Biomedical subjects

A Op De Beeck

Publications and source records attributed to A Op De Beeck.

7 recordsLinked to original sources

PubMed2001

NS1- and minute virus of mice-induced cell cycle arrest: involvement of p53 and p21(cip1).

The nonstructural protein NS1 of the autonomous parvovirus minute virus of mice (MVMp) is cytolytic when expressed in transformed cells. Before causing extensive cell lysis, NS1 induces a multistep cell cycle arrest in G(1), S, and G(2), well reproducing the arrest in S and G(2) observed upon MVMp infection. In this work we investigated the molecular mechanisms of growth inhibition mediated by NS1 and MVMp. We show that NS1-mediated cell cycle arrest correlates with the accumulation of the cyclin-dependent kinase (Cdk) inhibitor p21(cip1) associated with both the cyclin A/Cdk and cyclin E/Cdk2 complexes but in the absence of accumulation of p53, a potent transcriptional activator of p21(cip1). By comparison, MVMp infection induced the accumulation of both p53 and p21(cip1). We demonstrate that p53 plays an essential role in the MVMp-induced cell cycle arrest in both S and G(2) by using p53 wild-type (+/+) and null (-/-) cells. Furthermore, only the G(2) arrest was abrogated in p21(cip1) null (-/-) cells. Together these results show that the MVMp-induced cell cycle arrest in S is p53 dependent but p21(cip1) independent, whereas the arrest in G(2) depends on both p53 and its downstream effector p21(cip1). They also suggest that induction of p21(cip1) by the viral protein NS1 arrests cells in G(2) through inhibition of cyclin A-dependent kinase activity.

Animals↗

PubMed2000

The transmembrane domains of hepatitis C virus envelope glycoproteins E1 and E2 play a major role in heterodimerization.

Oligomerization of viral envelope proteins is essential to control virus assembly and fusion. The transmembrane domains (TMDs) of hepatitis C virus envelope glycoproteins E1 and E2 have been shown to play multiple functions during the biogenesis of E1E2 heterodimer. This makes them very unique among known transmembrane sequences. In this report, we used alanine scanning insertion mutagenesis in the TMDs of E1 and E2 to examine their role in the assembly of E1E2 heterodimer. Alanine insertion within the center of the TMDs of E1 or E2 or in the N-terminal part of the TMD of E1 dramatically reduced heterodimerization, demonstrating the essential role played by these domains in the assembly of hepatitis C virus envelope glycoproteins. To better understand the alanine scanning data obtained for the TMD of E1 which contains GXXXG motifs, we analyzed by circular dichroism and nuclear magnetic resonance the three-dimensional structure of the E1-(350-370) peptide encompassing the N-terminal sequence of the TMD of E1 involved in heterodimerization. Alanine scanning results and the three-dimensional molecular model we obtained provide the first framework for a molecular level understanding of the mechanism of hepatitis C virus envelope glycoprotein heterodimerization.

Alanine↗

PubMed2000

Glycosylation of the hepatitis C virus envelope protein E1 is dependent on the presence of a downstream sequence on the viral polyprotein.

The addition of N-linked oligosaccharides to Asn-X-(Ser/Thr) sites is catalyzed by the oligosaccharyltransferase, an enzyme closely associated with the translocon and generally thought to have access only to nascent chains as they emerge from the ribosome. However, the presence of the sequon does not automatically ensure core glycosylation because many proteins contain sequons that remain either nonglycosylated or glycosylated to a variable extent. In this study, hepatitis C virus (HCV) envelope protein E1 was used as a model to study the efficiency of N-glycosylation. HCV envelope proteins, E1 and E2, were released from a polyprotein precursor after cleavage by host signal peptidase(s). When expressed alone, E1 was not efficiently glycosylated. However, E1 glycosylation was improved when expressed as a polyprotein including full-length or truncated forms of E2. These data indicate that glycosylation of E1 is dependent on the presence of polypeptide sequences located downstream of E1 on HCV polyprotein.

Glycoproteins↗

PubMed1997

Viruses and the cell cycle.

Viruses depend on the host's machineries to replicate and express their genome. Actively replicating cells have large pools of deoxynucleotides and high levels of key enzyme activities that viruses exploit to their own needs. Some viruses have developed strategies for driving quiescent cells into the S phase of the cell cycle, e.g. adenovirus, others, such as parvovirus, wait until the host itself begins to replicate. Viruses may also force the host cell to stay in a favourable phase, e.g. Epstein-Barr virus, or, if necessary, they may inhibit apoptotic cell death, e.g. human cytomegalovirus. In this review, we focus on the different strategies that viruses use to create in infected cells an environment favourable to the accomplishment of the viral life cycle through acting on cell cycle regulators.

Animals↗

PubMed1997

The NS1 protein of the autonomous parvovirus minute virus of mice blocks cellular DNA replication: a consequence of lesions to the chromatin?

The nonstructural protein NS1 of the autonomous parvovirus minute virus of mice interferes with cell division and can cause cell death, depending on the cell transformation state. Upon infection, the synthesis of NS1 protein is massively initiated during S phase. In this article, we show that minute virus of mice-infected cells accumulate in this phase. To investigate the link between NS1 accumulation and S-phase arrest, we have used stably transfected cells in which NS1 expression is under the control of a glucocorticoid-inducible promoter (the long terminal repeat of mouse mammary tumor virus). NS1 expression interferes with cell DNA replication, and consequently, the cell cycle stops in S phase. NS1 expression also induces nicks in the cell chromatin, as detected by an in situ nick translation assay. The nicks are observed several hours before any cell cycle perturbation. As cell cycle arrest is a common consequence of DNA damage, we propose that NS1 exerts its cytostatic activity by inducing lesions in cell chromatin.

Animals↗

PubMed1995

The nonstructural proteins of the autonomous parvovirus minute virus of mice interfere with the cell cycle, inducing accumulation in G2.

The nonstructural (NS) proteins of the autonomous parvovirus minute virus of mice (prototype strain) are involved in viral DNA replication and in the regulation of parvoviral and heterologous promoters. By constructing cell lines having integrated the NS coding sequence under the control of an inducible promoter, we were able to demonstrate that NS proteins are toxic, once expressed in the transformed cells. Cell killing appears after several days of NS expression, suggesting that NS toxicity involved cellular factors. In this paper, we show that NS proteins are cytotoxic and interfere with the cell cycle in proliferating cells only NS expression is innocuous in resting cells, whereas in growing cells, it induces the accumulation of G2 cells. This cytostatic effect is enhanced upon neoplastic transformation, which sensitized the cells to NS killing. Moreover, as clones resistant to NS toxicity undergo no alteration of their cycle, this cytostatic effect of NS proteins could be an early step on the way to cell killing. These observations strongly suggest that NS toxicity involves cellular factors associated with the regulation of the cell cycle.

Animals↗

PubMed1994

Madin Darby bovine kidney cell synchronization by lovastatin: application to bovine herpesvirus-1 gene expression.

The number of investigations involving cell proliferation has increased rapidly in the last years. One of the major difficulties in studying cell-cycle-related events is obtaining highly synchronous cell populations without metabolic imbalance. This study demonstrates that the Madin Darby bovine kidney (MDBK) cells, a commonly used cell line in veterinary research, can be effectively synchronized using lovastatin (Lov), a drug used to treat hypercholesteremia in humans. This was demonstrated by the following results: (i) Lov inhibits cell proliferation in a dose-dependent manner; (ii) Lov synchronizes MDBK cells mainly in the G1 and secondarily in the G2+M cell-cycle phases; (iii) the cytostatic effect of Lov can be specifically inhibited by addition of mevalonate (Mev) (Lov inhibits the synthesis of Mev); (iv) removal of Lov from G1-arrested cultures, followed by addition of Mev, resulted in the synchronous recovery of DNA synthesis; and (v) 5-bromo2'-deoxyuridine incorporation experiments revealed that MDBK cells synchronization by Lov can be followed for at least 3 cycles after removal of Lov and addition of Mev. Furthermore, as an application of investigations based on the availability of synchronized MDBK, we showed that bovine herpesvirus-1 gene expression is independent on the cell cycle.

Animals↗