The immune response to a fungus in pancreatic cancer samples

Pancreatic ductal adenocarcinoma (PDAC) is a poor prognosis cancer with an .aggressive growth profile that is often diagnosed at late stage and that has few curative or therapeutic options. PDAC growth has been linked to alterations in the pancreas microbiome, which could include the presence of the fungus Malassezia. We used RNA-sequencing to compare 14 paired tumor and normal (tumor adjacent) pancreatic cancer samples and found Malassezia RNA in both the PDAC and normal tissues. Although the presence of Malassezia was not correlated with tumor growth, a set of immune- and inflammatory-related genes were up-regulated in the PDAC compared to the normal samples, suggesting that they are involved in tumor progression. Gene set enrichment analysis suggests that activation of the complement cascade pathway and inflammation could be involved in pro PDAC growth.

Parelaphostrongylus tenuis Cerebrospinal Nematodiasis in a Horse with Cervical Scoliosis and Meningomyelitis

There are reports of horses with acute onset acquired cervical scoliosis and cutaneous analgesia. The underlying dorsal gray column myelitis that produces these neurologic signs has been only presumptively attributed to migration of Parelaphostrongylus tenuis within the spinal cord. Despite previous confirmation brain by polymerase chain reaction testing, of P. tenuis within the brain of horses by polymerase chain reaction testing, genetic testing has failed to definitively identify the presence of this parasite in cases of equine myelitis. This case report provides molecular confirmation via polymerase chain reaction of P. tenuis within the cervical spinal cord of a horse with scoliosis and cutaneous analgesia.

Randomized trial of adjunctive topiramate therapy in infants with refractory partial seizures

OBJECTIVE

To evaluate the efficacy and safety of adjunctive topiramate (sprinkle capsules or oral liquid) in reducing daily rates of partial-onset seizures (POS) in infants with refractory POS.

METHODS

In this double-blind, placebo-controlled, parallel-group, international study, infants (n = 149) with clinical or EEG evidence of refractory POS were randomly allocated (1:1:1:1) to receive adjunctive topiramate 5, 15, or 25 mg/kg/d or placebo for 20 days. The primary variable was the median percentage reductions in daily POS rate from baseline to final assessment as recorded on a 48-hour video-EEG.

RESULTS

Of the 149 infants (mean age 12 months) included in the intent-to-treat analysis set, 130 completed the study. Median percentage reduction from baseline in daily POS rate was not significantly different (p = 0.97) between topiramate 25 mg/kg (20.4%) and placebo (13.1%). Lower doses were not formally tested, but nominal p values for comparisons with placebo were not significant (15-mg/kg/d dose: p = 0.97; 5-mg/kg/d dose: p = 0.91). Treatment-emergent fever, diarrhea, vomiting, anorexia, weight decrease, somnolence, and viral infection occurred more frequently (> or = 10% difference) with topiramate than with placebo.

CONCLUSION

In infants aged 1-24 months, topiramate 5, 15, or 25 mg/kg/d was not effective as adjunctive treatment for refractory partial-onset seizures. No new safety concerns associated with topiramate use were noted.

CLASSIFICATION OF EVIDENCE

This interventional study provides Class I evidence that topiramate 5, 15, or 25 mg/kg/d compared with placebo does not significantly reduce seizure rates in infants aged 1 month to 2 years with refractory partial-onset seizures.

Oncogenic mutations cause dramatic, qualitative changes in the transcriptional activity of c-Myb

The v-Myb oncoprotein encoded by Avian Myeloblastosis Virus is highly oncogenic, induces leukemias in chickens and mice and transforms immature hematopoietic cells in vitro. The v-Myb protein is a mutated and truncated version of c-Myb, a DNA-binding transcription factor expressed in many cell types that is essential for normal hematopoiesis. Previous studies suggested that two types of differences, DNA binding domain mutations and the deletion of a C-terminal negative regulatory domain were important for increasing the transforming activity of v-Myb. Here, we combined structure-function studies of the v-Myb and c-Myb proteins with unbiased microarray-based transcription assays to compare the transcriptional specificities of the two proteins. In human cells, the v-Myb and c-Myb proteins displayed strikingly different activities and regulated overlapping, but largely distinct sets of target genes. Each type of mutation that distinguished v-Myb from c-Myb, including the N- and C-terminal deletions, DNA binding domain changes and mutations in the transcriptional activation domain, affected different sets of target genes and contributed to the different activities of c-Myb and v-Myb. The results suggest that v-Myb is not just a de-repressed version of c-Myb. Instead, it is a distinct transcriptional regulator with a unique set of activities.

The conserved DNA binding domain mediates similar regulatory interactions for A-Myb, B-Myb, and c-Myb transcription factors

The vertebrate A-Myb, B-Myb, and c-Myb proteins comprise a family of related transcription factors that share a highly conserved DNA binding domain. Although all three proteins are capable of binding the same sites in DNA, they have distinct, but overlapping patterns of expression and are presumed to be regulated independently. Here we show that the transcriptional activity of all three vertebrate Myb proteins can be severely inhibited by coexpression of a dominant-negative allele of p100, a coactivator protein that interacts with Myb DNA binding domains. Thus, the conserved Myb domains mediate interactions with common sites in DNA, as well as common regulators, suggesting that the proteins provide alternative or complementary responses to common upstream signaling pathways.

The MHC class II-associated chicken invariant chain shares functional properties with its mammalian homologs

The nucleotide sequence of chicken invariant chain (Ii) was determined, and the amino acid sequence similarity with human Ii is 61%. Certain regions important for the biological function of human Ii are highly conserved between chicken and mammals. The cytoplasmic tail of chicken Ii fused to the plasma membrane reporter molecule neuraminidase relocated the protein to endosomes. Moreover, like the mammalian orthologs, the cytoplasmic tail was found to contain two independent leucine-based endosomal sorting signals. Chicken Ii was found to interact with human Ii and crosslinking studies also indicate that chicken Ii assembles as a trimer. The chicken Ii can furthermore bind the human MHC class II (HLA-DR1). Many of the functional properties between the chicken Ii and its mammalian orthologs are thus maintained in spite of their sequence differences.

Structure-based design guides the improved efficacy of deacylation transition state analogue inhibitors of TEM-1 beta-Lactamase(,)

Transition state analogue boronic acid inhibitors mimicking the structures and interactions of good penicillin substrates for the TEM-1 beta-lactamase of Escherchia coli were designed using graphic analyses based on the enzyme's 1.7 A crystallographic structure. The synthesis of two of these transition state analogues, (1R)-1-phenylacetamido-2-(3-carboxyphenyl)ethylboronic acid (1) and (1R)-1-acetamido-2-(3-carboxy-2-hydroxyphenyl)ethylboronic acid (2), is reported. Kinetic measurements show that, as designed, compounds 1 and 2 are highly effective deacylation transition state analogue inhibitors of TEM-1 beta-lactamase, with inhibition constants of 5.9 and 13 nM, respectively. These values identify them as among the most potent competitive inhibitors yet reported for a beta-lactamase. The best inhibitor of the current series was (1R)-1-phenylacetamido-2-(3-carboxyphenyl)ethylboronic acid (1, K(I) = 5.9 nM), which resembles most closely the best known substrate of TEM-1, benzylpenicillin (penicillin G). The high-resolution crystallographic structures of these two inhibitors covalently bound to TEM-1 are also described. In addition to verifying the design features, these two structures show interesting and unanticipated changes in the active site area, including strong hydrogen bond formation, water displacement, and rearrangement of side chains. The structures provide new insights into the further design of this potent class of beta-lactamase inhibitors.

Myb binding proteins: regulators and cohorts in transformation

The c-Myb and v-Myb proteins are transcription factors that regulate cell proliferation and differentiation. Both Myb proteins have been shown to interact with a number of cellular proteins, some of which are transcription factors that cooperate to activate specific promoters, while others regulate the transcriptional activity of Myb in specific contexts. By comparing and analysing the types of proteins that bind Myb, and the conserved domains of Myb that interact with other proteins, conclusions can be drawn regarding the role of specific partner proteins in the regulation of gene expression, cell proliferation and disease.

Pim-1 kinase and p100 cooperate to enhance c-Myb activity

The pim-1 oncogene is regulated by hematopoietic cytokine receptors, encodes a serine/threonine protein kinase, and cooperates with c-myc in lymphoid cell transformation. Using a yeast two-hybrid screen, we found that Pim-1 protein binds to p100, a transcriptional coactivator that interacts with the c-Myb transcription factor. Pim-1 phosphorylated p100 in vitro, formed a stable complex with p100 in animal cells, and functioned downstream of Ras to stimulate c-Myb transcriptional activity in a p100-dependent manner. Thus, Pim-1 and p100 appear to be components of a novel signal transduction pathway affecting c-Myb activity, linking all three to the cytokine-regulated control of hematopoietic cell growth, differentiation, and apoptosis.

Tumor necrosis factor alpha gene regulation: enhancement of C/EBPbeta-induced activation by c-Jun

Tumor necrosis factor alpha (TNF alpha) is a key regulatory cytokine whose expression is controlled by a complex set of stimuli in a variety of cell types. Previously, we found that the monocyte/macrophage-enriched nuclear transcription factor C/EBPbeta played an important role in the regulation of the TNF alpha gene in myelomonocytic cells. Abundant evidence suggests that other transcription factors participate as well. Here we have analyzed interactions between C/EBPbeta and c-Jun, a component of the ubiquitously expressed AP-1 complex. In phorbol myristate acetate (PMA)-treated Jurkat T cells, which did not possess endogenous C/EBPbeta, expression of c-Jun by itself had relatively little effect on TNF alpha promoter activity. However, the combination of C/EBPbeta and c-Jun was synergistic, resulting in greater than 130-fold activation. This effect required both the leucine zipper and DNA binding domains, but not the transactivation domain, of c-Jun, plus the AP-1 binding site centered 102/103 bp upstream of the transcription start site in the TNF alpha promoter. To determine if C/EBPbeta and c-Jun might cooperate to regulate the cellular TNF alpha gene in myelomonocytic cells, U937 cells that possess endogenous C/EBPbeta and were stably transfected with either wild-type c-Jun or the transactivation domain deletion mutant (TAM-67) were examined. U937 cells expressing ectopic wild-type c-Jun or TAM-67 secreted over threefold more TNF alpha than the control line in response to PMA plus lipopolysaccharide. Transient transfection of the U937 cells expressing TAM-67 suggested that TAM-67 binding to the -106/-99-bp AP-1 binding site cooperated with endogenous C/EBPbeta in the activation of the -120 TNF alpha promoter-reporter. DNA binding assays using oligonucleotides derived from the TNF alpha promoter suggested that C/EBPbeta and c-Jun interact in vitro and that the interaction may be DNA dependent. Our data demonstrate that the TNF alpha gene is regulated by the interaction of the ubiquitous AP-1 complex protein c-Jun and the monocyte/macrophage-enriched transcription factor C/EBPbeta and that this interaction contributes to the expression of the cellular TNF alpha gene in myelomonocytic cells. This interaction was unique in that it did not require the c-Jun transactivation domain, providing new insight into the cell-type-specific regulation of the TNF alpha gene.

Point mutations in v-Myb disrupt a cyclophilin-catalyzed negative regulatory mechanism

The c-Myb protein is controlled by intramolecular interactions, and point mutations can enhance its oncogenic activity. We tested whether conformational changes regulate c-Myb and found that Cyp-40, a widely distributed cyclophilin and peptidyl-prolyl isomerase, could inhibit c-Myb DNA binding activity. Inhibition by Cyp-40 required both its C-terminal protein-interaction domain, which bound specifically to c-Myb, and its N-terminal catalytic domain and was blocked by the competitive inhibitor cyclosporin A. Cyp-40 failed to bind or inhibit the oncogenic derivative v-Myb, which has a mutated Cyp-40 binding site. These results suggest that mutations in v-Myb allow it to evade a negative regulatory mechanism mediated by enzymes such as Cyp-40, and implicate peptidyl-prolyl isomerases in the regulation of transcription, transformation, and differentiation.

Magnetic resonance properties of ex vivo breast tissue at 1.5 T

The magnetic resonance absorption spectrum, T1 and T2 relaxation time distributions, and magnetization transfer properties of ex vivo breast tissue have been characterized at 1.5 T and 37 degrees C. The fraction of fibroglandular tissue within individual tissue samples (n = 31) was inferred from the tissue volumetric water content obtained by integration of resolvable broad-line fat and water resonances. The spectroscopically estimated water content was strongly correlated with that extracted enzymatically (Pearson correlation coefficient 0.98, P < < 0.01), which enabled the assignment of principal relaxation components for fibroglandular tissue (T2=0.04+/-0.01, T1=1.33+/-0.24 s), and for adipose tissue (T2=0.13+/-0.01, T1=0.23+/-0.01 s, and T2=0.38+/-0.03, T1=0.62+/-0.16 s). Th e relaxation components for fibroglandular tissue exhibited strong magnetization transfer, whereas those for adipose tissue showed little magnetization transfer effect. These results ultimately have applicability to the optimization of clinical magnetic resonance imaging and research investigations of the breast.

Dermal interstitial glucose as an indicator of ambient glycemia

OBJECTIVE

Using a novel minimally invasive (< or = 1.4 mm) technique to sample minuscule (0.5 microliter) amounts of dermal interstitial fluid (ISF), we assessed the accuracy of its glucose concentrations in predicting concurrently measured venous plasma and capillary plasma glucose concentrations.

RESEARCH DESIGN AND METHODS

A total of 67 adult (37 male and 30 female) volunteers (57 with and 10 without diabetes) with venous plasma glucose levels from 1.6 to 28.4 mmol/l underwent forearm ISF, antecubetal venous, and fingertip capillary sampling.

RESULTS

Rank correlations were 0.974 for ISF 1 vs. 2, 0.954 for ISF vs. venous, 0.935 for ISF vs. capillary, and 0.987 for venous vs. capillary. Median absolute differences were 0.53 mmol/l for ISF 1 vs. 2, 1.33 mmol/l for ISF vs. venous, 1.06 mmol/l for ISF vs. capillary, and 0.56 mmol/l for capillary vs. venous. Equations expressing ISF glucose as a function of venous and capillary glucose and equations expressing capillary glucose as a function of venous glucose had slopes of 0.995, 0.936, and 1.021, respectively (none significantly different from unity), and intercepts of 1.03 mmol/l (P = 0.024), 0.94 mmol/l (P = 0.131), and 0.56 mmol/l (P = 0.041), respectively. Error grid analysis of ISF vs. venous glucose and of capillary vs. venous glucose showed that 97% of the measurements fell within grids A and B.

CONCLUSIONS

Dermal ISF sampling is a bloodless minimally invasive technique that provides a medium for glucose measurement, the concentrations of which closely reflect ambient glycemia to a degree comparable with that of capillary glucose measurements.

The EVES motif mediates both intermolecular and intramolecular regulation of c-Myb

The c-Myb transcription factor is a proto-oncoprotein whose latent transforming activity can be unmasked by truncation of either terminus. Because both ends of Myb are involved in negative regulation, we tested whether they could associate in a two-hybrid assay and identified a carboxy-terminal motif that interacts with the amino-terminal DNA-binding domain. The EVES motif is highly conserved in vertebrate c-Myb proteins and contains a known site of phosphorylation previously implicated in the negative regulation of c-Myb. Interestingly, a related EVES motif is present in p100, a ubiquitously expressed transcriptional coactivator found in diverse species. We show that p100 interacts with and influences the activity of c-Myb, implicating it in the regulation of c-Myb, differentiation, and cell growth. Our results suggest that Myb is regulated by a novel mechanism in which intramolecular interactions and conformational changes control the intermolecular associations among Myb, p100, and the transcriptional apparatus.

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.

C/EBP beta regulation of the tumor necrosis factor alpha gene

Activated macrophages contribute to chronic inflammation by the secretion of cytokines and proteinases. Tumor necrosis factor alpha (TNF alpha) is particularly important in this process because of its ability to regulate other inflammatory mediators in an autocrine and paracrine fashion. The mechanism(s) responsible for the cell type-specific regulation of TNF alpha is not known. We present data to show that the expression of TNF alpha is regulated by the transcription factor C/EBP beta (NF-IL6). C/EBP beta activated the TNF alpha gene promoter in cotransfection assays and bound to it at a site which failed to bind the closely related protein C/EBP alpha. Finally, a dominant-negative version of C/EBP beta blocked TNF alpha promoter activation in myeloid cells. Our results implicate C/EBP beta as an important regulator of TNF alpha by myelomonocytic cells.

Myb and NF-M: combinatorial activators of myeloid genes in heterologous cell types

The c-Myb transcription factor regulates the differentiation of immature erythroid, lymphoid, and myeloid cells, although only the latter cells become transformed by the v-myb oncogene. These are also the only cells that express the Myb-regulated gene mim-1, suggesting that Myb requires tissue-specific, cooperating factors to activate such genes. Here, we investigated the tissue-specific regulation of the mim-1 promoter and found that it not only contains binding sites for Myb but also for NF-M, a myeloid-specific transcription factor that probably corresponds to mammalian C/EBP beta. Both types of binding sites were found to be required for full activity of the promoter. Remarkably, ectopic coexpression of Myb and NF-M proteins in erythroid cells or fibroblasts was sufficient to induce endogenous markers of myeloid differentiation, like the mim-1 and lysozyme genes. Our results indicate that c-Myb and NF-M proteins act as a bipartite, combinatorial signal that regulates the expression of myeloid-specific genes, even in heterologous cell types.

The NF-M transcription factor is related to C/EBP beta and plays a role in signal transduction, differentiation and leukemogenesis of avian myelomonocytic cells

Retroviral oncogenes encode nuclear regulators of gene expression or signal transduction molecules, such as protein kinases, which stimulate the activity of cellular transcription factors. Here we describe the cloning of NF-M, a myeloid-specific transcription factor related to C/EBP beta, which is a target of activated protein kinases. NF-M stimulates the expression of the gene encoding cMGF, a myeloid cell-specific growth factor, creating an autocrine growth loop crucial to oncogene transformation of myeloid cells. The NF-M protein bound directly to the cMGF gene promoter and activated its transcription, even in erythroid cells where the promoter is usually inactive. In addition, a truncated, dominant-negative form of NF-M inhibited cMGF expression in macrophages, indicating that NF-M is required for the normal activation of the gene. When multipotent hematopoietic progenitor cells were stimulated to differentiate, NF-M expression was induced at a very early stage, suggesting that the transcription factor plays a role in lineage commitment. The stimulation of transformed myelomonocytic cells or of normal peripheral blood macrophages with kinases or LPS or TPA respectively, led to the rapid redistribution of NF-M protein from the cell bodies to the nucleus, consistent with the notion that NF-M was directly affected by such treatments. Our data indicate that NF-M plays a key role in myelomonocytic differentiation, in signal transduction during macrophage activation and in the development of myelogenous leukemia.

Unusual properties of a replication-defective mutant SV40 large T antigen

The C11A mutant of SV40 large T antigen is unable to support the replication of viral origin containing DNA (ori-DNA) in vivo or in vitro. The mutation within C11A at residue 522 (pro-->ser) is located within the presumptive ATPase region of T antigen. While C11A T antigen was previously reported to be defective in ATPase and DNA helicase activities, it was shown to be capable of binding specifically to DNA containing the viral replication origin. As the positions of many conditional mutations of SV40 T antigen are located within the ATPase domain we asked whether C11A might also exhibit temperature-sensitive defects. We found that several activities of C11A T antigen are conditionally defective. C11A T antigen was able to hydrolyze ATP, assemble into hexamers, and display ATP-dependent alterations in DNA binding and ori-DNA structure at 33 degrees but not 41 degrees. Wild-type T antigen did not exhibit temperature-sensitive defects in these activities. C11A T antigen was completely unable to unwind ori-DNA at either temperature. This defect in unwinding was trans-dominant; C11A T antigen inhibited ori-DNA unwinding by wild-type T antigen. These data show that a mutant displaying a nonconditional defective phenotype may contain a subset of relevant properties that are temperature sensitive.

Expression patterns of c-myb and of v-myb induced myeloid-1 (mim-1) gene during the development of the chick embryo

The v-myb oncogene of the acute avian leukemia virus E26 encodes a transcription factor that directly regulates the promyelocyte-specific mim-1 gene (Ness, S.A., Marknell, A. and Graf, T. Cell, 59, 1115–1125). We have investigated the relationship between the c-myb proto-oncogene and the transcription of the mim-1 gene both in vitro and in vivo. We demonstrate that the c-myb protein can transactivate the transcription of mim-1 in a transient transfection assay. In the chick embryo, we confirm that mim-1 is specifically expressed during granulopoiesis and we show that the expression of c-myb and mim-1 are perfectly correlated in the granulocytic spleen and pancreas. However we suggest that mim-1 is efficiently transcribed in the absence of c-myb in the yolk sac and in the promyelocytes at the onset of the colonization of the bursa of Fabricius. On the other hand c-myb transcripts detected in the early hemopoietic progenitor cells, in lymphoid cells and in proliferative epithelia are never associated with mim-1 transcription. We conclude that the granulocyte-specific mim-1 gene is regulated by c-myb-dependent and c-myb-independent mechanisms depending upon the environment in which granulocytic precursor cells differentiate.

Proposed structure for the DNA-binding domain of the Myb oncoprotein based on model building and mutational analysis

Myb-related proteins from plants to humans are characterized by a DNA-binding domain which contains two to three imperfect repeats of approximately 50 amino acids each. Based on the evolutionary conservation of specific residues, secondary structural predictions suggest an arrangement of alpha helices homologous to that seen in the homeodomains, members of the helix-turn-helix family of DNA-binding proteins. We have used molecular modelling in conjunction with site-directed mutagenesis to test the feasibility of this structure. We propose that each Myb repeat consists of three alpha helices packed over a hydrophobic core which is built around the three highly conserved tryptophan residues. The C-terminal helix forms part of the helix-turn-helix motif and can be positioned into the major groove of B-form DNA, allowing prediction of residues critical for specificity of interaction. Modelling also allowed positioning of adjacent repeats around the major groove over an 8 bp binding site.

Mutations in v-myb alter the differentiation of myelomonocytic cells transformed by the oncogene

Chick myelomonocytic cells transformed by the v-myb oncogene-containing viruses E26 and AMV differ in that the former resemble myeloblasts and express the v-myb-regulated granulocyte-specific mim-1 gene, while the latter resemble monoblasts and are mim-1 negative. We constructed a series of AMV-E26 chimeras and localized the critical differences between these viruses to three point mutations within the second repeat of the v-myb DNA binding domain. These three positions are altered in the v-myb protein of AMV relative to the proteins encoded by c-myb or E26 v-myb. Back mutating AMV v-myb at any of these three sites restored the oncogene's ability to activate the mim-1 gene. Surprisingly, two of these changes led to the transformation, in vitro and in vivo, of cells having a promyelocyte-like phenotype. These results indicate that different forms of v-myb impose alternate phenotypes of differentiation on transformed myeloid cells, probably by regulating unique sets of differentiation-specific genes.

Ectopic expression of the erythrocyte band 3 anion exchange protein, using a new avian retrovirus vector

A retrovirus vector was constructed from the genome of avian erythroblastosis virus ES4. The v-erbA sequences of avian erythroblastosis virus were replaced by those coding for neomycin phosphotransferase, creating a gag-neo fusion protein which provides G418 resistance as a selectable marker. The v-erbB sequences following the splice acceptor were replaced by a cloning linker allowing insertion of foreign genes. The vector has been tested in conjunction with several helper viruses for the transmission of G418 resistance, titer, stability, transcription, and the transduction and expression of foreign genes in both chicken embryo fibroblasts and the QT6 quail cell line. The results show that the vector is capable of producing high titers of Neor virus from stably integrated proviruses. These proviruses express a balanced ratio of genome length to spliced transcripts which are efficiently translated into protein. Using the Escherichia coli beta-galactosidase gene cloned into the vector as a test construct, expression of enzyme activity could be detected in 90 to 95% of transfected target cells and in 80 to 85% of subsequently infected cells. In addition, a cDNA encoding the avian erythrocyte band 3 anion exchange protein has been expressed from the vector in both chicken embryo fibroblasts and QT6 cells and appears to function as an active, plasma membrane-based anion transporter. The ectopic expression of band 3 protein provides a visual marker for vector function in these cells.

The v-myb oncogene product binds to and activates the promyelocyte-specific mim-1 gene

The v-myb oncogene induces myeloid leukemias in chickens, transforms myeloid cells in vitro, and encodes a sequence-specific DNA binding protein. We used differential hybridization to screen for v-myb-regulated genes in cells transformed by a temperature-sensitive mutant of the oncogene and identified a new gene, mim-1, which encodes a specifically expressed, secretable protein contained in the granules of both normal and v-myb-transformed promyelocytes. The promoter of the mim-1 gene contains three closely spaced binding sites for v-myb protein and is strongly activated by v-myb in a cotransfection assay. Synthetic copies of the binding sites are both necessary and sufficient to confer v-myb protein-dependent activation to a heterologous promoter. We conclude that mim-1 is a cellular gene that is directly regulated by the product of the v-myb oncogene.

Molecular cloning of the chicken myelomonocytic growth factor (cMGF) reveals relationship to interleukin 6 and granulocyte colony stimulating factor

Normal as well as retrovirally transformed avian myeloid precursor cells require the colony stimulating factor cMGF for their survival, proliferation and colony formation in vitro. cMGF has been shown to be a glycoprotein which is active in the picomolar concentration range. Co-expression of kinase type oncogenes in v-myb or v-myc transformed myeloid cells induces cMGF expression and confers factor independence via an autocrine mechanism. Here we describe the molecular cloning of cMGF from a myeloblast cDNA library and show that it is a 201 amino acid residue secretory protein which is modified by signal peptide cleavage and glycosylation during translocation into the lumen of membrane vesicles. A bacterially expressed trpE-cMGF fusion protein induces proliferation of E26 transformed myeloblasts in a cMGF bioassay suggesting that glycosylation is not absolutely necessary for biological activity. Sequence comparison reveals that cMGF is distantly related to G-CSF and IL-6.

Characterization of a new serotype of infectious pancreatic necrosis virus isolated from Atlantic salmon

Virus particles isolated from hatchery reared fish with infectious pancreatic necrosis (IPN) were neutralized by homologous immune sera but not by immune sera raised against IPN virus serotype 1, 2, and 3. This virus isolate, called the N1 strain, was detected in one year old Atlantic salmon (Salmo salar) during an outbreak with histopathological lesions of IPN and slightly increased mortality. The polypeptide pattern of N1 virus differed markedly from that of the three classical IPN virus serotypes. Double stranded RNA isolated from the N1 virus particles, co-migrated during agarose gel electrophoresis with nucleic acid isolated from the IPN virus Jasper and Ab strains. Nucleic acid hybridizations using low stringency washing conditions and a synthetic DNA oligonucleotide probe (representing the 3' end of the A segment of the Jasper strain) gave positive results with the IPN virus Jasper, Ab, Sp, and N1 strains. The results presented in this paper show that the N1 isolate differs immunologically and biochemically from the IPN virus serotypes 1, 2, and 3 and may represent a new serotype of IPNV.

v-myb dominance over v-myc in doubly transformed chick myelomonocytic cells

Chick myelomonocytic cells transformed by the v-myc oncogene resemble mature macrophages; those transformed by v-myb or v-myb,ets exhibit an immature phenotype. We have analyzed whether these oncogenes are capable of altering the differentiation phenotype of transformed cells by introducing both v-myc plus either v-myb or v-myb,ets into the same cells. Surprisingly, the doubly transformed cells were found to be essentially indistinguishable from cells transformed by v-myb or v-myb,ets alone even when they expressed a high level of v-myc protein. These results demonstrate that v-myb is dominant over v-myc and that, while v-myc induces cell proliferation without affecting differentiation, v-myb induces in the same target cells both proliferation and a block or reversal of differentiation.

Carboxyl-terminal sequences influence the import of mitochondrial protein precursors in vivo

The large subunit of carbamoyl phosphate synthase A [carbon-dioxide: L-glutamine amido-ligase (ADP-forming, carbamate-phosphorylating), EC 6.3.5.5] from Neurospora crassa is encoded by a nuclear gene but is localized in the mitochondrial matrix. We have utilized N. crassa strains that produce both normal and carboxyl-terminal-truncated forms of carbamoyl phosphate synthase A to ask whether the carboxyl terminus affects import of the carbamoyl phosphate synthase A precursor. We found that carboxyl-terminal-truncated precursors were directed to mitochondria but that they were imported less efficiently than full-length proteins that were synthesized in the same cytoplasm. Our results suggest that effective import of proteins into mitochondria requires appropriate combinations of targeting sequences and three-dimensional structure.

Simultaneous purification of three mitochondrial enzymes. Acetylglutamate kinase, acetylglutamyl-phosphate reductase and carbamoyl-phosphate synthetase from Neurospora crassa

The early enzymes of arginine biosynthesis in Neurospora crassa are localized in the mitochondrion and catalyze the conversion of glutamate to citrulline. The final conversion of citrulline to arginine occurs via two enzymatic steps in the cytoplasm. We have devised a method for the isolation and purification of three of the mitochondrial arginine biosynthetic enzymes from a single extract. Acetylglutamate kinase and acetylglutamyl-phosphate reductase (both products of the complex arg-6 locus) were purified to homogeneity and near homogeneity, respectively. The large catalytic subunit of carbamoyl-phosphate synthetase was also purified to homogeneity. The three enzymes were resolved into separate fractions by chromatography on three dye-ligand affinity resins, which are specific for nucleotide binding enzymes and have a high protein binding capacity. High performance liquid chromatography was employed in the final stages of purification and was extremely effective in fractionating both acetylglutamate kinase and acetylglutamyl-phosphate reductase from proteins with very similar properties, which were not removed by other techniques. The purified proteins were used to raise specific antisera against these proteins. Acetylglutamate kinase and acetylglutamyl-phosphate reductase were shown to be immunologically unrelated. This finding suggests that the arg-6 locus encompasses two nonoverlapping cistrons. The antisera raised against carbamoyl-phosphate synthetase has been shown to cross-react with related enzymes in Saccharomyces cerevisiae, Escherichia coli, and rat liver (Ness, S. A., and Weiss, R. L. (1985) J. Biol. Chem. 260, 14355-14362). Acetylglutamate kinase is a regulatory enzyme and has been shown to be feedback-inhibited by arginine. We have determined the submitochondrial localization of acetylglutamate kinase and the second arg-6 product, acetylglutamyl-phosphate reductase. Both enzymes were shown to be soluble matrix enzymes. We discuss the relevance of this finding with respect to possible mechanisms for end product inhibition of a mitochondrial enzyme by a cytoplasmic effector.

Carbamoyl-phosphate synthetases from Neurospora crassa. Immunological relatedness of the enzymes from Neurospora, bacteria, yeast, and mammals

Neurospora crassa contains two carbamoyl-phosphate synthetases: a mitochondrial enzyme (CPS-A) which supplies carbamoyl phosphate for arginine biosynthesis, and a nuclear enzyme whose product is used for the synthesis of pyrimidines. We have prepared antiserum against a highly purified preparation of the large subunit of CPS-A and have used the antiserum to demonstrate that the large subunit is, like most mitochondrially localized proteins, initially synthesized as a higher molecular weight precursor. The CPS-A antiserum cross-reacts with the nuclear enzyme, allowing us to identify the product of the complex N. crassa pyr-3 genetic locus as a protein with a subunit molecular weight of 180,000. Finally, we have found that the CPS-A antiserum also cross-reacts with carbamoyl-phosphate synthetases from bacteria, yeast, and mammals. The immunological relatedness of carbamoyl-phosphate synthetases from such diverse species suggests that the protein sequences required for carbamoyl phosphate production have been highly conserved during the course of evolution.