Molecular cloning and characterization of mutant and wild-type human beta-actin genes

Expression of Hoxa2 in cells entering chondrogenesis impairs overall cartilage development

Vertebrate Hox genes act as developmental architects by patterning embryonic structures like axial skeletal elements, limbs, brainstem territories, or neural crest derivatives. While active during the patterning steps of development, these genes turn out to be down-regulated in specific differentiation programs like that leading to chondrogenesis. To investigate why chondrocyte differentiation is correlated to the silencing of a Hox gene, we generated transgenic mice allowing Cre-mediated conditional misexpression of Hoxa2 and induced this gene in Collagen 2 alpha 1-expressing cells committed to enter chondrogenesis. Persistent Hoxa2 expression in chondrogenic cells resulted in overall chondrodysplasia with delayed cartilage hypertrophy, mineralization, and ossification but without proliferation defects. The absence of skeletal patterning anomaly and the regular migration of precursor cells indicated that the condensation step of chondrogenesis was normal. In contrast, closer examination at the differentiation step showed severely impaired chondrocyte differentiation. In addition, this inhibition affected structures independently of their embryonic origin. In conclusion, for the first time here, by a cell-type specific misexpression, we precisely uncoupled the patterning function of Hoxa2 from its involvement in regulating differentiation programs per se and demonstrate that Hoxa2 displays an anti-chondrogenic activity that is distinct from its patterning function.

Mixl1 and oct4 proteins are transiently co-expressed in differentiating mouse and human embryonic stem cells

Embryonic stem cells (ESCs) have the capacity to form all the tissues in the body and hence, directed differentiation of ESCs along specific lineages represents a means to generate therapeutically useful cell types. It has been postulated that, during in vitro differentiation, ES cells sequentially pass through similar developmental stages as cells in the embryo. The availability of reagents that identify these stages would facilitate the monitoring and optimization of ESC differentiation. One key stage, the development of endodermal and mesodermal precursors in the early embryo, is marked by the transient expression of the transcription factor, Mixl1 and the stem cell gene, Oct4. In order to identify corresponding cells during ESC differentiation, we generated monoclonal antibodies to the Mixl1 protein that robustly detected both mouse and human proteins. Intracellular flow cytometry was used to show that approximately 90% of differentiating mouse ESCs transiently co-expressed Oct4 and Mixl1 proteins and that a subset of differentiating human ES cells also coexpressed MIXL1 and OCT4 proteins. These experiments have demonstrated for the first time by protein expression that both human and mouse ESCs passed through developmental stages during in vitro differentiation that corresponded to those observed in early mammalian development. Furthermore, these studies confirmed that anti-Mixl1 antibodies are a valuable reagent for monitoring ESC differentiation and will facilitate the efficient generation of clinically relevant cell types.

Treatment of surgically induced acute liver failure by transplantation of HNF4-overexpressing embryonic stem cells

OBJECTIVE

Tissue-specific stem cells from differentiating embryonic stem (ES) cells are both pluripotent and genetically flexible. Recent observations indicate that ES cells can differentiate into hepatocytes. Therefore, cell-based therapy can potentially be a therapeutic alternative to liver transplantation. In this study the treatment of acute liver failure in rats by transplantation of hepatocyte nuclear factor 4 (HNF4)-overexpressing ES cells was investigated.

METHODS

The HNF4 was transfected into ES cells and ES cell clones overexpressing HNF4 were selected. The levels of markers of hepatocyte differentiation, including albumin, transthyretin, glucose-6-phosphates (G-6-P) and SAPK/ERK kinase-1 (SEK1) mRNA, were tested in spontaneously differentiated HNF4-overexpressing ES cells by reverse transcription-polymerase chain reaction (RT-PCR). The ultrastructure of the spontaneously differentiated HNF4-overexpressing ES cells was examined by electron microscopy. To induce acute liver failure, Sprague-Dawley rats were subjected to 90% hepatectomy and given 5% oral dextrose. The rats were divided into three groups. The rats in the treatment group (n = 12) received intraliver injection of 2 x 10(7) undifferentiated HNF4-overexpressing ES cells from the same clone, the rats in control group 1 (n = 12) received 2 x 10(7) undifferentiated ES cells, and the rats in control group 2 (n = 12) received the same volume of media without any cells.

RESULTS

All rats in control group 1 and control group 2 died within 72 h, while 33% of rats that received undifferentiated HNF4-overexpressing ES cells transplantation survived more than 1 month. Spontaneously differentiated HNF4-overexpressing ES cells only expressed transthyretin mRNA. The cells were rich in mitochondrion and catalase-containing peroxisomes in ultrastructure.

CONCLUSIONS

Transplantation of ES cells could be a potential treatment in supporting life during acute liver insufficiency and could be a bridge to orthotopic liver transplantation.

Nuclear actin and actin-related proteins in chromatin remodeling

The existence and function of actin in the nucleus has been hotly debated for forty years. Recently, beta-actin was found to be a component of mammalian SWI/SNF-like BAF chromatin remodeling complexes and still more recently other SWI/SNF-related chromatin remodeling complexes in yeast, flies, and man. Although the function of actin in these chromatin remodeling complexes is only starting to be explored, the fact that actin is one of the most regulated proteins in the cell suggests that control of nuclear actin may be a critical regulatory point in the control of chromatin remodeling. Actin rapidly shuttles between the nucleus and the cytoplasm offering additional sites and modes of regulation. In addition, actin-related proteins (Arps) are also components of these chromatin remodeling complexes and have been implicated in transcriptional control in yeast. The observation that the BAF chromatin remodeling complex in which actin was originally identified, is also a human tumor suppressor complex necessary for the actions of the retinoblastoma protein indicates that the study of nuclear actin is likely to contribute to understanding cell growth control.

mRNA-specific reverse transcription-polymerase chain reaction from human tissue extracts

Reverse transcription-polymerase chain reaction (RT-PCR) has become the method of choice for detection of mRNA transcripts, including those of low abundance obtained from small precious samples of human tissue. A major confounding problem for standard reverse-transcription-priming strategies is the presence of contaminating genomic DNA (gDNA) carried over from the original "RNA" extract into the RT and PCR steps. The contaminating gDNA contains a processed pseudogene sequence-which lacks introns but contains a poly(A) tail-for commonly studied internal reference genes beta-actin and GAPDH, and target genes GSTM1, GSTP1, and others. These pseudogene sequences therefore confound standard-design "RNA-specific" PCR primer pairs which rely, for cDNA versus gDNA specificity, on the pair-spanning introns, or one of the individual primer oligos spanning an exon/exon splice site, because these features are lacking in processed pseudogene sequences. The result is false RT-PCR positives for these "housekeeper" genes in total RNA extracts; the gDNA processed pseudogene is mistaken for mRNA gene transcript. A universal RT primer has been designed that targets the poly(A) tail of mRNA and adds a unique tag sequence not otherwise existing in the human genome. Genomic DNA does not incorporate this RT-inserted unique tag. PCR is then performed using a transcript-specific forward primer and a reverse primer that is identical to the unique tag incorporated at RT. Only cDNA made with this RT primer is compatible with this reverse PCR primer, thus eliminating confounding signal from contaminating gDNA. This method performs RNA-specific qualitative and quantitative evaluation of gene expression, while preserving the sensitivity of standard RT-PCR techniques. Applications to low-copy transcripts in human samples are demonstrated.

Resistance of keratinocytes to TGFβ-mediated growth restriction and apoptosis induction accelerates re-epithelialization in skin wounds

The pleiotropic growth factor TGFβ plays an important role in regulating responses to skin injury. TGFβ targets many different cell types and is involved in all aspects of wound healing entailing inflammation,re-epithelialization, matrix formation and remodeling. To elucidate the role of TGFβ signal transduction in keratinocytes during cutaneous wound healing, we have used transgenic mice expressing a dominant negative type II TGFβ receptor exclusively in keratinocytes. We could demonstrate that this loss of TGFβ signaling in keratinocytes led to an accelerated re-epithelialization of full thickness excisional wounds accompanied by an increased proliferation in keratinocytes at the wound edge. Furthermore, we show that impaired TGFβ signaling in keratinocytes reduces apoptosis in re-epithelialized wounds of transgenic animals.

A cDNA array identified the transcription factor early growth response factor 1 (Egr1) as a target gene for TGFβ in late phases of the wound healing process. As a member of the immediate-early gene family, Egr1 is upregulated shortly after injury and induces the expression of growth factor genes. We could demonstrate that Egr1 expression is also upregulated in skin wounds which have already undergone re-epithelialization. In conclusion, we attribute the enhanced re-epithelialization in our transgenics to the resistance of keratinocytes to TGFβ-mediated growth restriction and apoptosis induction. We also propose a new role for TGFβ induced Egr1 in late phase wound repair.

Specific changes to the mechanism of cell locomotion induced by overexpression of (β)-actin

Overexpression of (β)-actin is known to alter cell morphology, though its effect on cell motility has not been documented previously. Here we show that overexpressing (β)-actin in myoblasts has striking effects on motility, increasing cell speed to almost double that of control cells. This occurs by increasing the areas of protrusion and retraction and is accompanied by raised levels of (β)-actin in the newly protruded regions. These regions of the cell margin, however, show decreased levels of polymerised actin, indicating that protrusion can outpace the rate of actin polymerisation in these cells. Moreover, the expression of (β)*-actin (a G244D mutant, which shows defective polymerisation in vitro) is equally effective at increasing speed and protrusion. Concomitant changes in actin binding proteins show no evidence of a consistent mechanism for increasing the rate of actin polymerisation in these actin overexpressing cells. The increase in motility is confined to poorly spread cells in both cases and the excess motility can be abolished by blocking myosin function with butanedione monoxime (BDM). Our observations on normal myoblasts are consistent with the view that they protrude by the assembly and cross linking of actin filaments. In contrast, the additional motility shown by cells overexpressing (β)-actin appears not to result from an increase in the rate of actin polymerisation but to depend on myosin function. This suggests that the additional protrusion arises from a different mechanism. We discuss the possibility that it is related to retraction-induced protrusion in fibroblasts. In this phenomenon, a wave of increased protrusion follows a sudden collapse in cell spreading. This view could explain why it is only the additional motility that depends on spreading, and has implications for understanding the differences in locomotion that distinguish tissue cells from highly invasive cell types such as leucocytes and malignant cells.

Identification of an optimal Ncx binding sequence required for transcriptional activation

The Ncx gene encodes a homeobox containing transcription factor that belongs to the Hox11 gene family. We determined specific Ncx protein binding consensus DNA sequences. Optimal Ncx binding sequences were 5'-CGGTAATTGG-3' (TAAT core) and 5'-CGGTAAGTGG-3' (TAAG core), which coincided with the Hox11 binding sequence. Both Ncx and Hox11 could bind to the TAAT and the TAAG core oligonucleotide in vitro. However, they could efficiently transactivate the reporter plasmid linked to the TAAT core sequence but not to the TAAG core sequence. Thus, Ncx and Hox11 act as transcriptional activators via their target sequence, 5'-CGGTAATTGG-3'.

A supraspliceosome model for large nuclear ribonucleoprotein particles based on mass determinations by scanning transmission electron microscopy

Pre-mRNA splicing is an important regulatory step in the expression of most eukaryotic genes. In vitro studies have shown splicing to occur within 50-60 S multi-component ribonucleoprotein (RNP) complexes termed spliceosomes. Studies of mammalian cell nuclei have revealed larger complexes that sediment at 200 S in sucrose gradients, termed large nuclear RNP (lnRNP) particles. These particles contain all factors required for pre-mRNA splicing, including the spliceosomal U snRNPs and protein splicing factors. Electron microscopy has shown them to consist of four apparently similar substructures. In this study, mass measurements by scanning transmission electron microscopy of freeze-dried mammalian lnRNP preparations, both confirm the similarity between the lnRNP particles and reveal the mass uniformity of their subunits. Thus, the tetrameric lnRNP particle has a mass of 21.1(+/-1.6) MDa, while each repeating subunit has a mass of 4.8(+/-0.5) MDa, which is close to the estimated mass of the fully assembled 60 S spliceosome. The 1.9 MDa discrepancy between the lnRNP particle's mass and the cumulative masses of its four subunits may be attributed to an additional domain frequently observed in the micrographs. Notably, strands and loops of RNA were often seen emanating from lnRNP particles positively stained with uranyl formate. Our results support the idea that the nuclear splicing machine is a supraspliceosome complex. For clarity, we define spliceosomes devoid of pre-mRNA as spliceosome cores, and propose that the supraspliceosome is constructed from one pre-mRNA, four spliceosome cores, each composed mainly of U snRNPs, and additional proteins. In this way a frame is provided to juxtapose exons about to be spliced.

Tumor necrosis factor-alpha regulates expression of vascular endothelial growth factor receptor-2 and of its co-receptor neuropilin-1 in human vascular endothelial cells

Tumor necrosis factor-alpha (TNF-alpha) modulates gene expression in endothelial cells and is angiogenic in vivo. TNF-alpha does not activate in vitro migration and proliferation of endothelium, and its angiogenic activity is elicited by synthesis of direct angiogenic inducers or of proteases. Here, we show that TNF-alpha up-regulates in a dose- and time-dependent manner the expression and the function of vascular endothelial growth factor receptor-2 (VEGFR-2) as well as the expression of its co-receptor neuropilin-1 in human endothelium. As inferred by nuclear run-on assay and transient expression of VEGFR-2 promoter-based reporter gene construct, the cytokine increased the transcription of the VEGFR-2 gene. Mithramycin, an inhibitor of binding of nuclear transcription factor Sp1 to the promoter consensus sequence, blocked activation of VEGFR-2, suggesting that the up-regulation of the receptor required Sp1 binding sites. TNF-alpha increased the cellular amounts of VEGFR-2 protein and tripled the high affinity 125I-VEGF-A165 capacity without affecting the Kd of ligand-receptor interaction. As a consequence, TNF-alpha enhanced the migration and the wound healing triggered by VEGF-A165. Since VEGFR-2 mediates angiogenic signals in endothelium, our data indicate that its up-regulation is another mechanism by which TNF-alpha is angiogenic and may provide insight into the mechanism of neovascularization as occurs in TNF-alpha-mediated pathological settings.

Early region 4 modulates adenovirus DNA replication by two genetically separable mechanisms

Three viral proteins, all products of early region 2 (E2), participate directly in adenovirus DNA replication. Three products of early region 4 (E4) also affect viral DNA synthesis: the product of E4 ORF4 inhibits viral DNA accumulation, while the products of E4 ORFs 3 and 6 antagonize that effect of ORF4 expression. Because no E4 products are required for DNA synthesis, these proteins probably act indirectly. The E4 ORF3, 4, and 6 proteins all participate in aspects of the regulation of viral gene expression. To determine whether they modulate DNA replication by effects on expression of viral replication proteins, we examined E2 expression in E4 mutant-infected cells. In cells infected by ORF3-, 6- mutants, expression of ORF4 substantially depressed the steady-state levels of replication proteins and E2 mRNAs, reduced E2 transcription rates, and profoundly inhibited viral DNA replication. Thus, in the absence of E4 ORFs 3 and 6, ORF4 acts as a transcriptional regulator of E2 expression, and reduced replication protein levels largely account for the inhibition of DNA replication by ORF4. Cells infected by viruses that express ORFs 3 and 6 in addition to ORF4 accumulated much larger quantities of viral DNA than did cells infected by the ORF3-, 6-, 4+ mutant. Increased DNA accumulation was not accompanied by a comparable increase in E2 expression. Therefore, the ORF3 and 6 products counteract the ORF4-induced reduction of DNA replication by a mechanism other than reversing the inhibitory effect of ORF4 on E2 expression. The effect of ORF4 on E2 expression is consistent with its ability to regulate levels of the transcription factor AP-1 (Müller et al., 1992, J. Virol. 66, 5867-5878); the mechanism by which ORFs 3 and 6 enhance replication is unknown.

Activation of the lac repressor in the transgenic mouse

We have introduced sequences encoding the lac repressor of Escherichia coli into the genome of the mouse. One sequence was derived from the bacterial lac operon and the other was created by re-encoding the amino acid sequence of lacI with mammalian codons. Both versions are driven by an identical promoter fragment derived from the human beta-actin locus and were microinjected into genetically identical pronuclear stage embryos. All transgenes utilizing the bacterial coding sequence were transcriptionally silent in all somatic tissues tested. The sequence re-encoded with mammalian codons was transcriptionally active at all transgene loci and expressed ubiquitously. Using methylation-sensitive enzymes, we have determined the methylation status of lac repressor transgenes encoded by either the bacterial or mammalian sequence. The highly divergent bacterial sequence was hypermethylated at all transgene loci, while the mammalian sequence was only hypermethylated at a high copy number locus. This may reflect a normal process that protects the genome from acquiring new material that has an abnormally divergent sequence or structure.

Reinterpretation of the RACTK1 K+ channel

The RACTK1 cDNA cloned from rabbit kidney cortical collecting duct cells was associated with inwardly rectifying pH-regulated K+ channel activity (M. Suzuki, K. Takahashi, M. [keda, H Hayakawa, A. Ogawa, Y. Kawaguchi, and O. Sakai. Nature Lond. 367: 642-645, 1994). The deduced amino acid sequence of the encoded novel polypeptide lacked the signature sequence of a K(+)-selective pore region but predicted a topography suggestive of the inward rectifier K+ channel family. In subsequent articles a RACTK1 epitope was immunolocalized to the apical surface of kidney collecting duct and to arteriolar smooth muscle [M. Suzuki, T. Takigawa, K. Kimura, C. Koseki, and M. Imai. Am. J. Physiol. 269 (Cell Physiol, 38): C496-C503, 1995], and apamin-sensitive K+ currents displaying Ca(2+)-dependent and voltage-independent activation accompanied stable heterologous overexpression of RACTK1 [M. Suzuki, M. Murata, M. Ikeda, T. Miyoshi, and M. Imai. Am. J. Physiol. 270 (Cell Physiol, 39): C964-C968, 1996]. We now report that the "RACTK1" open reading frame is a frame-shifted translation of the antisense strand of an Escherichia coli gene member of a coenzyme A transferase gene family. "RACTK1" mRNA was absent from tissues free of E. coli contamination, and the "RACTK1" gene was undetectable in Southern blots of human and rabbit genomic DNA. We conclude that the immunostaining patterns and Ca(2+)-activated K+ channel activity heretofore attributed to RACTK1 must be otherwise explained.

Repair of some active genes in Cockayne syndrome cells is at the genome overall rate

Repair of UV (254 nm)-induced DNA damage in cells from patients with the genetic disease Cockayne syndrome (CS; CS3BE, CS2BE) has been examined in several different genomic regions. These regions include those that contain the actively transcribed beta-actin and adenosine deaminase (ADA) genes and the inactive insulin and 754 loci. The beta-actin, ADA and insulin regions are repaired at about the same rate, one which is equal to the genome overall repair rate. The 754 locus is repaired considerably more slowly. The insulin region is repaired at the same rate in both CS and normal cells as is the 754 locus. The only difference from normal is that the active genes, while repaired well, are not preferentially repaired relative to the genome overall. Our results are consistent with the hypothesis that the repair defect in CS is due to an inactive transcription-repair coupling factor (TRCF). However, the results also indicate that factors other than TRCF and active transcription must also promote repair of some regions relative to others in both normal and CS cells.

Inhibition of beta-amyloid formation identifies proteolytic precursors and subcellular site of catabolism

Cerebral deposition of beta-amyloid protein is a pathological feature central to Alzheimer's disease. Production of beta-amyloid by proteolytic processing of the beta-amyloid precursor protein (beta APP) is a critical initial step in beta-amyloidogenesis. We use an inhibitor of beta APP processing to block beta-amyloid peptide formation. Application of the inhibitor to cultured cells results in an accumulation of proteolytic intermediates of beta APP, enabling a precursor-product relationship between beta APP carboxy-terminal fragments and beta-amyloid peptides to be demonstrated directly. In the presence of inhibitor, these amyloidogenic carboxy-terminal fragments can be degraded to nonamyloidogenic products. The catabolism of beta APP carboxy-terminal intermediates and the formation of beta-amyloid peptides are likely to involve an early endosomal compartment as the subcellular site of processing.

Intragenic regions of the murine Pgk-1 locus enhance integration of transfected DNAs into genomes of embryonal carcinoma cells

Introduction of recombinant genes into mammalian cells in culture has been an important procedure in establishing the molecular mechanisms of various cellular processes. The efficiency with which plasmid borne recombinant genes are expressed following stable integration into genomes of embryonal carcinoma cells is low. Using the P19 embryonal carcinoma cells as recipients, we found that constructs carrying the promoter and intragenic regions of the murine Pgk-1 gene were expressed with high efficiency. This elevated expression was associated with increased numbers of copies of the transfected plasmid DNA stably associated with the genomes of recipient cells. The elevated plasmid copy numbers may result from enhanced ligation of transfected plasmids because cotransfected plasmids were also integrated in increased numbers. The enhanced integration and expression of transfected plasmids required active transcription through an intragenic region of Pgk-1, perhaps resulting in more recombinogenic plasmid DNAs.

Discovery and characterization of two novel human cancer-related proteins using two-dimensional gel electrophoresis

Comparative examination of protein synthesis in normal and neoplastic human fibroblasts led to the discovery of two novel microfilament proteins with roles in human neoplasia. One protein, a mutant beta-actin was found to convert nontumorigenic human fibroblasts to tumorigenicity. Recently, the oncogenic potential of this mutant beta-actin was verified independently and shown to alter the metastatic phenotype of human cells in conjunction with the myc and ras oncogenes. A second protein, leukocyte plastin, was discovered to be a marker of a majority of human cancer cells of nonhemopoietic origin. A survey of SV40-transformed human fibroblasts and human sarcoma and carcinoma cell types demonstrated that the L-plastin gene was activated at widely varying degrees in nearly all human cancer cells. Activation of the L-plastin gene was not detected in normal nonhemopoietic cells using sensitive reverse transcript-polymerase chain reaction, excepting those cells that expressed estrogen and progesterone receptors which mediate activation of L-plastin synthesis in reproductive tissues. Our most recent findings have revealed that activation of L-plastin synthesis in neoplastic cells that cannot phosphorylate L-plastin (e.g. those neoplastic cell types that express only trace amounts of L-plastin) results in the coinduction of two alternative inflammatory programs of gene expression which mediate cytolytic effects on surrounding cells. This inflammatory response appears to be mediated by "inappropriate" constitutive synthesis of L-plastin and failure of the induced cell to phosphorylate L-plastin. Our findings suggest explanations for the novel resistance of human cells to in vitro transformation and one role of oncogene activation in cancer. As a consequence of the interplay of two-dimensional (2-D) gel electrophoretic analyses with other sophisticated techniques of molecular biology, the formal characterization of two fundamentally important multigene families was completed with determination of many aspects of the structure and function of these proteins and their genes. The discovery and characterization of the mutant beta-actin and L-plastin and their relationship to the human neoplastic phenotype serve as useful models for the discovery of other important disease-related proteins/genes using 2-D gel electrophoresis.

Southwestern blot mapping of potential regulatory proteins binding to the DNA encoding plasminogen activator inhibitor type 2

In order to investigate the molecular basis for the regulated expression of plasminogen activator inhibitor type 2 (PAI-2), we sought to identify monocyte-derived nuclear factors which interact with the PAI-2 gene. We have explored the application of Southwestern blot mapping as an approach for identifying specific DNA-protein interactions and targeting potential regulatory DNA elements. The procedure involves an initial global screening of a crude preparation of nuclear proteins with radiolabelled DNA fragments (200-300 bp) derived from a large region (8.8 kb) of PAI-2. The bound DNA fragments are eluted and their location within PAI-2 mapped by Southern blot hybridization analysis. We have used this procedure to examine the differential binding of nuclear factors from the U937 monocytic cell in the absence and in the presence of the differentiating agent, 12-phorbol 13-myristate acetate (PMA), in order to identify proteins that bind specifically to the 5' flanking promoter region and first intron of PAI-2. Eleven DNA-binding proteins ranging in molecular mass from 27 to 92 kDa were identified, and the results define three regions of the gene which contain DNA-binding sites which may be involved in the transcriptional regulation of PAI-2. Deletion analysis using a series of 5' deletion mutants spanning PAI-2 fused to a chloramphenicol acetyltransferase-encoding reporter gene (cat) demonstrates that two of the regions identified by Southwestern blot mapping contain elements which can function to modulate PAI-2 expression in transient transfections of U937 cells.

Neuroepithelial carcinomas in mice transgenic with human papillomavirus type 16 E6/E7 ORFs

The effect of the human papillomavirus (HPV) oncogenes E6 and E7 was examined in transgenic mice with a construct containing the human beta-actin promoter regulating HPV16 E6 and E7 open reading frames. In the sole line of mice that transmitted the transgene, neuroepithelial tumors appeared at 2.5 months of life, and by 10 months, 87 of 122 (71%) of the animals were dead from brain tumors. The most frequent type of tumor (74%) was an anaplastic neuroepithelial tumor associated with the ependyma of the third and fourth ventricles, which locally invaded adjacent brain tissue and spread for considerable distances along the ventricular surface. The other two types of tumor were well-differentiated choroid plexus carcinomas (26%) and rare pituitary carcinomas (8.7%). HPV16 E6 RNA and E7 oncoprotein expression were demonstrated in tumor tissue and primary cell lines derived from the tumors. Examination of two tumor suppressor gene products, the retinoblastoma protein and p53, known to bind to HPV16 E7 and E6 oncoproteins, respectively, showed both were expressed in the primary tumor cell lines. These data support a causative role for the HPV oncoproteins in epithelial carcinogenesis.

Accumulation of transcripts coding for prion protein in human astrocytes during infection with human immunodeficiency virus

The abnormal isoforms of the normal cellular prion protein (PrP), also termed Scrapie-associated fibril protein, are assumed to be one causative factor of spongiform encephalopathies. The mRNA of PrP contains stem-loop structures which are very similar to the human immunodeficiency virus-1 (HIV-1) cis-acting sequence TAR within the LTR; both structures contain the pentanucleotide CUGGG in the loop, and the uridine- and adenine-bulge in the stem. In this study, using purified HIV-encoded trans-activator, Tat, and HIV-1 TAR-RNA or PrP-mRNA containing the stem-loop structure, we demonstrate by use of gel-retardation and filter binding assays that Tat binds to TAR- and PrP-RNA with the dissociation constants of 2.9 or 37.0 nM, respectively, at a molar ratio of 0.7 mol of Tat to 1 mol of RNA fragment. The Tat-RNA (TAR or PrP) complexes bind to protein(s) in the nuclear matrix, isolated from human astrocytes (glial fibrillary acidic protein positive brain cells). Infection of astrocytes with HIV-1 resulted in an increased level of PrP mRNA. The data presented led us to assume that certain sequences in the PrP mRNA might be targets for proteins acting in trans.

Genetic immunization is a simple method for eliciting an immune response

To produce an immune reaction against a foreign protein usually requires purification of that protein, which is then injected into an animal. The isolation of enough pure protein is time-consuming and sometimes difficult. Here we report that such a response can also be elicited by introducing the gene encoding a protein directly into the skin of mice. This is achieved using a hand-held form of the biolistic system which can propel DNA-coated gold microprojectiles directly into cells in the living animal. Genetic immunization may be time- and labour-saving in producing antibodies and may offer a unique method for vaccination.

A method for detecting the expression of a toxic gene in cultured cells

We have devised a rapid method for examining the expression of a toxin gene following in vitro transfection using a bacterial beta-galactosidase (lacZ) gene as a reporter gene. Ricin A chain DNA and the lacZ gene, both under the control of the immunoglobulin gene promoter and enhancer, were transfected into mouse fibroblast cells (L cells). Transient expression of the lacZ gene was detected 2 days after transfection by histochemical staining of the transfectants with 5-bromo-3-indolyl-beta-D-galactoside. Cotransfection of the ricin A chain gene resulted in a progressive reduction in the number of lacZ transfectants as the expressed toxin killed the cells. A ricin construct with the intervening sequence from the human beta-actin gene required 4 days instead of 2 days to produce the toxic effect. This is a useful method for examining the expression of toxin gene in a cell.

Repression of the human papillomavirus type 18 enhancer by the cellular transcription factor Oct-1

The role of cellular factors involved in the transcriptional regulation of the cancer-associated human papillomavirus type 18 (HPV18) is yet poorly understood. The presence of an Oct-1-binding site within the HPV18 upstream regulatory region led us to investigate the influence of Oct-1 on viral transcription. Cotransfection of Oct-1 expression plasmids together with luciferase reporter constructs containing HPV18 regulatory sequences indicated that Oct-1 can transcriptionally repress the HPV18 upstream regulatory region. In contrast, heterologous control regions were not affected by Oct-1. HPV18 cis elements that can be repressed by Oct-1 mapped to a 135-bp subregion of the viral constitutive enhancer. Analysis of an Oct-1 mutant defective in DNA binding suggested that HPV18 down-modulation does not require direct binding of Oct-1 to DNA. These results make Oct-1 a candidate factor involved in the intracellular surveillance of HPV18 transcription and support the notion of a host cell mechanism that can specifically repress HPV E6-E7 transforming gene expression.

Epigenetic control of tumor cell morphology

XC cell line derived from a single rat cell transformed by the Prague strain of Rous sarcoma virus produced morphologically different colonies. Among them, two distinct cell types consisting of thick, fusiform cells (L-type), and of flat, polygonal cells (R-type) were apparent. By repeated subclonings, pure cultures, L1 and R1, respectively, were obtained. These clones underwent morphological conversion during prolonged culture; L-type colonies appeared in the R-type clone and vice versa. The kinetic curve suggested that the conversion was multi-stepped. When inoculated into nude mice, L-type cells produced much larger tumors at a higher frequency than R-type cells, and the tumors induced by these two clones were histologically different. The expression of v-src gene was higher in L-type than in R-type cells at both mRNA and protein levels.

A nonsecretable cell surface mutant of tumor necrosis factor (TNF) kills by cell-to-cell contact

In addition to the induction of tumor regression, tumor necrosis factor (TNF) has been implicated as the causative agent in a number of pathologies, including cachexia, septic shock, rheumatoid arthritis, autoimmunity, and induction of HIV expression. We propose that this complex physiology might be manifest by different forms of TNF: the 17 kd secretory component, the 26 kd transmembrane form, or both. To determine whether the 26 kd form of TNF was biologically active and whether its biology differed from that of the secretory component, we generated uncleavable and solely secretable mutants of TNF and studied their biological activities. We found that an uncleavable mutant of the 26 kd cell surface transmembrane form of TNF kills tumor cells and virus-infected cells by cell-to-cell contact, and that TNF need not be internalized by its target to kill. Thus, the 26 kd integral transmembrane form of TNF may function in vivo to kill tumor cells and other targets locally in contrast to the systemic bioactivity of the secretory component.

Newly identified type of beta actin reduces invasiveness of mouse B16-melanoma

Low metastatic parent B16 melanoma and isolated B16-F1 cell lines have a third actin designated as beta m(Ax:previously). beta m actin is scantily or not at all detected in highly metastatic cell lines, such as B16-F10 and BL6. To directly assess the physiological role of beta m in phenotypic changes of B16 melanoma, we transfected expression plasmids of beta m into B16-F10 cells. The actin expressed in the transfectants is located largely in cytoskeletal fractions. The transfectants exhibited a larger number of stress fibers and a lower invasiveness than did the recipient cells. Thus, beta m actin plays an important role in the organization of actin stress fibers, the result being a decrease in invasiveness of B16 melanoma.

C-myc gene binding factors in peripheral blood mononuclear cells from patients with systemic lupus erythematosus (SLE)

We characterized the nuclear proteins with specific binding ability against c-myc gene by gel-shift assay in cell extracts of peripheral blood mononuclear cells (PBMC) from SLE patients and SLE-prone mice with use of distinct c-myc fragments. With the fragment named Fmyc in our experiments, two kinds of complexes which we call C1 and C2 respectively were found in PBMC from SLE patients and SLE-prone mice. The C1 was shown to be inducible in PBMC from healthy persons without nascent protein synthesis after lectin binding to the cell and found to be elevated in the SLE patients and in all of the established cell lines we examined. The C2 seemed to be peculiar to SLE subjects. The binding site of the C1 factor (C1F) and C2 factor (C2F) which forms C1 and C2 respectively with Fmyc appeared to be common and were found to reside at 51 kbp sequence (from XhoI to Sau3A) of exon I of c-myc gene. Interestingly, XhoI site of the binding site was highly demethylated in PBMC of SLE patients as compared with healthy persons. The roles of these binding factors for the pathogenesis of SLE are discussed.

A developmental study of the abnormal expression of alpha-cardiac and alpha-skeletal actins in the striated muscle of a mutant mouse

BALB/c mice possess a 5' duplication of the alpha-cardiac actin gene which is associated with abnormal levels of alpha-cardiac and alpha-skeletal actin mRNAs in adult cardiac tissue. This mutation therefore provides a potential tool for the study of the inter-relationship between the striated muscle actins. We have examined the expression of this actin gene pair throughout the development of skeletal and cardiac muscle in BALB/c mice. During embryonic and fetal development, the expression of these two genes is indistinguishable from that in normal mice, as determined by in situ hybridization. A quantitative postnatal study demonstrates that in the hearts of normal mice the level of alpha-cardiac actin mRNA declines, whereas that of alpha-skeletal actin increases. In mutant mice, these trends are exaggerated so that whereas normal mice have 95.8% alpha-cardiac mRNA and 4.2% alpha-skeletal mRNA in the adult heart, BALB/c mice have 52.4 and 47.6% of these mRNAs, respectively. This difference is also reflected at the protein level. In developing skeletal muscle, the expression of these genes follows kinetics similar to that observed in the heart with a decrease in the relative level of alpha-cardiac mRNA as the muscle matures. Cardiac actin mRNA levels are again lower in the mutant mouse, but here the effect is less striking because skeletal actin is the predominant isoform. These results are discussed in the context of the interaction between this actin gene pair in developing and adult striated muscle.

Expression of the three unlinked isocoding actin genes of Physarum polycephalum

The actin gene family in Physarum polycephalum contains four unlinked loci: ardA, ardB, ardC, and ardD. The ardA locus is complex and probably contains two genes which we designated ardA2-7 and ardA2-17. cDNA clones corresponding to the ardB and ardC loci were isolated. Nucleic acid sequencing showed that these two cDNAs coded for the only abundant form of Physarum actin, which is 96% homologous to human gamma-cytoplasmic actin. The ardA2-17 gene also codes for this same actin protein (Nader et al., Gene 48, 133-144, 1986). The coding regions of ardB and ardC differ by 15 nucleotides. A comparison of the ardB and ardC sequences with ardA2-17 showed 73 and 77 nucleotide substitutions, respectively, in the coding regions. The noncoding regions of these three sequences were not homologous to each other or to the noncoding regions of actin genes from other organisms. Southern genomic hybridizations indicated that the ardA2-7 and ardD genes have weak sequence similarities to the three isocoding actin genes and thus form a different subclass of the family. Northern hybridizations showed that the ardB and ardC transcripts varied in abundance but were present in all the developmental stages. No ardA2-17 transcripts were seen. The relative abundance of the ardB and ardC transcripts was measured in amoebae and plasmodia by S1 nuclease protection and dot hybridization assays. A ratio of approximately 3:1 for ardC versus ardB was found for both stages. P. polycephalum is the first organism shown to contain three unlinked isocoding actin genes, of which at least two are expressed.

Macromolecular changes accompanying immortalization and tumorigenic conversion in a human fibroblast model system

Mutagenesis of a diploid human fibroblast strain, KD, with the chemical carcinogen 4 nitroquinolin-1-oxide led to the isolation of stably immortalized neoplastic substrains. Four of these transformed strains, HuT-11, -12, -13, and -14, have been characterized in great detail with regard to morphology and changes in gene expression from the parental KD strain. The HuT-11, -12 and -13 substrains are immortalized and non-tumorigenic, in contrast to HuT-14 which is both immortalized and tumorigenic. The HuT-14 substrain expresses a defective beta-actin as a consequence of a point mutation in 1 of the 2 functional beta-actin alleles. All 4 HuT strains have induced expression of the phosphoprotein plastin and 2 EGF-related polypeptides, and down-regulated expression of the transformation-sensitive tropomyosin isoforms. KD and HuT cells expressing high levels of exogenous mutant beta-actin after gene transfection show morphological alterations. HuT-12 transfectants with excessive mutant beta-actin expression exhibit an elevated tumorigenic potential and tropomyosin-isoform switching characteristic of the tumorigenic HuT-14 strain.

Induction of gamma-interferon by avarol in human peripheral blood lymphocytes

Avarol is a cytostatic and anti-human immunodeficiency virus (HIV) agent. In this study, the avarol caused induction of gamma-interferon (IFN-gamma) in buffy coat cells (human peripheral blood lymphocytes) is demonstrated by immunological and molecular biological techniques. IFN-gamma production was detected after a 24-hr incubation period with avarol; maximal production was obtained after 5 days in the presence of the optimal avarol concentration of 0.75 microgram/ml. Blotting experiments using human IFN-gamma cDNA and beta-actin cDNA containing plasmids showed that in the absence of avarol no IFN-gamma transcripts were present in lymphocytes. Already after a 24-hr incubation with avarol, IFN-gamma gene induction was detected, and maximal induction was found after a 5-day incubation period. The enhanced IFN-gamma production seems to be caused by a change at the transcriptional and/or post-transcriptional level, but not during subsequent nucleocytoplasmic transport of mRNA. This molecular event is specific, at least in relation to the expression of the beta-actin gene. Our studies demonstrate that avarol displays, besides its potential anti-tumor and anti-HIV activity, a potential immunomodulating effect.

Regulation of expression of T cell gamma chain, L3T4 and Ly-2 messages in Abelson/Moloney virus-transformed T cell lines

Recent results have suggested that T cells may exist in two distinct pathways, one expressing alpha and beta chain of the T cell receptor genes with either or both of the cell surface markers CD4 and CD8, while the other is negative for these cell surface markers and expresses the T cell-specific gamma chain genes. The relationship between these two pathways is not known. In this study, we have examined a series of either Abelson virus or Moloney virus-derived T cell lines for their expression of these T cell receptor and cell surface marker genes. Results indicate that the Abelson T cell lines do not express the cell surface markers CD4 and CD8, but express relatively high levels of gamma chain transcripts. After culture of these cell lines with the phorbol ester phorbol myristate acetate and interleukin 2, a down-regulation of these gamma chain transcripts can be observed. More interestingly, we found that the Moloney virus-derived T cell lines, which express the cell surface markers CD4 and/CD8, contain high levels of alpha and beta chain T cell receptor transcripts but little or no gamma transcripts even though they have rearranged these latter genes. The gamma transcripts, however, can be induced to high levels after culture with phorbol myristate acetate and interleukin 2. In the process, the cell surface markers CD4 and CD8 and their transcripts were dramatically down-regulated resulting in cells with high levels of gamma chain transcripts and a CD4-CD8- phenotype. The regulation of expression of these genes is reversible. Taken together, these results indicate that the T cell receptor gamma chain genes and those of the cell surface markers CD4 CD8 can be regulated in vitro by external factors and it opens up the possibility of studying the regulatory sequences associated with these genes.

A 60-kDa polypeptide in mammalian cells with epitopes related to actin

We have identified a novel actin-related 60-kDa polypeptide in mammalian cells. The relatedness of this polypeptide to actin is indicated by its affinity for DNase I, two monoclonal anti-actin antibodies, and two independent peptide-specific anti-actin antibodies which bind to actin at around amino acid 244. It is not incorporated into cytoskeletal stress fibers, although it is a stable protein. Its expression (60-kDa polypeptide, pI of 5.4 to 5.5) is inhibited by the K+ ionophore, nonactin, which is known to collapse the energy-dependent translocation of cytoplasmically synthesized proteins into mitochondria.

Methylation of c-myc gene changes in human lymphoproliferative diseases

The degree of methylation at the c-myc proto-oncogene was found to change in human lymphoproliferative diseases, when examined using a methylation-sensitive restriction enzyme. In peripheral blood mononuclear cells (PBMC) c-myc DNA showed hypomethylation in human lymphoproliferative diseases, in comparison to normal subjects matched in age and sex. In cases of chronic lymphocytic leukemia (CLL), the change was amplified in the crisis. When the DNA was examined at the actin gene, no significant change was observed. The results suggest that the change in c-myc protooncogene methylation might become an important clue in understanding the relationship between levels of gene expression and methylation in human lymphoproliferative diseases.

Isolation of a mouse heat-shock gene (hsp68) by recombinational screening

We have used cloned fragments from a Drosophila melanogaster hsp70 gene and a mouse hsp68 cDNA in recombinational screens of mouse genomic libraries. Using the mouse probe we have isolated two overlapping recombinant lambda phages comprising 22 kb of cloned DNA. Southern analysis has localized the homology with the Drosophila hsp70 coding region to a 2.2-kb fragment containing the mouse heat-shock gene. Insertion accompanying recombinational screening can disrupt interesting sequences; we have overcome this inconvenience by developing a simple one-step genetic selection for phage which have precisely excised the microplasmid probe.

Gene-specific expression of the actin multigene family of Dictyostelium discoideum

We have investigated the expression of 14 cloned genes of the 20-member actin multigene family of Dictyostelium discoideum using gene-specific mRNA complementary probes and an RNase protection assay. Actin gene expression was studied in vegetative cells and in cells at a number of developmental stages chosen to represent the known major shifts in actin mRNA and protein synthesis. At least 13 of these genes are expressed. A few genes are expressed very abundantly at 10% or more of total actin mRNA; however, the majority are maximally expressed at 1 to 5% of actin message. Although all of the genes are transcribed in vegetative cells, most genes appear to be independently regulated. Actin 8 appears to be transcribed at constant, high levels throughout growth and development. Actin 12 mRNA is maximally expressed in vegetative cells but the level is reduced appreciably by the earliest stage of development examined, while Actin 7 mRNA is specifically induced approximately sevenfold at this time. The rest of the genes appear to be induced 1.5 to 2-fold early in development, coincident with the increase in total actin mRNA. Since 12 of the genes code for extremely homologous proteins, it is possible that the large number of actin genes in Dictyostelium is utilized for precise regulation of the amount of actin produced at any stage of development, even though individual gene expression appears in some cases to be very stage-specific. In addition to these 13 actin genes, at least two and possibly four more genes are known to be expressed, because they are represented by complementary DNA clones, and an additional one or two expressed genes are indicated by primer extension experiments. Only one known gene, Actin 2-sub 2, is almost certainly a pseudogene. Thus the vast majority of Dictyostelium actin genes are expressed.