The abortive infection of Syrian hamster cells with human adenovirus type 12

Human adenovirus type 12 (Ad12) induces undifferentiated tumors in newborn Syrian hamsters, and this tumor model has been investigated in detail in our laboratory. One of the characteristics of the Ad12-hamster cell system is a strictly abortive infection cycle. In this chapter, we summarize previous and more recent results of studies on the interaction of Ad12 with the nonpermissive BHK21 hamster cell line. The block of Ad12 replication lies before viral DNA replication and late gene transcription which cannot be detected with the most sensitive techniques. Ad12 adsorption, cellular uptake and transport of the viral DNA to the nucleus are less efficient in the nonpermissive hamster cells than in permissive human cells. However, most of the early functions of the Ad12 genome are expressed in BHK21 cells, though at a low level. In the downstream region, the first exon, of the major late promoter (MLP) of Ad12 DNA, a mitigator element of 33 nucleotide pairs in length has been identified which contributes to the inactivity of the MLP in hamster cells and its markedly decreased activity in human cells. The E1 functions of Ad2 or Ad5 are capable of partly complementing the Ad12 deficiencies in hamster cells in that Ad12 viral DNA replication and late gene transcription can proceed, e.g. in a BHK hamster cell line, BHK297-C131,which carries in an integrated form and constitutively expresses the E1 region of Ad5 DNA. Nevertheless, the late Ad12 mRNAs, which are synthesized in this system with the authentic nucleotide sequence, fail to be translated to structural viral proteins. Hence, infectious virions are not produced in the partly complementing system. Probably there is also a translational block for late Ad12 mRNAs in hamster cells. We have recently shown that the overexpression of the Ad12 preterminal protein (pTP) gene or of the E1A gene facilitates the synthesis of full-length, authentic Ad12 DNA in BHK21 cells infected with Ad12. Apparently the pTP has a hitherto unknown function in eliciting full cycles of Ad12 DNA replication even in nonpermissive BHK21 cells when sufficient levels of Ad12 pTP are produced. We pursue the possibility that the completely abortive infection cycle of Ad12 in hamster cells ensures the survival of Ad12-induced hamster tumor cells which all carry, integrated in their genomes, multiple copies of Ad12 DNA. In this way, the viral genomes are immortalized and expanded in a huge number of tumor cells.

Cellular and early viral factors in the interaction of adenovirus type 12 with hamster cells: the abortive response

The interaction of human adenovirus type 12 (Ad12) with Syrian hamster cells is remarkable in that there is a block of viral DNA replication and late gene transcription. We have screened several cellular factors known to play a role in adenovirus replication for their possible contributions to the interactions of Ad12 in the abortive BHK21 hamster cell system. (1) Western blot analyses of total protein extracts from Ad12- or Ad2-infected BHK21 cells do not reveal a significant difference in the accumulation of NFIII protein at different times after infection. Transcriptional levels of the NFIII gene in BHK21 cells are not altered upon the abortive infection with Ad12 or the productive infection with Ad2. The amount of NFIII protein is markedly reduced in nuclear extracts from BHK21 cells as compared with extracts from C131 hamster cells or human HeLa cells. A presumptive defect in NFIII transport to the nuclei rather than overall reduced NFIII gene transcription might explain the low abundance of NFIII in the nuclei of uninfected or Ad12-infected BHK21 cells. The productive infection of BHK21 or C131 cells with Ad2 leads to an increase in the NFIII concentration in the nuclei of infected cells, late after infection to a decrease; (2) NFI levels in the nuclei of mock-infected or Ad2- or Ad12-infected BHK21 cells are comparable with those in HeLa or in C131 cells. Thus, deficiencies in NFI may not play a role in the abortive system; (3) The absence of morphological alterations in PML protein domains from globular to track-like structures in the nuclei of Ad12-infected hamster cells correlates with the inability of Ad12 DNA to replicate in BHK21 cells. In BHK21 cells, the E4-ORF3 of Ad12 DNA is only weakly transcribed and only small amounts of the gene product are synthesized. In Ad12-infected C131 cells, which allow the replication of Ad12 DNA, the E4-ORF3 of Ad12 DNA is expressed, and track-like PML protein structures are observed. Transfection of the 12-E4-ORF3-EGFP construct leads to the expression of both the green fluorescent protein (GFP) and of the 12-E4-ORF3 gene product in 20-30% of the transfected BHK21 cells and elicits the morphological reorganization of the PML protein structures in the successfully transfected BHK21 cells. Similar results are obtained upon transfection of the 2-E4-ORF3 construct. Untransfected cells or cells transfected with the empty pIRES2-pEGFP vector carry the globular PML protein phenotype; (4) The expression of the 12-E4-ORF3-EGFP and/or of the NFIII-EGFP constructs upon transfection following Ad12-infection of BHK21 cells fails to promote Ad12 DNA replication. Hence, the formation of track-like PML protein structures in BHK21 cells by itself is not a sufficient precondition for Ad12 DNA replication in this abortive system. The data demonstrate that the expression of NFI, NFIII, and/or the conversion of the PML domains do not suffice to elicit Ad12 DNA replication in the abortive hamster cell system.

[Self-mutilation in men--injury pattern and motivation]

6 cases of self-inflicted injuries in male individuals are reported. The age of the affected men was between 15 and 46 years whereas the younger age predominated. Alleged incidents were robberies in 3 cases, rape in one case, violation in custody in one case and an assault originating in personal motives in one case. In 4 cases, the typical injury pattern of self-infliction was present showing parallel course and superficiality of the wounds in areas accessable by the persons's own hands. In 2 cases, atypical injuries (i.e. deep cuts and massive signs of strangulation respectively) were found. However, in most cases, the underlying motive was to gain affection. An autoerotic accident was tried to be disguised in one case. Profit was the leading motive in another case.

Overexpression of the adenovirus type 12 (Ad12) pTP or E1A gene facilitates Ad12 DNA replication in nonpermissive BHK21 hamster cells

In the adenovirus type 12 (Ad12) hamster cell system, abortive virus infection is one of the factors associated with the highly efficient oncogenesis in newborn Syrian hamsters. We have shown earlier that the replication and efficient late transcription of the Ad12 genome are blocked in Syrian hamster cells. Some of the early Ad12 functions are transcribed in these cells, although at a minimal rate. In the present study, we demonstrate that low expression levels of the E1A and precursor to terminal protein (pTP) genes of Ad12 seem to be responsible for the lack of Ad12 DNA replication in hamster cells. The Ad12 genes for the E1A functions or for pTP were tethered to the strong early promoter of the human cytomegalovirus and transfected into BHK21 cells. Subsequently, these cells were infected with Ad12 virions. In Ad12-infected BHK21 cells, which overexpressed pTP or E1A, full-length Ad12 DNA was de novo synthesized, as documented by metabolic labeling with [3H]thymidine and by zone velocity sedimentation in alkaline sucrose gradients followed by gel electrophoresis of the 3H-labeled DNA and Southern blot hybridization to 32P-labeled Ad12 DNA. Transfection of the cloned E1A region of Ad2 yielded similar results. The newly synthesized Ad12 DNA was covalently linked to pTP. The Ad12 DNA binding protein (DBP) and DNA polymerase (pol) genes were transcribed at levels similar to those in merely Ad12-infected cells. In pTP or E1A gene-transfected and Ad12-infected BHK21 cells, marginal levels of late Ad12 mRNA were detectable. Late Ad12 proteins were, however, not synthesized. Apparently, Ad12 DNA replication in hamster cells is rendered impossible due to insufficient threshold levels of the viral E1A and/or pTP.

Dynamic nuclear localization of the baculovirus proteins IE2 and PE38 during the infection cycle: the promyelocytic leukemia protein colocalizes with IE2

The early gene products IE2 and PE38 of Autographa californica multicapsid nuclear polyhedrosis virus localize to distinct nuclear domains after transient expression. Here, the nuclear localization pattern and the putative association with cellular proteins have been determined during virus infection to shed light on the functional significance of the nuclear domains. IE2 was always localized to distinct nuclear structures while PE38 was partly present in nuclear dots. Confocal imaging indicated colocalization of PE38 and IE2 to common domains, prominently at 2 h p.i. The nuclear dot localization of PE38 in infected cells was different from that in transfected cells. Hence, we have performed cotransfection experiments that suggested that a viral factor influences the nuclear distribution. Since the promyelocytic leukemia protein (PML) that localizes to distinct nuclear multiprotein complexes termed ND10/PODs in mammalian cells functions as a target for some immediate early viral proteins, we have investigated whether baculovirus proteins act similarly. Transiently expressed IE2 and PE38 were found to be associated with endogenous PML in the mammalian cell line BHK21. Infection with a recombinant virus that expresses the human pml gene in insect cells reveals IE2 and PML to be colocalized during the early phase of infection followed by a redistribution of both proteins. Taken together our results provide first evidence that the early baculovirus protein IE2 associates at least with one component of mammalian PODs during virus infection, suggesting that POD-like structures can be formed in insect cells.

The human 20-kDa 5'-(CGG)(n)-3'-binding protein is targeted to the nucleus and affects the activity of the FMR1 promoter

Previous reports have described the human DNA CGG repeat-binding protein (CGGBP1 or p20), which binds specifically to nonmethylated, but not to methylated, 5'-(CGG)(n)-3' repeats in the promoter of the fragile X mental retardation 1 (FMR1) gene. The results of transfection experiments into human HeLa cells using a p20-green fluorescent protein fusion construct indicate that the p20 protein is targeted to the nucleus. By deletion analyses, a nuclear localization signal has been found between amino acids 80 and 84. Deletions between amino acids 69 and 71 and between 95 and 167 interfere with 5'-(CGG)(n)-3' binding. The results of electrophoretic mobility shift assays using DNA with 5'-(CGG)(n)-3' repeats of different lengths render it likely that oligomers of the p20 protein bind to the repeat. In cotransfection experiments, the activity of the FMR1 promoter is reduced by the presence of p20. Upon transfection of the p20 cDNA construct into HeLa cells, transcription of the endogenous FMR1 gene is decreased. The green fluorescent protein-p20 fusion protein associates preferentially with the telomeres of the short arms of human chromosomes 13, 14, 15, 21, and 22. Their telomeres carry the genes for the 28 S rRNA, which contain 5'-(CGG)(n)-3' repeats. The translated region of the p20 gene from three healthy, five fragile X syndrome, and five premutation-carrying individuals has been sequenced, but mutations have not been detected.

Adenovirus type 12 DNA firmly associates with mammalian chromosomes early after virus infection or after DNA transfer by the addition of DNA to the cell culture medium

Human adenovirus type 12 (Ad12) infects human cells productively and leads to viral replication, whereas infection of hamster cells remains abortive, with total blocks in viral DNA replication and late viral gene transcription. The intranuclear fate of Ad12 DNA in productively infected human cells and in abortively infected hamster cells was monitored by using the fluorescent in situ hybridization (FISH) technique. Human HeLa cells, primary human umbilical cord fibroblasts, hamster BHK21 cells, primary embryonal hamster cells, and the Ad12-transformed T637 hamster cell line were studied. As early as 2 h after infection, extensive association of Ad12 DNA with metaphase chromosomes was demonstrated by FISH in all of these cells. Chromosomal association continued until late (24 to 28 h) after infection, when about 100% of the human cell nuclei and 70 to 80% of the hamster cell nuclei showed distinct FISH signals. This chromosomal association of Ad12 DNA in infected cells seemed to be rather firm, since it proved to be resistant to mechanically stretching the chromosomes and to different types of chemical treatment. Moreover, laser scan microscopy of mechanically stretched chromosomes from Ad12-infected HeLa cells and from the Ad12-transformed T637 cell line, with about 20 copies of Ad12 DNA provably integrated, revealed identical FISH patterns. Therefore, it was likely that even in infected cells the chromosomal association of Ad12 DNA was very similar to the integrated state. Late in productively infected cells, large nuclear areas were taken over by viral DNA replication, as visualized by FISH in interphase nuclei. Chromosomal association at many sites was frequently limited to one chromatid, but signals in adjacent positions on both chromatids were also seen. Upon the long-term cultivation and passage of abortively infected BHK21 cells for 96 h after infection, a gradual decrease of viral DNA association with chromosomes was observed. Integration of Ad12 DNA in hamster cells early after infection was previously documented, and recombination between viral and cellular DNAs in human cells was also shown. The FISH data on extensive chromosomal association of Ad12 DNA suggest a means to study the pathway of Ad12 DNA from early steps in viral infection via chromosomal interactions to integration events. In a different approach, Ad12 DNA, Ad12 DNA with the terminal protein covalently linked to its ends (Ad12 DNA-TP), or Ad2 DNA was simply added to the culture medium of HeLa or BHK21 cells. Precipitation or selection procedures were avoided. Depending on the experimental conditions, up to 25 to 30% of the interphase nuclei of HeLa cells and 9 to 19% of the interphase nuclei of BHK21 cells showed positive FISH signals at 24 h after the addition of DNA. Viral DNA also became associated in some cases with both chromatids. The uptake of Ad12 DNA-TP appeared to be 10 to 20 times more efficient than that of Ad12 DNA completely freed of proteins. Control bacteriophage lambda, M13, or plasmid DNA could not be detected in the nuclei under these conditions.

The structure of adenovirus type 12 DNA integration sites in the hamster cell genome

Foreign DNA can integrate into the genomes of mammalian cells, and this process plays major roles in viral oncogenesis and in the generation of transgenic organisms and will be important in evolving regimens for human somatic gene therapy. In the present study, the insertion sites of adenovirus type 12 (Ad12) DNA genomes have been analyzed in detail in the Ad12-transformed hamster cell line T637, its revertants, which have lost most of the >20 Ad12 genome equivalents integrated chromosomally in cell line T637, and in the Ad12-induced tumor T191. Some of these junction sites have been molecularly cloned, and the nucleotide sequences at the sites of transition between viral and cellular DNAs have been determined. The sites of linkage between the hamster cellular and the foreign (viral) DNA are characterized by the frequent occurrence of patch homologies between the recombination partners. The cellular junction sites investigated here are not transcriptionally active. One of the cellular DNA sequences abutting the right Ad12 DNA terminus in cell line T637 (os2) is represented only once in the hamster genome and has a strikingly low abundance of 5'-CG-3' dinucleotide sequences. One 5'-GCGC-3' sequence close to the Ad12 DNA integration site is heavily methylated in normal cells, Ad12-transformed cells, and Ad12-induced tumor cells. The second such sequence is more remote from the junction site, is partly methylated in BHK21 hamster cells, and shows differences in methylation in different Ad12-transformed cell lines. This site is unmethylated in liver DNA. The cellular DNA sequence at the site of Ad12 linkage in the tumor T191 exhibits homologies to highly repetitive sequences of the Alu family and to an origin of hamster DNA replication containing an Alu element. A number of junction sites between Ad12 DNA and hamster or mouse DNA in Ad12-transformed cell lines or Ad12-induced tumor cell lines, investigated here and previously, are characterized by stem-loop structures encompassing the junction sites.

A general assay for antibody catalysis using acridone as a fluorescent tag

A simple and highly sensitive catalysis assay is demonstrated based on analyzing reactions with acridonetagged compounds by thin-layer chromatography. As little as 1 pmol of product is readily visualized by its blue fluorescence under UV illumination and identified by its retention factor (Rf). Each assay requires only 10 microliters of solution. The method is reliable, inexpensive, versatile, and immediately applicable in repetitive format for screening catalytic antibody libraries. Three examples are presented: (i) the epoxidation of acridone labeled (S)-citronellol. The pair of stereoisomeric epoxides formed is resolved on the plate, which provides a direct selection method for enantioselective epoxidation catalysts. (ii) Oxidation of acridone-labeled 1-hexanol to 1-hexanal. The activity of horse liver alcohol dehydrogenase is detected. (iii) Indirect product labeling of released aldehyde groups by hydrazone formation with an acridone-labeled hydrazide. Activity of catalytic antibodies for hydrolysis of enol ethers is detected.

On the insertion of foreign DNA into mammalian genomes: mechanism and consequences

We have studied the integration of adenovirus type 12 (Ad12) DNA in transformed and hamster tumor cells over many years. Upon infection of hamster cells with Ad12, viral DNA has been found in association with hamster chromosomes, possibly in part integrated into the host genome. Ad12 DNA integration is not sequence specific. Transcriptionally active sites of the host genome show a preponderance for foreign DNA insertion. We are pursuing the mechanism of Ad12 DNA integrative recombination in a cell-free system prepared from hamster cell nuclear extracts. In a number of Ad12-transformed hamster cell lines or in cell lines carrying foreign DNA, we have located the inserted Ad12 DNA copies on hamster chromosomes by fluorescent in situ hybridization (FISH). Among the consequences of Ad12 DNA integration, we have studied the de novo methylation of the integrated foreign (Ad12) DNA and increases in DNA methylation in several cellular genes and DNA segments in Ad12-transformed and hamster tumor cells. Several lines of evidence argue for the notion that parameters in addition to nucleotide sequence, in particular site of integration and/or the chromatin configuration of the integrated DNA, are important in generating de novo methylation patterns. The de novo methylation of integrated foreign DNA can be interpreted as an old cellular defense mechanism against the activity of foreign genes in an established genome. Pursuing this concept, we have asked for the most likely portal of entry of foreign DNA, supposedly the gastrointestinal tract in most animals. This hypothesis has been tested by feeding mice linearized or circular, double-stranded bacteriophage M13mp18 DNA.(ABSTRACT TRUNCATED AT 250 WORDS)