Rapid production of retroviruses for efficient gene delivery to mammalian cells using 293T cell-based systems

Rb-dependent cellular senescence, multinucleation and susceptibility to oncogenic transformation through PKC scaffolding by SSeCKS/AKAP12

A subset of AKAPs (A Kinase Anchoring Proteins) regulate signaling and cytoskeletal pathways through the spaciotemporal scaffolding of multiple protein kinases (PK) such as PKC and PKA, and associations with the plasma membrane and the actin-based cytoskeleton. SSeCKS/Gravin/Akap12 expression is severely downregulated in many advanced cancers and exhibits tumor- and metastasis-suppressing activity. akap12-null (KO) mice develop prostatic hyperplasia with focal dysplasia, but the precise mechanism how Akap12 prevents oncogenic progression remains unclear. Here, we show that KO mouse embryonic fibroblasts (MEF) exhibit premature senescence marked by polyploidy and multinucleation, and by increased susceptibility to oncogenic transformation. Although p53 and Rb pathways are activated in the absence of Akap12, senescence is dependent on Rb. Senescence is driven by the activation of PKCα, which induces p16(Ink4a)/Rb through a MEK-dependent downregulation of Id1, and PKCδ, which downregulates Lats1/Warts, a mitotic exit network kinase required for cytokinesis. Our data strongly suggest that Akap12 controls Rb-mediated cell aging and oncogenic progression by directly scaffolding and attenuating PKCα/δ.

Modulation of TGF-β-inducible hypermotility by EGF and other factors in human prostate epithelial cells and keratinocytes

Keratinocytes migrating from a wound edge or initiating malignant invasion greatly increase their expression of the basement membrane protein Laminin-322 (Lam332). In culture, keratinocytes initiate sustained directional hypermotility when plated onto an incompletely processed form of Lam332 (Lam332') or when treated with transforming growth factor beta (TGF-β), an inducer of Lam332 expression. The development and tissue architecture of stratified squamous and prostate epithelia are very different, yet the basal cells of both express p63, α6β4 integrin, and Lam332. Keratinocytes and prostate epithelial cells grow well in nutritionally optimized culture media with pituitary extract and certain mitogens. We report that prostate epithelial cells display hypermotility responses indistinguishable from those of keratinocytes. Several culture medium variables attenuated TGF-β-induced hypermotility, including Ca(++), serum, and some pituitary extract preparations, without impairing growth, TGF-β growth inhibition, or hypermotility on Lam322'. Distinct from its role as a mitogen, EGF proved to be a required cofactor for TGF-β-induced hypermotility and could not be replaced by HGF or KGF. Prostate epithelial cells have a short replicative lifespan, restricted both by p16(INK4A) and telomere-related mechanisms. We immortalized the normal prostate epithelial cell line HPrE-1 by transduction to express bmi1 and TERT. Prostate epithelial cells lose expression of p63, β4 integrin, and Lam332 when they transform to invasive carcinoma. In contrast, HPrE-1/bmi1/TERT cells retained expression of these proteins and normal TGF-β signaling and hypermotility for >100 doublings. Thus, keratinocytes and prostate epithelial cells possess common hypermotility and senescence mechanisms and immortalized prostate cell lines can be engineered using defined methods to yield cells retaining normal properties.

Synergistic Ca2+ responses by G{alpha}i- and G{alpha}q-coupled G-protein-coupled receptors require a single PLC{beta} isoform that is sensitive to both G{beta}{gamma} and G{alpha}q

Cross-talk between Gα(i)- and Gα(q)-linked G-protein-coupled receptors yields synergistic Ca(2+) responses in a variety of cell types. Prior studies have shown that synergistic Ca(2+) responses from macrophage G-protein-coupled receptors are primarily dependent on phospholipase Cβ3 (PLCβ3), with a possible contribution of PLCβ2, whereas signaling through PLCβ4 interferes with synergy. We here show that synergy can be induced by the combination of Gβγ and Gα(q) activation of a single PLCβ isoform. Synergy was absent in macrophages lacking both PLCβ2 and PLCβ3, but it was fully reconstituted following transduction with PLCβ3 alone. Mechanisms of PLCβ-mediated synergy were further explored in NIH-3T3 cells, which express little if any PLCβ2. RNAi-mediated knockdown of endogenous PLCβs demonstrated that synergy in these cells was dependent on PLCβ3, but PLCβ1 and PLCβ4 did not contribute, and overexpression of either isoform inhibited Ca(2+) synergy. When synergy was blocked by RNAi of endogenous PLCβ3, it could be reconstituted by expression of either human PLCβ3 or mouse PLCβ2. In contrast, it could not be reconstituted by human PLCβ3 with a mutation of the Y box, which disrupted activation by Gβγ, and it was only partially restored by human PLCβ3 with a mutation of the C terminus, which partly disrupted activation by Gα(q). Thus, both Gβγ and Gα(q) contribute to activation of PLCβ3 in cells for Ca(2+) synergy. We conclude that Ca(2+) synergy between Gα(i)-coupled and Gα(q)-coupled receptors requires the direct action of both Gβγ and Gα(q) on PLCβ and is mediated primarily by PLCβ3, although PLCβ2 is also competent.

Efficient in vivo vascularization of tissue-engineering scaffolds

The success of tissue engineering depends on the rapid and efficient formation of a functional blood vasculature. Adult blood vessels comprise endothelial cells and perivascular mural cells that assemble into patent tubules ensheathed by a basement membrane during angiogenesis. Using individual vessel components, we characterized intra-scaffold microvessel self-assembly efficiency in a physiological in vivo tissue engineering implant context. Primary human microvascular endothelial and vascular smooth muscle cells were seeded at different ratios in poly-L-lactic acid (PLLA) scaffolds enriched with basement membrane proteins (Matrigel) and implanted subcutaneously into immunocompromised mice. Temporal intra-scaffold microvessel formation, anastomosis and perfusion were monitored by immunohistochemical, flow cytometric and in vivo multiphoton fluorescence microscopy analysis. Vascularization in the tissue-engineering context was strongly enhanced in implants seeded with a complete complement of blood vessel components: human microvascular endothelial and vascular smooth muscle cells in vivo assembled a patent microvasculature within Matrigel-enriched PLLA scaffolds that anastomosed with the host circulation during the first week of implantation. Multiphoton fluorescence angiographic analysis of the intra-scaffold microcirculation showed a uniform, branched microvascular network. 3D image reconstruction analysis of human pulmonary artery smooth muscle cell (hPASMC) distribution within vascularized implants was non-random and displayed a preferential perivascular localization. Hence, efficient microvessel self-assembly, anastomosis and establishment of a functional microvasculture in the native hypoxic in vivo tissue engineering context is promoted by providing a complete set of vascular components.

Histone methyltransferase MLL1 regulates MDR1 transcription and chemoresistance

The multidrug resistance 1 gene (MDR1) encodes P-glycoprotein (Pgp), a member of the ATP-binding cassette (ABC) transporter family that confers tumor drug resistance by actively effluxing a number of antitumor agents. We had previously shown that MDR1 transcription is regulated by epigenetic events such as histone acetylation, and had identified the histone acetylase P/CAF and the transcription factor NF-Y as the factors mediating the enzymatic and DNA-anchoring functions, respectively, at the MDR1 promoter. It has also been shown that MDR1 activation is accompanied by increased methylation on lysine 4 of histone H3 (H3K4). In this study, we further investigated histone methylation in MDR1 regulation and function. We show that the mixed lineage leukemia 1 (MLL1) protein, a histone methyltransferase specific for H3K4, is required for MDR1 promoter methylation, as knockdown of MLL1 resulted in a decrease in MDR1 expression. The regulation of MDR1 by MLL1 has functional consequences in that downregulation of MLL1 led to increased retention of the Pgp-specific substrate DIOC(2)(3), as well as increased cellular sensitivity to several Pgp substrates. Regulation of MDR1 by MLL1 was dependent on the CCAAT box within the proximal MDR1 promoter, similar to what we had shown for MDR1 promoter acetylation, and also requires NF-Y. Finally, overexpression of the most prevalent MLL fusion protein, MLL-AF4, led to increased MDR1 expression. This is the first identification of a histone methyltransferase and its leukemogenic rearrangement that regulates expression of an ABC drug transporter, suggesting a new target for circumvention of tumor multidrug resistance.

Nutrient withdrawal rescues growth factor-deprived cells from mTOR-dependent damage

Deregulated nutrient signaling plays pivotal roles in body ageing and in diabetic complications; biochemical cascades linking energy dysmetabolism to cell damage and loss are still incompletely clarified, and novel molecular paradigms and pharmacological targets critically needed. We provide evidence that in the retrovirus-packaging cell line HEK293-T Phoenix, massive cell death in serum-free medium is remarkably prevented or attenuated by either glucose or aminoacid withdrawal, and by the glycolysis inhibitor 2-deoxy-glucose. A similar protection was also elicited by interference with mitochondrial function, clearly suggesting involvement of energy metabolism in increased cell survival. Oxidative stress did not account for nutrient toxicity on serum-starved cells. Instead, nutrient restriction was associated with reduced activity of the mTOR/S6 Kinase cascade. Moreover, pharmacological and genetic manipulation of the mTOR pathway modulated in an opposite fashion signaling to S6K/S6 and cell viability in nutrient-repleted medium. Additionally, stimulation of the AMP-activated Protein Kinase concomitantly inhibited mTOR signaling and cell death, while neither event was affected by overexpression of the NAD+ dependent deacetylase Sirt-1, another cellular sensor of nutrient scarcity. Finally, blockade of the mTOR cascade reduced hyperglycemic damage also in a more pathophysiologically relevant model, i.e. in human umbilical vein endothelial cells (HUVEC) exposed to hyperglycemia. Taken together these findings point to a key role of the mTOR/S6K cascade in cell damage by excess nutrients and scarcity of growth-factors, a condition shared by diabetes and other ageing-related pathologies.

Functional selection of phagocytosis-promoting genes: cell sorting-based selection

Phagocytosis is a critical host defense mechanism that clears invading pathogens, apoptotic cells, and cell debris; it is an essential process for normal development, tissue remodeling, immune response, and inflammation. Here, a functional selection strategy was used to isolate novel phagocytosis-promoting genes. After the retroviral transfer of mouse brain cDNA library into NIH3T3 mouse fibroblast cells, cell sorting was used to select the cells that phagocytosed fluorescent zymosan particles. The cDNAs were retrieved from the selected cells and identified by DNA sequencing as eIF5A, Meg3, Tubb5, Sparcl-1, Uchl-1, Bsg (CD147), Ube2v1, and Pamr1. The phagocytosis-promoting activity for some of these cDNAs was confirmed by transient transfection in the independent phagocytosis assays. Thus, the unbiased selection procedure successfully identified multiple phagocytosis-promoting genes. The selection method can be applied to other cell-based assays where cells with a desired phenotype can be physically separated. Moreover, the new gene targets uncovered in this study could be relevant to biomolecule screening in search of phagocytosis-regulating agents. In a small-scale screen, a series of imidazopyridine compounds was tested to identify the small molecules that modulate eIF5A-mediated phagocytic activity. Several compounds that influenced the phagocytic activity can be further used as chemical-genetic tools to delineate the mechanisms of eIF5A action and be potential drug candidates that are capable of therapeutically modulating phagocytic activity.

Reprogramming of committed lymphoid cells by enforced transcription factor expression

Reprogramming of committed cells from one lineage to another is possible in the hematopoietic system using enforced expression of transcription factors. Here we describe methods to convert committed B and T progenitors into macrophages. In order to obtain a labeled population of starting cells, we employ a lineage ancestry system using a cross between lineage-specific Cre recombinase mice and Rosa26 reporter mice. After infection of these well-defined cell populations with a transcription factor containing retroviral vector that also harbors an infection marker, cells are cultured under conditions permissive for both lymphoid and myeloid development. Multicolor flow cytometry is then used to monitor changes in marker expression on the cell surface reflecting changes in cellular identity. These protocols may be modified to trace cellular reprogramming induced by other transcription factors and in other cellular contexts.

Mutations in the M112/M113-coding region facilitate murine cytomegalovirus replication in human cells

Cytomegaloviruses, representatives of the Betaherpesvirinae, cause opportunistic infections in immunocompromised hosts. They infect various cells and tissues in their natural host but are highly species specific. For instance, human cytomegalovirus (HCMV) does not replicate in mouse cells, and human cells are not permissive for murine cytomegalovirus (MCMV) infection. However, the underlying molecular mechanisms are so far poorly understood. In the present study we isolated and characterized a spontaneously occurring MCMV mutant that has gained the capacity to replicate rapidly and to high titers in human cells. Compared to the parental wild-type (wt) virus, this mutant formed larger nuclear replication compartments and replicated viral DNA more efficiently. It also disrupted promyelocytic leukemia (PML) protein nuclear domains with greater efficiency but caused less apoptosis than did wt MCMV. Sequence analysis of the mutant virus genome revealed mutations in the M112/M113-coding region. This region is homologous to the HCMV UL112-113 region and encodes the viral early 1 (E1) proteins, which are known to play an important role in viral DNA replication. By introducing the M112/M113 mutations into wt MCMV, we demonstrated that they are sufficient to facilitate MCMV replication in human cells and are, at least in part, responsible for the efficient replication capability of the spontaneously adapted virus. However, additional mutations probably contribute as well. These results reveal a previously unrecognized role of the viral E1 proteins in regulating viral replication in different cells and provide new insights into the mechanisms of the species specificity of cytomegaloviruses.

Ras activation of Erk restores impaired tonic BCR signaling and rescues immature B cell differentiation

B cell receptors (BCRs) generate tonic signals critical for B cell survival and early B cell development. To determine whether these signals also mediate the development of transitional and mature B cells, we examined B cell development using a mouse strain in which nonautoreactive immunoglobulin heavy and light chain–targeted B cells express low surface BCR levels. We found that reduced BCR expression translated into diminished tonic BCR signals that strongly impaired the development of transitional and mature B cells. Constitutive expression of Bcl-2 did not rescue the differentiation of BCR-low B cells, suggesting that this defect was not related to decreased cell survival. In contrast, activation of the Ras pathway rescued the differentiation of BCR-low immature B cells both in vitro and in vivo, whereas extracellular signal-regulated kinase (Erk) inhibition impaired the differentiation of normal immature B cells. These results strongly suggest that tonic BCR signaling mediates the differentiation of immature into transitional and mature B cells via activation of Erk, likely through a pathway requiring Ras.

Mechanistic consequences of hnRNP C binding to both RNA termini of poliovirus negative-strand RNA intermediates

The poliovirus 3' noncoding region (3' NCR) is necessary for efficient virus replication. A poliovirus mutant, PVDelta3'NCR, with a deletion of the entire 3' NCR, yielded a virus that was capable of synthesizing viral RNA, albeit with a replication defect caused by deficient positive-strand RNA synthesis compared to wild-type virus. We detected multiple ribonucleoprotein (RNP) complexes in extracts from poliovirus-infected HeLa cells formed with a probe corresponding to the 5' end of poliovirus negative-strand RNA (the complement of the genomic 3' NCR), and the levels of these RNP complexes increased during the course of viral infection. Previous studies have identified RNP complexes formed with the 3' end of poliovirus negative-strand RNA, including one that contains a 36-kDa protein later identified as heterogeneous nuclear ribonucleoprotein C (hnRNP C). We report here that the 5' end of poliovirus negative-strand RNA is capable of interacting with endogenous hnRNP C, as well as with poliovirus nonstructural proteins. Further, we demonstrate that the addition of recombinant purified hnRNP C proteins can stimulate virus RNA synthesis in vitro and that depletion of hnRNP C proteins in cultured cells results in decreased virus yields and a correspondingly diminished accumulation of positive-strand RNAs. We propose that the association of hnRNP C with poliovirus negative-strand termini acts to stabilize or otherwise promote efficient positive-strand RNA synthesis.

Comprehensive assessment of chemokine expression profiles by flow cytometry

The chemokines are a large family of mainly secreted molecules involved in the regulation of numerous physiological and pathophysiological processes. Despite many years of investigation, the precise cellular sources of most chemokines have remained incompletely defined as a consequence of the limited availability of suitable reagents to visualize the expression of chemokine proteins at the single-cell level. Here, we developed a simple flow cytometry-based assay using commercially available chemokine-specific antibodies for efficient cell-associated detection of 37 of 39 murine chemokines. To demonstrate the utility of this methodology, we used it to reevaluate the nature of homeostatic chemokines in the hematopoietic compartment, to delineate the complete chemokine profiles of NK cells and B cells in response to major polyclonal stimuli, and to assess the chemokine response of DCs to bacterial infection. The versatility of this analytical methodology was further demonstrated by its application to selected human chemokines and should greatly facilitate any future investigation into chemokine biology at large.

Gene trap mutagenesis in the mouse

Gene trapping in mouse embryonic stem (ES) cells is an efficient method for the mutagenesis of the mammalian genome. Insertion of a gene trap vector disrupts gene function, reports gene expression, and provides a convenient tag for the identification of the insertion site. The trap vector can be delivered to ES cells by electroporation of a plasmid, by retroviral infection, or by transposon-mediated insertion. Recent developments in trapping technology involve the utilization of site-specific recombination sites, which allow the induced modification of trap alleles in vitro and in vivo. Gene trapping strategies have also been successfully developed to screen for genes that are acting in specific biological pathways. In this chapter, we review different applications of gene trapping, and we provide detailed experimental protocols for gene trapping in ES cells by retroviral and transposon gene trap vectors.

Use of a modified alpha-N-acetylgalactosaminidase in the development of enzyme replacement therapy for Fabry disease

A modified alpha-N-acetylgalactosaminidase (NAGA) with alpha-galactosidase A (GLA)-like substrate specificity was designed on the basis of structural studies and was produced in Chinese hamster ovary cells. The enzyme acquired the ability to catalyze the degradation of 4-methylumbelliferyl-alpha-D-galactopyranoside. It retained the original NAGA's stability in plasma and N-glycans containing many mannose 6-phosphate (M6P) residues, which are advantageous for uptake by cells via M6P receptors. There was no immunological cross-reactivity between the modified NAGA and GLA, and the modified NAGA did not react to serum from a patient with Fabry disease recurrently treated with a recombinant GLA. The enzyme cleaved globotriaosylceramide (Gb3) accumulated in cultured fibroblasts from a patient with Fabry disease. Furthermore, like recombinant GLA proteins presently used for enzyme replacement therapy (ERT) for Fabry disease, the enzyme intravenously injected into Fabry model mice prevented Gb3 storage in the liver, kidneys, and heart and improved the pathological changes in these organs. Because this modified NAGA is hardly expected to cause an allergic reaction in Fabry disease patients, it is highly promising as a new and safe enzyme for ERT for Fabry disease.

Discrete domains of MARCH1 mediate its localization, functional interactions, and posttranscriptional control of expression

Within APCs, ubiquitination regulates the trafficking of immune modulators such as MHC class II and CD86 (B7.2) molecules. MARCH1 (membrane-associated RING-CH), a newly identified ubiquitin E3 ligase expressed in APCs, ubiquitinates MHC class II, thereby reducing its surface expression. Following LPS-induced maturation of dendritic cells, MARCH1 mRNA is down-regulated and MHC class II is redistributed to the cell surface from endosomal compartments. Here, we show that MARCH1 expression is also regulated at the posttranscriptional level. In primary dendritic cell and APC cell lines of murine origin, MARCH1 had a half-life of <30 min. MARCH1 degradation appears to occur partly in lysosomes, since inhibiting lysosomal activity stabilized MARCH1. Similar stabilization was observed when MARCH1-expressing cells were treated with cysteine protease inhibitors. Mutational analyses of MARCH1 defined discrete domains required for destabilization, proper localization, and functional interaction with substrates. Taken together, these data suggest that MARCH1 expression is regulated at a posttranscriptional level by trafficking within the endolysosomal pathway where MARCH1 is proteolyzed. The short half-life of MARCH1 permits very rapid changes in the levels of the protein in response to changes in the mRNA, resulting in efficient induction of Ag presentation once APCs receive maturational signals.

Intensive RNAi with lentiviral vectors in mammalian cells

RNAi is a powerful technology for analyzing gene function in human cells. However, its utility can be compromised by inadequate knockdown of the target mRNA or by interpretation of effects without rigorous controls. We review lentiviral vector-based methods that enable transient or stable knockdowns to trace mRNA levels in human CD4+ T cell lines and other targets. Critical controls are reviewed, including rescue of the pre-knockdown phenotype by re-expression of the targeted gene. The time from thinking about a potential knockdown target to analysis of phenotypes can be as short as a few weeks.

Murine retroviruses re-engineered for lineage tracing and expression of toxic genes in the developing chick embryo

We describe two replication incompetent retroviral vectors that co-express green fluorescent protein (GFP) and beta-galactosidase. These vectors incorporate either the avian reticuloendotheliosis (spleen necrosis virus; SNV) promoter or the chick beta-actin promoter, into the backbone of the murine leukemia (MLV) viral vector. The additional promoters drive transgene expression in avian tissue. The remainder of the vector is MLV-like, allowing high titer viral particle production by means of transient transfection. The SNV promoter produces high and early expression of introduced genes, enabling detection of the single copy integrated GFP gene in infected cells and their progeny in vivo. Substitution of the LacZ coding DNA with a relevant gene of interest will enable its co-expression with GFP, thus allowing visualization of the effect of specific and stable changes in gene expression throughout development. As the VSV-G pseudotyped viral vector is replication incompetent, changes in gene expression can be controlled temporally, by altering the timing of introduction.

Combinatorial probabilistic chromatin interactions produce transcriptional heterogeneity

Gene regulation often appears deterministic in the average cell population, but transcription is a probabilistic process at the single-cell level. Although many mechanisms are invoked to account for this behavior, it is difficult to determine how cell-to-cell variation in the interactions of transcription factors with target chromatin impact transcriptional output. Here, we use cells that contain a 200-copy tandem array of promoter or reporter gene units to simultaneously visualize transient interaction, equilibrium or steady-state binding of fluorescent-protein-labeled glucocorticoid receptor with its DNA response elements, the recruitment of diverse coregulators, and transcriptional output at the single-cell level. These regulatory proteins associate with target chromatin via a probabilistic mechanism that produces cell-to-cell variability in binding. The multiple steps of this process are partially independent and differ between individual regulators. The association level of each regulator influences the transcriptional output in individual cells, but this does not account for all transcriptional heterogeneity. Additionally, specific combinatorial interactions of the glucocorticoid receptor and coregulators with response elements regulate transcription at the single-cell level. Like many endogenous genes, the average array transcriptional activity evolves over time. This apparently deterministic average temporal promoter progression involves changes in the probability that specific combinatorial glucocorticoid receptor and coregulator interactions will occur on the response elements in single cells. These data support the emerging ;return-to-template' transcription model, which mechanistically unifies the observed extremely transient interactions between the transcription factor and response elements, cell-to-cell variability in steady-state association of factors with chromatin, and the resulting heterogeneous gene expression between individual cells.

Chemoprotection by transfer of resistance genes

Dose-limiting toxicity of chemotherapeutic agents, i.e., myelosuppression, can limit their effectiveness. The transfer and expression of drug-resistance genes might decrease the risks associated with acute hematopoietic toxicity. Protection of hematopoietic stem/progenitor cells by transfer of drug-resistance genes provides the possibility of intensification or escalation of antitumor drug doses and consequently an improved therapeutic index. This chapter reviews drug-resistance gene transfer strategies for either myeloprotection or therapeutic gene selection. Selecting candidate drug-resistance gene(s), gene transfer methodology, evaluating the safety and the efficiency of the treatment strategy, relevant in vivo models, and oncoretroviral transduction of human hematopoietic stem/progenitor cells under clinically applicable conditions are described.

Alpha-E-catenin binds to dynamitin and regulates dynactin-mediated intracellular traffic

Alpha-epithelial catenin (E-catenin) is an important cell-cell adhesion protein. In this study, we show that alpha-E-catenin also regulates intracellular traffic by binding to the dynactin complex component dynamitin. Dynactin-mediated organelle trafficking is increased in alpha-E-catenin(-/-) keratinocytes, an effect that is reversed by expression of exogenous alpha-E-catenin. Disruption of adherens junctions in low-calcium media does not affect dynactin-mediated traffic, indicating that alpha-E-catenin regulates traffic independently from its function in cell-cell adhesion. Although neither the integrity of dynactin-dynein complexes nor their association with vesicles is affected by alpha-E-catenin, alpha-E-catenin is necessary for the attenuation of microtubule-dependent trafficking by the actin cytoskeleton. Because the actin-binding domain of alpha-E-catenin is necessary for this regulation, we hypothesize that alpha-E-catenin functions as a dynamic link between the dynactin complex and actin and, thus, integrates the microtubule and actin cytoskeleton during intracellular trafficking.

Hypomorphic nuclear factor-kappaB essential modulator mutation database and reconstitution system identifies phenotypic and immunologic diversity

BACKGROUND

Human hypomorphic nuclear factor-kappaB essential modulator (NEMO) mutations cause diverse clinical and immunologic phenotypes, but understanding of their scope and mechanistic links to immune function and genotype is incomplete.

OBJECTIVE

We created and analyzed a database of hypomorphic NEMO mutations to determine the spectrum of phenotypes and their associated genotypes and sought to establish a standardized NEMO reconstitution system to obtain mechanistic insights.

METHODS

Phenotypes of 72 individuals with NEMO mutations were compiled. NEMO L153R and C417R were investigated further in a reconstitution system. TNF-alpha or Toll-like receptor (TLR)-5 signals were evaluated for nuclear factor-kappaB activation, programmed cell death, and A20 gene expression.

RESULTS

Thirty-two different mutations were identified; 53% affect the zinc finger domain. Seventy-seven percent were associated with ectodermal dysplasia, 86% with serious pyogenic infection, 39% with mycobacterial infection, 19% with serious viral infection, and 23% with inflammatory diseases. Thirty-six percent of individuals died at a mean age of 6.4 years. CD40, IL-1, TNF-alpha, TLR, and T-cell receptor signals were impaired in 15 of 16 (94%), 6 of 7 (86%), 9 of 11 (82%), 9 of 14 (64%), and 7 of 18 (39%), respectively. Hypomorphism-reconstituted NEMO-deficient cells demonstrated partial restoration of NEMO functions. Although both L153R and C417R impaired TLR and TNF-alpha-induced NF-kappaB activation, L153R also increased TNF-alpha-induced programmed cell death with decreased A20 expression.

CONCLUSION

Distinct NEMO hypomorphs define specific disease and genetic characteristics. A reconstitution system can identify attributes of hypomorphisms independent of an individual's genetic background. Apoptosis susceptibility in L153R reconstituted cells defines a specific phenotype of this mutation that likely contributes to the excessive inflammation with which it is clinically associated.

PKC eta directs induction of IRF-4 expression and Ig kappa gene rearrangement in pre-BCR signaling pathway

Pre-B cell receptor (pre-BCR) signals promote pre-B cell differentiation, in which the adaptor protein B-cell linker (BLNK) plays a crucial role. However, the molecular pathways downstream of BLNK are currently unclear. Utilizing pre-B leukemia cell lines (BKO84 and others) derived from BLNK-deficient mice as in vitro models of the pre-B cell differentiation, we have demonstrated that reconstitution of BLNK as well as an active form of protein kinase C (PKC)eta induces the differentiation events, such as pre-BCR down-regulation and kappa gene rearrangement. Here we show that the same events are induced by cross-linking of pre-BCR with anti-mu antibody in these pre-B cell lines, as well as in ex vivo pre-B cells from BLNK-deficient mice, suggesting a function of BLNK as an internal cross-linker of pre-BCR. Anti-mu treatment of BKO84 cells up-regulated membrane recruitment of PKC eta and the expression of IRF-4, a transcription factor known to promote light chain gene rearrangements. Anti-mu induction of surface kappa chain on BKO84 cells was blocked by reagents that inhibit phospholipase C or PKC. Enforced expression of the active PKC eta in BKO84 cells resulted in up-regulation of IRF-4 expression. Conversely, siRNA-mediated silencing of PKC eta expression strikingly attenuated the anti-mu-induced IRF-4 expression and kappa gene rearrangement, which were restored by PKC eta reconstitution. Finally, enforced expression of IRF-4, but not of BLNK, in the PKC eta-silenced BKO84 cells resulted in kappa gene rearrangement. These results indicate that PKC eta directs the induction of IRF-4 expression downstream of BLNK in the pre-BCR signaling pathway promoting kappa gene rearrangement.

The psoriasis drug monomethylfumarate is a potent nicotinic acid receptor agonist

Nicotinic acid has been used for several decades to treat dyslipidemia. In mice, the lipid-lowing effect of nicotinic acid is mediated by the Gi coupled receptor PUMA-G. In humans, high (GPR109A) and low (GPR109B) affinity nicotinic acid receptors have been characterized. Here we identify monomethylfumarate as a GPR109A agonist. Monomethylfumarate is the active metabolite of the psoriasis drug Fumaderm. We show that monomethylfumarate activates GPR109A in a calcium based aequorin assay, cAMP assay and demonstrate competitive binding with nicotinic acid. We show that GPR109A is highly expressed in neutrophils and epidermal keratinocytes, and that its expression is increased in human psoriatic lesions. Our findings provide evidence that GPR109A is a target for the drug Fumaderm and suggest that niacin should be investigated to treat psoriasis in addition to its role in treating lipid disorders.

Identification of serine 205 as a site of phosphorylation on Pax3 in proliferating but not differentiating primary myoblasts

Pax3, a member of the paired class homeodomain family of transcription factors, is essential for early skeletal muscle development. Previously, others and we have shown that the stability of Pax3 is regulated on a post-translational level. Evidence in the literature and from our laboratory suggests that phosphorylation, a common form of regulation, may play a role. However, at present, the sites of Pax3 phosphorylation are not known. We demonstrate here the first evidence that Pax3 exists as a phosphoprotein in proliferating mouse primary myoblasts. Using an in vitro kinase assay, deletion, and point mutant analysis, we conclusively identify Ser205 as a site of phosphorylation. The phosphorylation of Ser205 on endogenously expressed Pax3 was confirmed in vivo using antibodies specific for phosphorylation at Ser205. Finally, we demonstrate for the first time that the phosphorylation status of endogenous Pax3 changes rapidly upon the induction of myogenic differentiation. The presence of phosphorylation in a region of Pax3 important for mediating protein-protein interactions, and the fact that phosphorylation is lost upon induction of differentiation, allow for speculation on the biological relevance of phosphorylation.

Recombinant adenoviral vectors can induce expression of p73 via the E4-orf6/7 protein

Despite the utility of recombinant adenoviral vectors in basic research, their therapeutic promise remains unfulfilled. Most engineered adenoviral vectors use a heterologous promoter to transcribe a foreign gene. We show that adenoviruses containing the cytomegalovirus immediate-early promoter induce the expression of the proapoptotic cellular protein TAp73 via the cyclin-dependent kinase-retinoblastoma protein-E2F pathway in murine embryonic fibroblasts. Cells transduced with these vectors also expressed high levels of the adenoviral E4-orf6/7 and E2A proteins. By contrast, adenoviruses containing the ubiquitin C promoter failed to elicit these effects. E4-orf6/7 is necessary and sufficient for increased TAp73 expression, as shown by using retrovirus-mediated E4-orf6/7 expression and adenovirus with the E4-orf6/7 gene deleted. Activation of TAp73 likely occurs via E4-orf6/7-induced dimerization of E2F and subsequent binding to the inverted E2F-responsive elements within the TAp73 promoter. In addition, adenoviral vectors containing the cytomegalovirus immediate-early promoter, but not the ubiquitin C promoter, cooperated with chemotherapeutic agents to decrease cellularity in vitro. In contrast to murine embryonic fibroblasts, adenoviruses containing the ubiquitin C promoter, but not the cytomegalovirus immediate-early promoter, induced both E4-orf6/7 and TAp73 in human foreskin fibroblasts, emphasizing the importance of cellular context for promoter-dependent effects. Because TAp73 is important for the efficacy of chemotherapy, adenoviruses that increase TAp73 expression may enhance cancer therapies by promoting apoptosis. However, such adenoviruses may impair the long-term survival of transduced cells during gene replacement therapies. Our findings reveal previously unknown effects of foreign promoters in recombinant adenoviral vectors and suggest means to improve the utility of engineered adenoviruses by better controlling their impact on viral and cellular gene expression.

RACK1 regulates Ki-Ras-mediated signaling and morphological transformation of NIH 3T3 cells

Activating Ras mutations are involved in a significant fraction of human tumors. A suppressor screen using a retroviral mouse fibroblast cDNA library was performed to identify novel factors in Ras-mediated transformation. We identified a novel potent inhibitor of Ras-mediated morphological transformation encoded by a truncated version of the receptor for activated C-kinase (RACK1). The truncated protein, designated RACK1DeltaWD1, lacked the N-terminal 49 amino acids encoding the first of the 7 WD40 repeats in RACK1. RACK1DeltaWD1 expression restored contact inhibition, stress fiber formation and reduced ERK phosphorylation in Ki-Ras transformed NIH 3T3 cells. We demonstrate that truncated RACK1 is involved in complexes consisting of wild-type RACK1 and protein kinase C isoforms alpha, betaI and delta, compromising the transduction of an activated Ras signal to the Raf-MEK-ERK pathway. The cellular localization of RACK1DeltaWD1 differed from wtRACK1, indicating that signaling complexes containing the truncated version of RACK1 are incorrectly localized. Notably, 12-O-tetradecanoyl-13-phorbol acetate (TPA) mediated intracellular translocation of RACK1-interacting PKC alpha and delta was abrogated in RACK1DeltaWD1-expressing cells. Our data support a model where RACK1 acts as a key factor in Ki-Ras-mediated morphological transformation.

Effect of an hdm-2 antagonist peptide inhibitor on cell cycle progression in p53-deficient H1299 human lung carcinoma cells

The hdm-2 oncogene is overexpressed in several types of malignancies including osteosarcomas, soft tissue sarcomas and gliomas and hdm-2 has been associated with accelerated tumor formation in both hereditary and sporadic cancers. Among the other key binding partners, hdm-2 forms a complex with the tumor suppressor p53, resulting in a rapid proteasome-mediated degradation of the p53 protein. This positions the hdm-2-p53 complex as an attractive target for the development of anticancer therapy and recently the first small molecule hdm-2 antagonist has been reported. Development of hdm-2 antagonists is currently focused on malignancies containing a wild-type p53 genotype, which is the case in approximately half of human cancer indications. However, hdm-2 has also been implicated in oncogenesis in the absence of p53. We therefore studied the effect of hdm-2 antagonists in p53-deficient human H1299 lung carcinoma cells. The hdm-2 antagonistic peptide caused G1 cell cycle arrest, inhibited colony growth and induced expression of G1 checkpoint regulatory proteins, such as p21(waf1,cip1). These data demonstrate that hdm-2 regulates the G1 cell cycle checkpoint in a p53-independent manner, suggesting that hdm-2 antagonists represent a novel class of anticancer therapeutics with broad applicability towards tumors with different p53 genetic backgrounds.

The ETS factor TEL2 is a hematopoietic oncoprotein

TEL2/ETV7 is highly homologous to the ETS transcription factor TEL/ETV6, a frequent target of chromosome translocation in human leukemia. Although both proteins are transcriptional inhibitors binding similar DNA recognition sequences, they have opposite biologic effects: TEL inhibits proliferation while TEL2 promotes it. In addition, forced expression of TEL2 but not TEL blocks vitamin D3-induced differentiation of U937 and HL60 myeloid cells. TEL2 is expressed in the hematopoietic system, and its expression is up-regulated in bone marrow samples of some patients with leukemia, suggesting a role in oncogenesis. Recently we also showed that TEL2 cooperates with Myc in B lymphomagenesis in mice. Here we show that forced expression of TEL2 alone in mouse bone marrow causes a myeloproliferative disease with a long latency period but with high penetrance. This suggested that secondary mutations are necessary for disease development. Treating mice receiving transplants with TEL2-expressing bone marrow with the chemical carcinogen N-ethyl-N-nitrosourea (ENU) resulted in significantly accelerated disease onset. Although the mice developed a GFP-positive myeloid disease with 30% of the mice showing elevated white blood counts, they all died of T-cell lymphoma, which was GFP negative. Together our data identify TEL2 as a bona fide oncogene, but leukemic transformation is dependent on secondary mutations.

Multiple roles for the receptor tyrosine kinase axl in tumor formation

A focus of contemporary cancer therapeutic development is the targeting of both the transformed cell and the supporting cellular microenvironment. Cell migration is a fundamental cellular behavior required for the complex interplay between multiple cell types necessary for tumor development. We therefore developed a novel retroviral-based screening technology in primary human endothelial cells to discover genes that control cell migration. We identified the receptor tyrosine kinase Axl as a novel regulator of endothelial cell haptotactic migration towards the matrix factor vitronectin. Using small interfering RNA-mediated silencing and overexpression of wild-type or mutated receptor proteins, we show that Axl is a key regulator of multiple angiogenic behaviors including endothelial cell migration, proliferation, and tube formation in vitro. Moreover, using sustained, retrovirally delivered short hairpin RNA (shRNA) Axl knockdown, we show that Axl is necessary for in vivo angiogenesis in a mouse model. Furthermore, we show that Axl is also required for human breast carcinoma cells to form a tumor in vivo. These findings indicate that Axl regulates processes vital for both neovascularization and tumorigenesis. Disruption of Axl signaling using a small-molecule inhibitor will hence simultaneously affect both the tumor and stromal cell compartments and thus represents a unique approach for cancer therapeutic development.

A Novel E3 Ubiquitin Ligase TRAC-1 Positively Regulates T Cell Activation

TRAC-1 (T cell RING (really interesting new gene) protein identified in activation screen) is a novel E3 ubiquitin ligase identified from a retroviral vector-based T cell surface activation marker screen. The C-terminal truncated TRAC-1 specifically inhibited anti-TCR-mediated CD69 up-regulation in Jurkat cells, a human T leukemic cell line. In this study, we show that TRAC-1 is a RING finger ubiquitin E3 ligase with highest expression in lymphoid tissues. Point mutations that disrupt the Zn(2+)-chelating ability of its amino-terminal RING finger domain abolished TRAC-1's ligase activity and the dominant inhibitory effect of C-terminal truncated TRAC-1 on TCR stimulation. The results of in vitro biochemical studies indicate that TRAC-1 can stimulate the formation of both K48- and K63-linked polyubiquitin chains and therefore could potentially activate both degradative and regulatory ubiquitin-dependent pathways. Antisense oligonucleotides to TRAC-1 specifically reduced TRAC-1 mRNA levels in Jurkat and primary T cells and inhibited their activation in response to TCR cross-linking. Collectively, these results indicate that the E3 ubiquitin ligase TRAC-1 functions as a positive regulator of T cell activation.

Autocrine CSF-1R activation promotes Src-dependent disruption of mammary epithelial architecture

Elevated coexpression of colony-stimulating factor receptor (CSF-1R) and its ligand, CSF-1, correlates with invasiveness and poor prognosis of a variety of epithelial tumors (Kacinski, B.M. 1995. Ann. Med. 27:79–85). Apart from recruitment of macrophages to the tumor site, the mechanisms by which CSF-1 may potentiate invasion are poorly understood. We show that autocrine CSF-1R activation induces hyperproliferation and a profound, progressive disruption of junctional integrity in acinar structures formed by human mammary epithelial cells in three-dimensional culture. Acini coexpressing receptor and ligand exhibit a dramatic relocalization of E-cadherin from the plasma membrane to punctate intracellular vesicles, accompanied by its loss from the Triton-insoluble fraction. Interfering with Src kinase activity, either by pharmacological inhibition or mutation of the Y561 docking site on CSF-1R, prevents E-cadherin translocation, suggesting that CSF-1R disrupts cell adhesion by uncoupling adherens junction complexes from the cytoskeleton and promoting cadherin internalization through a Src-dependent mechanism. These findings provide a mechanistic basis whereby CSF-1R could contribute to invasive progression in epithelial cancers.

Oligonucleotide-directed site-specific integration of high complexity libraries into ssDNA templates

We present an approach that generates an oligomer-based library with minimal need for restriction site modification of sequences in the target vector. The technique has the advantage that it can be applied for generating peptide aptamer libraries at sites within proteins without the need for introducing flanking enzyme sites. As an example we present a phagemid retroviral shuttle vector that can be used to achieve stable expression of the library in mammalian cells for the purpose of screening for peptides with desired biological activity.

Paternal and maternal genomes confer opposite effects on proliferation, cell-cycle length, senescence, and tumor formation

Loss of imprinting is the silencing of active imprinted genes or the activation of silent imprinted genes, and it is one of the most common epigenetic changes associated with the development of a wide variety of tumors. Here, we have analyzed the effects that global imprinted gene expression has on cell proliferation and transformation. Primary mouse embryonic fibroblasts (MEFs), whose entire genome is either exclusively paternal (androgenetic) or maternal (parthenogenetic), exhibit dramatically contrasting patterns of growth. In comparison with biparental MEFs, andro-genetic proliferation is characterized by a shorter cell cycle, increased saturation density, spontaneous transformation, and formation of tumors at low passage number. Parthenogenetic MEFs reach a lower saturation density, senesce, and die. The maternally expressed imprinted genes p57kip2 and M6P/Igf2r retard proliferation and reduce the long-term growth of MEFs. In contrast, the paternally expressed growth factor Igf2 is essential for the long-term proliferation of all genotypes. Increased Igf2 expression in primary MEFs not only stimulates proliferation, but also results in their rapid conversion to malignancy with tumor formation of short latency. Our results reveal that paternally expressed imprinted genes, in the absence of maternal imprinted genes, predispose fibroblasts to rapid transformation. A potent factor in their transformation is IGF2, which on increased expression results in the rapid conversion of primary cells to malignancy. These results reveal a route by which malignant choriocarcinoma may arise from molar pregnancies. They also suggest that the derivation of stem cells from parthenogenetic embryos, for the purposes of therapeutic cloning, may be ineffective.

Requirements for selective recruitment of Ets proteins and activation of mb-1/Ig-alpha gene transcription by Pax-5 (BSAP)

Pax-5, a member of the paired domain family of transcription factors, is a key regulator of B lymphocyte-specific transcription and differentiation. A major target of Pax-5-mediated activation is the mb-1 gene, which encodes the essential transmembrane signaling protein Ig-alpha. Pax-5 recruits three members of the Ets family of transcription factors: Ets-1, Fli-1 and GABPalpha (with GABPbeta1), to assemble ternary complexes on the mb-1 promoter in vitro. Using the Pax-5:Ets-1:DNA crystal structure as a guide, we defined amino acid requirements for transcriptional activation of endogenous mb-1 genes using a novel cell-based assay. Mutations in the beta-hairpin/beta-turn of the DNA-binding domain of Pax-5 demonstrated its importance for DNA sequence recognition and activation of mb-1 transcription. Mutations of amino acids contacting Ets-1 in the crystal structure reduced or blocked mb-1 promoter activation. One of these mutations, Q22A, resulted in greatly reduced mb-1 gene transcript levels, concurrent with the loss of its ability to recruit Fli-1 to bind the promoter in vitro. In contrast, the mutation had no effect on recruitment of the related Ets protein GABPalpha (with GABPbeta1). These data further define requirements for Pax-5 function in vivo and reveal the complexity of interactions required for cooperative partnerships between transcription factors.

Abolition of cyclin-dependent kinase inhibitor p16Ink4a and p21Cip1/Waf1 functions permits Ras-induced anchorage-independent growth in telomerase-immortalized human fibroblasts

Human cells are more resistant to both immortalization and malignant transformation than rodent cells. Recent studies have established the basic genetic requirements for the transformation of human cells, but much of this work relied on the expression of transforming proteins derived from DNA tumor viruses. We constructed an isogenic panel of human fibroblast cell lines using a combination of gene targeting and ectopic expression of dominantly acting mutants of cellular genes. Abolition of p21(Cip1/Waf1) and p16(Ink4a) functions prevented oncogenically activated Ras from inducing growth arrest and was sufficient for limited anchorage-independent growth but not tumorigenesis. Deletion of the tumor suppressor p53 combined with abolition of p16(Ink4a) function failed to mimic the introduction of simian virus 40 large T antigen, indicating that large T antigen may target additional cellular functions. Ha-Ras and Myc cooperated only to a limited extent, but in the absence of Ras, Myc cooperated strongly with the simian virus 40 small t antigen to elicit aggressive anchorage-independent growth. The experiments reported here further define specific components of human transformation pathways.

Activation of the early B-cell-specific mb-1 (Ig-alpha) gene by Pax-5 is dependent on an unmethylated Ets binding site

Methylation of cytosine in CpG dinucleotides promotes transcriptional repression in mammals by blocking transcription factor binding and recruiting methyl-binding proteins that initiate chromatin remodeling. Here, we use a novel cell-based system to show that retrovirally expressed Pax-5 protein activates endogenous early B-cell-specific mb-1 genes in plasmacytoma cells, but only when the promoter is hypomethylated. CpG methylation does not directly affect binding of the promoter by Pax-5. Instead, methylation of an adjacent CpG interferes with assembly of ternary complexes comprising Pax-5 and Ets proteins. In electrophoretic mobility shift assays, recruitment of Ets-1 is blocked by methylation of the Ets site (5'CCGGAG) on the antisense strand. In transfection assays, selective methylation of a single CpG within the Pax-5-dependent Ets site greatly reduces mb-1 promoter activity. Prior demethylation of the endogenous mb-1 promoter is required for its activation by Pax-5 in transduced cells. Although B-lineage cells have only unmethylated mb-1 genes and do not modulate methylation of the mb-1 promoter during development, other tissues feature high percentages of methylated alleles. Together, these studies demonstrate a novel DNA methylation-dependent mechanism for regulating transcriptional activity through the inhibition of DNA-dependent protein-protein interactions.

Inhibition of histone deacetylases by chlamydocin induces apoptosis and proteasome-mediated degradation of survivin

The naturally occurring cyclic tetrapeptide chlamydocin is a very potent inhibitor of cell proliferation. Here we show that chlamydocin is a highly potent histone deacetylase (HDAC) inhibitor, inhibiting HDAC activity in vitro with an IC(50) of 1.3 nM. Like other HDAC inhibitors, chlamydocin induces the accumulation of hyperacetylated histones H3 and H4 in A2780 ovarian cancer cells, increases the expression of p21(cip1/waf1), and causes an accumulation of cells in G(2)/M phase of the cell cycle. In addition, chlamydocin induces apoptosis by activating caspase-3, which in turn leads to the cleavage of p21(cip1/waf1) into a 15-kDa breakdown product and drives cells from growth arrest into apoptosis. Concomitant with the activation of caspase-3 and cleavage of p21(cip1/waf1), chlamydocin decreases the protein level of survivin, a member of the inhibitor of apoptosis protein family that is selectively expressed in tumors. Although our data indicate a potential link between degradation of survivin and activation of the apoptotic pathway induced by HDAC inhibitors, stable overexpression of survivin does not suppress the activation of caspase-3 or cleavage of p21(cip1/waf1) induced by chlamydocin treatment. The decrease of survivin protein level is mediated by degradation via proteasomes since it can be inhibited by specific proteasome inhibitors. Taken together, our results show that induction of apoptosis by chlamydocin involves caspase-dependent cleavage of p21(cip1/waf1), which is strikingly associated with proteasome-mediated degradation of survivin.

Covalent modifications of the ebola virus glycoprotein

The role of covalent modifications of the Ebola virus glycoprotein (GP) and the significance of the sequence identity between filovirus and avian retrovirus GPs were investigated through biochemical and functional analyses of mutant GPs. The expression and processing of mutant GPs with altered N-linked glycosylation, substitutions for conserved cysteine residues, or a deletion in the region of O-linked glycosylation were analyzed, and virus entry capacities were assayed through the use of pseudotyped retroviruses. Cys-53 was the only GP(1) ( approximately 130 kDa) cysteine residue whose replacement resulted in the efficient secretion of GP(1), and it is therefore proposed that it participates in the formation of the only disulfide bond linking GP(1) to GP(2) ( approximately 24 kDa). We propose a complete cystine bridge map for the filovirus GPs based upon our analysis of mutant Ebola virus GPs. The effect of replacement of the conserved cysteines in the membrane-spanning region of GP(2) was found to depend on the nature of the substitution. Mutations in conserved N-linked glycosylation sites proved generally, with a few exceptions, innocuous. Deletion of the O-linked glycosylation region increased GP processing, incorporation into retrovirus particles, and viral transduction. Our data support a common evolutionary origin for the GPs of Ebola virus and avian retroviruses and have implications for gene transfer mediated by Ebola virus GP-pseudotyped retroviruses.

Myb-binding protein 1a augments AhR-dependent gene expression

We have studied the mechanism by which an acidic domain (amino acids 515-583) of the aromatic hydrocarbon receptor (AhR) transactivates a target gene. Studies with glutathione S-transferase fusion proteins demonstrate that the wild-type acidic domain associates in vitro with Myb-binding protein 1a, whereas a mutant domain (F542A, I569A) does not. AhR-defective cells reconstituted with an AhR containing the wild-type acidic domain exhibit normal AhR function; however, cells reconstituted with an AhR containing the mutant acidic domain do not function normally. Transient transfection of Myb-binding protein 1a into mouse hepatoma cells is associated with augmentation of AhR-dependent gene expression. Such augmentation does not occur when Myb-binding protein 1a is transfected into AhR-defective cells that have been reconstituted with an AhR that lacks the acidic domain. We infer that 1) Myb-binding protein 1a associates with AhR, thereby enhancing transactivation, and 2) the presence of AhR's acidic domain is both necessary and sufficient for Myb-binding protein 1a to increase AhR-dependent gene expression.

CCAAT/enhancer-binding proteins are required for granulopoiesis independent of their induction of the granulocyte colony-stimulating factor receptor

Potential redundancy among members of the CCAAT/enhancer-binding protein (C/EBP) family in myeloid cells is indicated by the ability of C/EBPbeta to replace C/EBPalpha in vivo, by the expression of granulocyte colony-stimulating factor receptor (G-CSFR) on C/EBPalpha(-/-) cell lines, and by our finding that as with C/EBPalpha-estrogen receptor (C/EBPalpha-ER), either C/EBPbeta-ER or C/EBPdelta-ER can induce terminal granulopoiesis in 32D cl3 cells. To assess the consequences of globally inhibiting C/EBPs, we employed KalphaER, containing a Kruppel-associated box (KRAB) transrepression domain, the C/EBPalpha DNA-binding domain, and an ER ligand-binding domain. C/EBPs have a common DNA-binding consensus, and activation of KalphaER repressed transactivation by endogenous C/EBPs 50-fold and reduced endogenous G-CSFR expression. In 32D cl3 cells coexpressing exogenous G-CSFR, activation of KalphaER prevented and even reversed myeloperoxidase, lysozyme, lactoferrin, and C/EBPepsilon RNA induction by G-CSF. In contrast, induction of PU.1 and CD11b, a gene regulated by PU.1 but not by C/EBPs, was unaffected. A KalphaER variant incapable of binding DNA owing to an altered leucine zipper did not affect 32D cl3 differentiation. Transduction of KalphaER into murine hematopoietic progenitor cells suppressed the formation of granulocyte colony-forming units, even in cytokines that enable C/EBPalpha(-/-) progenitors to differentiate into neutrophils. The formation of macrophage and of granulocyte-macrophage colony-forming units were also inhibited, but erythroid burst-forming units grew normally. Thus, in 32D cl3 cells and perhaps normal progenitors, C/EBPs are required for granulopoiesis beyond their ability to induce receptors for G-CSF and other cytokines. One requisite activity may be activation of the C/EBPepsilon gene by C/EBPalpha, as either C/EBPalpha-ER or C/EBPbeta-ER rapidly elevated C/EBPepsilon RNA in 32D cl3 cells in the presence of cycloheximide but not actinomycin D.

The cytoplasmic domain of the integrin alpha9 subunit requires the adaptor protein paxillin to inhibit cell spreading but promotes cell migration in a paxillin-independent manner

The integrin alpha9 subunit forms a single heterodimer, alpha9beta1. The alpha9 subunit is most closely related to the alpha4 subunit, and like alpha4 integrins, alpha9beta1 plays an important role in leukocyte migration. The alpha4 cytoplasmic domain preferentially enhances cell migration and inhibits cell spreading, effects that depend on interaction with the adaptor protein, paxillin. To determine whether the alpha9 cytoplasmic domain has similar effects, a series of chimeric and deleted alpha9 constructs were expressed in Chinese hamster ovary cells and tested for their effects on migration and spreading on an alpha9beta1-specific ligand. Like alpha4, the alpha9 cytoplasmic domain enhanced cell migration and inhibited cell spreading. Paxillin also specifically bound the alpha9 cytoplasmic domain and to a similar level as alpha4. In paxillin(-/-) cells, alpha9 failed to inhibit cell spreading as expected but surprisingly still enhanced cell migration. Further, mutations that abolished the alpha9-paxillin interaction prevented alpha9 from inhibiting cell spreading but had no effect on alpha9-dependent cell migration. These findings suggest that the mechanisms by which the cytoplasmic domains of integrin alpha subunits enhance migration and inhibit cell spreading are distinct and that the alpha9 and alpha4 cytoplasmic domains, despite sequence and functional similarities, enhance cell migration by different intracellular signaling pathways.

Dioxin-inducible transactivation in a chromosomal setting. Analysis of the acidic domain of the Ah receptor

We analyzed the transactivation function of the acidic segment of the Ah receptor (amino acids 515-583) by reconstituting AhR-defective mouse hepatoma cells with mutants. Our data reveal that both hydrophobic and acidic residues are important for transactivation and that these residues are clustered in two regions of the acidic segment of AhR. Both regions are crucial for function, because disruption of either one substantially impairs transactivation of the chromosomal CYP1A1 target gene. Neither region contains an amino acid motif that resembles those reported for other acidic activation domains. Furthermore, proline substitutions in both regions do not impair transactivation in vivo, a finding that implies that alpha-helix formation is not required for function.

Ross River virus glycoprotein-pseudotyped retroviruses and stable cell lines for their production

Pseudotyped retroviruses have important applications as vectors for gene transfer and gene therapy and as tools for the study of viral glycoprotein function. Recombinant Moloney murine leukemia virus (Mo-MuLV)-based retrovirus particles efficiently incorporate the glycoproteins of the alphavirus Ross River virus (RRV) and utilize them for entry into cells. Stable cell lines that produce the RRV glycoprotein-pseudotyped retroviruses for prolonged periods of time have been constructed. The pseudotyped viruses have a broadened host range, can be concentrated to high titer, and mediate stable transduction of genes into cells. The RRV glycoprotein-pseudotyped retroviruses and the cells that produce them have been employed to demonstrate that RRV glycoprotein-mediated viral entry occurs through endocytosis and that membrane fusion requires acidic pH. Alphavirus glycoprotein-pseudotyped retroviruses have significant advantages as reagents for the study of the biochemistry and prevention of alphavirus entry and as preferred vectors for stable gene transfer and gene therapy protocols.