Shut-off of actin biosynthesis in adenovirus serotype-2-infected cells

A20 RNA expression is associated with undifferentiated nasopharyngeal carcinoma and poorly differentiated head and neck squamous cell carcinoma

A20 is an anti-apoptotic gene that can be induced in human epithelial cell lines in response to expression of the Epstein-Barr virus (EBV) gene product latent membrane protein 1 (LMP1). EBV is a ubiquitous, persistent human herpesvirus that is consistently associated with undifferentiated nasopharyngeal carcinoma (NPC), in which antigen expression includes LMP1. Consistent with a potential role in the development of NPC, LMP1 has profound effects on epithelial cell growth. A20 may be a key downstream effector of LMP1 in NPC, as LMP1-induced A20 blocks p53-mediated apoptosis in H1299 epithelial cells and most NPCs have wild-type p53. Moreover, the potential role of A20 in the development of epithelial malignancies may extend to tumours not associated with EBV. The purpose of this study was to develop an in situ hybridization assay to assess expression of A20 RNA in undifferentiated NPC and in non-EBV-associated poorly differentiated head and neck squamous cell carcinomas (SCCs) and well-differentiated SCCs of the skin. A20 RNA expression was also examined in normal samples of oral mucosa and skin. Expression of A20 was demonstrated in 76 per cent of undifferentiated NPCs and in 80 per cent of poorly differentiated head and neck SCCs, suggesting a role for A20 in the pathogenesis of these epithelial malignancies. By contrast, A20 RNA was not detected in well-differentiated SCCs of the skin, or in any normal samples of squamous epithelial tissue. The pathway leading to A20 expression in non-EBV-associated poorly differentiated head and neck SCCs is clearly LMP1-independent. LMP1 expression was demonstrated in 29 per cent of NPC biopsies, suggesting an LMP1-independent pathway to A20 induction in undifferentiated NPC.

Lipopolysaccharide-Induced Desensitization of junB Gene Expression in a Mouse Macrophage-Like Cell Line, P388D1

Treatment of a mouse macrophage cell line, P388D1, for 1 h with bacterial LPS caused a transient increase in the level of junB mRNA expression. These cells became refractory in terms of the junB gene response to exposure to a second round of LPS or lipid A, but not to PMA. The LPS-induced desensitized state was not due to the shortening of the half-life of junB mRNA, but was suggested, by nuclear run-on analysis, to be caused by reduction of junB gene transcription. Pretreating cells with herbimycin A, a tyrosine kinase inhibitor, substantially inhibited LPS-induced expression of junB mRNA and decreased tyrosine phosphorylation of 38- to 42-kDa proteins, which comigrated with p38 and p42 mitogen-activated protein (MAP) kinases. Parallel to down-regulation of junB mRNA expression, activation of the p38 MAP kinase was markedly reduced in LPS-tolerant cells, whereas activation of p42 MAP kinase was relatively constant. The specific p38 MAP kinase inhibitor, SB202190, potently inhibited LPS-induced junB mRNA expression. These results suggest that the LPS-induced desensitization of junB gene expression occurs at or upstream of the level of gene transcription and may be involved in a defective LPS-induced p38 MAP kinase pathway.

Biological consequences of a point mutation at codon 969 of the FMS gene

The FMS proto-oncogene encodes the cell surface receptor for colony stimulating factor-1 (CSF-1). Mutations of the FMS gene at codon 969, in the C-terminal region of the gene, have been detected in haematological malignancies. To ascertain the biological significance of a mutation at this codon, we have used a murine haematopoietic cell line, FDC-P1, containing a mutation at codon 969 that results in a phenylalanine replacing a tyrosine. FMS 969 mutant cells and v-fms transfected cells conferred interleukin 3 (IL-3) independent stimulation of FDC-P1 cells, whereas cells transfected with a wild-type FMS construct required exogenous IL-3 for growth. FDC-P1 cells containing a FMS 969 mutation and v-fms transfected cells were tumorigenic in nude mice. Binding studies with radioidonated CSF-1 revealed saturable specific binding in FMS wild-type cells with a Km of 0.9 mM; however, mutant FMS-containing cells did not display saturation kinetics, but instead exhibited a linear relationship between ligand concentration and amount bound. Constitutive expression of FOS was detected in 969 mutant cells in the absence of exogenous CSF-1, a phenotype that was only inducible in wild-type cells in response to CSF-1. FOS and JUNB expression by v-FMS transfected cells showed a similar pattern to FMS wild-type cells. This mutation has been detected in patients with haematological malignancies, and illustrates that the pathway of FMS 969 phenylalanine mutations and v-fms induced pathogenesis can be distinguished. These data indicate that there is a biological role for FMS codon 969 phenylalanine mutation which results in transformation of FDC-P1 cells.

Dexamethasone inhibits nitric oxide-mediated cytotoxicity via effects on both macrophages and target cells

In order to evaluate the mode of action of dexamethasone (DEX) on macrophage-mediated cytotoxicity and to understand its association with nitric oxide (NO) production, the effect of DEX on macrophage- and spermine NONOate-mediated cytotoxicity was studied. DEX caused 100% inhibition of cytotoxicity by LPS- and IFN gamma-activated macrophages whereas it caused only partial inhibition of NO production. Inhibition of macrophage-mediated cytotoxicity by DEX was not reversed by supplementation of rTNF alpha. The partial inhibition of NO production by DEX was due to partial inhibition of iNOS mRNA expression. Incubation of macrophages with DEX for up to 24 h prior to activation did not cause further inhibition of NO production. DEX failed to inhibit NO production if added 6 h after addition of LPS and IFN gamma. Addition of P815 cells after the onset of NO production resulted in partial restoration of cytotoxicity in DEX-treated macrophages. Incubation of P815 cells with spermine NONOate, a synthetic NO donor, resulted in P815 cell lysis, which was dose-dependent, had a lag phase of 3 h and was blocked by hemoglobin. DEX also inhibited spermine NONOate-mediated tumor cell lysis, indicating that DEX may have a protective effect on tumor targets. These results indicate that DEX inhibits macrophage-mediated cytotoxicity by decreasing NO production and by inhibiting the cytotoxic effects of NO on the target cells.

Dissection of functional domains in the adenovirus 2 early 1B 55K polypeptide by suppressor-linker insertional mutagenesis

To determine whether the viral replication functions of the adenovirus E1B 55K protein play a role in its ability to transform cloned rat embryo fibroblast cells in culture, we constructed an extensive series of insertion mutations throughout the 55K gene. The mutations were recombined into infectious virus and characterized for their abilities to produce stable 55K protein in HeLa cells, replicate virus in HeLa cells, express late viral proteins efficiently, and transform CREF cells following infection. Mutant 55K transforming activity in primary baby rat kidney cells was also assayed following DNA transfection. The functions required for viral replication are encoded in several patches of the 55K linear sequence, while the CREF transforming functions are sensitive to all of the insertions. An insertion at amino acid 380 created a mutant virus which was reduced in transforming activity, but was not reduced for viral replication. Therefore, a function required for efficient transformation of CREF cells can be separated from functions required for late gene expression and viral replication. Transformation of BRK cells following DNA transfection was reduced by complete disruption of the 55K protein gene, but was not significantly affected by any of the insertions.

Enteric adenovirus type 40: expression of E1B mRNA and proteins in permissive and nonpermissive cells

The enteric adenovirus type 40 (strain Dugan) grows well in tissue culture only when the E1B 55K protein of Ad5 or Ad12 is supplied in trans, either constitutively expressed in an established cell line or by coinfection with an appropriate helper virus (V. Mautner, N. Mackay, and V. Steinthorsdottir, 1989, Virology 171, 619-622). The synthesis of Ad40 E1B mRNAs and proteins has been examined under permissive and nonpermissive conditions: At late times postinfection in permissive cells, E1B-specific mRNA species of 22 and 13-14 S are made, as well as 15 and 9 S messages for the late IVa2 and ppIX proteins. None of these are detected before the onset of DNA replication and none of them accumulate in the presence of a cytosine arabinoside block to DNA replication. The failure to detect cytoplasmic mRNAs as early times cannot be attributed to a failure of mRNA transport from the nucleus as there is no accumulation of nuclear E1 RNA. In nonpermissive Hela cells only traces of E1B- and ppIX-specific mRNAs are detectable, at very late times postinfection. Antibodies raised to synthetic oligopeptides corresponding to the N- and C-terminal domains of the putative E1B 19K and 55K proteins show a high titer against the cognate peptide by ELISA, but only the E1B 19K C-terminus-specific sera have detected a unique polypeptide in Ad40-infected cells, at late times postinfection. There is no shut-off of host protein synthesis in permissive cells, despite the expression of Ad2 55K protein.

The adenovirus L4 100-kilodalton protein is necessary for efficient translation of viral late mRNA species

When screening a number of adenovirus type 5 (Ad5) temperature-sensitive mutants for defects in viral gene expression, we observed that H5ts1-infected 293 cells accumulated reduced levels of newly synthesized viral late proteins. Pulse-labeling and pulse-chase experiments were used to establish that the late proteins synthesized in H5ts1-infected cells under nonpermissive conditions were as stable as those made in Ad5-infected cells. H5ts1-infected cells contained normal levels of viral late mRNAs. Because these observations implied that translation of viral mRNA species was defective in mutant virus-infected cells, the association of viral late mRNAs with polyribosomes was examined during the late phase of infection at a nonpermissive temperature. In Ad5-infected cells, the majority of the viral L2, L3, L4, pIX, and IVa2 late mRNA species were polyribosome bound. By contrast, these same mRNA species were recovered from H5ts1-infected cells in fractions nearer the top of polyribosome gradients, suggesting that initiation of translation was impaired. During the late phase of infection, neither the polyribosome association nor the translation of most viral early mRNA species was affected by the H5ts1 mutation. This lesion, mapped by marker rescue to the L4 100-kilodalton (kDa) nonstructural protein, has been identified as a single base pair substitution that replaces Ser-466 of the Ad5 100-kDa protein with Pro. A set of temperature-independent revertants of H5ts1 was isolated and characterized. Either true reversion of the H5ts1 mutation or second-site mutation of Pro-466 of the H5ts1 100-kDa protein to Thre, Leu, or His restored both temperature-independent growth and the efficient synthesis of viral late proteins. We therefore conclude that the Ad5 L4 100-kDa protein is necessary for efficient initiation of translation of viral late mRNA species during the late phase of infection.

Platelet-derived growth factor-stimulated c-myc RNA accumulation in MG-63 human osteosarcoma cells is independent of both protein kinase A and protein kinase C

Treatment of quiescent MG-63 cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) or platelet-derived growth factor (PDGF) stimulates the rapid accumulation of c-myc RNA. We have now determined that a similar effect can be induced by cAMP. Treatment with forskolin (an activator of adenylate cyclase), IBMX (a phosphodiesterase inhibitor), PGE1, and isoproterenol stimulated accumulation of both cAMP and c-myc RNA, but no increase in either cAMP or c-myc RNA was seen with the inactive forskolin analog 1,9-dideoxyforskolin. Forskolin and IBMX acted synergistically in stimulating accumulation of both cAMP and c-myc RNA. However, three lines of evidence indicated that PDGF action is not mediated by cAMP. First, PDGF treatment caused no elevation of cAMP within 1 h, even in the presence of IBMX. Second, the kinetics of c-myc RNA elevation after treatment with PDGF or forskolin were similar, ruling out delayed onset of cAMP stimulation. Finally, simultaneous treatment with forskolin and the calcium ionophore A23187 enhanced the elevation of c-myc RNA levels; no such effect was seen with PDGF. We had previously shown that PDGF action is not affected by prior treatment of MG-63 cells with TPA, a treatment which desensitizes the c-myc response to TPA. Similarly, TPA pretreatment had minimal effect on forskolin or IBMX-induced c-myc expression. These data suggest that cAMP, phorbol esters, and PDGF act independently to stimulate c-myc RNA expression in MG-63 cells. However, nuclear runoff experiments and RNA half-life measurements demonstrated that PDGF, phorbol ester, and cAMP all act to increase the transcription of the MYC gene.

Platelet-derived growth factor-stimulated c-myc RNA accumulation in MG-63 human osteosarcoma cells is independent of both protein kinase A and protein kinase C

Treatment of quiescent MG-63 cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) or platelet-derived growth factor (PDGF) stimulates the rapid accumulation of c-myc RNA. We have now determined that a similar effect can be induced by cAMP. Treatment with forskolin (an activator of adenylate cyclase), IBMX (a phosphodiesterase inhibitor), PGE1, and isoproterenol stimulated accumulation of both cAMP and c-myc RNA, but no increase in either cAMP or c-myc RNA was seen with the inactive forskolin analog 1,9-dideoxyforskolin. Forskolin and IBMX acted synergistically in stimulating accumulation of both cAMP and c-myc RNA. However, three lines of evidence indicated that PDGF action is not mediated by cAMP. First, PDGF treatment caused no elevation of cAMP within 1 h, even in the presence of IBMX. Second, the kinetics of c-myc RNA elevation after treatment with PDGF or forskolin were similar, ruling out delayed onset of cAMP stimulation. Finally, simultaneous treatment with forskolin and the calcium ionophore A23187 enhanced the elevation of c-myc RNA levels; no such effect was seen with PDGF. We had previously shown that PDGF action is not affected by prior treatment of MG-63 cells with TPA, a treatment which desensitizes the c-myc response to TPA. Similarly, TPA pretreatment had minimal effect on forskolin or IBMX-induced c-myc expression. These data suggest that cAMP, phorbol esters, and PDGF act independently to stimulate c-myc RNA expression in MG-63 cells. However, nuclear runoff experiments and RNA half-life measurements demonstrated that PDGF, phorbol ester, and cAMP all act to increase the transcription of the MYC gene.

Effect of 2',5'-oligoadenylate on herpes simplex virus-infected cells and preventive action of 2',5'-oligoadenylate on the lethal effect of HSV-2

Antiviral effects of ppp(A2'p)nA, (2-5A) on herpes simplex virus type 1 or type 2 (HSV-1 or HSV-2)-infected baby hamster kidney fibroblasts (BHK cells) and HSV-2-infected female guinea pigs were examined. 2-5A was introduced into BHK cells in the form of a calcium phosphate precipitate and as an ointment of polyethylene glycol (PEG) into guinea pig vagina. Under optimum conditions, 2-5A trimer and other 2-5A derivatives inhibited over 90% of HSV-1 syncytia formation and over 50% of HSV-2 plaque formation. The growth of uninfected cells was only slightly and transiently inhibited under these conditions. Northern analysis of viral immediate early mRNAs and cellular mRNAs showed that all transcripts determined were reduced in amount by the 2-5A trimer treatment. The reduction in level of viral mRNAs (ICP4, ICP22, and ICP47) by 2-5A trimer was significantly more than that of cellular mRNAs (represented by beta-actin). HSV-2 (strain 186) inoculation into the vagina of female guinea pigs causes severe symptoms in the genital area and high mortality. Topically applied 2-5A trimer almost completely prevented the lethal effect of HSV-2. These data are discussed from the viewpoint of mechanism of interferon action.

Analysis of the transcript of the herpes simplex virus DNA polymerase gene provides evidence that polymerase expression is inefficient at the level of translation

We have mapped the termini and determined the relative abundance and ribosome density of the major cytoplasmic transcript of the DNA polymerase (pol) gene of herpes simplex virus type 1. Nuclease protection and primer extension analyses located the 5' end of the major pol transcript at two closely spaced sites 51 and 57 nucleotides to the left of a BamHI site at map position 0.413. S1-sensitive sites corresponding to additional minor transcripts were found to map further upstream within a palindromic sequence that contains a viral replication origin. The major 3' end was found to map 90 nucleotides upstream of a KpnI site at map position 0.439. Quantitative S1 nuclease assays revealed that pol transcripts were nearly as abundant as transcripts encoded by the viral thymidine kinase gene. However, relatively few pol transcripts were found on large polysomes at 5.5 h after infection, when pol transcripts were most abundant. This was in marked contrast to the polyribosome distribution of transcripts from the thymidine kinase gene and the major DNA-binding protein gene. These results and sequence features of the pol transcript suggest that pol expression is regulated, in part, at the level of translation.

Inhibition of gene expression at the translational level by cotransfection with competitor plasmids

We have investigated the effect of cotransfection with other recombinant plasmids on the expression of a test plasmid, p2A9PrCAT, in which the calcyclin promoter directs the expression of the bacterial chloramphenicol transferase (CAT) coding sequence. The expression of CAT is markedly inhibited when p2A9PrCAT is cotransfected with any of several plasmids in which a promoter controls the expression of complete or partial transcribed sequences. A series of experiments indicates that the inhibition is not sequence specific, does not require a full-length protein product, but it requires a transcript, since cotransfection with a vector containing only a promoter gives only a modest inhibition. Although CAT activity is decreased markedly in these competition experiments, the amount of CAT mRNA is unaffected, indicating that the inhibition must take place at a translational level.

Adenovirus proteins associated with mRNA and hnRNA in infected HeLa cells

The proteins that interact with cytoplasmic and nuclear polyadenylated RNA in adenovirus type 5 (Ad5) infection of HeLa cells were examined by UV-induced RNA-protein cross-linking in intact cells. The Ad5 100-kilodalton late nonvirion protein (100K protein) was cross-linked to both host and viral polyadenylated cytoplasmic RNA (mRNA). The cross-linking of the 100K protein to mRNA appears to correlate with productive infection, because the protein is not cross-linked to mRNA in abortive infection of wild-type Ad5 in monkey cells (CV-1) even though normal amounts of it are produced. However, when CV-1 cells are infected with Ad5 hr404, and Ad5 mutant which overcomes the host restriction to wild-type Ad5 infection in these cells, the 100K protein is cross-linked to mRNA. To identify and obtain antibodies to RNA-contacting proteins, a mouse was immunized with oligo(dT)-selected cross-linked RNA-protein complexes from Ad5-infected cells and the serum was used for immunoblotting experiments. It was found that in addition to the 100K protein, the Ad5 72K DNA-binding protein is also associated with RNA in the infected cells. The 72K DNA-binding protein is cross-linked to polyadenylated nuclear RNA sequences. These findings indicate that adenovirus proteins interact with RNAs in the infected cell and suggest possible mechanisms for the effects of the virus on mRNA metabolism.

Cellular mRNA translation is blocked at both initiation and elongation after infection by influenza virus or adenovirus

During influenza virus infection, protein synthesis is maintained at high levels and a dramatic switch from cellular to viral protein synthesis occurs despite the presence of high levels of functional cellular mRNAs in the cytoplasm of infected cells (M. G. Katze and R. M. Krug, Mol. Cell. Biol. 4:2198-2206, 1984). To determine the step at which the block in cellular mRNA translation occurs, we compared the polysome association of several representative cellular mRNAs (actin, glyceraldehyde-3-phosphate dehydrogenase, and pHe7 mRNAs) in infected and uninfected HeLa cells. We showed that most of these cellular mRNAs remained polysome associated after influenza viral infection, indicating that the elongation of the proteins encoded by these cellular mRNAs was severely inhibited. Because the polysomes containing these cellular mRNAs did not increase in size but either remained the same size or decreased in size, the initiation step in cellular protein synthesis must also have been defective. Several control experiments established that the cellular mRNAs sedimenting in the polysome region of sucrose gradients were in fact associated with polyribosomes. Most definitively, puromycin treatment of infected cells caused the dissociation of polysomes and the release of cellular, as well as viral, mRNAs from the polysomes, indicating that the cellular mRNAs were associated with polysomes that were capable of forming at least a single peptide bond. A similar analysis was performed with HeLa cells infected by adenovirus, which also dramatically shuts down cellular protein synthesis. Again, it was found that most of the cellular mRNAs, which were translatable in reticulocyte extracts, remained associated with polysomes and that there was a combined initiation-elongation block to cellular protein synthesis. In cells infected by both adenovirus and influenza virus, influenza viral mRNAs were on larger polysomes than were several late adenoviral mRNAs with comparably sized coding regions. In addition, after influenza virus superinfection of cells infected by the adenovirus mutant dl331, a situation in which there is a limitation in the amount of functional initiation factor eIF-2 (M. G. Katze, B. M. Detjen, B. Safer, and R. M. Krug, Mol. Cell. Biol. 6:1741-1750, 1986), influenza viral mRNAs, but not late adenoviral mRNAs, were on polysomes. These results indicate that influenza viral mRNAs are better initiators of translation than are late adenoviral mRNAs.

Adenovirus E1B proteins are required for accumulation of late viral mRNA and for effects on cellular mRNA translation and transport

Late in adenovirus infection, large amounts of viral mRNA accumulate while cell mRNA transport and translation decrease. Viruses deleted in the E1B region of type 5 adenovirus do not produce the same outcome: (i) viral mRNA synthesis by the mutants is normal, delivery to the cytoplasm is 50 to 75% of normal, but steady-state levels of viral mRNA are decreased 10-fold; (ii) cell mRNA synthesis and transport continue normally in the mutant virus-infected cell; and (iii) translation of preexisting cell mRNA which is disrupted in wild-type infection remains normal in mutant-virus-infected cells. Thus E1B proteins are required for accumulation of virus mRNA and for induction of the failure of host cell mRNA transport and translation. If a single function is involved, by inference the transport and some aspect of translation of mRNAs could be linked.

Analysis of the 3' flanking region of the human c-myc gene in lymphomas with the t(8;22) and t(2;8) chromosomal translocations

We have cloned and mapped the sequences extending 38 kb 3' of the c-myc gene. This region is found to be highly repetitive in nature and hybridizes extensively with a BLUR 8 Alu probe. Unique sequence probes derived from this region were used to map the chromosomal breakpoints of a number of lymphoma cell lines with t(2;8) or t(8;22) translocations. In five of the cell lines (PA682, LY67, LY47, LY66 and LY91), the immunoglobulin light chain locus translocates into a region which is greater than 47 kb downstream of c-myc. For one of the cell lines, JI, the location of the breakpoint on the 8q+ chromosome was found to be 25-32 kb 3' of c-myc. The breakpoint for the BL2 cell line had been previously mapped at 10 kb 3' of the c-myc oncogene. Analyses of steady-state levels of c-myc mRNA in cell lines with chromosomal breakpoints ranging from 10 kb to greater than 47 kb 3' of c-myc range from 0.5 to 10X the levels in lymphoblast controls. The different levels of c-myc transcripts is not a direct function of the distance between the c-myc gene and the translocated immunoglobulin light chain locus.

Adenovirus E1B proteins are required for accumulation of late viral mRNA and for effects on cellular mRNA translation and transport

Late in adenovirus infection, large amounts of viral mRNA accumulate while cell mRNA transport and translation decrease. Viruses deleted in the E1B region of type 5 adenovirus do not produce the same outcome: (i) viral mRNA synthesis by the mutants is normal, delivery to the cytoplasm is 50 to 75% of normal, but steady-state levels of viral mRNA are decreased 10-fold; (ii) cell mRNA synthesis and transport continue normally in the mutant virus-infected cell; and (iii) translation of preexisting cell mRNA which is disrupted in wild-type infection remains normal in mutant-virus-infected cells. Thus E1B proteins are required for accumulation of virus mRNA and for induction of the failure of host cell mRNA transport and translation. If a single function is involved, by inference the transport and some aspect of translation of mRNAs could be linked.

Actin mRNAs in HeLa cells. Stabilization after adenovirus infection

We have carried out a comparative analysis of the expression of the actin genes in HeLa and adenovirus-infected HeLa cells. The rate of actin gene transcription was examined in these cells by pulse-labeling of the newly synthesized RNA and/or by in vitro transcription in nuclei isolated from uninfected or infected HeLa cells. In addition, accumulation of actin-specific heterogeneous nuclear RNA, and rate of appearance of the actin mRNAs in the cytoplasm were examined by dot and Northern blot analysis. The rate of actin gene transcription remained constant after infection of HeLa cells with adenovirus serotype 2, while the level of the actin precursor in the nuclei was slightly reduced. In the infected cells, newly synthesized actin mRNA enters the cytoplasm at a very reduced rate. The deficiency of transport does not affect the steady-state level of the messages in the cytoplasm. The half-life of cytoplasmic actin mRNAs was analyzed by traditional pulse-chase experiments and by a novel procedure using 5-6-diCl-1-beta-d-ribofuranosylbenzimidazole, which does not rely on labeled RNA. Both procedures gave identical results. Uninfected HeLa cells have actin mRNAs with relatively short half-lives, from less than six to 12 hours. In contrast, the half-lives of the actin-specific mRNAs, in the cytoplasm of adenovirus-infected cells, is greater than 14 to 24 hours. These observations suggest that, although the rate of transport of actin mRNAs to the cytoplasm is reduced upon infection with adenovirus, increased half-lives result in accumulation of actin mRNAs to normal levels in the cytoplasm.