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M B Mathews

Publications and source records attributed to M B Mathews.

At least 91 records · Page 5Linked to original sources
PubMed1990

Control of translation in adenovirus-infected cells.

The initiation of protein synthesis in adenovirus-infected cells is regulated during the late phase in two ways, which may be related. The overall translation rate is maintained by a small viral RNA, VA RNAI, which prevents the phosphorylation of initiation factor eIF-2 by a double-stranded RNA-activated protein kinase, DAI. In addition, the relative efficiency of translation of host cell and viral mRNA populations is regulated in the infected cell during the late phase such that viral mRNAs are selectively utilized. Three viral elements have been implicated in this process: the 5' leader present on most late viral mRNAs; the late protein, 100K; and VA RNA. This article reviews the mechanisms underlying these translational control phenomena.

Adenoviridae↗
PubMed1989

Identification of a 90-kDa polypeptide which associates with adenovirus VA RNAI and is phosphorylated by the double-stranded RNA-dependent protein kinase.

Interferon treatment of mammalian cells induces a double-stranded (ds) RNA-dependent protein kinase known as DAI. When activated, DAI phosphorylates the alpha-subunit of eukaryotic initiation factor eIF-2, impairing its ability to be recycled and leading to the inhibition of protein synthesis. We have identified a novel DAI substrate in the ribosomal salt wash of rabbit reticulocyte lysates. This substrate is a 90-kDa polypeptide which has been purified to apparent homogeneity. It can be cross-linked by ultraviolet irradiation to adenovirus VA RNAI, a small RNA polymerase III transcript RNA which acts as an inhibitor of DAI. As assayed by a nitrocellulose filter binding assay, the 90-kDa polypeptide is also able to associate with authentic double-stranded RNA, but not single-stranded RNA, made in vitro. Thus, this newly identified substrate of DAI appears to have affinity for dsRNA structures and may be involved in dsRNA-regulated processes in the reticulocyte. Polyclonal and monoclonal antibodies directed against the 90-kDa polypeptide co-precipitate DAI, suggesting that these two proteins may exist as a complex.

Adenoviruses, Human↗
PubMed1989

HIV-1 Tat protein increases transcriptional initiation and stabilizes elongation.

We studied regulation of human immunodeficiency virus-1 (HIV-1) transcription by Tat and, for comparative purposes, by the adenovirus E1A protein. These two trans-activators exerted different effects. Two classes of HIV-1-promoted cytoplasmic RNA were detected, one class corresponding to full-length transcripts and the other to transcripts ending 55 and 59 nucleotides from the transcription start. Tat increased the level of the full-length class only, whereas E1A increased the levels of both classes of RNA. We also measured the effects of Tat and E1A on RNA synthesis rates. Without trans-activators, HIV-1-directed transcription was relatively weak and exhibited a marked polarity. Both Tat and E1A dramatically increased promoter-proximal transcription, while only Tat suppressed transcriptional polarity. Mutations in the TAR element did not influence basal transcription rates or the response to E1A, but eliminated trans-activation by Tat. We propose that Tat acts through TAR to increase initiation complex formation on the HIV-1 promoter and to stabilize complexes during elongation.

Adenovirus Early Proteins↗
PubMed1989

Regulation of proliferating cell nuclear antigen during the cell cycle.

The proliferating cell nuclear antigen (PCNA), also known as cyclin and DNA polymerase delta auxiliary factor, is present in reduced amounts in nongrowing cells and is synthesized at a greater rate in the S phase of growing cells. The recently discovered involvement of PCNA in DNA replication suggested that this pattern of expression functions to regulate DNA synthesis. We have investigated this possibility further by examining the synthesis, stability, and accumulation of PCNA in HeLa cells fractionated by centrifugal elutriation into nearly synchronous populations of cells at various positions in the cell cycle. In these fractionated cells we found that there is an increase in the rate of PCNA synthesis with a peak in early S phase of the cell cycle, but the magnitude of the increase is only 2-3-fold. This change reflects similar changes in the amount of PCNA mRNA. The fluctuating synthesis of PCNA maintains this protein at a roughly constant proportion of the total cell protein, although the amount doubles/cell in the cell cycle. Consistent with this observation, the stability of PCNA does not differ significantly from that of total cellular protein in synchronized HeLa cells. We also observed that a maximum of one-third of the total PCNA is tightly associated with the nucleus, presumably in replication complexes, at the peak of S phase. We conclude that the cyclic synthesis of PCNA in cycling HeLa cells maintains PCNA in excess of the amount involved directly in DNA replication and the amount of the protein neither fluctuates significantly with the cell cycle nor is limiting for DNA synthesis.

Antigens, Neoplasm↗
PubMed1989

Modification of protein synthesis initiation factors and the shut-off of host protein synthesis in adenovirus-infected cells.

A substantial body of data, largely derived from study of cell extracts, indicates that protein synthesis in adenovirus-infected cells requires VA RNAI at late times of infection to prevent the activation of a protein kinase known as DAI, and the consequent phosphorylation of the alpha-subunit of initiation factor eIF-2. To verify this conclusion, we have measured the steady-state levels of eIF-2 alpha phosphorylation in cells infected with wild-type virus (Ad2) and a mutant that produces no VA RNAI (Ad5dl331). Consistent with the proposed mechanism, the alpha-subunit was very highly phosphorylated (approximately 90%) at late times of infection with Ad5dl331. Surprisingly, eIF-2 alpha phosphorylation also increased (to approximately 30%) at late times of infection with Ad2, suggesting that VA RNA and DAI might be involved in the selective translation of viral mRNA and the shut-off of host cell protein synthesis during the late phase. In agreement with this model, host protein synthesis shut-off is defective in cells expressing low levels of DAI.

Adenoviruses, Human↗
PubMed1989

The adenovirus E1B 19-kilodalton protein stimulates gene expression by increasing DNA levels.

In transient expression assays, the adenovirus E1B 19-kilodalton (19K) tumor antigen increases expression from viral promoters and the promoter for the cellular 70-kilodalton heat shock protein (hsp70). To study the mechanism of this effect, we constructed HeLa cell lines that contain stably integrated copies of the 19K gene. Compared with a 19K- control cell line, 19K+ cells produced a significantly higher level of expression from every promoter introduced into the cells by transfection. The 19K protein also increased expression of an RNA polymerase III-transcribed gene but did not affect the level of expression of the endogenous hsp70 gene. The rate of transcription from transfected promoters, as measured by a nuclear run-on assay, was higher in the 19K+ cells than in the 19K- control cells. Furthermore, the level of plasmid DNA remained higher in the 19K+ cell line, suggesting that the 19K protein stabilizes transfected plasmid DNA. The elevated DNA levels seemed to account in full for the increased transcription. The role of the 19K protein in increasing gene expression during viral infection was found to be due to a replication-dependent increase in viral DNA levels. Thus, the 19K protein activates transcription indirectly by producing a higher level of viral or plasmid DNA. The DNA stabilization function of the 19K protein is probably related to the protective role of the 19K protein during viral infection and represents the first example of a viral oncogene product that modulates gene expression by regulating viral and plasmid DNA levels.

Adenovirus Early Proteins↗
PubMed1989

Purification and activation of the double-stranded RNA-dependent eIF-2 kinase DAI.

The double-stranded RNA (dsRNA)-dependent protein kinase DAI (also termed dsI and P1) possesses two kinase activities; one is an autophosphorylation activity, and the other phosphorylates initiation factor eIF-2. We purified the enzyme, in a latent form, to near homogeneity from interferon-treated human 293 cells. The purified enzyme consisted of a single polypeptide subunit of approximately 70,000 daltons, retained its dependence on dsRNA for activation, and was sensitive to inhibition by adenovirus VA RNAI. Autophosphorylation required a suitable concentration of dsRNA and was second order with respect to DAI concentration, which suggests an intermolecular mechanism in which one DAI molecule phosphorylates a neighboring molecule. Once autophosphorylated, the enzyme could phosphorylate eIF-2 but seemed unable to phosphorylate other DAI molecules, which implies a change in substrate specificity upon activation. VA RNAI blocked autophosphorylation and activation but permitted the activated enzyme to phosphorylate eIF-2. VA RNAI also blocked the binding of dsRNA to the enzyme. The data are consistent with a model in which activation requires the interaction of two molecules of DAI with dsRNA, followed by intermolecular autophosphorylation of the latent enzyme. VA RNAI would block activation by preventing the interaction between DAI and dsRNA.

Binding Sites↗
PubMed1988

Transcriptional but not translational regulation of HIV-1 by the tat gene product.

Human immunodeficiency virus-1 (HIV-1), which causes AIDS (acquired immune deficiency syndrome), possesses an essential gene, tat, whose product, acting through the long terminal repeat (LTR) sequences of HIV-1, activates viral genes and replication. The mechanism by which tat trans-activates HIV genes is unclear. Some studies have reported that an increase in messenger RNA accumulation directed by the HIV-1 LTR can explain the action of tat, but others suggest that this increase in mRNA levels can only partially explain trans-activation, and that translational control mechanisms may also be involved. To test those possibilities we have established an efficient adenovirus system for delivering the HIV-1 LTR attached to a reporter gene (chloramphenicol acetyltransferase; CAT) into cells and monitoring its activity. The HIV-1 LTR expressed from this adenovirus responds to trans-activation in a HeLa cell line constitutively expressing the tat protein by increasing the transcription rate of the HIV-1 LTR and the accumulation of mRNA encoding CAT. In this system the translational efficiency of this CAT mRNA in the cell is unaffected by the presence of tat.

Adenoviridae↗
PubMed1988

Effects of mutations in stem and loop regions on the structure and function of adenovirus VA RNAI.

Adenovirus virus-associated (VA) RNAI is required for efficient protein synthesis at late times of adenoviral infection, and in some other situations where double-stranded RNA (dsRNA) is present. It prevents inhibition of protein synthesis by a dsRNA-activated protein kinase and the secondary structure of VA RNAI is though to be important for its activity. To test this idea and to define structures and sequences responsible for VA RNAI activity, we constructed several mutant VA RNA genes and tested them in a transient expression assay. Activity is unaffected by deletions within a small region near the center of the gene, nt 72-85, but it is greatly diminished by deletion or substitution of sequences on the 3' side of this region. The structures of wild-type and mutant RNAs were examined by nuclease-sensitivity analysis. We propose a model for wild-type VA RNAI which differs from that predicted to be the most stable structure. Surprisingly disruption of the longest duplex region in the molecule is tolerated, provided that adjacent structural elements are not rearranged. However, perturbations of elements located in the center of the structure correlate well with loss of function.

Adenoviruses, Human↗
PubMed1988

Characterization of the double-stranded RNA implicated in the inhibition of protein synthesis in cells infected with a mutant adenovirus defective for VA RNA.

In the absence of VA RNAI, protein synthesis in adenovirus-infected HeLa cells fails at late times of infection because of defective initiation. The defect is due to the activation of a protein kinase that phosphorylates the alpha-subunit of initiation factor eIF-2. The kinase responsible for the translational defect is DAI, the double-stranded RNA (dsRNA)-activated inhibitor of protein synthesis, which is present in uninfected HeLa cells at a basal level and in a largely inactive, latent state. In vitro it can be activated by incubation with ATP and low concentration of dsRNA. Previous studies suggested that RNA generated during the course of infection can activate DAI. We show here that the activator RNA has the properties of dsRNA: it chromatographs with dsRNA, can be denatured and reannealed, and is destroyed by a dsRNA-specific nuclease. At least some of the dsRNA is viral. It hybridizes to DNA sequences in the center of the viral genome, principally between map units 47 and 51 and 73 and 76, consistent with an origin in the symmetrical transcription of both viral DNA strands.

Adenosine Triphosphate↗
PubMed1988

Trans-activation of the human immunodeficiency virus long terminal repeat sequences, expressed in an adenovirus vector, by the adenovirus E1A 13S protein.

The human immunodeficiency virus 1 (HIV-1) long terminal repeat (LTR) sequences were inserted into adenovirus in place of the E1 region. The HIV-1 LTR contained in this recombinant adenovirus responds to trans-activation by tatIII in a HeLa cell line constitutively expressing that HIV-1 gene product. In addition, the HIV-1 LTR is activated by the adenovirus E1A 13S, but not 12S or 9S, gene product when it is supplied in trans by a coinfecting wild-type adenovirus. The Rous sarcoma virus LTR, in a similar recombinant adenovirus, is insensitive to tatIII but is also trans-activated by the E1A 13S protein. The action of the 13S E1A and tatIII proteins are additive for the HIV-1 LTR in the context of adenovirus and they appear to act at the transcriptional level. As in HeLa cells, the adenovirus-borne HIV-1 LTR is inactive in the absence of a trans-activator in H9 and Jurkat cells, two human leukemic T-cell lines. This suggests that recombinant adenoviruses have diagnostic potential for the detection of trans-activators of the HIV-1 LTR that are present in circulating human lymphocytes.

Adenovirus Early Proteins↗
PubMed1987

Autoreactive epitope defined as the anticodon region of alanine transfer RNA.

Autoantibodies to aminoacyl-transfer RNA (tRNA) synthetases are common in the human autoimmune diseases polymyositis and dermatomyositis. Sera of the PL-12 specificity contain separate antibodies reacting with alanyl-tRNA synthetase and alanine tRNA (tRNAAla). The antibodies to tRNA recognize at least six distinguishable human tRNAAla species grouped into two sequence families. The antibody-reactive determinants on the tRNA were identified through ribonuclease protection and oligonucleotide binding experiments. The antibody binding site is a seven- to nine-nucleotide sequence containing the anticodon loop and requires an intact anticodon. No requirement for anticodon stem structure or sequence is observed, although the 5' portion of the stem is protected from nuclease attack. Antibodies from several patients appear to share the same specificitym, indicating that the antibodies are induced by a unique sequence feature in the immunogen.

Alanine-tRNA Ligase↗
PubMed1987

Effect of an elastin growth substrate on cholesteryl ester synthesis and foam cell formation by cultured aortic smooth muscle cells.

Exposure of smooth muscle cells cultured on plastic or glass to hyperlipidemic serum did not result in the formation of foam cells. Since elastin binds serum lipids, and vascular smooth muscle cells are normally closely associated with elastin, we investigated the effects of an elastin substrate on lipid metabolism and on the accumulation of lipid vacuoles by rabbit aortic smooth muscle cells in culture. When cells were grown in plastic petri dishes, cholesteryl ester synthesis, as measured by [14C]oleate incorporation into cholesteryl esters, was 3 times greater in rabbit hyperlipidemic serum (HLS) than in normolipemic serum (NLS) (P less than 0.001). For cells of the same subculture grown on the elastin substrate, the synthetic rate was 6-fold greater in HLS compared to NLS (P less than 0.005). The cells grown on the elastin membranes in the presence of HLS contained large numbers of Oil red O stainable lipid vacuoles and resembled foam cells, while those grown in petri dishes and exposed to HLS showed only an occasional cell containing a few vacuoles. Pre-incubation in lipoprotein-deficient serum markedly enhanced the stimulatory effect of HLS on cholesteryl ester synthesis for cells growing in plastic petric dishes but had much less stimulatory effect on the cells growing on elastin membranes. These studies indicate that close association with elastin modulates the response of smooth muscle cells to hyperlipidemia and suggest a role for elastin in the formation of foam cells of smooth muscle origin during atherogenesis.

Animals↗
PubMed1987

Different functional domains of the adenovirus E1A gene are involved in regulation of host cell cycle products.

We have analyzed the cell cycle effects that different domains of the adenovirus E1A proteins have on quiescent primary BRK cells. Studies with deletion mutants that in combination removed all but the N-terminal 85 amino acids common to both the 12S and 13S proteins suggest that this region may be sufficient for the induction of synthesis of proliferating cell nuclear antigen and the stimulation of DNA synthesis. A second domain also common to the N-terminal exon of the 12S and 13S proteins was required for the induction of mitosis and stimulation of proliferation of primary BRK cells. A virus containing a mutation in this region was still able to stimulate DNA synthesis efficiently. A third domain, unique to the 13S protein, was required for the accelerated activation of the cellular thymidylate synthase gene in a manner similar to the 13S-dependent stimulation of adenovirus early region genes.

Adenovirus Early Proteins↗
PubMed1987

Autoantibodies to intracellular antigens, with particular reference to transfer RNA and related proteins in myositis.

The common autoantibody systems are relatively few in number. The antibodies often exhibit associations with particular diseases and with one another. Furthermore, many of the corresponding antigens also exhibit striking biochemical interrelationships. In some cases the antigens comprise elements of a macromolecular complex or particle, suggesting that the complexes are likely to be the immunogens. The complexes frequently contain or interact with nucleic acids. Detailed analysis of the nature of the antigens and their interactions with autoantibodies offers promising insights into the origin of the antibodies and of autoimmune disease. This thesis is illustrated with particular reference to the myositis specific antigens.

Antibody Specificity↗
PubMed1987

Response of individual adenovirus promoters to the products of the E1A gene.

Adenovirus E1A genes possess transcriptional activation and repression activities. Three major gene products have been characterized, derived from the 13S, 12S and 9S mRNAs. Using transient expression assays in HeLa cells, we have investigated the effect of these gene products on the activity of the nine major Ad2 (or Ad5) promoters driving the expression of a reporter gene. Based on the results, we could separate the promoters into three classes: (a) E1A, which is active by itself, and is unaffected or slightly stimulated by the E1A 13S product (depending on the HeLa cell line used); (b) the other classical early promoters (E1B, E2e, E3, E4), all of which are active alone and are stimulated by the 13S product and repressed by the 12S product; and (c) the late promoters (IX, IVa2, MLP, E2L) which are not active alone and are substantially unaffected by the 13S or 12S products. Thus the 13S and 12S gene products have antagonistic effects on at least four adenovirus promoters. The 9S product did not influence the activity of any of the adenovirus promoters. Upon transfection into 293 cells, all the early promoters were active and all the late promoters were inactive, except for the major late promoter (MLP). We demonstrate that the combination of the E1A and E1B genes is a potent activator of the MLP in HeLa cells and discuss these results in the context of the infectious cycle.

Adenovirus Early Proteins↗
PubMed1987

Transactivation of host and viral genes by the adenovirus E1B 19K tumor antigen.

Adenovirus contains two nuclear oncogenes, the EIA and EIB genes, which cooperatively can transform cells through mechanisms that are not understood. The transcriptional activities of the E1A gene (transactivation and repression) are well studied. Using transient expression assays, we show here that the 19,000-Da E1B gene product can also activate all the adenovirus early promoters (E1A, E1B, E2e, E3 and E4) and a cellular heat shock gene promoter (hsp70), but not the adenovirus late promoters (IX, IVa2, MLP and E2L). The effect is greatest under conditions where cell growth is inhibited, and appears to operate at the transcriptional level. Possible interactions with enhancer elements are discussed. Although the E1B stimulatory effect does not require the presence of E1A gene products, a synergistic effect is obtained in the presence of E1A 13S product. This activity of the E1B gene is also observed during virus infection and is likely to have important consequences in lytically infected and transformed cells.

Adenovirus Early Proteins↗