Congenital disorders of glycosylation - an umbrella term for rapidly expanding group of rare genetic metabolic disorders - importance of physical investigation

AIM

Congenital disorders of glycosylation (CDG) belong to an expanding group of rare genetic metabolic disorders caused by defects in the complex chemical enzymatic process of glycosylation. The study is aimed at presenting a case report of a premature dysmorphic newborn, clinical presentation of the condition, the way it was diagnosed and treated, as well as its comparison with the known cases.

RESULTS

The result of glycan analysis supports the assumption of a supposed glycosylation disorder and also specifies a specific subtype: CDG-1, subtype ALG12-CDG (Ig).

CONCLUSION

CDG have an extremely wide clinical spectrum and should be considered in any child with unexplained developmental delay, failure to thrive, seizures, and abnormalities in liver enzymes, coagulation and immunologic factors. The treatment of most forms of CDG depends upon numerous factors such as specific symptoms present, severity of the disorder, age and overall health of the patients and tolerance to certain medications or procedures. For these reasons, the treatment is specific for every individual. It is based on the symptoms and requires a coordination of efforts of a team of specialists (Tab. 4, Fig. 3, Ref. 19).

Interferon lambda 2 promotes mammary tumor metastasis via angiogenesis extension and stimulation of cancer cell migration

Myeloid-derived suppressor cells (MDSCs) support tumor development by stimulation of angiogenesis and immune response inhibition. In our previous study, we showed that interferon lambda 2 (IFN-λ2), secreted by MDSCs, enhances production of pro-angiogenic factors by cancer cells via phosphorylation of STAT3 and therefore promotes blood vessels formation. In the present study IFN-λ2 level was evaluated by ELISA in serum of tumor-bearing mice, whereas its expression in MDSCs isolated from the lungs with metastatic tumors and normal lungs was assessed by qPCR. The effect of IFN-λ2 on mouse mammary cancer cells motility was tested in Boyden chamber migration assay. In order to evaluate its pro-angiogenic function we performed in vitro tubule formation assay and in ovo angiogenesis assay on chicken embryo chorioallantoic membrane (CAM). Moreover, in order to design small molecule inhibitors of IFN-λ2 and its receptor we performed molecular modeling followed by the identification of potential natural inhibitors. Then, we examined their ability to inhibit angiogenesis in vitro. Our results showed that IFN-λ2 predisposed mouse mammary cancer cells to migration in vitro. It also enhanced angiogenesis induced by mouse mammary cancer cells in vitro and in ovo. For the first time we selected potential IFN-λ2 inhibitors and we validated that they were capable to abolish pro-angiogenic effect of IFN-λ2, similarly to blocking antibodies. Therefore, IFN-λ2 and its receptor may become targets of anti-cancer therapy, but their mechanism of action requires further investigation.

Tumour-associated macrophages influence canine mammary cancer stem-like cells enhancing their pro-angiogenic properties

Cancer stem-like cells as cells with ability to self-renewal and potential to differentiate into various types of cells are known to be responsible for tumour initiation, recurrence and drug resistance. Hence a comprehensive research is concentrated on discovering cancer stem-like cells biology and interdependence between them and other cells. The aim of our study was to evaluate the impact of macrophages on cancer stem-like cells in canine mammary carcinomas. As recent studies indicated presence of macrophages in cancer environment stimulates cancer cells into more motile and invasive cells by acquisition of macrophage phenotypes. From two canine mammary tumour cell lines, CMT-U27 and P114 cancer stem-like cells were stained with Sca1, CD44 and EpCAM monoclonal antibodies and isolated. Those cells were next co-cultured with macrophages for 5 days and used for further experiments. Canine Gene Expression Microarray revealed 29 different expressed transcripts in cancer stem-like cells co-cultured with macrophages compared to those in mono-culture. Up-regulation of C-C motif chemokine 2 was considered as the most interesting for further investigation. Additionally, those cells showed overexpression of genes involved in non-canonical Wnt pathway. The results of 3D tubule formation in endothelial cells induced by cancer stem-like cells co-cultured with macrophages compared to cancer stem-like cells from mono-cultures and with addition of Recombinant Canine CCL2/MCP-1 revealed the same stimulating effect. Based on those results we can conclude that macrophages have an impact on cancer stem-like cells increasing secretion of pro-angiogenic factors.

Immunosuppression in Dogs During Mammary Cancer Development

Cancer immunosuppression that facilitates tumor progression and metastasis evolves by development of an immunosuppressive network. The aim of this study was to assess this network in dogs with benign or malignant tumors with or without confirmed metastasis. The authors showed that the number of various T cell subpopulations was constant during tumor development; however the number of regulatory T cells (Tregs) was significantly higher in tumor-bearing dogs than in healthy individuals. The number of myeloid-derived suppressor cells (MDSCs) and their p-STAT3 expression (which is a negative regulator of hematopoiesis and regulates VEGF expression) were higher in cancer patients than in control dogs, however their number increased significantly in late-stage cancer patients. Canine mammary carcinomas with confirmed metastases to either lymph nodes or internal organs had greater MDSCs and Treg infiltration than benign mammary tumors or malignant mammary tumors for which metastases had not been detected. Similarly, expression of p-STAT3 and VEGF-C was the highest in tumors with confirmed metastases. This research shows changes occurring in the blood (n = 30 patients) and tumor tissue of patients (n = 100) during canine mammary tumor development. The findings should be considered preliminary because of the small number of samples. Nonetheless, the findings suggest that a high level of Tregs and MDSCs as well as high expression of p-STAT3 and VEGF-C may significantly contribute to mammary tumor progression and metastasis in dogs.

Analysis of microRNA expression in canine mammary cancer stem-like cells indicates epigenetic regulation of transforming growth factor-beta signaling

Cancer stem cells (CSCs) display both unique self-renewal ability as well as the ability to differentiate into many kinds of cancer cells. They are supposed to be responsible for cancer initiation, recurrence and drug resistance. Despite the fact that a variety of methods are currently employed in order to target CSCs, little is known about the regulation of their phenotype and biology by miRNAs. The aim of our study was to assess miRNA expression in canine mammary cancer stem-like cells (expressing stem cell antigen 1, Sca-1; CD44 and EpCAM) sorted from canine mammary tumour cell lines (CMT-U27, CMT-309 and P114). In order to prove their stem-like phenotype, we conducted a colony formation assay that confirmed their ability to form colonies from a single cell. Profiles of miRNA expression were investigated using Agilent custom-designed microarrays. The results were further validated by real-time rt-PCR analysis of expression of randomly selected miRNAs. Target genes were indicated and analysed using Kioto Encyclopedia of Genes and Genomes (KEGG) and BioCarta databases. The results revealed 24 down-regulated and nine up-regulated miRNAs in cancer stem-like cells compared to differentiated tumour cells. According to KEGG and BioCarta databases, target genes (n=240) of significantly down-regulated miRNAs were involved in transforming growth factor-beta signaling, mitogen-activated protein kinases (MAPK) signaling pathway, anaplastic lymphoma receptor tyrosine kinase (ALK) and peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (PGC1A) pathways. The analysis of single-gene overlapping with different pathways showed that the most important genes were: TGFBR1, TGFBR2, SOS1, CHUK, PDGFRA, SMAD2, MEF2A, MEF2C and MEF2D. All of them are involved in tumor necrosis factor-beta signaling and may indicate its important role in cancer stem cell biology. Increased expression of TGFBR2, SMAD2, MEF2A and MEF2D in canine mammary cancer stem-like cells was further confirmed by real-time-qPCR. The results of our study point at epigenetic differences between cancer stem-like cells and differentiated tumour cells, which may be important not only for veterinary medicine but also for comparative oncology.

Expression, purification and preliminary crystallographic analysis of Drosophila melanogaster lysosomal α-mannosidase

The lysosomal α-mannosidases are class II mannosidases that belong to glycoside hydrolase family 38 and play an important role in the degradation of asparagine-linked carbohydrates of glycoproteins. Based on peptide similarity to human and bovine lysosomal mannosidase (LM), recombinant α-mannosidase from Drosophila melanogaster (dLM408) was cloned and heterologously expressed in Pichia pastoris. The recombinant form of dLM408 designed for structural analysis lacks the transmembrane domain and was crystallized using standard vapour-diffusion and counter-diffusion techniques. The crystals grew as flat plates and as tetragonal bipyramids, respectively. The plate-shaped crystals exhibited the symmetry of space group P2(1)2(1)2(1) and diffracted to a minimum d-spacing of 3.5 Å.

Analysis of the raffinose family oligosaccharide pathway in pea seeds with contrasting carbohydrate composition

Raffinose family oligosaccharides (RFOs) are synthesized by a set of galactosyltransferases, which sequentially add galactose units from galactinol to sucrose. The accumulation of RFOs was studied in maturing seeds of two pea (Pisum sativum) lines with contrasting RFO composition. Seeds of the line SD1 accumulated stachyose as the predominant RFO, whereas verbascose, the next higher homolog of stachyose, was almost absent. In seeds of the line RRRbRb, a high level of verbascose was accumulated alongside with stachyose. The increase in verbascose in developing RRRbRb seeds was associated with galactinol-dependent verbascose synthase activity. In addition, a galactinol-independent enzyme activity was detected, which catalyzed transfer of a galactose residue from one stachyose molecule to another. The two enzyme activities synthesizing verbascose showed an optimum at pH 7.0. Both activities were almost undetectable in SD1. Maximum activity of stachyose synthase was about 4-fold higher in RRRbRb compared with SD1, whereas the activities of galactinol synthase and raffinose synthase were only about 1.5-fold higher in RRRbRb. The levels of galactinol synthase and stachyose synthase activity were reflected by steady-state levels of corresponding mRNAs. We suggest that the accumulation of verbascose in RRRbRb was controlled by a coordinated up-regulation of the last steps of verbascose biosynthesis.

Analysis of the raffinose family oligosaccharide pathway in pea seeds with contrasting carbohydrate composition

Raffinose family oligosaccharides (RFOs) are synthesized by a set of galactosyltransferases, which sequentially add galactose units from galactinol to sucrose. The accumulation of RFOs was studied in maturing seeds of two pea (Pisum sativum) lines with contrasting RFO composition. Seeds of the line SD1 accumulated stachyose as the predominant RFO, whereas verbascose, the next higher homolog of stachyose, was almost absent. In seeds of the line RRRbRb, a high level of verbascose was accumulated alongside with stachyose. The increase in verbascose in developing RRRbRb seeds was associated with galactinol-dependent verbascose synthase activity. In addition, a galactinol-independent enzyme activity was detected, which catalyzed transfer of a galactose residue from one stachyose molecule to another. The two enzyme activities synthesizing verbascose showed an optimum at pH 7.0. Both activities were almost undetectable in SD1. Maximum activity of stachyose synthase was about 4-fold higher in RRRbRb compared with SD1, whereas the activities of galactinol synthase and raffinose synthase were only about 1.5-fold higher in RRRbRb. The levels of galactinol synthase and stachyose synthase activity were reflected by steady-state levels of corresponding mRNAs. We suggest that the accumulation of verbascose in RRRbRb was controlled by a coordinated up-regulation of the last steps of verbascose biosynthesis.

Tissues of the clawed frog Xenopus laevis contain two closely related forms of UDP-GlcNAc:alpha3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I

UDP-GlcNAc:alpha3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I (GnTI; EC 2.4.1.101) is a medial-Golgi enzyme that is essential for the processing of oligomannose to hybrid and complex N-glycans. On the basis of highly conserved sequences obtained from previously cloned mammalian GnTI genes, cDNAs for two closely related GnTI isoenzymes were isolated from a Xenopus laevis ovary cDNA library. As typical for glycosyltransferases, both proteins exhibit a type II transmembrane protein topology with a short N-terminal cytoplasmic tail (4 amino acids); a transmembrane domain of 22 residues; a stem region with a length of 81 (isoenzyme A) and 77 (isoenzyme B) amino acids, respectively; and a catalytic domain consisting of 341 residues. The two proteins differ not only in length but also at 13 (stem) and 18 (catalytic domain) positions, respectively. The overall identity of the catalytic domains of the X. laevis GnTI isoenzymes with their mammalian and plant orthologues ranges from 30% (Nicotiana tabacum) to 67% (humans). Isoenzymes A and B are encoded by two separate genes that were both found to be expressed in all tissues examined, albeit in varying amounts and ratios. On expression of the cDNAs in the baculovirus/insect cell system, both isoenzymes were found to exhibit enzymatic activity. Isoenzyme B is less efficiently folded in vivo and thus appears of lower physiological relevance than isoenzyme A. However, substitution of threonine at position 223 with alanine was sufficient to confer isoenzyme B with properties similar to those observed for isoenzyme A.

Structural and functional features of glycosyltransferases

Most of the glycosylation reactions that generate the great diversity of oligosaccharide structures of eukaryotic cells occur in the Golgi apparatus. This review deals with the most recent data that provide insight into the functional organization of Golgi-resident glycosyltransferases. We also focus on the recent successes in X-ray crystal structure determination of glycosyltransferases. These new structures begin to shed light on the molecular bases accounting for donor and acceptor substrate specificities as well as catalysis.

Cloning and expression of cDNAs encoding alpha1,3-fucosyltransferase homologues from Arabidopsis thaliana

The core alpha1,3-fucosyltransferases are involved in the synthesis of glycans specific to plants and invertebrates which are known to be immunogenic and allergenic. We report the identification, isolation and characterisation of the cDNAs of three genes (FucTA, FucTB and FucTC) encoding proteins similar to alpha1,3-fucosyltransferases in Arabidopsis thaliana. Reverse transcription-polymerase chain reaction was used to amplify the full length coding sequence of FucTA. The FucTA gene, which consists of seven exons, encodes a presumptive protein of 501 amino acids showing an overall sequence identity of 66% to the protein encoded by the recently isolated mung bean Fuc-T C3 cDNA. FucTA was expressed in Pichia pastoris under the control of the AOX1 gene promoter. The soluble enzyme was found to catalyse the same reaction as mung bean core alpha1,3-fucosyltransferase as judged by analyses of the products by MALDI-TOF and high-performance liquid chromatography. The FucTB cDNA was isolated from a lambda-ZAP library, but the clone used an alternative splicing site between the second and third exon resulting in a premature stop codon. The FucTC gene encodes a protein with less than 40% identity to FucTA across 115 amino acids of a total of 401 amino acids and is a member of a new sub-family of plant alpha1,3/4-fucosyltransferase homologues.

Molecular cloning and functional expression of beta1, 2-xylosyltransferase cDNA from Arabidopsis thaliana

The transfer of xylose from UDP-xylose to the core beta-linked mannose of N-linked oligosaccharides by beta1,2-xylosyltransferase (XylT) is a widespread feature of plant glycoproteins which renders them immunogenic and allergenic in man. Here, we report the isolation of the Arabidopsis thaliana XylT gene, which contains two introns and encodes a 60.2 kDa protein with a predicted type II transmembrane protein topology typical for Golgi glycosyltransferases. Upon expression of A. thaliana XylT cDNA in the baculovirus/insect cell system, a recombinant protein was produced that exhibited XylT activity in vitro. Furthermore, the recombinant enzyme displayed XylT activity in vivo in the insect cells, as judged by the acquired cross-reaction of cellular glycoproteins with antibodies against the beta1,2-xylose epitope. The cloned XylT cDNA as well as the recombinant enzyme are essential tools to study the role of beta1,2-xylose in the immunogenicity and allergenicity of plant glycoproteins at the molecular level.

Stachyose synthesis in seeds of adzuki bean (Vigna angularis): molecular cloning and functional expression of stachyose synthase

Stachyose is the major soluble carbohydrate in seeds of a number of important crop species. It is synthesized from raffinose and galactinol by the action of stachyose synthase (EC 2.4.1.67). We report here on the identification of a cDNA encoding stachyose synthase from seeds of adzuki bean (Vigna angularis Ohwi et Ohashi). Based on internal amino acid sequences of the enzyme purified from adzuki bean, oligonucleotides were designed and used to amplify corresponding sequences from adzuki bean cDNA by RT-PCR, followed by rapid amplification of cDNA ends (RACE-PCR). The complete cDNA sequence comprised 3046 nucleotides and included an open reading frame which encoded a polypeptide of 857 amino acid residues. The entire coding region was amplified by PCR, engineered into the baculovirus expression vector pVL1393 and introduced into Spodoptera frugiperda (Sf21) insect cells for heterologous expression. The recombinant protein was immunologically reactive with polyclonal antibodies raised against stachyose synthase purified from adzuki bean and was shown to be a functional stachyose synthase with the same catalytic properties as its native counterpart. High levels of stachyose synthase mRNA were transiently accumulated midway through seed development, and the enzyme was also present in mature seeds and during germination.

Molecular cloning of cDNA encoding N-acetylglucosaminyltransferase II from Arabidopsis thaliana

N-acetylglucosaminyltransferase II (GnTII, EC 2.4.1.143) is a Golgi enzyme involved in the biosynthesis of glycoprotein-bound N-linked oligosaccharides, catalysing an essential step in the conversion of oligomannose-type to complex N-glycans. GnTII activity has been detected in both animals and plants. However, while cDNAs encoding the enzyme have already been cloned from several mammalian sources no GnTII homologue has been cloned from plants so far. Here we report the molecular cloning of an Arabidopsis thaliana GnTII cDNA with striking homology to its animal counterparts. The predicted domain structure of A. thaliana GnTII indicates a type II transmembrane protein topology as it has been established for the mammalian variants of the enzyme. Upon expression of A. thaliana GnTII cDNA in the baculovirus/insect cell system, a recombinant protein was produced that exhibited GnTII activity.

Molecular cloning and characterization of cDNA coding for beta1, 2N-acetylglucosaminyltransferase I (GlcNAc-TI) from Nicotiana tabacum

In plants as well as in animals beta1, 2N-acetylglucosaminyltransferase I (GlcNAc-TI) is a Golgi resident enzyme that catalyzes an essential step in the biosynthetic pathway leading from oligomannosidic N-glycans to complex or hybrid type N-linked oligosaccharides. Employing degenerated primers deduced from known GlcNAc-TI genes from animals, we were able to identify the cDNA coding for GlcNAc-TI from a Nicotiana tabacum cDNA library. The complete nucleotide sequence revealed a 1338 base pair open reading frame that codes for a polypeptide of 446 amino acids. Comparison of the deduced amino acid sequence with that of already known GlcNAc-TI polypeptides revealed no similarity of the tobacco clone within the putative cytoplasmatic, transmembrane, and stem regions. However, 40% sequence similarity was found within the putative C-terminal catalytic domain containing conserved single amino acids and peptide motifs. The predicted domain structure of the tobacco polypeptide is typical for type II transmembrane proteins and comparable to known GlcNAc-TI from animal species. In order to confirm enzyme activity a truncated form of the protein containing the putative catalytic domain was expressed using a baculovirus/insect cell system. Using pyridylaminated Man(5)- or Man(3)GlcNAc(2)as acceptor substrates and HPLC analysis of the products GlcNAc-TI activity was shown. This demonstrates that the C-terminal region of the protein comprises the catalytic domain. Expression of GlcNAc-TI mRNA in tobacco leaves was detected using RT-PCR. Southern blot analysis gave two hybridization signals of the gene in the amphidiploid genomes of the two investigated species N. tabacum and N.benthamiana.

Purification, cDNA cloning, and expression of GDP-L-Fuc:Asn-linked GlcNAc alpha1,3-fucosyltransferase from mung beans

Substitution of the asparagine-linked GlcNAc by alpha1,3-linked fucose is a widespread feature of plant as well as of insect glycoproteins, which renders the N-glycan immunogenic. We have purified from mung bean seedlings the GDP-L-Fuc:Asn-linked GlcNAc alpha1,3-fucosyltransferase (core alpha1,3-fucosyltransferase) that is responsible for the synthesis of this linkage. The major isoform had an apparent mass of 54 kDa and isoelectric points ranging from 6. 8 to 8.2. From that protein, four tryptic peptides were isolated and sequenced. Based on an approach involving reverse transcriptase-polymerase chain reaction with degenerate primers and rapid amplification of cDNA ends, core alpha1,3-fucosyltransferase cDNA was cloned from mung bean mRNA. The 2200-base pair cDNA contained an open reading frame of 1530 base pairs that encoded a 510-amino acid protein with a predicted molecular mass of 56.8 kDa. Analysis of cDNA derived from genomic DNA revealed the presence of three introns within the open reading frame. Remarkably, from the four exons, only exon II exhibited significant homology to animal and bacterial alpha1,3/4-fucosyltransferases which, though, are responsible for the biosynthesis of Lewis determinants. The recombinant fucosyltransferase was expressed in Sf21 insect cells using a baculovirus vector. The enzyme acted on glycopeptides having the glycan structures GlcNAcbeta1-2Manalpha1-3(GlcNAcbeta1-2Manalpha1- 6)Manbeta1-4GlcNAcbet a1-4GlcNAcbeta1-Asn, GlcNAcbeta1-2Manalpha1-3(GlcNAcbeta1-2Manalpha1- 6)Manbeta1-4GlcNAcbet a1-4(Fucalpha1-6)GlcNAcbeta1-Asn, and GlcNAcbeta1-2Manalpha1-3[Manalpha1-3(Manalpha1-6 )Manalpha1-6]Manbeta1 -4GlcNAcbeta1-4GlcNAcbeta1-Asn but not on, e.g. N-acetyllactosamine. The structure of the core alpha1,3-fucosylated product was verified by high performance liquid chromatography of the pyridylaminated glycan and by its insensitivity to N-glycosidase F as revealed by matrix-assisted laser desorption/ionization time of flight mass spectrometry.

Removal of 106 amino acids from the N-terminus of UDP-GlcNAc: alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I does not inactivate the enzyme

UDP-GlcNAc: alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I (GnTI, EC 2.4.1.101) plays an essential role in the conversion of oligomannose to complex and hybrid N-glycans. Rabbit GnTI is 447 residues long and has a short four-residue N-terminal cytoplasmic tail, a 25-residue putative signal-anchor hydrophobic domain, a stem region of undetermined length and a large C-terminal catalytic domain, a structure typical of all glycosyltransferases cloned to date. Comparison of the amino acid sequences for human, rabbit, mouse, rat, chicken, frog and Caenorhabditis elegans GnTI was used to obtain a secondary structure prediction for the enzyme which suggested that the location of the junction between the stem and the catalytic domain was at about residue 106. To test this hypothesis, several hybrid constructs containing GnT I with N- and C-terminal truncations fused to a mellitin signal sequence were inserted into the genome of Autographa californica nuclear polyhedrosis virus (AcMNPV), Sf9 insect cells were infected with the recombinant baculovirus and supernatants were assayed for GnTI activity. Removal of 29, 84 and 106 N-terminal amino acids had no effect on GnTI activity; however, removal of a further 14 amino acids resulted in complete loss of activity. Western blot analysis showed strong protein bands for all truncated enzymes except for the construct lacking 120 N-terminal residues indicating proteolysis or defective expression or secretion of this protein. The data indicate that the stem is at least 77 residues long.

Caffeic acid phenethyl ester stimulates human antioxidant response element-mediated expression of the NAD(P)H:quinone oxidoreductase (NQO1) gene

Caffeic acid phenethyl ester (CAPE) is a phenolic antioxidant derived from the propolis of honeybee hives. CAPE was shown to inhibit the formation of intracellular hydrogen peroxide and oxidized bases in DNA of 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated HeLa cells and was also found to induce a redox change that correlated with differential growth effects in transformed cells but not the nontumorigenic parental ones. Mediated via the electrophile or human antioxidant response element (hARE), induction of the expression of NAD(P)H quinone oxidoreductase (NQO1) and glutathione S-transferase Ya subunit genes by certain phenolic antioxidants has been correlated with the chemopreventive properties of these agents. Here, we determined by Northern analysis that CAPE treatment of hepatoma cells stimulates NQO1 gene expression in cultured human hepatoma cells (HepG2), and we characterized the effects of CAPE treatment on the expression of a reporter gene either containing or lacking the hARE or carrying a mutant version of this element in rodent hepatoma (Hepa-1) transfectants. A dose-dependent transactivation of human hARE-mediated chloramphenicol acetyltransferase (cat) gene expression was observed upon treatments of the Hepa-1 transfectants with TPA, a known inducer, as well as with CAPE. The combined treatments resulted in an apparent additive stimulation of the reporter expression. To learn whether this activation of cat gene expression was effected by protein kinase C in CAPE-treated cells, a comparison was made of cat gene activity after addition of calphostin, a protein kinase C inhibitor. Calphostin reduced the cat gene induction by TPA but not by CAPE, suggesting that stimulation of gene expression in this system by these agents proceeds via distinct mechanisms. Band-shift experiments to examine binding of transactivator proteins from nuclear extracts of treated and untreated cells to a hARE DNA probe showed that TPA exposure increased the binding level. In contrast, binding of factors to this probe was inhibited after either in vivo treatment of cells with CAPE or in vitro addition of this compound to the nuclear extract. In view of the clear stimulation by CAPE of gene expression mediated by hARE, possible explanations of this result are discussed.

A mutational hot spot induced by N-hydroxy-aminofluorene in dihydrofolate reductase mutants of Chinese hamster ovary cells

Eighteen mutants deficient in dihydrofolate reductase (DHFR) activity were induced with 0.5 microM N-hydroxy-aminofluorene in four separate experiments. This carcinogen dose killed approximately 80% of the treated cells and resulted in a mutational frequency approximately 3 x 10(-6). The nature of the induced changes in each of the mutants was determined by direct sequencing following polymerase chain reaction amplification, or in one instance, by Southern blot analysis. Nearly all (15/17) of the mutations were single base changes. Consistent with the binding specificity of this chemical, all mutations were targeted to guanine bases. The predominant change was G:C-->T:A transversion which was evident in 11/15 mutants. A single dG-AF mutational hotspot was noted at a site in the DHFR coding sequence of exon 4; one-third of the induced point mutations arose at this position. These results are compared with our previous analyses of mutants induced with the related aromatic amine, N-2-acetoxy-2-acetyl-aminofluorene.

DNA strand-specific repair of (+-)-3 alpha,4 beta-dihydroxy-1 alpha,2 alpha-epoxy-1,2,3,4-tetrahydrobenzo[c]phenanthrene adducts in the hamster dihydrofolate reductase gene

We evaluated the formation and removal of (+-)-3 alpha,4 beta-dihydroxy-1 alpha,2 alpha-epoxy-1,2,3,4- tetrahydrobenzo[c]phenanthrene (BcPHDE)-DNA adducts in two Chinese hamster ovary (CHO) cell lines. One line of repair-proficient cells (MK42) carries a stable 150-fold amplification of the dihydrofolate reductase (DHFR) locus. The other line of repair-deficient cells (UV-5) is diploid for this gene and is defective in excision of bulky DNA lesions. Two methods were used to quantitate adduct levels in treated cells: Escherichia coli UvrABC excision nuclease cleavage and 32P-postlabeling. DNA repair was examined in the actively transcribed DHFR gene, in an inactive region located 25 kilobases downstream, and in the overall genome. Between 8 and 24 hr after BcPHDE exposure, preferential repair of the DHFR gene compared to the noncoding region was apparent in MK42 cells. This gene-specific repair was associated with adduct removal from the DHFR transcribed strand. However, UV-5 cells showed no lesion reduction from this strand of the gene. By both quantitation methods, regions accessible to repair in MK42 cells showed a 2-fold reduction in DNA adduct levels by 24 hr. That the decline in adducts reflects genomic repair was demonstrated by the constant damage level remaining in UV-5 cells. Since BcPHDE-induced mutations in DHFR apparently arise from adducted purines on the nontranscribed strand, results from the present study support the idea that a consequence of strand-specific repair is strand-biased mutations.

A new diagnostic method for the detection of endogenous Rous-associated virus-type provirus in chickens

A quick and simple method has been developed to detect the presence or absence of the endogenous Rous-associated virus (RAV) element ev1 in chickens. The procedure consists of a one-tube multiplex polymerase chain reaction (PCR) involving three oligonucleotide primers that are specific for the upstream flanking region, the long terminal repeat (LTR), and the downstream flanking region of the proviral insert, respectively. The multiplex reaction allows for the unambiguous discrimination between ev1+/ev1+ homozygote, ev1-/ev1- homozygote, and ev1+/ev1- heterozygote birds. The method works best with purified genomic DNA as substrate, but can also be used with rapidly prepared, "crude" DNA samples. The combination of speed with the safety of a nonradioactive procedure, and the ability to perform large numbers of assays by a semi-automated procedure, make this method attractive for large-scale screening projects. The ev1 locus has been used as a model system to demonstrate the feasibility of the PCR diagnostic approach. However the same principle should be applicable to the analysis of other RAV-type ev loci, as well as endogenous elements belonging to other families of viruses as sequence information for the flanking regions of these inserts becomes available.

DNA strand-specific mutations induced by (+/-)-3 alpha,4 beta-dihydroxy- 1 alpha,2 alpha-epoxy-1,2,3,4-tetrahydrobenzo[c]phenanthrene in the dihydrofolate reductase gene

We previously showed that the preferred mutation induced by (+/-)-3 alpha,4 beta-dihydroxy-1 alpha,2 alpha-epoxy- 1,2,3,4-tetrahydrobenzo[c]phenanthrene (BcPHDE) in the dihydrofolate reductase gene in Chinese hamster ovary cells was a purine to thymine transversion on the nontranscribed strand at the sequence 5'-RRR-3' (R is a purine and the mutated base is underlined). To determine whether the observed mutational strand specificity was due to bias in the phenotypic selection, we designed a nonsense-codon reversion assay in which a triple purine target was present on both strands and all R----T transversion mutations yielded amino acid substitutions that were compatible with dihydrofolate reductase enzyme activity. From the size of the targets, a 2:1 ratio of mutations at the purines on the nontranscribed strand was expected if the DNA strands were mutationally equivalent. We isolated a total of 66 BcPHDE-induced revertants of two mutants that carry point mutations at either the 5' or the 3' end of the gene. All reversions at the 5' end arose by substitution on the nontranscribed strand; those at the 3' end showed a strand bias that favored this strand by 7:1. For both mutants, R----T transversions accounted for 88% of all the induced base changes. Thus, in this system, mutational strand bias is independent of the selection for phenotype. The results are consistent with the model of preferential repair of the transcribed strand as proposed by others. The involvement of RNA polymerase in the selective repair recruitment is discussed.

Characterization of three abundant mRNAs from human ovarian granulosa cells

Three cDNA clones, pHGR122, pHGR11, and pHGR74 containing the coding information for abundant mRNAs were identified from a human ovarian granulosa cell cDNA library. Characterization by nucleotide sequencing revealed that pHGR122 was specific for a collagenase inhibitor and pHGR11 for melanoma-associated antigen ME491. Relative quantification by Northern analysis indicated that collagenase inhibitor mRNA is a major species in granulosa cells. This finding provides evidence for the origin of this protein in follicular fluid as a secretory product of granulosa cells. pHGR11 identified melanoma-associated antigen ME491 as the unexpected product of normal, noncarcinogenic, granulosa cells. pHGR74 has the complete coding information for an unknown protein. Three independent experiments: (i) cell-free translation of pHGR74 RNA; (ii) transcription of suitable restriction fragments followed by cell-free translation; (iii) hydrolysis of the cell-free translation product of pHGR74 RNA by endoproteinase Lys-C, identified one open reading frame coding for an acidic, highly hydrophilic protein of 111 amino acid residues. pHGR74 mRNA is expressed in human testis, prostate, seminal vesicle, and ovarian granulosa cells. A comparative Southern analysis indicates pHGR74 mRNA is species specific and encoded by a single-copy gene.

Splicing mutations in the CHO DHFR gene preferentially induced by (+/-)-3 alpha,4 beta-dihydroxy-1 alpha,2 alpha-epoxy-1,2,3,4- tetrahydrobenzo[c]phenanthrene

Cultured Chinese hamster ovary (CHO) cells were treated with the polycyclic aromatic hydrocarbon racemic 3 alpha,4 beta-dihydroxy-1 alpha,2 alpha-epoxy-1,2,3,4- tetrahydrobenzo[c]phenanthrene. Mutants deficient in dihydrofolate reductase activity were isolated. A carcinogen treatment at 0.1 microM yielded at 46% survival of the treated population and an induced frequency of mutation of 1.7 x 10(-4), 10(3)-fold greater than the spontaneous rate. By polymerase chain reaction amplification and direct DNA sequencing, we determined the base changes in 38 mutants. Base substitutions accounted for 78% (30/38) of the mutations. We obtained, in addition, four frameshift and four complex mutations. The preferred type of mutation was transversion (A.T----T.A and G.C----T.A) occurring in 69% of the analyzed mutants. A purine was on the 3' side of the putative adduct site in every mutant. Mutations were favored at sequences AGG, CAG, and AAG (the underlined base is the target). Surprisingly, 42% of the mutations created mRNA splicing defects (16/38), especially at splice acceptor sites for each of the five introns. Thus, this chemical carcinogen may recognize some aspect of DNA structure in regions corresponding to pre-mRNA splice sites.

Restriction fragment length polymorphism of chromosome 3 (3p) and the epidermal growth factor receptor gene in human non-small cell lung carcinomas

We have examined the possible loss of 3p alleles in lung tumor samples from 28 patients with non-small cell lung cancers (non-SCLC), using tumor adjacent lung tissue from the same patients as controls. Of the 14 patients with squamous cell carcinoma only 2 (14%) displayed constitutional heterozygosity at the 3p locus and the tumors of both of these cases did not show reduction to homozygosity. Of the 14 patients with adenocarcinomas, 50% had constitutional heterozygosity, and two of the tumors displayed a loss of heterozygosity. We have also examined restriction fragment length polymorphisms (RFLPs) of the epidermal growth factor (EGF) receptor gene in 29 non-SCLC tumor samples and in the tumor adjacent lung tissue samples obtained from the same cases. Digestion of the DNA samples with the BstEII enzyme and hybridization to a HER-A64-3 probe revealed four different types of polymorphic patterns. We did not, however, detect significant differences in the specific polymorphic bands between tumor and paired non-tumor lung tissues or between the different types of carcinomas.

Point mutation analysis in a mammalian gene: rapid preparation of total RNA, PCR amplification of cDNA, and Taq sequencing by a novel method

We have developed a very rapid procedure for DNA sequence analysis of induced mutations in a typically large mammalian gene. We are able to determine the nature of chemical carcinogen-induced point mutations in the 25 kb Chinese hamster ovary (CHO) cell dihydrofolate reductase gene within two days starting with 5 to 10 x 10(6) cells. The approach is based on the use of rapidly prepared total RNA from which a 730 bp dhfr cDNA is synthesized by reverse transcriptase and amplified by the polymerase chain reaction (PCR) procedure. Genomic DNA can simultaneously be prepared from the same cells. The amplified double-stranded cDNA is then sequenced directly by the dideoxy method using Taq polymerase in the Thermal Cycler (Perkin Elmer/Cetus). We have previously shown that nonsense codons in the dhfr coding sequence often result in greatly reduced steady-state levels of dhfr mRNA (2). The methods described are suitable for mutants of this type which contain only 1 to 2 copies of mRNA per cell. This approach is readily adaptable to other selectable genes and other cell types provided the necessary primers can be prepared.

Cloning and sequence analysis of a cDNA from human ovarian granulosa cells encoding the C-terminal part of human elongation factor 2

A cDNA clone, pHGR81, encoding 358 amino-acid residues of the C-terminal region of human elongation factor 2 (EF-2), was isolated from a human ovarian granulosa cell cDNA library. The deduced amino-acid sequence of pHGR81, when compared with the known identical amino-acid sequences of hamster as well as rat EF-2 revealed a substitution of a glutamine by an alanine residue in the partially determined human sequence. The 15 amino-acid-residue sequence comprising the histidine-715, supposed to be of importance for the biological function of EF-2, is preserved in human EF-2. The coding region of the cDNA insert of pHGR81 displays a homology of 87% to hamster and of 88% to rat EF-2 cDNA. In Northern-transfer analysis, pHGR81 specifically hybridizes with an mRNA species of 3.1 kb.