Role of phosphoinositide 3-OH kinase in cell transformation and control of the actin cytoskeleton by Ras

The pathways by which mammalian Ras proteins induce cortical actin rearrangement and cause cellular transformation are investigated using partial loss of function mutants of Ras and activated and inhibitory forms of various postulated target enzymes for Ras. Efficient transformation by Ras requires activation of other direct effectors in addition to the MAP kinase kinase kinase Raf and is inhibited by inactivation of the PI 3-kinase pathway. Actin rearrangement correlates with the ability of Ras mutants to activate PI 3-kinase. Inhibition of PI 3-kinase activity blocks Ras induction of membrane ruffling, while activated PI 3-kinase is sufficient to induce membrane ruffling, acting through Rac. The ability of activated Ras to stimulate PI 3-kinase in addition to Raf is therefore important in Ras transformation of mammalian cells and essential in Ras-induced cytoskeletal reorganization.

Reversion of the malignant phenotype of human breast cells in three-dimensional culture and in vivo by integrin blocking antibodies

In a recently developed human breast cancer model, treatment of tumor cells in a 3-dimensional culture with inhibitory beta1-integrin antibody or its Fab fragments led to a striking morphological and functional reversion to a normal phenotype. A stimulatory beta1-integrin antibody proved to be ineffective. The newly formed reverted acini re-assembled a basement membrane and re-established E-cadherin-catenin complexes, and re-organized their cytoskeletons. At the same time they downregulated cyclin D1, upregulated p21(cip,wat-1), and stopped growing. Tumor cells treated with the same antibody and injected into nude mice had significantly reduced number and size of tumors in nude mice. The tissue distribution of other integrins was also normalized, suggesting the existence of intimate interactions between the different integrin pathways as well as adherens junctions. On the other hand, nonmalignant cells when treated with either alpha6 or beta4 function altering antibodies continued to grow, and had disorganized colony morphologies resembling the untreated tumor colonies. This shows a significant role of the alpha6/beta4 heterodimer in directing polarity and tissue structure. The observed phenotypes were reversible when the cells were disassociated and the antibodies removed. Our results illustrate that the extracellular matrix and its receptors dictate the phenotype of mammary epithelial cells, and thus in this model system the tissue phenotype is dominant over the cellular genotype.

Dominant-negative mutants of cJun inhibit AP-1 activity through multiple mechanisms and with different potencies

We have previously described a dominant-negative mutant of cJun that lacks the transactivation domain (TAD) of cJun and prevents AP-1-mediated transcriptional activation by quenching endogenous Jun or Fos proteins. We now report the development of a panel of cJun mutants that have inactivating mutations in the TAD, DNA-binding domain (DBD), or leucine zipper domain. These mutants are all unable to activate transcription, but only TAD and DBD mutants function in a dominant-negative fashion by inhibiting both cJun-induced transcriptional activation and transformation induced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate in ras-transfected rat embryo cells. Although the TAD and DBD mutants both function as transdominant inhibitors, they work through different mechanisms and with different inhibitory potencies. The DBD mutants, which function by inhibiting DNA binding, are relatively weak inhibitors, whereas the TAD mutants inhibit by quenching and are much more potent. Dimerization assays demonstrate that mutations in the DBD decrease the dimerization affinity of these mutants with cJun. These results demonstrate that the most potent dominant-negative mutants of cJun are proteins that have intact DBDs and quench the activity of the endogenous transcription factors.

Changes in the cytoskeletal and nuclear matrix proteins in rat hepatocyte neoplastic nodules in their relation to the process of transformation

In a previous paper (Barboro et al., 1993, Biophys. J. 65, 1690-1699) we have shown that cancer development in the resistant hepatocyte model of Solt and Farber is characterized by the progressive unfolding of the higher-order structure of chromatin. A possible functional role of decondensation phenomena in cell transformation cannot be ruled out. Genetic activation involves the relaxation of the superstructure of chromatin, which may be, at least in part, modulated by its interaction with the nuclear matrix. Moreover, recent observations suggest that gene expression can be stimulated by alterations in the organization of the cytoskeleton. Therefore, we have characterized the changes in composition that the nuclear matrix-intermediate filament complex undergoes during the evolution of rat hepatocyte nodules. Dramatic changes in the expression of both the nuclear matrix and intermediate filament proteins occur during transformation; they are, however, related in a different way to the stages of carcinogenesis. Several new nuclear matrix proteins appear in early nodules, isolated 9 weeks after initiation. The subsequent evolution of persistent nodules is also characterized by discrete changes in the composition. Thus, the new synthesis of nuclear matrix proteins reflects the emergence of successive cellular populations, in line with the recent finding that a subset of components of the nuclear matrix is cell type-specific. In contrast, intermediate filament proteins undergo continuing changes. A new keratin with apparent molecular weight of 39 kDa, analogous to human keratin 19, appears in early nodules, and its expression steadily increases up to the 32nd week from initiation; at the same time, the amount of the proteolytic fragments of keratins A and D increases sharply. These findings suggest that the inappropriate expression of keratin 19 may be involved in the epigenetic activation of new cellular programs, through the rearrangement of the cytoskeleton which in turn may perturb nuclear matrix function.

Implication of involvement of rat chromosome #2 in spontaneous transformation of the rat-2 cell line

Using an in vitro model for cell transformation, the relationship between specific chromosomal aberration and phenotypic changes was studied at different passages of Rat-2 cell line. A marker chromosome resulting from a translocation [t(2;7)] was found to be associated with focus formation in soft agar. Conversely, the loss of this marker chromosome was found to be associated with phenotypic reversion. These results suggest an association of this marker chromosome with phenotypic transformation for the Rat-cell line.

Suppression of platelet-derived growth factor alpha- and beta-receptor mRNA levels in human fibroblasts by SV40 T/t antigen

It is known that down-regulation of cell surface platelet-derived growth factor (PDGF) receptors accompanies transformation by SV40. In this work human embryonic lung fibroblasts were used as a model system to study the effects of SV 40 on PDGF receptor expression. It is shown that transformation by SV 40 early region leads to a total loss of PDGF alpha-receptor and partial loss of beta-receptor mRNA. Microinjection experiments revealed that receptor down-regulation was a primary effect, and not only secondary to transformation and clonal selection. Total loss of PDGF alpha-receptor expression requires both large T and small t, and down-regulation of the PDGF alpha-receptor occurs independently of p53 and Rb binding to large T.

Comparative analysis of glucose and glutamine metabolism in transformed mammalian cell lines, insect and primary liver cells

Glucose and glutamine metabolism in several cultured mammalian cell lines (BHK, CHO, and hybridoma cell lines) were investigated by correlating specific utilization and formation rates with specific maximum activities of regulatory enzymes involved in glycolysis and glutaminolysis. Results were compared with data from two insect cell lines and primary liver cells. Flux distribution was measured in a representative mammalian (BHK) and an insect (Spodoptera frugiperda) cell line using radioactive substrates. A high degree of similarity in many aspects of glucose and glutamine metabolism was observed among the cultured mammalian cell lines examined. Specific glucose utilization rates were always close to specific hexokinase activities, indicating that formation of glucose-6-phosphate from glucose (catalyzed by hexokinase) is the rate limiting step of glycolysis. No activity of the key enzymes connecting glycolysis with the tricarboxylic acid cycle, such as pyruvate dehydrogenase, pyruvate carboxylase, and phosphoenolpyruvate carboxykinase, could be detected. Flux distribution in BHK cells showed glycolytic rates very similar to lactate formation rates. No glucose- or pyruvate-derived carbon entered the tricarboxylic acid cycle, indicating that glucose is mainly metabolized via glycolysis and lactate formation. About 8% of utilized glucose was metabolized via the pentose phosphate shunt, while 20 to 30% of utilized glucose followed pathways other than glycolysis, the tricarboxylic acid cycle, or the pentose phosphate shunt. About 18% of utilized glutamine was oxidized, consistent with the notion that glutamine is the major energy source for mammalian cell lines. Mammalian cells cultured in serum-free low-protein medium showed higher utilization rates, flux rates, and enzyme activities than the same cells cultured in serum-supplemented medium. Insect cells oxidized glucose and pyruvate in addition to glutamine. Furthermore, insect cells produced little or no lactate and were able to channel glycolytic intermediates into the tricarboxylic acid cycle. Metabolic profiles of the type presented here for a variety of cell lines may eventually enable one to interfere with the metabolic patterns of cells relevant to biotechnology, with the hope of improving growth rate and/or productivity.

Persistent effects of phorbol 12-myristate 13-acetate: possible implication of vesicle traffic

Relative to their normal counterparts, transformed epithelial cells have a distinctive and quantifiable three-dimensional shape. Biophysical and mathematical methods are used to distinguish these extremes in cells from two lines, cultured from rat liver and tracheal epithelium, respectively. Cells adopted a more transformed-looking configuration transiently when exposed to phorbol 12-myristate 13-acetate (PMA) (Plummer and Heckman, [1990] Exp. Cell Res., 188:66-74). The purpose of the present work was to dissect the physiological processes involved in the shape change. Ruffling activity, known to be PMA-stimulated in other cells, was investigated. Although the ruffles appeared less robust than normal, PMA stimulated ruffling activity over a 5 h period. The number of sites where ruffling was initiated declined by 5 h, however, and suppression was seen by 10 h. Cells from both lines adopted the transformed shape configuration when exposed for 2 h to monensin. When the subset of shape features changed by this treatment was compared with those originally changed during transformation, it was found that monensin-treated cells mimicked the features of transformed cells. Its effect on ruffling was, however, unlike PMA's. Thus, the phenotype was unlikely to arise from ruffling itself but might be a process driven by ruffling. Chloroquine also stimulated cells to assume characteristics of transformed cells. Since both it and monensin could interfere with endosomes and with the processing of endocytosed contents, this was a likely site of action. Experiments were done to determine whether PMA also affected the processing of extracellular fluids. When the accumulation of horseradish peroxidase (HRP) was measured, the rate was found to be higher in PMA-treated cells from 5 min, the earliest time assayed, onward. The results suggest that the transformed type of cell in these cell lines showed a constitutive dilation and/or reorganization of some portion of the endosomal pathway.

Growth hormone receptor: structure and signal transduction

The growth hormone receptor (GHR) belongs to the superfamily of transmembrane proteins that includes the prolactin receptor and a number of cytokine receptors. Two forms exist for the GHR: the full-length membrane-bound human receptor is a protein of 620 amino acids with a single transmembrane region; and the GH binding protein (GHBP) is a short soluble from corresponding to the extracellular domain of the full-length receptor. In rodents, GHBP is encoded by a specific mRNA of 1.2-1.5 kb, whereas in man and other species GHBP is believed to result from proteolytic cleavage of the membrane receptor. Growth hormone binding protein prolongs the half-life of GH but other functions for GHBP remain to be demonstrated. Recombinant GHBP complexed to human GH shows a 2:1 stoichiometric crystal structure. Growth hormone-induced dimerization of the cell surface GHR appears to be a prerequisite for biological activity of the hormone. JAK2 has been identified as a tyrosine kinase associated with GHR and other receptors of the superfamily. Binding of GH to its receptor results in dimerization of the GHR, phosphorylation of JAK2 and of the GHR. Other substrates for JAK2 have to be identified. Transcription factors belonging to the STAT (signal transducers and activators of transcriptions) family are involved in the transcriptional effects of GH. The activity of mutants of the GHR has been measured in functional tests to identify sequences of the cytoplasmic domain of the receptor that are important for signal transduction. A proline-rich sequence, called Box I, conserved among members of the receptor family has been shown to be crucial for GH effects on gene transcription. MAP kinase activity and cell proliferation. The C-terminal region of the GHR is required for tyrosine phosphorylation of the receptor and for a hormonal effect on gene transcription, whereas only 46 membrane proximal amino acids of the cytoplasmic domain are necessary for activation of JAK2 and transduction of the GH proliferative signal. Much work remains to be done to identify other protein kinases and signalling molecules involved in the mechanism of action of GH.

p19Skp1 and p45Skp2 are essential elements of the cyclin A-CDK2 S phase kinase

In normal human fibroblasts, cyclin A-CDK2 exists in a quaternary complex that contains p21 and PCNA. In many transformed cells, p21 disappears, and a substantial fraction of cyclin A-CDK2 complexes with p9CKS1/CKS2, p19, and p45. To investigate the significance of these rearrangements, we have isolated cDNAs encoding p19 and p45. In vitro reconstitution demonstrated that binding of p19 to cyclin A-CDK2 requires p45. Addition of these proteins to the kinase had no substantial effect on the kinase activity in vitro. Interference with p45 function in vivo by microinjection of antibodies or antisense oligonucleotides prevented entry into S phase in both normal and transformed cells. Cyclin A-CDK2 has previously been identified as a kinase whose activity is essential for S phase. Our results identify p45 as an essential element of this activity. The abundance of p45 is greatly increased in many transformed cells. This could result in changes in cell cycle control that contribute to the process of cellular transformation.

Serine phosphorylation in the NH2 terminus of p53 facilitates transactivation

Murine tumor suppressor p53 is phosphorylated in the NH2-terminal transactivating domain at serines 9, 18, and 37. Change of any one of these serines to either alanine or aspartic acid did not alter p53 suppression of transformation of rat embryo fibroblasts by activated ras and E1A. Change of any two of these serines to alanines, however, led to a significant decrease in suppressor function. Substitution of alanines for all three serines caused the most severe loss of suppression and also reduced transactivation functions. The triple substitution had no apparent effects on intracellular accumulation or localization of p53, oligomerization, DNA binding, or interaction with the TFIID TATA-binding protein. In contrast, triple substitution of aspartic acid for serines 9, 18, and 37 had minimal effects on suppression and transactivation by p53. These results argue strongly that phosphorylation of serines 9, 18, and 37 facilitates the suppression and transactivation functions of p53.

Highly insect-resistant transgenic tobacco plants containing both B.t. and CpTI genes

The cowpea trypsin inhibitor (CpTI) gene was synthesized according to its cDNA sequence using DNA synthesizer and confirmed by DNA sequencing. The CpTI gene and modified Bacillus thuringiensis (B.t.) delta-endotoxin gene were cotransformed to tobacco explants mediated by Agrobacterium tumefaciens. The integrations of B.t and CpTI genes were confirmed by PCR and Southern hybridization. Three kinds of transgenic plants were obtained: (1) containing CpTI gene, (2) containing B.t gene, (3) containing both CpTI and B.t genes. Bioassays showed that all these transgenic plants were toxic to the larvae of Heliothis armigera and that the tobacco plants containing both genes had enhanced toxicity to larvae by comparison with plants containing only CpTI or B.t gene.

Microencapsulation and the grafting of genetically transformed cells as therapeutic strategies to rescue degenerating neurons of the CNS

A number of approaches have been developed to deliver growth factors within the central nervous system of adult mammals. Initially a variety of neurotrophic factors were administered either by single intracerebroventricular or local injections directly into brain tissues or via permanently installed cannulae for chronic administrations. More recently delivery systems including conjugates, biodegradable and non-biodegradable implants and microspheres as well as genetically engineered cells have been introduced in order to provide a prolonged supply of neurotrophic factors and to prevent their enzymatic degradation. In this review we examine a variety of means of delivering neurotrophic factors (mainly nerve growth factor) with the primary focus upon the use of microencapsulated neurotrophins and cells genetically modified to produce them. In addition, this review highlights some difficulties and future trends in the development of novel delivery systems hopefully more suitable for investigations in different areas of neuroscience.

Mutations which alter the kinetics of calcium transport alter the regulation of competence in Streptococcus pneumoniae

In Streptococcus pneumoniae, Ca2+ induces a stress response which is regulated by a proteic activator known as competence factor (CF). This stress response is expressed as the induction of competence for DNA uptake and genetic transformation in exponentially growing cultures and by autolysis in late exponential phase. DNA transport during competence can be described as a homeostatic response that prevents autolysis of the cultures. Electrogenic and cooperative calcium transport with a Hill number (nH) of 2 appears to mediate this Ca2+ response. Mutant strains altered in their kinetics for Ca2+ transport, with nHs of 1 and 4, were isolated and characterized in order to address the role of the kinetics of Ca2+ transport in the Ca2+ response. The reduced cooperativity of Ca2+ uptake in mutant strain Cp2200 was associated with an absolute requirement for added CF to develop competence and with resistance to autolysis. The enhanced cooperativity of Ca2+ uptake in mutant strain Cp3300 was associated with facilitated competence and hypersensitivity to autolysis. Moreover, the mutation carried by strain Cp3300 increases the CF response of previously described competence-defective mutants. The pleiotropic mutants Cp2200 and Cp3300 allowed us to demonstrate that cooperativity of transport determines the Ca2+ response in S. pneumoniae.

Tissue specific expression of an alpha-skeletal actin-lacZ fusion gene during development in transgenic mice

Transgenic mice carrying a chimaeric transgene containing 730 bp of the 5'-flanking sequences and the entire first intron of the rat alpha-skeletal actin gene fused to the lacZ reporter gene have been produced by microinjection. The lacZ reporter gene was used to verify the suitability of using the rat alpha-actin promoter elements to target expression of genes of agricultural and therapeutic value exclusively to skeletal and heart muscle cells and fibres of transgenic mice. Expression of the transgene indicates a tightly regulated developmental and muscle specific control of the rat alpha-skeletal actin gene, making it a useful promoter for gene targeting to muscle tissues. The cells destined to form muscle tissues in these transgenic mice are readily visualized in intact embryos by staining for beta-galactosidase activity, making them a suitable animal model for studying the origin and development of skeletal and cardiac muscle tissues.

Expression of a human S-adenosylmethionine decarboxylase cDNA in transgenic tobacco and its effects on polyamine biosynthesis

S-adenosylmethionine decarboxylase (SAMDC; EC 4.1.1.50) is a key regulatory enzyme in the polyamine biosynthetic pathway. Numerous studies have shown that the enzyme activity and polyamine levels are generally correlated with cellular growth in plants, animals and bacteria. In order to gain more insight into the role of polyamines in plants, human SAMDC cDNA under control of 35S promoter of cauliflower mosaic virus, along with a neomycin phosphotransferase gene, was transferred to tobacco (Nicotiana tabacum cv.Xanthi) via Agrobacterium tumefaciens. Transgenic plants showed the presence of SAMDC mRNA and a 2-4-fold increase in SAMDC activity. In the transformed tissues, putrescine levels were significantly reduced, while spermidine content was 2-3 times higher than the control tissues. Cellular spermine content was either increased or remained unchanged. Excised leaf segments from transformed plants frequently produced shoots even on callus inducing medium.

Expression of human lysozyme mRNA in the mammary gland of transgenic mice

Owing to its inherent antimicrobial effect and positive charge, the expression of human lysozyme in bovine milk could be beneficial by altering the overall microbial level and the functional and physical properties of the milk. We have used transgenic mice as model systems to evaluate the expression of human lysozyme containing fusion gene constructs in the mammary gland. Expression of human lysozyme was targeted to the mammary gland by using the 5' promoter elements of either the bovine beta (line B mice) or alpha s1 (line H mice) casein genes coupled to the cDNA for human lysozyme. Expression of human lysozyme mRNA was not found in mammary tissue from any of line B mice. Tissues were analysed from six lines of H mice and two, H6 and H5, were found to express human lysozyme mRNA in the mammary gland at 42% and 116%, respectively, of the levels of the endogenous mouse whey acidic protein gene. At peak lactation, female mice homozygous for the H5 and H6 transgene have approximately twice the amount of mRNA encoding human lysozyme as hemizygous animals. Expression levels of human lysozyme mRNA in the mammary gland at time points representing late pregnancy, early, peak and late lactation corresponded to the profile of casein gene expression. Human lysozyme mRNA expression was not observed in transgenic males, virgin females or in the kidney, liver, spleen or brain of lactating females. A very low level of expression of human lysozyme mRNA was observed in the salivary gland of line H5.

Multiple pathways for gene activation in rodent cells by the smaller adenovirus 5 E1A protein and their relevance to growth and transformation

By immunoprecipitating protein products from virus-infected baby rat kidney (BRK) cells with specific antibodies, we found that the smaller, 243 residue (243R) E1A protein of human adenovirus 5 (Ad5) activated expression of the virus genes for E1B 55K, E2A 72K, E3 19K, hexon, fibre and penton base and the cellular gene for PCNA. The 243R protein also activated the E2A 72K gene in several rodent cell lines. In transient expression assays, this protein trans-activated the E2 early and major late promoters, suggesting that its effect was at least partially transcriptional. Similar assays with mutants of the E2 early promoter suggested that the ATF- and distal E2F-binding sites were required for this activation. Using mutant viruses with deletions in E1A, we found evidence for three separate pathways by which the 243R protein activated gene expression: one depended on sequences in exon 1 required for this protein to bind to p300, a second depended on sequences in exon 1 required for the protein to bind to pRb and the third appeared to be independent of exon 1 altogether and to depend on exon 2. The relative importance of these pathways for activation varied with the gene and cell. We conclude that a major role of E1A in the transformation of BRK cells by Ad5 is to activate specific genes by at least the first two pathways.

A conditional mutant of vRel containing sequences from the human estrogen receptor

The mechanism by which the v-rel oncogene of the avian Rev-T retrovirus transforms chicken spleen cells is not known. We have created v-rel mutants that show conditional properties by fusing sequences encoding the ligand-binding domain of the human estrogen receptor (ER) in-frame at the 3' end of the v-rel oncogene. Two vRel-ER fusion proteins showed estrogen-dependent subcellular localization in chicken embryo fibroblasts (CEF): vRel-ER proteins were located in the cytoplasm of CEF in the absence of estrogen and were located in the nucleus of CEF in the presence of estrogen. Wild-type vRel was located in the nucleus of CEF in the presence or absence of estrogen. Mobility shift assays using extracts from infected CEF showed that the ability of vRel-ER to bind DNA was also dependent on estrogen. However, the ability of vRel-ER to repress transcription from kappa B site-containing promoters was not dependent on estrogen. Finally, we were able to isolate a vRel-ER-transformed avian spleen cell line whose growth is dependent on estrogen; this indicates that a vRel function is needed for both the initiation and the maintenance of the transformed state. The vRel-Er protein may be useful for determining genes controlled by vRel.

Binding of bovine papillomavirus E1 to the origin is not sufficient for DNA replication

Replication of the bovine papillomavirus (BPV-1) DNA requires both the viral E1 and E2 gene products. The minimal origin of replication, which resides in a 60-basepair fragment centered on the unique HpaI site of the BPV-1 genome, can be bound by the E1 protein and is flanked by E2 binding sites. The integrity of the region surrounding the unique HpaI restriction enzyme site is important for E1 binding and DNA replication, but the E2 binding sites are not required. The ability of E1 to complex with E2 and the requirement for both factors in DNA replication have led to the hypothesis that the E1/E2 complex may have a direct role in replication. Therefore we have studied mutations in the BPV-1 origin region for E1, E2, and E1/E2 complex binding and for their effect on transformation and replication in the context of the complete viral genome. Transformation and DNA replication were observed with some mutated viral genomes dramatically reduced for E1 binding. These mutated origins could bind significant amounts of E1 in the presence of E2, suggesting that binding of the E1/E2 complex could compensate for the loss of E1 binding in DNA replication. One mutation, with an eight-nucleotide insertion at the HpaI site, was still bound by E1 and the E1/E2 complex, yet did not replicate or transform efficiently. Thus although the binding of E1 or the E1/E2 complex to the origin appears to be necessary for replication, it is not sufficient.

Induction of pre-B lymphoid leukemia following reconstitution of lethally irradiated mice with v-erb-B virus-infected bone marrow progenitor cells

We have previously shown that v-erb-B contained within a recombinant murine retroviral vector is capable of transforming pre-B lymphocytes (M. Miller, A. K. Kennewell, and G. Symonds, Leukemia, 6: 18-28, 1992) and early erythroid precursor cells [blast-forming units (erythroid) (M. Miller, A. Kennewell, Y. Takayama, A. Bruskin, J. M. Bishop, G. Johnson, and G. Symonds, Oncogene, 5: 1125-1131, 1990)] in vitro. To determine the sites and nature of v-erb-B-induced transformation in vivo, the hematopoietic systems of lethally irradiated mice were repopulated with v-erb-B-infected bone marrow. All mice became moribund within 4-12 weeks of reconstitution, with a median onset of disease at 6 weeks. Histopathological and flow cytometric evaluation of tissues from diseased mice, as well as morphological and phenotypic analysis (cytochemical as well as molecular) of the cell lines established from the mice, revealed that all but one of the mice examined at postmortem had developed a pre-B lymphoid leukemia or lymphoma. Abnormally high levels of mast cells in the spleen and bone marrow of the remaining mouse indicated a mast cell disease. The development of pre-B lymphoid malignancy in the majority of the reconstituted mice indicates a marked predisposition of v-erb-B to transform cells of the pre-B lymphoid lineage. The reconstitution of lethally irradiated mice with v-erb-B virus-infected bone marrow provides a model system for the analysis of events involved in the initiation and maintenance of acute lymphoid leukemia.

Establishment and maintenance of stable spatial patterns in lacZ fusion transformants of Polysphondylium pallidum

Polysphondylium pallidum cells were transformed with a construct containing the Dictyostelium discoideum ecmA promoter fused to a lacZ reporter gene. Two stably transformed lines, one in which beta-galactosidase (beta-gal) is expressed in apical cells of the fruiting body (p63/2.1), and one in which it is expressed in basal cells (p63/D), have enabled us to infer how cells move during aggregation and culmination. Several types of cell movement proposed to occur during slime mold culmination, such as random cell mixing and global cell circulation, can be ruled out on the basis of our observations. Cells of the two transformant lines express beta-gal very early in development. In both cases, stained cells are randomly scattered in a starving population. By mid to late aggregation, characteristic spatial patterns emerge. Marked cells of p63/2.1 are found predominantly at tips of tight aggregates; those of p63/D accumulate at the periphery. These patterns are conserved throughout culmination, showing that marked cells maintain their relative positions within the multicellular mass following aggregation. Neither the apical nor the basal pattern appears to be regulated within the primary sorogen by de novo gene expression or by cell sorting as whorls are formed. However, marked cells within a whorl re-establish the original pattern in secondary sorogens. This must be achieved by cell migration, since beta-gal is not re-expressed.

Mutational analysis of mouse Wnt-1 identifies two temperature-sensitive alleles and attributes of Wnt-1 protein essential for transformation of a mammary cell line

The proto-oncogene Wnt-1 encodes a cysteine-rich, secretory glycoprotein implicated in virus-induced mouse mammary cancer and intercellular signaling during vertebrate neural development. To attempt to correlate structural motifs of Wnt-1 protein with its function, 12 mutations were introduced singly and in several combinations into the coding sequence of Wnt-1 cDNA by site-directed mutagenesis. Mutant alleles in a retroviral vector were tested for their ability to transform the mouse mammary epithelial cell line C57MG in two ways: by direct infection of C57MG cells and by infection of NIH3T3 cells that serve as donors of Wnt-1 protein to adjacent C57MG cells in a secretion-dependent (paracrine) assay. In addition, the synthesis and secretion of mutant proteins were monitored in multiple cell types by immunological assays. Deletion of the signal peptide demonstrated that transformation in both direct and paracrine assays depends upon entry of Wnt-1 protein into the endoplasmic reticulum. Changes in potential proteolytic processing sites (two basic dipeptides and a probable signal peptidase cleavage site) did not adversely impair biological activity or protein processing and uncovered a second site for cleavage by signal peptidase. Replacement of each of the four asparagine-linked glycosylation sites did not affect transforming activity at normal temperatures, but one glycosylation site mutant was found to be temperature-sensitive for transformation. An allele encoding a protein that lacks all four glycosylation sites was also transformation competent. In two of four cases, substitution of serine for a cysteine residue impaired transforming activity at the usual temperature, and transformation was temperature sensitive in a third case, implying that at least some of the highly conserved cysteine residues are important for Wnt-1 function.

Fluctuating asymmetry: a biological monitor of environmental and genomic stress

Increased fluctuating asymmetry (FA) of morphological traits occurs under environmental and genomic stress. Such conditions will therefore lead to a reduction in developmental homeostasis. Based upon temperature extreme experiments, relatively severe stress is needed to increase FA under field conditions. Increasing asymmetry tends, therefore, to occur in stressed marginal habitats. Genetic perturbations implying genomic stress include certain specific genes, directional selection, inbreeding, and chromosome balance alterations. It is for these reasons that transgenic organisms may show increased FA. As there is evidence that the effects of genomic and environmental stress are cumulative, organisms in a state of genomic stress may provide sensitive biological monitors of environmental stress.

The nature of extra-chromosomal maintenance of transforming plasmids in the filamentous basidiomycete Phanerochaete chrysosporium

The nature of extra-chromosomal maintenance of the transforming plasmid p12-6 in Phanerochaete chrysosporium was studied. Our results indicate that the plasmid is maintained in the fungal transformants extra-chromosomally as part of a larger endogenous plasmid (designated pME) of P. chrysosporium. Using the total DNA of p12-6 fungal transformants, p12-6, as well as a larger plasmid, p511, were recovered in recA- E. coli strains while only p12-6 was recovered in recA+ E. coli strains. The results also showed that the cytosine methylation system has no apparent effect on the strain-dependent recovery of p12-6 and p511 in E. coli from the total DNA of fungal transformants.

Molecular cloning of CSF-1 receptor from rat myoblasts. Sequence analysis and regulation during myogenesis

We have isolated and sequenced a cDNA (mrfms) encoding rat c-fms gene (CSF-1 receptor) from proliferating L6 alpha 1 myoblasts. The predicted amino acid sequence was highly identical with the c-fms protein found in monocytes and macrophages (98, 76 and 84% identity from mouse, cat and human c-fms proteins, respectively). The mechanisms responsible for the regulation of mrfms gene expression during myogenesis were examined. Mrfms products were observed during proliferation of L6 alpha 1 myoblasts and were downregulated during differentiation. Run-on transcription assays demonstrated that the mrfms gene was transcriptionally active only in undifferentiated myoblasts. These findings suggested that mrfms levels in L6 alpha 1 myoblasts are controlled by transcriptional mechanisms. The half-life of mrfms transcripts was found to be at least 5 hr while inhibition of protein synthesis with cycloheximide (CHX) decreased this half-life to 30 min without changes in the rate of mrfms gene transcription. In addition oncogenic transformation of L6 alpha 1 myoblasts by the v-fms induced constitutive upregulation of mrfms mRNAs, and nuclear run-on assays demonstrated that mrfms transcription was not growth-factor dependent. Furthermore, these findings with others previously published indicate that mrfms gene products may play a role in the normal and neoplastic growth of muscular cells.

Synthesis of a highly efficient cDNA library

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The FIS protein binds and bends the origin of chromosomal DNA replication, oriC, of Escherichia coli

The FIS protein (factor for inversion stimulation) is known to stimulate site-specific recombination processes, such as the inversion of the G segment of bacteriophage Mu, by binding to specific enhancer sequences. It has also been shown to activate transcription from rRNA promoters both in vitro and in vivo. We have identified a specific binding site for FIS in the center of the origin of chromosomal DNA replication, oriC. The DNA bends upon FIS binding. Occupation of the FIS site and binding of DnaA, the initiator protein, to its adjacent binding site (R3) are mutually exclusive. A fis mutant strain can not be efficiently transformed with plasmids which carry and replicate from oriC, suggesting that FIS is required for minichromosome replication.

Analysis of unstable RNA transcripts of insecticidal crystal protein genes of Bacillus thuringiensis in transgenic plants and electroporated protoplasts

We have examined expression of several insecticidal crystal protein (ICP) genes of Bacillus thuringiensis in transgenic tobacco plants and electroporated carrot protoplasts. We determined that low levels of lepidopteran toxin cryIA(b) ICP gene expression in plants and electroporated carrot cells is due to RNA instability. We used a series of 3' deleted by cryIA(b) constructs directed by the cauliflower mosaic virus 35S promoter to demonstrate that this instability is minimally contained in the first 579 bases of the gene in both systems. This instability may result from 5'----3' as well as 3'----5' RNA metabolism. The coleopteran toxic cryIIIA gene was also examined in electroporated carrot cells, and found to be poorly expressed. A model for improvement of ICP RNA stability in plants is presented.

Different promoter regions control level and tissue specificity of expression of Agrobacterium rhizogenes rolB gene in plants

Expression of the rolB gene of A. rhizogenes T-DNA triggers root differentiation in transformed plant cells. In order to study the regulation of this morphogenetic gene, the GUS reporter gene was placed under the control of several deleted fragments of the rolB 5' non-coding region: carrot disc transformations and the analysis of transgenic tobacco plants containing these constructions identified the presence of distinct regulatory domains in the rolB promoter. Two regions (located from positions -623 to -471 and from -471 to -341, from the translation start codon) control the level but not the tissue specificity of rolB expression: progressive deletions of the rolB promoter starting from position -1185 to -341, although at different levels, maintained the same pattern of GUS expression-maximal in root meristems and less pronounced in the vascular tissue of aerial organs. Further deletion of 35 bp, from -341 to -306, drastically affected tissue specificity: GUS activity was still clearly detectable in the vascular tissue of the aerial organs while expression in the root meristem was totally suppressed. Analysis of transgenic embryos and seedlings confirmed that distinct promoter domains are responsible for meristematic (root) and differentiated (vascular) expression of rolB. Finally, we present data concerning the effects of plant hormones on the expression of rolB-GUS constructions.

Differential accumulation of four phaseolin glycoforms in transgenic tobacco

An intron-less phaseolin gene was used to express phaseolin polypeptides in transgenic tobacco plants. The corresponding amounts of phaseolin immunoreactive polypeptides and mRNA were similar to those found in plants transformed with a bean genomic DNA sequence that encodes an identical beta-phaseolin subunit. These results justified the use of the intron-less gene for engineering of the phaseolin protein by oligonucleotide-directed mutagenesis. Each and both of the two Asn residues that serve as glycan acceptors in wild-type phaseolin were modified to prevent N-linked glycosylation. Wild-type (beta wti-) and mutant phaseolin glycoforms (beta dgly1, beta dgly2 and beta dgly1,2) were localized to the protein body matrix by immunogold microscopy. Although quantitative slot-blot hybridization analysis showed similar levels of phaseolin mRNA in transgenic seed derived from all constructs, seed from the beta dgly1 and beta dgly2 mutations contained only 41% and 73% of that expressed from the wild-type control; even less (23%) was present in seed of plants transformed with the phaseolin beta dgly1,2 gene. Additionally, the profile of 25-29 kDa processed peptides was different for each of the glycoforms, indicating that processing of the full-length phaseolin polypeptides was modified. Thus, although targeting of phaseolin to the protein body was not eliminated by removal of the glycan side-chains, decreased accumulation and stability of the full-length phaseolin protein in transgenic tobacco seed were evident.

Barley aleurone layer cell protoplasts as a transient expression system

Protoplasts were prepared from barley aleurone layers using 'Onozuka' cellulase digestion and purification through a Percoll gradient. Protoplasts prepared by this procedure had a viability ranging from 60% to 80% during the first two days of culture. They were responsive to gibberellic acid (GA) as measured by the stimulation of alpha-amylase synthesis. The GA stimulation was counteracted by abscisic acid (ABA). In the presence of polyethylene glycol (PEG), the protoplasts took up exogenously added plasmid DNA containing the reporter gene coding for chloramphenicol acetyl transferase (CAT) linked to a 35S promoter from cauliflower mosaic virus (CaMV) or to barley alpha-amylase gene promoters and expressed CAT activity. Therefore, barley aleurone layer protoplasts are suitable for analysis of hormone-responsive elements in hydrolase genes.

Genetic alterations in human gastric cancer

Most types of human tumors display a consistent set of genetic alterations that are thought to play a role in tumor development and progression. In the case of gastric carcinomas, consistent genetic changes have been difficult to identify because (1) the tumor DNA samples are often heavily contaminated with DNA from normal stromal cells and (2) the tumors are heterogeneous in origin. However, with the recent application of more refined molecular genetic techniques, it has become clear that gastric carcinomas display some of the same genetic alterations observed in other common carcinomas. These changes include point mutation of the ras oncogene and the p53 tumor suppressor gene, gene amplification, and chromosomal loss of heterozygosity.

[Design of an expression integrative vector and its application for introducing the human recombinant alfa interferon gene into plants]

Integrative expression vector pST6 was developed for dicote plant transformation. The vector contains neomycin phosphotransferase gene under control of PNOS promoter which confers kanamycin resistance to transformed plant cells. The vector also includes expression cassette with strong constitutive 35S CaMV promoter for cloning of foreign genes. The human recombinant alfa interferon gene has been inserted into the expression cassette of pST6. Recombinant plasmid obtained was transferred into Agrobacterium tumefaciens cells, where the plasmid integrated into disarmed Ti plasmid pVG2260. Transgenic tobacco plants were obtained via transformation of leaf discs. It was determined that the interferon gene was inserted into plant genome. Transcription and translation of human interferon was observed in the plants transformed.

Silver accumulation and resistance in Escherichia coli R1

E. coli R1 contains at least 2 large plasmids (83 and 77 kb) while E. coli S1 was previously cured of the 83 kb plasmid. Transformation using artificial competence, high-voltage electroporation, and plasmid mobilization experiments with the mobilizing plasmid RP4, failed to ascertain the 83 kb plasmid was responsible for Ag(+)-resistance. Silver accumulation by an Ag(+)-sensitive E. coli S1 strain was 5-fold higher than an Ag(+)-resistant E. coli R1 strain. The Ag(+)-resistant E. coli R1 strain produced 33% more H2S and 32% more intracellular acid labile SH than the Ag(+)-sensitive E. coli R1 strain when grown in the absence of AgNO3. Hydrophobic interaction chromatography revealed E. coli R1 displayed higher cell surface hydrophobicity than E. coli S1. HPLC protein analysis of cell-free extracts also revealed differences between protein fractions in E. coli R1 and S1 strains.

Method and parameters for genetic transformation of Streptococcus sanguis Challis

A simple procedure for genetic transformation of Streptococcus sanguis Challis was developed and standardized. During the exponential phase of growth, cells became competent while growing as diplococci in broth containing 10% foetal calf serum. High levels of competence were maintained by the cultures for 60 min. Competent cells could be stored frozen without loss of competence for at least three years. Using total chromosomal DNA as donor, the dose-response curve for transformation of a point mutation (streptomycin resistance) showed one-hit kinetics, as the DNA concentration varied from 0.000001 to 10 micrograms/ml. At 10 micrograms/ml, more than 2.2% of the colony-forming units were transformed to streptomycin resistance, while transforming activity remained detectable with 1 pg of DNA/ml. Optimal time of exposure of competent cells to transforming DNA was 30 min. The transformation reaction was inhibited at 0 and 4 degrees C, whereas it occurred efficiently both at 25 and 37 degrees C.

Transformation injury and the unicellular phenotype of malignant cells

In 1984, Philippe Shubik wrote in an editorial in the Journal of the National Cancer Institute that: 'In terms of general biology, the multicellular organisms have evolved a complex series of defensive responses to extracellular injury involving various inflammatory reactions and their systemic concomitants. Needless to say, these reactions are by no means always successful from the standpoint of the host and indeed may well be the immediate cause of the obvious ill effects noted. The unicellular organisms, in contrast, react to injury by dividing and moving. In the search for the features that may link chemical, physical, and viral carcinogens apart from their ability to induce neoplasia, only one characteristic in common is obvious, namely, their ability to produce intracellular change or injury while leaving the cell viable. Perhaps the initial and fundamental characteristics of neoplasia is a reversion of the cell to unicellular behavior. Division and invasiveness are the characteristics of the neoplastic cell, and increased motility certainly seems to be the most likely mechanism for invasion'. Dr. Shubik presented these views as a basis for 'further discussion' regarding the nature of the neoplastic response. We hope that this presentation will augment Shubik's plea by reviewing his idea in the context of our current knowledge of tumor development. In addition, we will attempt to integrate the concept of the unicellular behavior of tumor cells with Foulds' and subsequently Nowell's insightful hypothesis concerning tumor progression.

Expression of ras oncogene leads to down-regulation of protein kinase C

The effect of mutated c-Ha-ras expression on Ca2+ and phospholipid-dependent protein kinase C (PKC) activity during the process of transformation was analysed using an inducible metallothionein-ras hybrid oncogene system. A close correlation was found between the timing of ras expression and the loss of PKC enzymatic activity measured in a cell-free system. Examination of the subcellular distribution of the enzyme in inducible and constitutive ras-transformants revealed that expression of ras was associated with an apparent translocation of PKC to the plasma membrane concomitant with down-regulation of PKC enzymatic activity in particulate as well as cytosolic fractions. Quantitation of PKC protein utilizing a PKC-specific antiserum showed that ras expression was associated with a decrease in the total amount of PKC protein present in the cell. We conclude that transformation by c-Ha-ras is accompanied by down-regulation of PKC activity and that the basis of this effect may, to a large extent, lie in the down-regulation of the amount of PKC protein.

Dissemination of amikacin resistance gene aphA6 in Acinetobacter spp

The distribution of the aphA6 gene, encoding a 3'-aminoglycoside phosphotransferase type VI, was studied by dot blot hybridization with 115 amikacin-resistant Acinetobacter strains from various geographical areas. Nucleotide sequences related to aphA6 were found in 109 strains belonging to seven species. As inferred from results of Southern hybridization, dissemination of amikacin resistance in Acinetobacter spp. is due to a gene rather than a strain or plasmid epidemic.

Proportion of DNA gyrase mutants among quinolone-resistant strains of Pseudomonas aeruginosa

The proportion of DNA gyrase mutants among quinolone-resistant strains of Pseudomonas aeruginosa was examined by introducing the cloned wild-type Escherichia coli gyrA and gyrB genes. Of 101 spontaneous mutants of P. aeruginosa PAO505, 33 (33%) were found to have gyrA mutations. Among 17 clinical isolates, 12 (71%) had gyrA mutations and 1 (6%) had a gyrB mutation.

Penicillin-binding proteins and ampicillin resistance in Haemophilus influenzae

Ampicillin-resistant, non-beta-lactamase-producing isolates of Haemophilus influenzae contain a variety of penicillin-binding protein (PBP) patterns that differ from the single pattern of eight PBPs characteristic of susceptible strains. During genetic transformation of resistance, only some of the anomalies in PBP pattern were transformed, specifically those relating to the penicillin-binding capacities of PBPs 4 (Mr of 62,000) and 5 (Mr of 59,000) and, in some transformations, PBP 3 (Mr of 71,000). Comparison of the binding of penicillin by PBPs 4 and 5 of three resistant transformants (derived with DNA from different donors) revealed a decrease in the rate of PBP acylation and no appreciable change in the rate of deacylation as compared to the susceptible recipient. Thus, rapid turnover of these PBPs does not play a role. Retransformation studies confirm that altered PBPs 3, 4, and 5 are associated with resistance and suggest that these PBPs are major targets for the beta-lactam antibiotics in H. influenzae.

Biotinylated probes for epidemiological studies of drug resistance in Salmonella krefeld

A gene probe for ampicillin resistance and one for sulphonamide resistance were prepared to study the origin and the relation of multiple drug resistances in Salmonella krefeld. The resistance genes were cloned into the pACYC184 vector of Escherichia coli from a common plasmid of S. krefeld that encoded for resistance to ampicillin, chloramphenicol, kanamycin, streptomycin, sulphonamide and tetracycline resistance. Restriction map analysis and deletion analysis of a recombinant plasmid (pACSS1) showed that the gene determining ampicillin resistance was located on a 1.34 and 1.12 kb PstI fragment, and that the gene for sulphonamide resistance was located on a 0.85 kb PstI fragment. These fragments were used as probes. Their specificity was tested by colony hybridization with various bacterial species, including sensitive and resistance S. krefeld isolates. Further study indicated that the ampicillin resistance gene probe reacted with the gene for TEM-1 beta-lactamase and that the gene probe for sulphonamide resistance reacted with the gene for type II dihydropteroate synthase. The two probes were sufficiently specific to allow study of the epidemiology of resistance in S. krefeld and other enteric bacteria.

Malignant transformation of human endometrial stromal cells by transfection of c-myc: effects of pRSVneo cotransfection and treatment with MNNG

Stromal cells isolated from normal human endometrium were cotransfected in primary culture with pSVc-myc, a plasmid containing a truncated c-myc gene regulated by simian virus 40 promoter, and pRSV neo, a plasmid containing a neomycin resistance gene regulated by Rous sarcoma virus (RSV) promoter. These cells demonstrated properties of transformed cells in vitro, including altered morphology, focus formation, anchorage-independent growth, chromosomal alterations, and tumor formation in athymic mice. When these cells were treated subsequently with a direct-acting carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine, they demonstrated higher colony-forming efficiency in soft agar and reduced tumor latency. Cells transfected with pRSV neo alone exhibited some properties associated with neoplastic transformation, including altered morphology and formation of colonies in soft agar. It is presumed that in normal cells transfected with pRSV neo, RSV long terminal repeats activated cellular genes that normally regulate growth of human endometrial stromal cells.

Phenotypic effects of overexpression of PKC beta 1 in rat liver epithelial cells

We have used a previously described retroviral expression vector pMV7-PKC beta 1 to develop derivatives of two rat liver epithelial cell lines, K16 and K22, that stably express about tenfold-higher PKC activity than control cells. Despite these high levels of PKC, these cells did not exhibit gross morphologic changes, anchorage-independent growth, or tumorigenicity. K16PKC-4 and K22PKC-2, two lines with the highest PKC enzyme activity, were studied further in terms of several responses to the phorbol ester tumor promoter TPA. When treated with 100 ng/ml of TPA, the control K16MV7 and K22MV7 cells displayed a slight change in morphology, whereas the K16PKC-4 and K22PKC-2 cells displayed a marked change in morphology. Northern blot analyses demonstrated that TPA induced increased levels of fos, myc, phorbin, and ODC RNAs in control K16MV7 and K22MV7 cells, with maximum induction occurring at about 0.5, 1, 8, and 8 h, respectively. In K16PKC-4 and K22PKC-2 cells, TPA induction of phorbin and ODC RNAs was markedly enhanced, but this was not the case for myc and fos RNAs. In addition, the levels of myc RNA were constitutively higher in both K16PKC-4 and K22PKC-2 cells than in the control cells. Taken together, these results provide direct evidence that PKC plays a critical role in modulating the expression of myc, phorbin, and ODC RNAs. On the other hand, overexpression of PKC beta 1 is not itself sufficient to cause cell transformation.

Transformation in restriction-deficient Salmonella typhimurium LT2

Stable restriction-deficient, modification-proficient galE (JR501) and F'galE+ (JR502) strains of Salmonella typhimurium were constructed and the effects of restriction on transformation by plasmid pBR322 were tested. Several factors which affect transformation efficiency were systematically examined to determine optimum transformation conditions and a simplified method is presented.