transgene into mice lacking endogenous bcr protein. Our finding, that the P190 BCR/ABL oncogene is still capable of producing leukemia in these mice with indistinguishable latency and clinical pattern as in genetically matched counterparts, rules out any significant or major contribution of the bcr protein as a whole to leukemia development in these mice.

MPc2, a new murine homolog of the Drosophila polycomb protein is a member of the mouse polycomb transcriptional repressor complex

The evolutionarily conserved polycomb and trithorax-group genes are required to maintain stable expression patterns of homeotic genes and other target genes throughout development. Here, we report the cloning and characterization of a novel mouse polycomb homolog, MPc2, in addition to the previously described M33 polycomb gene. Co-immunoprecipitations and subnuclear co-localization studies show that MPc2 interacts with the mouse polycomb-group oncoprotein Bmi1 and is a new member of the mouse polycomb multiprotein complex. Gal4DB-MPc2 or -M33 fusion proteins mediate a five- to tenfold repression of stably integrated reporter constructs carrying GAL4 binding sites, demonstrating that these proteins are transcriptional repressors. The MPc2 gene is localized on chromosome 11, in close proximity to the classical mouse mutations tail short (Ts) and rabo torcido (Rbt). Ts and Rbt hemizygous mice display anemia and transformations of the axial skeleton reminiscent of phenotypes observed in mice with mutated polycomb or trithorax-group genes, suggesting that MPc2 is a candidate gene for Ts and Rbt.

A mouse model for the human lysosomal disease aspartylglycosaminuria

Aspartylglycosaminuria (AGU), the most common disorder of glycoprotein degradation in humans, is caused by mutations in the gene encoding the lysosomal enzyme glycosylasparaginase (Aga). The resulting enzyme deficiency allows aspartylglucosamine (GlcNAc-Asn) and other glycoasparagines to accumulate in tissues and body fluids, from early fetal life onward. The clinical course is characterized by normal early development, slowly progressing to severe mental and motor retardation in early adulthood. The exact pathogenesis of AGU in humans is unknown and neither therapy nor an animal model for this debilitating and ultimately fatal disease exists. Through targeted disruption of the mouse Aga gene in embryonic stem cells, we generated mice that completely lack Aga activity. At the age of 5-10 months a massive accumulation of GlcNAc-Asn was detected along with lysosomal vacuolization, axonal swelling in the gracile nucleus and impaired neuromotor coordination. A significant number of older male mice had massively swollen bladders, which was not caused by obstruction, but most likely related to the impaired function of the nervous system. These findings are consistent with the pathogenesis of AGU and provide further data explaining the impaired neurological function in AGU patients.

BCR/ABL P210 and P190 cause distinct leukemia in transgenic mice

DNA constructs encoding BCR/ABL P210 have been introduced into the mouse germ line using microinjection of one-cell fertilized eggs. Kinetics of BCR/ABL P210 expression in transgenic mice were very similar to those of BCR/ABL P190 constructs in transgenic mice. mRNA transcripts were detectable early in embryonic development and also in hematopoietic tissue of adult animals. Expression of BCR/ABL in peripheral blood preceded development of overt disease. P210 founder and progeny transgenic animals, when becoming ill, developed leukemia of B, T-lymphoid, or myeloid origin after a relatively long latency period. In contrast, P190-transgenic mice exclusively developed leukemia of B-cell origin, with a relatively short period of latency. The observed dissimilarities are most likely due to intrinsically different properties of the P190 and P210 oncoproteins and may also involve sequences that control transgene expression. The delayed progression of BCR/ABL P210-associated disease in the transgenic mice is consistent with the apparent indolence of human chronic myeloid leukemia during the chronic phase. We conclude that, in transgenic models, comparable expression of BCR/ABL P210 and BCR/ABL P190 results in clinically distinct conditions.

Abnormal lung development and cleft palate in mice lacking TGF-beta 3 indicates defects of epithelial-mesenchymal interaction

A broad spectrum of biological activities has been proposed for transforming growth factor-beta 3 (TGF-beta 3). To study TGF-beta 3 function in development, TGF-beta 3 null mutant mice were generated by gene-targeting. Within 20 hours of birth, homozygous TGF-beta 3-/- mice die with unique and consistent phenotypic features including delayed pulmonary development and defective palatogenesis. Unlike other null mutants with cleft palate, TGF-beta 3-/- mice lack other concomitant craniofacial abnormalities. This study demonstrates an essential function for TGF-beta 3 in the normal morphogenesis of palate and lung, and directly implicates this cytokine in mechanisms of epithelial-mesenchymal interaction.

Tyrosine phosphorylation of murine Crkl

The SH2/SH3 adaptor protein Crkl is abnormally phosphorylated on tyrosine by the Bcr/Abl protein in leukemic cells from patients with Philadelphia-chromosome (Ph)positive leukemia. However, the state of tyrosine-phosphorylation of crkl in normal tissues is unknown. In the current study, we identified mouse crkl by cDNA cloning and examined expression levels and tyrosine-phosphorylation of the mouse crkl protein during embryogenesis and in adult tissues. Tyrosine-phosphorylation of crkl was prominent during early development, but decreased at later embryonic stages and in newborn mice. Expression of both crkl and the related crk was ubiquitous in the adult. However, crkl differed considerably from crk in relative tissue distribution, and was more abundant in hematopoietic tissues. With exception of the lung, crkl was mostly present in a non-tyrosine phosphorylated form. Consistent with our previous findings in human patients, murine crkl was phosphorylated on tyrosine in leukemic tissues of BCR/ABL transgenic animals, but was non-tyrosine phosphorylated in normal mouse bone marrow. We conclude that this crkl tyrosine-phosphorylation by Bcr/Abl in hematopoietic cells is clearly aberrant and is consistently linked to the development of leukemia. Identification of proteins interacting with tyrosine-phosphorylated crkl in the leukemic cells of BCR/ABL transgenic mice should reveal members of signal transduction pathways activated in Ph-positive leukemia.

Increased neutrophil respiratory burst in bcr-null mutants

Philadelphia (Ph)-positive leukemias invariably contain a chromosomal translocation fusing BCR to ABL. The BCR-ABL protein is responsible for leukemogenesis. Here we show that exposure of bcr-null mutant mice to gram-negative endotoxin led to severe septic shock and increased tissue injury by neutrophils. Neutrophils of bcr (-/-) mice showed a pronounced increase in reactive oxygen metabolite production upon activation and were more sensitive to priming stimuli. Activated (-/-) neutrophils displayed a 3-fold increased p21rac2 membrane translocation compared with (+/+) neutrophils. These results connect Bcr in vivo with the regulation of Rac-mediated superoxide production by the NADPH-oxidase system of leukocytes and suggest a link between Bcr function and the cell type affected in Ph-positive leukemia.

Regional localization and developmental expression of the BCR gene in rodent brain

The BCR gene is implicated in the development of Ph-positive leukemia through its fusion with the nonreceptor tyrosine kinase gene ABL. The normal 160 kDa Bcr protein has several functional domains, and recently one specific role for Bcr was established in the regulation of respiratory burst activity in white blood cells. Bcr expression levels are relatively constant throughout mouse development until adulthood in brain and in hematopoietic tissues, a pattern that is distinctly different from that of the functionally related n-chimerin gene. In the present study, RNA in situ hybridization was used to explore the normal cellular function of Bcr in rodent brain and hematopoietic organs. The data pinpoint the high bcr expression in the brain to the hippocampal pyramidal cell layer and the dentate gyrus, and to the piriform cortex and the olfactory nuclei, reflecting a potentially interesting function for Bcr in these highly specialized brain regions.

Cellular interactions of CRKL, and SH2-SH3 adaptor protein

Chronic myelogenous leukemia is characterized by a specific chromosomal translocation, t(9;22), in which the ABL protooncogene and the BCR gene become juxtaposed. The chimeric BCR/ABL gene produces a P210 fusion protein with deregulated tyrosine kinase activity. We have recently isolated a complementary DNA, CRKL, which could code for an adaptor protein consisting of one SH2 and two SH3 domains and lacking any catalytic domain. In the current study, we show that CRKL is highly phosphorylated in the chronic myelogenous leukemia cell line K562 and that it is a substrate for the p210 BCR/ABL and p145 ABL kinases. BCR/ABL and ABL are coimmunoprecipitated with CRKL in vivo, demonstrating that relatively stable complexes are formed. In addition, the nucleotide exchange factor mSOS1 was found to be coimmunoprecipitated with CRKL. These findings establish a putative signal transduction pathway way through which BCR/ABL mediates its oncogenic activity.

Ph-positive leukemia: a transgenic mouse model

The presence of the BCR/ABL chimeric gene is the hallmark of defined types of human leukemia. To increase our knowledge of the oncogenic processes and to develop a model for this type of leukemia we generated a BCR/ABL (P190) transgenic mouse line. Over 95% of mice of this line die of leukemia or leukemia/lymphoma within 35-200 days of age. Karyotypically visible genetic alterations were absent from the early stages of BCR/ABL generated leukemia. A high frequency of aneuploidy was found in advanced leukemia indicating a primary and pivotal role for BCR/ABL in leukemogenesis. Moreover, the data suggest that BCR/ABL has a destabilizing effect on the regulation of the cell cycle. BCR/ABL expression was also found in tissues other than hematopoietic cells. However, this did not result in the development of solid tumors, strongly suggesting that the oncogenicity of BCR/ABL is limited to the hematopoietic lineage.

Restricted oncogenicity of BCR/ABL p190 in transgenic mice

A chimeric BCR/ABL oncogene encoding the p190 protein has been introduced into the mouse germline using microinjection of one-cell fertilized eggs. Founder and progeny transgenic animals, when becoming ill, were found to develop lymphoblastic leukemia/lymphoma which was transplantable to compatible recipients. Lymphoblasts were arrested at the pre-B stage of development. Expression of BCR/ABL was not detected in peripheral blood during the early stages of leukemia but became evident as the disease progressed. However, the transgene was expressed early in development in bone marrow and was also transcribed in nonhematopoietic tissues although this did not result in tumorigenesis. These results strongly suggest that the oncogenicity of BCR/ABL is limited to hematopoietic cells, including pre-B cells or their progenitors.

Clonal characteristics of acute lymphoblastic cells derived from BCR/ABL p190 transgenic mice

The clonal and immunophenotypic characteristics of blood leukemic cells from BCR/ABL p190 transgenic mice were investigated. All cell populations evaluated in vivo and in vitro had B-lymphocyte progenitor immunophenotypes. Immunoglobulin (JH) rearrangement patterns provided evidence for clonal diversification at different sites in vivo. Multiple clones were established in vitro from two of these mice (nos. 730 and 753). These cells expressed BCR/ABL p190 protein tyrosine kinase (PTK) and were highly malignant on transfer to secondary recipients. Cells independently cloned in vitro shared identical immunophenotypes and clonal IgH rearrangements, but these were distinct from those of the dominant clones in the mouse from which they were derived. Nevertheless, in vitro clones from mouse no. 753 had an abnormal karyotype (chromosome 14 trisomy) in common with the dominant clone in blood, providing evidence for a hierarchy or clonal selection in vivo and in vitro. Two sets of in vitro clones proliferated independently of exogenous growth factors and stroma and released autocrine interleukin 7 growth factor activity. These data provide evidence for rapid divergent clonal evolution and selection of B-cell progenitors initiated by BCR/ABL p190, followed by other, secondary genetic events mirroring similar changes in the equivalent, highly malignant human leukemia Philadelphia (Ph)-positive/B-precursor acute lymphoblastic leukemia (ALL).

Clonal development and karyotype evolution during leukemogenesis of BCR/ABL transgenic mice

The Philadelphia (Ph) translocation is responsible for the generation of the chimeric BCR/ABL oncogene. The Ph chromosome constitutes the earliest detectable chromosome abnormality in chronic myelogenous leukemia and is also found in acute lymphoblastic leukemia. Mice transgenic for a P190 BCR/ABL-producing DNA construct develop lymphoblastic leukemia/lymphoma and provide an opportunity to study early stages of the disease as well as progression. In this study, we have karyotyped the bone marrow of 10 19-day-old BCR/ABL P190 transgenic mice from a line that reproducibly develops leukemia/lymphoma. Leukemic cells from 17 terminally ill transgenic founders and progeny were also karyotyped as well as bone marrow transplant recipients of leukemic donor marrow. Karyotypically visible aberrations were absent from the early stages of BCR/ABL P190-generated leukemia and normal metaphases could be found even in the terminal stages of the disease. A high frequency of aneuploidy was found in advanced leukemia, with a marked preference for the gain of mouse chromosomes 12, 14, or 17. These results point to a primary role for BCR/ABL in leukemogenesis and suggest a destabilizing effect of the BCR/ABL gene on the regulation of cell division.

Detection and analysis of Autographa californica nuclear polyhedrosis virus mutants with defective interfering properties

Defective interfering particles (DIPs) were generated upon continuous production of Autographa californica nuclear polyhedrosis virus (AcNPV) in bioreactors. This configuration mimicked the serial undiluted passaging of virus, which is known to result in plaque-morphology mutants. Restriction enzyme analysis of DIP-containing preparations of extracellular virus showed the presence of many DNA fragments in less than equimolar amounts. These fragments were colinear on the physical map of AcNPV and extended from map position 1.7 to 45. These DIPs thus lacked 43% of the genetic information of the standard virus, including the polyhedrin and DNA polymerase genes. The existence of DIPs was confirmed by electron microscopy, where virions were observed with reduced length. Among the less than equimolar fragments in DIP-containing preparations, fragments were observed linking sequences from map positions 1.7 and 45 via a TGTT linker of unknown origin. The DIPs could not be plaque-purified and needed standard (helper) virus to replicate; DIP-containing preparations interfered with standard virus replication in an interference assay, which explained the reduction in productivity of an AcNPV expression vector-insect cell system in continuous bioreactor operations. The origin of these DIPs and their possible generation mechanism are discussed.

The oxidation of tetrachloro-1,4-hydroquinone by microsomes and purified cytochrome P-450b. Implications for covalent binding to protein and involvement of reactive oxygen species

The enzymatic oxidation of tetrachloro-1,4-hydroquinone (1,4-TCHQ), resulting in covalent binding to protein of tetrachloro-1,4-benzoquinone (1,4-TCBQ), was investigated, with special attention to the involvement of cytochrome P-450 and reactive oxygen species. 1,4-TCBQ itself reacted very rapidly and extensively with protein (58% of the 10 nmol added to 2 mg of protein, in a 5-min incubation). Ascorbic acid and glutathione prevented covalent binding of 1,4-TCBQ to protein, both when added directly and when formed from 1,4-TCHQ by microsomes. In microsomal incubations as well as in a reconstituted system containing purified cytochrome P-450b, 1,4-TCHQ oxidation and subsequent protein binding was shown to be completely dependent on NADPH. The reaction was to a large extent, but not completely, dependent on oxygen (83% decrease in binding under anaerobic conditions). Inhibition of cytochrome P-450 by metyrapone, which is also known to block the P-450-mediated formation of reactive oxygen species, gave a 80% decrease in binding, while the addition of superoxide dismutase prevented 75% of the covalent binding, almost the same amount as found in anerobic incubations. A large part of the conversion of 1,4-TCHQ to 1,4-TCBQ is apparently not catalyzed by cytochrome P-450 itself, but is mediated by superoxide anion formed by this enzyme. The involvement of this radical anion is also demonstrated by microsomal incubations without NADPH but including the xantine/xantine oxidase superoxide anion generating system. These incubations resulted in a 1.6-fold binding as compared to the binding in incubations with NADPH but without xantine/xantine oxidase. 1,4-TCHQ was shown to stimulate the oxidase activity of microsomal cytochrome P-450. It is thus not unlikely that 1,4-TCHQ enhances its own microsomal oxidation.