Transcripts from the cellular homologs of retroviral oncogenes: distribution among chicken tissues

Transcription Factors as the "Blitzkrieg" of Plant Defense: A Pragmatic View of Nitric Oxide's Role in Gene Regulation

Plants are in continuous conflict with the environmental constraints and their sessile nature demands a fine-tuned, well-designed defense mechanism that can cope with a multitude of biotic and abiotic assaults. Therefore, plants have developed innate immunity, R-gene-mediated resistance, and systemic acquired resistance to ensure their survival. Transcription factors (TFs) are among the most important genetic components for the regulation of gene expression and several other biological processes. They bind to specific sequences in the DNA called transcription factor binding sites (TFBSs) that are present in the regulatory regions of genes. Depending on the environmental conditions, TFs can either enhance or suppress transcriptional processes. In the last couple of decades, nitric oxide (NO) emerged as a crucial molecule for signaling and regulating biological processes. Here, we have overviewed the plant defense system, the role of TFs in mediating the defense response, and that how NO can manipulate transcriptional changes including direct post-translational modifications of TFs. We also propose that NO might regulate gene expression by regulating the recruitment of RNA polymerase during transcription.

MYB induces the expression of the oncogenic corepressor SKI in acute myeloid leukemia

Acute myeloid leukemia (AML) arises through clonal expansion of transformed myeloid progenitor cells. The SKI proto-oncogene is highly upregulated in different solid tumors and leukemic cells, but little is known about its transcriptional regulation during leukemogenesis. MYB is an important hematopoietic transcription factor involved in proliferation as well as differentiation and upregulated in most human acute leukemias. Here, we find that MYB protein binds within the regulatory region of the SKI gene in AML cells. Reporter gene assays using MYB binding sites present in the SKI gene locus show MYB-dependent transcriptional activation. SiRNA-mediated depletion of MYB in leukemic cell lines reveals that MYB is crucial for SKI gene expression. Consistently, we observed a positive correlation of MYB and SKI expression in leukemic cell lines and in samples of AML patients. Moreover, MYB and SKI both were downregulated by treatment with histone deacetylase inhibitors. Strikingly, differentiation of AML cells induced by depletion of MYB is attenuated by overexpression of SKI. Our findings identify SKI as a novel MYB target gene, relevant for the MYB-induced differentiation block in leukemic cells.

Early Evolution of Vertebrate Mybs: An Integrative Perspective Combining Synteny, Phylogenetic, and Gene Expression Analyses

The genes in the Myb superfamily encode for three related transcription factors in most vertebrates, A-, B-, and c-Myb, with functionally distinct roles, whereas most invertebrates have a single Myb. B-Myb plays an essential role in cell division and cell cycle progression, c-Myb is involved in hematopoiesis, and A-Myb is involved in spermatogenesis and regulating expression of pachytene PIWI interacting RNAs, a class of small RNAs involved in posttranscriptional gene regulation and the maintenance of reproductive tissues. Comparisons between teleost fish and tetrapods suggest that the emergence and functional divergence of the Myb genes were linked to the two rounds of whole-genome duplication early in vertebrate evolution. We combined phylogenetic, synteny, structural, and gene expression analyses of the Myb paralogs from elephant shark and lampreys with data from 12 bony vertebrates to reconstruct the early evolution of vertebrate Mybs. Phylogenetic and synteny analyses suggest that the elephant shark and Japanese lamprey have copies of the A-, B-, and c-Myb genes, implying their origin could be traced back to the common ancestor of lampreys and gnathostomes. However, structural and gene expression analyses suggest that their functional roles diverged between gnathostomes and cyclostomes. In particular, we did not detect A-Myb expression in testis suggesting that the involvement of A-Myb in the pachytene PIWI interacting RNA pathway is probably a gnathostome-specific innovation. We speculate that the secondary loss of a central domain in lamprey A-Myb underlies the functional differences between the cyclostome and gnathostome A-Myb proteins.

Soluble IFN receptor potentiates in vivo type I IFN signaling and exacerbates TLR4-mediated septic shock

Circulating levels of a soluble type I IFNR are elevated in diseases, such as chronic inflammation, infections, and cancer, but whether it functions as an antagonist, agonist, or transporter is unknown. In this study, we elucidate the in vivo importance of the soluble type I IFNAR, soluble (s)IFNAR2a, which is generated by alternative splicing of the Ifnar2 gene. A transgenic mouse model was established to mimic the 10-15-fold elevated expression of sIFNAR2a observed in some human diseases. We generated transgenic mouse lines, designated SolOX, in which the transgene mRNA and protein-expression patterns mirrored the expression patterns of the endogenous gene. SolOX were demonstrated to be more susceptible to LPS-mediated septic shock, a disease model in which type I IFN plays a crucial role. This effect was independent of "classical" proinflammatory cytokines, such as TNF-α and IL-6, whose levels were unchanged. Because the increased levels of sIFNAR2a did not affect the kinetics of the increased interferonemia, this soluble receptor does not potentiate its ligand signaling by improving IFN pharmacokinetics. Mechanistically, increased levels of sIFNAR2a are likely to facilitate IFN signaling, as demonstrated in spleen cells overexpressing sIFNAR2a, which displayed quicker, higher, and more sustained activation of STAT1 and STAT3. Thus, the soluble IFNR is an important agonist of endogenous IFN actions in pathophysiological processes and also is likely to modulate the therapeutic efficacy of clinically administered IFNs.

Robust, reversible gene knockdown using a single lentiviral short hairpin RNA vector

Manipulation of gene expression is an invaluable tool to study gene function in vitro and in vivo. The application of small inhibitory RNAs to knock down gene expression provides a relatively simple, elegant, but transient approach to study gene function in many cell types as well as in whole animals. Short hairpin structures (shRNAs) are a logical advance as they can be expressed continuously and are hence suitable for stable gene knockdown. Drug-inducible systems have now been developed; however, application of the technology has been hampered by persistent problems with low or transient expression, leakiness or poor inducibility of the short hairpin, and lack of reversibility. We have developed a robust, versatile, single lentiviral vector tool that delivers tightly regulated, fully reversible, doxycycline-responsive knockdown of target genes (FOXP3 and MYB), using single short hairpin RNAs. To demonstrate the capabilities of the vector we targeted FOXP3 because it plays a critical role in the development and function of regulatory T cells. We also targeted MYB because of its essential role in hematopoiesis and implication in breast cancer progression. The versatility of this vector is hence demonstrated by knockdown of distinct genes in two biologically separate systems.

c-Myb promotes the survival of CD4+CD8+ double-positive thymocytes through upregulation of Bcl-xL

Mechanisms that regulate the lifespan of CD4(+)CD8(+) double-positive (DP) thymocytes help shape the peripheral T cell repertoire. However, the molecular mechanisms controlling DP thymocyte survival remain poorly understood. The Myb proto-oncogene encodes a transcription factor required during multiple stages of T cell development. We demonstrate that Myb mRNA expression is upregulated as thymocytes differentiate from the double-negative into the metabolically quiescent, small, preselection DP stage during T cell development. Using a conditional deletion mouse model, we demonstrate that Myb-deficient DP thymocytes undergo premature apoptosis, resulting in a limited Tcralpha repertoire biased toward 5' Jalpha segment usage. Premature apoptosis occurs specifically in the small preselection DP compartment in an alphabetaTCR-independent manner and is a consequence of decreased Bcl-xL expression. Forced Bcl-xL expression is able to rescue survival, and reintroduction of c-Myb restores both Bcl-xL expression and the small preselection DP compartment. We further demonstrate that c-Myb promotes transcription at the Bcl2l1 locus via a genetic pathway that is independent of the expression of T cell-specific factor-1 or RORgammat, two transcription factors that induce Bcl-xL expression in T cell development. Thus, Bcl-xL is a novel mediator of c-Myb activity during normal T cell development.

Islet protein profiling

Islet protein profiling is defined as generation of extended protein expression data sets from islets or islet cells. Islets from rodent control and animal models of type 1 and type 2 diabetes mellitus and healthy humans and insulin- and glucagon-producing cell lines have been used. Protein profiling entails separation, differential expression determination, identification and expression analysis. Protein/peptide separation is either gel-based or by chromatography. Differential expression is based on comparison of visualized spots/proteins between gels or by sample labelling in gel-free systems. Identification of proteins is made by tryptic fragmentation of proteins, fragment mass determination and mass comparison with protein databases. Analysis of expression data sets interprets the complex protein changes into cellular mechanisms to generate hypotheses. The importance of such protein expression sets to elucidate islet cellular events is evidenced by the observation that only about 50% of the differentially expressed proteins and transcripts showed concordance when measured in parallel. Using protein profiling, different areas related to islet dysfunction in type 1 and type 2 diabetes mellitus have been addressed, including dysfunction induced by elevated levels of glucose and fatty acids and cytokines. Because islets from individuals with type 1 or type 2 diabetes mellitus have not yet been protein profiled, islets from rat (BB-DP) and mouse (NOD, ob/ob, MKR) models of the disease have been used, and mechanisms responsible for islet dysfunction delineated offering avenues of intervention.

Apoptotic pathways in tumor progression and therapy

Apoptosis is a cell suicide program that plays a critical role in development and tissue homeostasis. The ability of cancer cells to evade this programmed cell death (PCD) is a major characteristic that enables their uncontrolled growth. The efficiency of chemotherapy in killing such cells depends on the successful induction of apoptosis, since defects in apoptosis signaling are a major cause of drug resistance. Over the past decades, much progress has been made in our understanding of apoptotic signaling pathways and their dysregulation in cancer progression and therapy. These advances have provided new molecular targets for proapoptotic cancer therapies that have recently been used in drug development. While most of those therapies are still at the preclinical stage, some of them have shown much promise in the clinic. Here, we review our current knowledge of apoptosis regulation in cancer progression and therapy, as well as the new molecular targeted molecules that are being developed to reinstate cancer cell death.

CD36/fatty acid translocase in rats: distribution, isolation from hepatocytes, and comparison with the scavenger receptor SR-B1

The new mAb UA009 recognizes an antigen expressed by microvascular endothelium, by lymphatic endothelium, and by some epithelia in a number of organs, including the small intestine, lactating mammary gland, kidney, lung, sebaceous glands, and circumvallate papillae of the tongue. This antigen is also expressed abundantly in the splenic red pulp and marginal zone and by monocytes, macrophages, and erythrocytes (but not by platelets). Among tissues that store or metabolize fatty acids, the antigen is expressed by adipocytes, cardiomyocytes, and red skeletal muscle. Importantly, it is expressed by steroidogenic cells in the adrenal gland, testis, and ovary, whereas in the liver it is expressed by hepatocytes in a pattern that is dependent on gender and genetic background. mAb UA009 immunoprecipitated a mol wt 85-kDa surface protein from detergent extracts of hepatocytes from Dark Agouti female rats. The N-terminal amino acid sequence of this protein was identical to fatty acid translocase (FAT), the rat cluster of differentiation 36 (CD36) ortholog. The mAb also reacted with COS-7 cells transfected with cDNA encoding FAT. cDNAs encoding a CD36/FAT-like polypeptide were prepared from both liver and heart RNA by RT-PCR. The nucleotide sequences obtained from these cDNAs (Dark Agouti rats) revealed identity and 99% similarity, respectively, with the published sequences of Cd36/Fat in rats of the Wistar and Sprague-Dawley strains. The absence of the UA009 antigen in CD36/FAT-deficient SHR/N rats confirmed the identity of the UA009 antigen and CD36/FAT. We suggest that CD36/FAT might function in the liver as a sex-regulated accessory molecule, either in reverse cholesterol transport and/or in fatty acid uptake.

Rescue of the lethal scl(-/-) phenotype by the human SCL locus

The stem cell leukemia (SCL) gene encodes a basic helix-loop-helix transcription factor with a critical role in the development of both blood and endothelium. Loss-of-function studies have shown that SCL is essential for the formation of hematopoietic stem cells, for subsequent erythroid development and for yolk sac angiogenesis. SCL exhibits a highly conserved pattern of expression from mammals to teleost fish. Several murine SCL enhancers have been identified, each of which directs reporter gene expression in vivo to a subdomain of the normal SCL expression pattern. However, regulatory elements necessary for SCL expression in erythroid cells remain to be identified and the size of the chromosomal domain needed to support appropriate SCL transcription is unknown. Here we demonstrate that a 130-kilobase (kb) yeast artificial chromosome (YAC) containing the human SCL locus completely rescued the embryonic lethal phenotype of scl(-/-) mice. Rescued YAC(+) scl(-/-) mice were born in appropriate Mendelian ratios, were healthy and fertile, and exhibited no detectable abnormality of yolk sac, fetal liver, or adult hematopoiesis. The human SCL protein can therefore substitute for its murine homologue. In addition, our results demonstrate that the human SCL YAC contains the chromosomal domain necessary to direct expression to the erythroid lineage and to all other tissues in which SCL performs a nonredundant essential function.

Mutation screening of the c-MYB negative regulatory domain in acute and chronic myeloid leukaemia

Over-expression of the c-myb gene and expression of activated forms of myb are known to transform haemopoietic cells, particularly cells of the myeloid lineage. Truncations or mutations that disrupt the negative regulatory domain (NRD) of the Myb protein confer an increased ability to transform cells. Although it has proved difficult to link mutations in c-MYB to human leukaemia, no studies investigating the presence of mutations within the c-MYB NRD have been reported. Therefore, we have performed mutational analysis of this region, using polymerase chain reaction-single-stranded conformation polymorphism and sequence analysis, in 26 patients with acute or chronic myeloid leukaemia. No mutations were detected, indicating that mutation of this region of the Myb protein is not common in the pathogenesis or progression of these diseases.

Identification and validation of candidate Myb target genes

While a considerable number of candidate Myb target genes have been reported to date, most of these are likely to play little or no role in transformation by myb oncogenes. Here we have used a conditionally myb-transformed myeloid cell line (ERMYB) to further examine Myb regulation of one candidate target gene--c-myc--that has the potential to affect cell proliferation. It was found that the major influence on c-myc expression was the presence of cytokine (GM-CSF) rather than Myb activity. We also describe the application of PCR-based subtractive hybridization and low-density cDNA array screening, in conjunction with the ERMYB line, to the identification of additional Myb target genes. Preliminary identification of a number of candidates is reported; these include myeloperoxidase, which is known to have essential Myb-binding sites in its regulatory region.

The soluble murine type I interferon receptor Ifnar-2 is present in serum, is independently regulated, and has both agonistic and antagonistic properties

The ability to modify responses to type I interferons (IFNs) could alter processes such as hematopoiesis and immunity, which involve endogenous IFNs and responses to exogenous IFNs. The data presented here support a significant role for a recently identified soluble isoform of the murine type I IFN receptor, muIfnar-2a, as an efficient regulator of IFN responses. The messenger RNA (mRNA) transcript encoding muIfnar-2a is generally more abundant than that encoding the transmembrane isoform, muIfnar-2c. Furthermore, the ratio of muIfnar-2a:2c transcripts varied from more than 10:1 in the liver and other organs to less than 1:1 in bone-marrow macrophages, indicating independent regulation of the 2 transcripts encoding receptor isoforms and suggesting that the soluble muIfnar-2a levels are biologically relevant in some organs. Western blot analysis showed that soluble muIfnar-2 was present at high levels in murine serum and other biologic fluids and bound type I IFN. Recombinant muIfnar-2a competitively inhibited the activity of both IFNalpha and beta in reporter assays using the L929 cell line and in antiproliferative and antiviral assays using primary cells. Surprisingly, using primary thymocytes from Ifnar-2(-/-) mice, recombinant muIfnar-2a formed a complex with IFN alpha or beta and muIfnar-1 at the cell surface and transmitted an antiproliferative signal. These data indicate potential dual actions of soluble muIfnar-2 and imply that a signal can be transduced through the Ifnar-1 chain of the receptor complex in the absence of the cytoplasmic domain of Ifnar-2. Therefore, our results suggest that soluble Ifnar-2 is an important regulator of endogenous and systemically administered type I IFN.

Terminal differentiation of chondrocytes is arrested at distinct stages identified by their expression repertoire of marker genes

During endochondral bone formation, cells in the emerging cartilaginous model transit through a cascade of several chondrocyte differentiation stages, each characterized by a specific expression repertoire of matrix macromolecules, until, as a final step, the hypertrophic cartilage is replaced by bone. In many permanent cartilage tissues, however, late differentiation of chondrocytes does not occur, due to negative regulation by the environment of the cells. Here, addressing the reason for the difference between chondrocyte fates in the chicken embryo sternum, cells from the caudal and cranial part were cultured separately in serum-free agarose gels with complements defined earlier that either permit or prevent hypertrophic development. Total RNA was extracted using a novel protocol adapted to agarose cultures, and the temporal changes in developmental stage-specific mRNA expression were monitored by Northern hybridization and phosphor image analysis. Kinetic studies of the mRNA accumulation not only showed significant differences between the expression patterns of cranial and caudal cultures after recovery, but also revealed two checkpoints of chondrocyte differentiation in keeping with cartilage development in vivo. Terminal differentiation of caudal chondrocytes is blocked at the late proliferative stage (stage Ib), while the cranial cells can undergo hypertrophic development spontaneously. The differentiation of cranial chondrocytes is reversible, since they can re-assume an early proliferative (stage Ia) phenotype under the influence of insulin, fibroblast growth factor-2 and transforming growth factor-beta in combination. Thus, the expression pattern in the latter culture resembles that of articular chondrocytes. We also provide evidence that the capacities of caudal and sternal chondrocytes to progress from the late proliferative (stage Ib) to hypertrophic stage (stage II) correlate with their differing abilities to express the Indian hedgehog gene.

Cloning and characterization of soluble and transmembrane isoforms of a novel component of the murine type I interferon receptor, IFNAR 2

This report describes the cloning of cDNAs encoding transmembrane and soluble isoforms of a novel chain of the murine type I interferon (IFN) receptor and characterization of its capability to bind ligand and transduce signals. The transmembrane receptor (murine IFNAR 2c) has an extracellular domain of 215 amino acids and an intracellular domain of 250 amino acids, with 48% amino acid and 71% nucleotide identity with human IFNAR 2c. The cDNA for the soluble murine receptor (IFNAR 2a) encodes a 221-amino acid polypeptide identical to the first 210 amino acids of IFNAR 2c plus a novel 11 amino acids. Northern blot analyses show that murine IFNAR 2 is expressed as two transcripts of 4 kilobases encoding the transmembrane isoform and 1.5 kilobases encoding the more abundant soluble isoform. Studies using primary murine cells that lack IFNAR 1 show that IFNAR 2 is expressed, and cells bind type I IFN ligand, but do not transduce signals as detected by electrophoretic mobility shift assays of ISGF3 or GAF complexes binding to their cognate oligonucleotides. These cells show no effects on the ability of IFNgamma to activate these complexes. These studies demonstrate that the IFNAR 2 transmembrane (2c) and soluble (2a) isoforms are conserved between the human and mouse and that IFNAR 2c has intrinsic ligand binding activity, but no intrinsic signal transducing activity as measured in this study.

Minimal truncation of the c-myb gene product in rapid-onset B-cell lymphoma

Oncogenic activation of c-myb by insertional mutagenesis has been implicated in rapid-onset B-cell lymphomas induced by the nonacute avian leukosis virus EU-8. In these tumors, proviruses are integrated either upstream of the c-myb coding region or within the first intron of c-myb. Tumors with either type of integration contained identical chimeric mRNAs in which the viral 5' splice site was juxtaposed to the 3' splice site of c-myb exon 2 and myb exon 1 was eliminated. Both classes of integrations generated truncated Myb proteins that were indistinguishable by Western analysis. In contrast to most other examples of c-myb activation, the truncation consisted of only 20 N-terminal amino acids and did not disrupt either the DNA binding domain near the N terminus or the negative regulatory domain near the C terminus of Myb. The significance of the 20-amino-acid Myb truncation to tumorigenesis was tested by infection of chicken embryos with retroviral vectors expressing different myb gene products. While virus expressing either wild-type c-myb or c-myb mutated at the N-terminal casein kinase II sites was only weakly oncogenic at 10 weeks, the minimally truncated myb virus induced a high incidence of rapid-onset tumors, including B-cell lymphomas, sarcomas, and adenocarcinomas.

A type I interferon signaling factor, ISF21, encoded on chromosome 21 is distinct from receptor components and their down-regulation and Is necessary for transcriptional activation of interferon-regulated genes

The type I interferons (IFNs) are a family of cytokines, comprising at least 17 subtypes, which exert pleiotropic actions by interaction with a multi-component cell surface receptor and at least one well characterized signal transduction pathway involving JAK/STAT (Janus kinase/signal transducer and activator of transcription) proteins. In a previous report, we showed that a signaling factor, encoded by a gene located on the distal portion of chromosome 21, distinct from the IFNAR-1 receptor, was necessary for 2'-5'-oligoadenylate synthetase activity and antiviral responses, but not for high affinity ligand binding. In the present studies using hybrid Chinese hamster ovary cell lines containing portions of human chromosome 21, we show that the type I IFN signaling molecule, designated herein as ISF21, is distinct from the second receptor component, IFNAR-2, which is expressed in signaling and non-signaling cell lines. The location of the gene encoding ISF21 is narrowed to a region between the 10;21 and the r21 breakpoints, importantly eliminating the Mx gene located at 21q22.3 (the product of which is involved in IFN-induced antiviral responses) as a candidate for the signaling factor. To characterize the action of this factor in the type I IFN signaling pathway, we show that it acts independently of receptor down-regulation following ligand binding, both of which occur equally in the presence or absence of the factor. In addition, we demonstrate that ISF21 is necessary for transcriptional activation of 2'-5'-oligoadenylate synthetase, 6-16, and guanylate-binding protein gene promoter reporter constructs, which are mediated by several signaling pathways. ISF21 represents a novel factor as the localization to chromosome 21, and the data presented in this study exclude any of the known type I IFN signal-transducing molecules.

The A-myb transcription factor in neoplastic and normal B cells

The myb family of transcription factors has been strongly implicated in the regulation of cell growth and differentiation in the haematopoietic system. The v-myb oncogene, carried by avian defective retroviruses, causes leukaemias in the chicken and transforms haematopoietic cells in vitro. Its normal cellular equivalent c-myb, has been shown to promote the proliferation and block the differentiation of haematopoietic cells in several experimental models and is required for fetal haematopoiesis. Two other members of the family have been cloned more recently, A-myb and B-myb, which show sequence homology with c-myb in several domains, of which the DNA binding domain as well as other regulatory domains. Both have been shown to be transcription factors. B-myb is also involved in the control of proliferation and differentiation, but, unlike c-myb, it is expressed in many cell types. The third member of the family, A-myb, shows the most restricted pattern of expression, suggesting a very specific role for this transcription factor. A-myb is expressed in a subpopulation of normal B lymphocytes activated in vivo and localised in the germinal center of peripheral lymphoid organs and is not detected at significant levels in all other mature or immature haematopoietic populations studied, including bone marrow cells, T lymphocytes, granulocytes, monocytes, either at rest or after in vitro activation. These studies indicate that A-myb plays a role during a narrow window of normal B cell differentiation. A-myb expression has also been studied in a wide range of neoplastic B cells, representing the whole spectrum of B cell differentiation. A-myb is strongly expressed in Burkitt's lymphomas (BL) and slg+ B-acute lymphoblastic leukaemias (B-ALL) and not in all other leukaemias/lymphomas tested, with the exception of a subset of CLL (about 25% of cases). It is intriguing that the A-myb genome has been localised relatively close to the c-myc gene on chromosome 8, suggesting that the c-myc translocation in BL and B-ALL may affect A-myb transcription. Studies are in progress to investigate the functional relationship between A-myb and c-myc, particularly in the context of BL cells and to determine whether A-myb is deregulated in these cells.

Metabolic support of Na+ pump in apically permeabilized A6 kidney cell epithelia: role of creatine kinase

The contribution of ATP-generating systems to Na+ pump (Na+-K+-ATPase) function was studied in Xenopus laevis A6 kidney epithelia apically permeabilized with digitonin. The ouabain-inhibitable Na+ pump current (I(P)) was measured in the presence of otherwise impermeant inhibitors and/or substrates at Na+ and K+ concentrations that allowed near-maximal pump function. Confocal fluorescence microscopy after apical addition of sulfosuccinimidobiotin (molecular weight of 443) showed that all cells were permeabilized. Less than 15% of the endogenous lactate dehydrogenase and creatine kinase (CK) were released into the apical medium. The I(P) was approximately 5 microA/cm2 in the presence of D-glucose. Blocking glycolysis with 2-deoxy-D-glucose or oxidative phosphorylation with antimycin A decreased it by > or = 50%. Exogenously added ATP prevented these decreases fully or partially, respectively. Two CK isoforms were detected, one likely being mitochondrial and the other corresponding to mammalian B isoform of CK. Phosphocreatine partially restored Na+ pump activity during inhibition of either ATP synthesis pathway. In conclusion, the ATP used by Na+ pumps of apically digitonin-permeabilized A6 epithelia is generated to a similar extent by glycolysis and oxidative phosphorylation. The CK system can partially support the ATP supply to the Na+ pumps.

Integrin-dependent induction of early growth response genes in capillary endothelial cells

Studies were carried out to explore how extracellular matrix molecules, such as fibronectin (FN), promote capillary endothelial (CE) cell growth. When G0-synchronized cells were plated on FN-coated dishes, expression of the immediate-early mRNAs, c-fos, c-myc and c-jun, was rapidly induced, even in the absence of serum or soluble growth factors. Moreover, plating cells on different FN densities (5-200 micrograms/150 mm dish), resulted in a dose-dependent increase in the steady state levels of these mRNAs. Addition of FGF potentiated gene activation and was required for maximal DNA synthesis, however, the overall steady-state level of gene induction was dictated primarily by the density of immobilized FN. Expression of junB also was induced when suspended cells bound RGD-peptide coated microbeads that promote integrin clustering, but not when the suspended cells bound beads coated with other receptor ligands (e.g. acetylated low density protein) or when they were stimulated by soluble FN or FGF in the absence of substrate adhesion. c-Jun exhibited a similar requirement for gene induction except that it also was partially induced by binding to soluble FN alone. In contrast, c-fos expression was induced by all stimuli tested. Interestingly, inhibition of Na+/H+ exchange using hexamethylene-amiloride prevented most of the FN-induced increase in c-jun expression whereas it was relatively ineffective when cells were simultaneously stimulated by both FN and FGF. These data demonstrate that cell adhesion to extracellular matrix and associated integrin binding can directly activate signaling cascades in quiescent CE cells that lead to induction of immediate-early genes associated with the G0/G1 transition and thereby, stimulate these cells to reenter the growth cycle.

Leukemia inhibitory factor and interleukin-6 are produced by diseased and regenerating skeletal muscle

The process of skeletal muscle regeneration following injury or disease involves locally produced growth factors which control cellular proliferation and differentiation. Leukemia inhibitory factor (LIF) and interleukin-6 (IL-6) have previously been shown to promote the proliferation of myoblasts in vitro, and thus may be involved in muscle regeneration. In the present investigation, the in vivo expression of these two myogenic growth factors was examined in regenerating muscle after a crush injury of wild type mice, and in diseased skeletal muscle and diaphragm of the mdxmouse. Using Reverse transcription polymerase chain reaction we have demonstrated that while normal muscle rarely expresses mRNA for these two molecules, there is significant up-regulation following injury, coinciding with the active period of muscle regeneration. This suggests these molecules act as locally produced trauma factors. This observation is reinforced in mdxmouse muscle, which is undergoing a cycle of degeneration and regeneration, and expresses both LIF and IL-6. Using in situ hybridization we have localized mRNA for LIF expression in the mdx diaphragm, suggesting that local production of these molecules by regenerating muscle itself, as well as by other cells in muscle, plays an important role in muscle regeneration.

Olfactory neuronal cell lines generated by retroviral insertion of the n-myc oncogene display different developmental phenotypes

Being genetically homogeneous, clonal cell lines are potentially important for investigating many aspects of cellular differentiation. We describe here the creation of clonal cell lines by immortalization of neuronal precursor cells from the adult mouse olfactory epithelium. Unlike neurons elsewhere in the vertebrate nervous system, the olfactory sensory neuron can be replaced throughout the lifespan of the animal. However, little is known about the molecular aspects of olfactory neurogenesis. Continuous cell lines were generated by retroviral transduction of the n-myc proto-oncogene into the mitotically active basal cells of the olfactory epithelium which give rise to the sensory neuron. Twenty-one clonal cell lines were produced which could be divided into three distinct morphological classes: one with flat, epithelial-like cells only; another with round, flat, and bipolar cells; and a third with large flat and large bipolar cells. These morphological classes had different patterns of intermediate filament expression, as shown by immunocytochemistry and immunoblot analysis. All cells in all cell lines expressed the intermediate filament protein vimentin. Most bipolar cells, but not other cell types, expressed neurofilament protein and in one morphological class the bipolar cells co-expressed neurofilament and glial fibrillary acidic protein. Several cell lines expressed mRNA for OMP, a marker of mature olfactory sensory neurons, and GOLF, a guanine nucleotide binding protein involved in olfactory sensory transduction. It is concluded that these cell lines were immortalized from sensory neuron precursors late in the lineage pathway. Other cell lines appear to have been immortalized at earlier stages in the lineage pathway. These cell lines therefore provide useful tools for the investigation of neuronal differentiation and sensory transduction in the olfactory epithelium.

Molecular basis of the soluble and membrane-bound forms of the murine leukemia inhibitory factor receptor alpha-chain. Expression in normal, gestating, and leukemia inhibitory factor nullizygous mice

The murine leukemia inhibitory factor receptor alpha-chain (mLIFR) exists in a membrane-bound and a soluble form. The two major classes of mRNA transcript correspond to either the soluble or membrane-bound form of the mLIFR. In this study we have identified a complex and heterogeneous pattern of expression of mRNA transcripts for this receptor in normal mouse tissues and cell lines. In order to understand the molecular basis of these transcripts, genomic clones encompassing the region of divergence from the soluble to the membrane-bound form of the receptor were isolated. cDNAs encoding the membrane-bound form of the mLIFR were generated by an alternative splicing event where an exon that is specific to the soluble mLIFR was skipped. The membrane-bound form of the mLIFR was heterogeneously polyadenylated with at least five different sites of polyadenylation. The mRNA transcript encoding the soluble form of the mLIFR contained a region highly homologous to a murine B2 repetitive element, thus providing a possible explanation for the genesis of this transcript. The different forms of the mLIFR were analyzed in a wide range of mouse tissues in pseudopregnant mice and in mice at various stages of pregnancy. Only liver, placenta, and uterus showed an increase in the levels of mLIFR mRNA expression during pregnancy, indicating an important role for the LIFR in this process. However, somewhat surprisingly, there was no detectable difference in mLIFR mRNA levels or levels of soluble protein in leukemia inhibitory factor nullizygous mice when compared with normal mice.

Up-regulation of leukaemia inhibitory factor and interleukin-6 in transected sciatic nerve and muscle following denervation

Leukaemia inhibitory factor (LIF) and Interleukin-6 (IL-6) are multifunctional cytokines that are related on the basis of their predicted structural similarities and shared signal transducing receptor components. Both these factors stimulate myoblast proliferation, and whereas LIF is neurotrophic for sensory neurons, and for the motor neurons which innervate muscle, IL-6 has only been reported to act on a population of septal neurons in the brain. We have looked at the effect of peripheral nerve trauma on the expression of these factors. We show here that whereas LIF and IL-6 mRNAs are expressed in low levels in normal sciatic nerve and skeletal muscle, there is significant up-regulation in the nerve segments after injury, with proximally and distally. There is also an increase in LIF and IL-6 expression in the denervated muscle located largely in the muscle cells. In addition, while there is retrograde axonal transport of LIF by the sciatic nerve, IL-6 is not retrogradely transported, and as a result, IL-6 does not stimulate the survival of sensory neurons in vitro. Both growth factors are produced by Schwann cells. These results show a rapid response in the expression of these genes after injury and suggest that LIF and IL-6 act as trauma factors but with different roles in injured peripheral nerve.

Regulation of hematopoietic cell proliferation and differentiation by the myb oncogene family of transcription factors

The myb family of genes include the virally encoded v-myb oncogene, its normal cellular equivalent c-myb and two related members called A-myb and B-myb. They are all transcription factors that recognize the same DNA sequence (PyAACG/TG) and are all involved in the regulation of proliferation and differentiation in different cell types, including hematopoietic cells. C-myb is most highly expressed in hematopoietic cells and its oncogenic activation leads to transformation of these cells. Several lines of evidence have demonstrated that c-myb regulates both the proliferation and differentiation of hematopoietic cells of different lineages. The mechanisms of action of c-myb and v-myb are becoming clearer, mostly through the study of the different genes that are regulated by these transcription factors and the cofactors with which c-myb and v-myb co-operate. More recently the biological and biochemical functions of the B-myb and A-myb gene products have been investigated. Evidence for the function of the different members of the myb family in relation to hematopoietic proliferation and differentiation is presented, and the different roles of the myb genes are discussed.

Leukaemia inhibitory factor or related factors promote the differentiation of neuronal and astrocytic precursors within the developing murine spinal cord

Previously we have shown that leukaemia inhibitory factor (LIF) potentiates the development of murine spinal cord neurons in vitro, suggesting that it, or related factors, may play an important regulatory role in neuronal development. We have further investigated this role and show here that the generation of neurons in cultures of embryonic day 10 spinal cord cells is inhibited by antibodies to the beta subunit of the LIF receptor. Since there are more undifferentiated precursors in antibody-treated cultures than in control and LIF-treated cultures, it is concluded that the primary action of LIF, or related molecules, is to promote neuronal differentiation, not precursor survival. In addition, the failure of LIF to support neuronal survival in the period immediately following differentiation suggests that the increased numbers of neurons generated with LIF are not attributable to its neurotrophic action. By selecting neuronal precursors on the basis of their inability to express class 1 major histocompatibility complex molecules, it was shown that LIF acted directly upon these cells and not via an intermediary cell. LIF also appears to be involved in regulating the differentiation of astrocytes, since it increases the number of glial fibrillary protein (GFAP)-positive cells present in the cultures and since the spontaneous production of GFAP-positive cells is blocked by antibodies to the LIF beta receptor. These findings suggest that LIF or related factors promote the differentiation of neural precursors in the spinal cord, but that they are not involved in preferentially promoting precursors down a specific differentiation pathway.

Nuclear matrix acceptor binding sites for steroid hormone receptors: a candidate nuclear matrix acceptor protein

Steroid/nuclear-hormone receptors are ligand-activated transcription factors that have been localized to the nuclear matrix. The classic model of hormone action suggests that, following activation, these receptors bind to specific "steroid response elements" on the DNA, then interact with other factors in the transcription initiation complex. However, evidence demonstrates the existence of specific chromatin proteins that act as accessory factors by facilitating the binding of the steroid receptors to the DNA. One such protein, the "receptor binding factor (RBF)-1", has been purified and shown to confer specific, high-affinity binding of the progesterone receptor to the DNA. Interestingly, the RBF-1 is localized to the nuclear matrix. Further, the RBF-1 binds specifically to a sequence of the c-myc proto-oncogene that has the appearance of a nuclear matrix attached region (MAR). These results, and other findings reviewed here, suggest that the nuclear matrix is involved intimately in steroid hormone-regulated gene expression.

FGF suppresses apoptosis and induces differentiation of fibre cells in the mouse lens

To determine whether fibroblast growth factor (FGF) has a role in lens development, we have generated transgenic mice expressing a dominant-negative form of the murine FGF receptor-1 (FGFRDN) in the lens. Using the fibre cell-specific alpha A-crystallin promoter to express the FGFRDN, we have asked whether FGF is required for fibre cell differentiation. The transgenic mice display diminished differentiation of fibre cells as indicated by their reduced elongation. In addition, transgenic lenses have an unusual refractile anomaly that morphological and biochemical data show results from the apoptosis of fibre cells in the central region of the lens. These results show that lens fibre cells are dependent on FGF for their survival and differentiation, and demonstrate that growth factor deprivation in vivo can lead to apoptosis.

Conditional inhibition of erythroid differentiation by c-Myb/oestrogen receptor fusion proteins

The c-myb proto-oncogene encodes a transcription factor that has been implicated in the regulation of haemopoietic cell differentiation and appears also to be required for cell proliferation in a number of different lineages. Typically, transcription of c-myb is down-regulated during haemopoietic cell differentiation, and it has been found in several erythroid and myeloid cell lines that constitutive c-myb expression, from a transfected plasmid, blocks this differentiation process. To investigate further the activity of c-myb in haemopoietic cell differentiation, we have transfected Friend murine erythroleukaemia (F-MEL) cells with plasmids encoding conditionally active c-Myb/oestrogen receptor (Myb/ER) fusion proteins. Transcriptional activity of the Myb/ER fusion proteins was found to be strictly hormone-dependent, and this property was correlated with the ability of these proteins to inhibit erythroid differentiation. From analysis of a Myb/ER protein that lacks the c-Myb transactivation domain, it was apparent that the C-terminal ER transactivation domain could substitute for that of c-Myb in inhibition of differentiation. Activation of Myb/ER in F-MEL cells had no effect upon the early and transient inhibition of entry into S phase associated with dimethyl sulfoxide (DMSO) induction. Further analyses of alpha-globin and PU.1 gene transcription suggested that c-Myb is unable to influence gene expression immediately following DMSO-induction and that inhibition of F-MEL cell differentiation must therefore result from the function of c-Myb in the post-commitment period. Nonetheless, c-Myb had effects on the erythroid differentiation programme that were clearly dissociated from its role in cell proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

Mutations in the DNA-binding and transcriptional activation domains of v-Myb cooperate in transformation

The v-Myb protein encoded by avian myeloblastosis virus causes oncogenic transformation of monoblastic cells committed to the monocyte/macrophage lineage. v-Myb is a doubly truncated form of its normal cellular counterpart, c-Myb. In addition to its N- and C-terminal deletions, v-Myb contains a number of amino acid substitutions relative to c-Myb. We have previously shown that neither overexpression of c-Myb nor introduction of these amino acid substitutions into c-Myb is sufficient for transformation of myelomonocytic cells. However, a doubly truncated form of c-Myb which lacked these substitutions transformed myeloblastic cells that appeared to be committed to the granulocytic pathway. We demonstrate here that mutations in both the DNA-binding and transcriptional activation domains of v-Myb are required for transformation of rapidly growing monoblasts rather than more slowly growing myeloblasts. These rapidly growing monoblasts do not express mim-1, a target gene for the Gag-Myb-Ets protein of E26 leukemia virus, or C/EBP proteins which cooperate with Myb to activate mim-1 expression. Furthermore, v-Myb proteins which contain both sets of these mutations are weaker transcriptional activators relative to proteins which lack these mutations. These results support a model in which amino acid substitutions in v-Myb have been selected for their ability to activate only a subset of those genes which can be activated by a doubly truncated form of c-Myb. In particular, mim-1 appears to represent a class of genes whose expression was selected against during the development of an increasingly virulent strain of avian myeloblastosis virus by passage in animals.

Pax-1, a regulator of sclerotome development is induced by notochord and floor plate signals in avian embryos

Pax-1 encodes for a DNA-binding transcriptional activator that was originally discovered in murine embryos using a probe from the Drosophila paired-box-containing gene, gooseberry-distal. We have cloned the avian Pax-1 gene as a basis for experimental studies of the induction of Pax-1 in the paraxial mesoderm. The amino acid sequence of the paired-domain is exactly the same in the quail and mouse, whereas outside the paired-domain there is 61% homology. Starting at about the eight-somite stage, quail Pax-1 is expressed in the paraxial mesoderm in a craniocaudal sequence. The unsegmented paraxial mesoderm and the two most recently formed somites do not express Pax-1. In the epithelial somite, the somitocoele cells and the cells of the ventral two-thirds of the epithelial wall are positive. As soon as the sclerotome is formed, only a subset of sclerotome cells expresses Pax-1. These are the cells that migrate towards the notochord to form the perinotochordal tube. Expression then becomes restricted to the intervertebral discs, the perichondrium of the vertebral bodies and the connective tissue surrounding the spinal ganglia. Additional expression domains are found in the scapula and the pelvic region, distinct areas of the head, and the epithelium of the second to the fourth visceral pouch. In later stages the thymus is positive. In vitro and in vivo experiments show that the notochord induces Pax-1 in the paraxial mesoderm, but limb bud mesoderm is not competent to respond to notochordal signals. Floor plate is also capable of inducing Pax-1 expression in sclerotome cells. Our studies show that in competent cells of the paraxial mesoderm, Pax-1 is a mediator of signals emanating from the notochord and the floor plate.

Members of the nuclear factor kappa B family transactivate the murine c-myb gene

Expression of the c-myb proto-oncogene is primarily detected in normal tissue and tumor cell lines of immature hematopoietic origin, and the down-regulation of c-myb expression is associated with hematopoietic maturation. Cell lines that represent mature, differentiated hematopoietic cell types contain 10-100-fold less c-myb mRNA than immature hematopoietic cell types. Differences in steady-state c-myb mRNA levels appear to be primarily maintained by a conditional block to transcription elongation that occurs in the first intron of the gene. The block to transcription elongation has been mapped, using nuclear run-on analysis, to a region of DNA sequence that is highly conserved between mouse and man. Two sets of DNA-protein interactions, flanking the site of the block to transcription elongation, were detected that exhibited DNA-binding activities that strongly correlated with low steady-state c-myb mRNA levels. Several criteria demonstrated that members of the nuclear factor kappa B (NF-kappa B) family of transcription factors were involved in the DNA-protein interactions identified in these two sets. Surprisingly, cotransfection experiments demonstrated that coexpression of members of the NF-kappa B family, specifically p50 with p65 and p65 with c-Rel, transactivated a c-myb/chloramphenicol acetyltransferase reporter construct that contained 5'-flanking sequences, exon I, intron I, and exon II of the c-myb gene. Transactivation by these heterodimer combinations was dependent on regions of the c-myb first intron containing the NF-kappa B-binding sites. These findings suggest that NF-kappa B family members may be involved in either modifying the efficiency of transcription attenuation or acting as an enhancer-like activity to increase transcription initiation. Thus, the regulation of c-myb transcription may be quite complex, and members of the NF-kappa B family likely play an important role in this regulation.

Presence of regulatory sequences within intron 4 of human and murine c-myb genes

The molecular mechanisms that modulate c-myb mRNA transcription in hematopoietic cells appear to involve intron regulatory sequences. We have characterized the fourth of ten introns from both human and murine c-myb genes in regard to nucleotide sequence and specific protein binding. For this approach complete genomic c-myb intron 4 fragments were isolated from mouse and human DNA using PCR amplification with flanking exon-primers derived from the mouse gene. Comparison of the obtained sequences revealed strong homology between the two species. Using crude nuclear protein extracts from mouse and human myb expressing cells (70Z/3B; Molt4) and gel shift experiments we found specific protein interaction for both introns and to determine the protein binding site in detail, we performed DNase I footprinting. Our results indicate that the binding factor is absent in control cell lines without c-myb transcriptional activity, suggesting a possible positive regulatory function of the DNA-protein complex. To confirm these findings we introduced the human c-myb intron 4 DNA sequence into the EcoRI site of the pCAT-Promoter plasmid and transfected Molt4 cells with this chimeric construct. The transient expression studies revealed that intron 4 sequences possess enhancer activity. Thus, we have demonstrated that intron 4 sequences can be important for the regulation of c-myb proto-oncogene expression.

Vintage reds and whites: combinatorial transcription factor utilization in hematopoietic differentiation

Pluripotent hematopoietic stem cells can differentiate into a number of distinct specialized cell types; however, no single lineage-specific master regulators have been identified that can activate individual patterns of gene expression. Recent evidence suggests that such lineage determination is regulated by a combinatorial matrix of regulatory proteins with overlapping tissue specificities which cooperate to define individual cell types.

Thrombin receptor expression and function in large granular lymphocyte proliferative disorders

It has recently been shown that peripheral blood NK-cells and a fraction of T-cells which co-express CD16 and either CD56 or CD57 express the platelet type thrombin receptor. Large granular lymphocytes exhibit a T- or NK-cell phenotype, and therefore these results raise the possibility that thrombin and its receptor may be involved in the biology of large granular lymphocytes in health and disease. It is difficult, however, to perform functional studies using normal blood as a source of large granular lymphocytes, because the small fraction of large granular lymphocytes cannot be separated from other lymphocytes in numbers sufficient for most in vitro experiments. Therefore patients with large granular lymphocyte proliferative disorders have been screened in order to identify a population of cells enriched in large granular lymphocytes that express the thrombin receptor. Expression of the receptor was analysed in polyclonal and clonal large granular lymphocyte proliferative disorders. Using flow cytometry, it was found that the proportion of thrombin receptor positive large granular lymphocytes varied from 3% to 86%. Northern analysis indicated a high level of expression of mRNA in a clonal expansion of large granular lymphocytes that stained positively for the receptor by flow cytometry. Thrombin was found to act as a chemotactic stimulus for large granular lymphocytes from a polyclonal expansion with high numbers of thrombin receptor positive cells. At an optimal concentration of 10(-9) M the chemotactic response to thrombin was roughly equivalent to that obtained with the potent chemoattractant 1-oleoyl 2-acetyl glycerol. These findings suggest that thrombin may play a role in the recruitment of large granular lymphocytes in sites of inflammation.

Differentiation primary response genes and proto-oncogenes as positive and negative regulators of terminal hematopoietic cell differentiation

By genetically manipulating hematopoietic cells of the myeloid lineage, including both normal cells and differentiation inducible leukemic cell lines, evidence was obtained to indicate that myeloid differentiation primary response (MyD) genes and proto-oncogenes, which are known to control cell growth, function as positive and negative regulators of terminal hematopoietic cell differentiation, which is associated with inhibition of cell growth, and, ultimately programmed cell death (apoptosis). Interferon regulatory factor-1 (IRF-1), an MyD gene induced by Interleukin 6 (IL-6) or Leukemia Inhibitory factor (LIF), plays a role in growth inhibition associated with terminal differentiation. Leucine zipper transcription factors of the fos/jun family, also identified as MyD genes, function as positive regulators of hematopoietic cell differentiation, increasing the propensity of myeloblastic leukemia cells to be induced for differentiation in vitro, and reducing the aggressiveness of their leukemic phenotype in vivo. The zinc finger transcription factor EGR-1, an MyD gene specifically induced upon macrophage differentiation, was shown to be essential for and to restrict differentiation along the macrophage lineage. Finally, evidence has been accumulating to indicate that the novel MyD genes--MyD116, MyD118 and gadd45 (a member in the MyD118 gene family)--play a role in growth arrest and apoptosis of hematopoietic cells, as well as other cell types. The proto-oncogenes c-myc and c-myb, known to regulate cellular growth, were shown to function as negative regulators of terminal differentiation. Both c-myc and c-myb are normally expressed in proliferating myeloblasts and suppressed following induction of differentiation. Deregulated and continuous expression of c-myc was shown to block terminal myeloid differentiation at an intermediate stage in the progression from immature blasts to mature macrophages, whereas deregulated and continuous expression of c-myb blocked the terminal differentiation program at the immature myeloblast stage. By manipulating myc function in conditional (differentiation inducible) mutant myeloblastic leukemia cell lines, expressing a chimeric mycer transgene, it was shown that there is a window during myeloid differentiation, after the addition of the differentiation inducer, when the terminal differentiation program switches from being dependent on c-myc suppression to becoming c-myc suppression independent, and where activation of c-myc has no apparent effect on mature macrophages. These myeloblastic leukemia cell lines provide a powerful tool to increase our understanding of the role of c-myc in normal hematopoiesis and in leukemogenesis, while also providing a strategy to clone myc target genes.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukemia inhibitory factor (LIF) infusion stimulates skeletal muscle regeneration after injury: injured muscle expresses lif mRNA

Leukemia inhibitory factor (LIF) is known to stimulate myoblast growth in culture via direct receptor mediated mechanisms, but it does not suppress myoblast fusion in vitro. We show here that LIF is also effective in vivo, using a muscle crush model. Administration of LIF to the site of the crush results in an increased rate of regeneration of the injured muscle. LIF stimulates an increase in the size of the muscle fibers rather than an increase in total number. Perfusion of 125I-labelled LIF (125I-LIF) at the site of the crush leads to uptake of the great majority of 125I-LIF into the muscle, which suggests that LIF is acting directly at the site of injury. Further, following crush injury LIF mRNA synthesis commences in the muscle. These data provide evidence that LIF is acting as a natural trauma factor in vivo and is actively involved in muscle regeneration.

Leukaemia inhibitory factor and interleukin 6 are expressed at very low levels in the normal adult mouse and are induced by inflammation

We have assessed the limitations of the polymerase chain reaction (PCR) as a semiquantitative technique for assessing very low level gene expression. Using PCR, the in vivo expression patterns of the cytokines Leukaemia Inhibitory Factor (LIF) and Interleukin 6 (IL-6) in the normal adult mouse, have been examined. We show that both LIF and IL-6 mRNA are constitutively expressed, albeit at extremely low levels, in most tissues. While it is unclear whether this low level of expression is of biological significance, it is possible that it reflects a local mode of action of these potent polyfunctional molecules. Lipopolysaccharide, the bacterial cell wall product responsible for endotoxic shock, when administered in vivo, was capable of inducing the expression of both LIF and IL-6 in all of the tissues examined. In addition, LIF and IL-6 expression was induced in lung tissue by in vitro culturing in serum-free media. This induction of LIF and IL-6, by LPS and culturing, may reflect the role of these molecules as mediators of the acute phase response to tissue damage.

Cloning and expression of the gene for the melanoma-associated ME20 antigen

Human melanoma cells, but not tumor cells of other histological origin, express a unique membrane-associated glycoprotein, designated ME20-M, and secrete a soluble glycoprotein, designated ME20-S, defined by monoclonal antibody ME20. Here we report the isolation and characterization of a cDNA clone that when transfected into COS cells directs the expression of ME20-M and ME20-S. This cDNA contains an open reading frame which encodes a 661-amino-acid-long precursor that contains a 23-amino-acid signal peptide and a 26-amino-acid transmembrane domain, separated by a hydrophilic region containing 5 potential Asn-linked and 14 predicted Pro-associated, Thr-linked glycosylation sites. The transmembrane domain is followed by a carboxy-terminal 45-amino-acid putative intracellular domain rich in Ser residues. Analysis of ME20-M by amino acid sequencing identified the proteolytic processing site. Signal peptide cleavage occurs at the Thr-24-Lys-25 peptide bond of the precursor and results in the 637-amino-acid ME20-M with a calculated molecular weight of 67,782. ME20-M is derived from a single 3.3- to 3.4-kb mRNA transcript that is expressed at varying levels in melanoma cell lines, correlating with immunofluorescence determination of protein expression. The amino acid sequence of the ME20 antigen deduced from the cDNA differs from the human neonatal melanocyte-specific Pmel 17 gene product by a single amino acid substitution and deletion of 7 amino acid residues, and it is 80% homologous with the bovine retinal pigment RPE1 cDNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Primary sequence and functional expression of a novel beta subunit of the P-ATPase gene family

The cortical collecting tubule (CCT) of the mammalian kidney reabsorbs sodium and potassium, processes that are mediated by Na/K-ATPase and H/K-ATPase. CCT is also an important site for proton secretion, which is driven, in part, by H/K-ATPase. Na/K-ATPase and H/K-ATPase are members of the ion-motive P-ATPase gene family. They are closely related plasma membrane proteins which consist of alpha beta heterodimers. The urinary bladder of the toad Bufo marinus is the amphibian counterpart of mammalian CCT. We have previously characterized a ouabain-resistant Na/K-ATPase [see ref. 17], from TBM cells, a clonal cell line derived from the toad bladder, which expresses transepithelial sodium transport. In the present study, we report the primary sequence and functional expression of a novel beta subunit (beta bladder = beta b1) isolated from a toad bladder epithelial cell cDNA library. The deduced polypeptide is 299 amino acids in length and has a predicted molecular mass of 33 kDa. The beta b1 protein exhibits 35% amino acid identity to the previously characterized beta 1 of B. marinus Na/K-ATPase and 39% identity with beta 3 of B. marinus Na/K-ATPase. It shares 38% identity with the mammalian beta gastric H/K-ATPase and 52% with the mammalian beta 2 Na/K-ATPase. Northern blot analysis shows that a 1.4 x 10(3)-base mRNA is expressed at a high level in bladder epithelial cells and eye and at a trace level in kidney; it is not detectable in significant amounts in the stomach, colon and small intestine.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the chicken GATA factor family during early erythroid development and differentiation

The DNA motif WGATAR has been identified within transcriptional regulatory domains of globin and other erythroid-specific genes and the activator proteins that bind to this regulatory element, the GATA factors, belong to a multi-gene family that is expressed in chicken erythroid cells. Here we show that, as in chickens, multiple members of the GATA factor family are expressed in human and murine erythroid cells. During the early stages of chicken embryogenesis (well before blood island formation), each of the GATA family members is transcribed with a unique temporal and spatial pattern. In the primitive erythroid lineage, transcription of the embryonic epsilon-globin gene parallels GATA-1 expression while the switch to beta-globin transcription in definitive erythroid cells is directly preceded by a pronounced increase in GATA-3 accumulation. The timing and pattern of expression of these different mRNAs during avian erythroid development and differentiation suggests that temporally regulated changes in GATA factor expression are required for vertebrate hematopoiesis.

A role for sialyl Lewis-X/A glycoconjugates in capillary morphogenesis

To identify cell adhesion molecules required for angiogenesis, we used an in vitro model in which bovine capillary endothelial cells can be induced to form capillary-like tubes. Monoclonal antibodies directed against the carbohydrate epitopes sialyl Lewis-X and sialyl Lewis-A inhibited capillary formation. We postulated that a member of the selectin family of adhesion molecules may be involved in capillary formation because these proteins bind to sialyl Lewis-X/A-containing ligands. We isolated a 2.8-kilobase complementary DNA from a bovine capillary endothelial cell cDNA library which encodes a polypeptide with 71% identity to human E-selectin. We report here that antibody directed against the bovine E-selectin inhibited capillary formation, suggesting that in addition to its role in leukocyte adhesion to endothelium, a form of E-selectin is involved in capillary morphogenesis.