1,720,983 research outputs found
Influence of amphotericin B on leucine uptake in 3T3 cells
No full textBy studying the effect of leucine competitors we found that activation of the specific leucine-transport system underlies the enhancement of leucine uptake in mouse 3T3 fibroblast cells induced by sublethal doses of Amphotericin B (synergic effect). The relation of the antibiotic activity and the alteration of the membrane cholesterol interaction with lipids is discussed
Interdependence between muscle differentiation and cell cycle control (Mini-Review)
No full textNo abstract availabl
Inhibition of in vitro muscle differentiation by the immortalizing oncogene Py LT-Ag
No full textThe interference of Polyomavirus (Py) early functions with in vitro myogenic differentiation is the object of this study. Single cell analysis of C2 myogenic Py infected cells showed a mutual exclusion between Py early functions and muscle gene expression. The morphological and biochemical analysis of clones obtained from C2 cells stably transfected with a plasmid carrying an ORI- Py genome, showed that myogenesis is blocked and cells display the transformed phenotype. By using plasmids separately encoding Middle T or Large T functions, the involvement of individual early viral gene products was determined. Py Middle T alone does not inhibit myotube formation even though cells are morphologically transformed. Myogenic differentiation, on the other hand, is inhibited by Py Large T. This inhibition, which is proportional to the level of Py Large T expression, does not entail to require alteration of cell growth properties and acts by blocking the expression of myogenin and terminal differentiation markers without altering the expression of the regulatory gene MyoD
Retinoblastoma antioncogene is involved in the inhibition of myogenesis by polyomavirus large T antigen
No full textThe expression of polyomavirus large T antigen in stably transfected C2 myoblast cells inhibits terminal differentiation without inducing a transformed phenotype. In the present work, we report on the lifting of this inhibition by a mutation that prevents polyomavirus large T antigen from binding to the product of the retinoblastoma susceptibility gene (p105 RB). In contrast with cells containing wild-type large T, those with the Rb binding site mutant large T showed the same up-regulation of myosine heavy chain and myogenin mRNA expression as control cells. Furthermore, we correlate the cell cycle alteration induced by polyomavirus large T antigen expression with the inability of the cells to undergo terminal differentiation
Inhibition of in vitro myogenic differentiation by a polyomavirus early function
No full textIn the present work we report on the role of a polyomavirus (Py) early function in interfering with both morphological and biochemical differentiation of the myogenic C2 cell line. The analysis of cell clones stably transfected with a plasmid carrying an ORI- Py genome showed that in the presence of the whole viral early region myogenesis is blocked and a transformed phenotype is evident. By using a plasmid that only encodes large-T function, the involvement of this individual early viral gene product was determined. Inhibition of myogenic differentiation by Py large T is proportional to the level of its expression. This inhibition does not appear to require alteration of cell growth properties. The analysis of muscle-specific functions expressed at different steps in the myogenic pathway showed that Py large T blocks the expression of terminal differentiation markers without altering the expression of the regulatory gene MyoD
MUTATIONS IN THE VP1 CODING REGION OF POLYOMAVIRUS DETERMINE DIFFERENTIATING STAGE SPECIFICITY
No full textPolyomavirus mutants capable of replicating in undifferentiated murine C2 myoblasts were selected and characterized. These mutants grow normally in 3T6 mouse fibroblast cells, and they do not complement the wild-type virus in coinfection experiments of C2 myoblasts. Of 12 isolates, 10 possess duplications of the regulatory region including the enhancer A domain. On the bases of the regulatory region structure and the presence and length of the enhancer duplication, the mutant viruses could be grouped into three classes. One mutant class (e.g., PyMB3) possesses an enhancer duplication of 91 bp identical to that of a previously characterized polyomavirus mutant, PyNB11/1. We have demonstrated that this enhancer duplication gives rise at its junction to a novel recognition motif for the transcriptional factor NF-1 (M. Caruso, C. Iacobini, C. Passananti, A. Felsani, and P. Amati, EMBO J. 9:947-955, 1990). The regulatory region PyMB3 virus recombined in a wild-type genome context maintains the mutant phenotype. The other two types of mutants, one with a 30-bp enhancer duplication (e.g., PyMB40) and one with a wild-type enhancer structure (e.g., PyMB27), possess two similar but distinct 6-bp deletions in the same region of the VP1 coding gene. In both cases, the ability to replicate in undifferentiated C2 myoblasts is strictly correlated to the mutation in the VPI coding region
Coordinate expression of myogenic functionsa and polyomavirus replication
No full textNo abstract availabl
Polyomavirus genome and polyomavirus enhancer-driven gene expression during myogenesis.
No full textThe mRNAs for myogenic functions are coordinately transcribed with polyomavirus (Py) early mRNA during in vitro differentiation of mouse C2 myoblast cells. Sequence analysis shows that the A domain of the Py enhancer includes an E1A-like consensus sequence that is also found in the 5' upstream region of two genes expressed during myoblast differentiation: alpha-actin and myosin light chain. Therefore, the coordinate expression of such genes with Py early mRNA may be activated by a common cellular regulatory factor. In the present work, we report that C2 cells surviving Py infection are unable to differentiate and do not express alpha-actin and myosin light-chain mRNAs. Hybrids between such Py-resistant myoblast cells and the parental cells exhibited dominance of the permissibility to Py growth and of the expression of myogenic mRNAs. In C2 cells transiently transfected with a chimeric plasmid (pSVPy12CAT) harboring the bacterial chloramphenicol acetyltransferase (CAT) gene driven by the Py enhancer-promoter region, the CAT gene was expressed irrespective of their stage of differentiation. Moreover, undifferentiated stably transfected cells expressing the CAT gene restricted viral growth. Py-resistant C2 myoblasts transiently transfected with pSVPy12CAT also expressed the CAT gene driven by the Py enhancer. This contradictory finding is similar to results previously obtained by other investigators with cloned genes specific for myogenic functions, and it may be explained by a structural difference between the pSVPy12CAT and the Py genomic organizations in which the viral enhancer operates
Selection of mouse neuroblastoma cell-specific polyoma virus mutants with stage differentiative advantages of replication.
No full textTwo mouse neuroblastoma cell lines were analyzed for their permissivity for polyoma virus growth. One (N18) is fully permissive for polyoma replication, the other (41A3) shows limited permissivity and the viral genome persists, without noticeable cell death. Virus persistence does not seem to alter the cells' ability to differentiate in vitro and leads to selection of viral mutants altered in the untranscribed regulatory region of the genome. The mutant types obtained appear to be related to the degree of host cell differentiation. Nucleotide sequence analysis of the restriction fragment covering the regulatory region shows that duplications are present in all mutants, while deletions in the non-duplicated segment are only present in mutants selected from less differentiated cells. These alterations involve both domains of the regulatory region that are considered to be essential for DNA replication and for enhancer activity. Mixed infections with polyoma wild type show that the selected mutants have cis-advantage in replication in neuroblastoma cells and not in 3T6 cells. Mutants carrying the deletion in the non-duplicated segment of the enhancer show a selective advantage in replication over the undeleted one in mixed infection. This advantage is much stronger in neuroblastoma cells in suspension (less-differentiated stage) than in monolayer cells (more-differentiated stage). An interpretation of the overall structure of the regulatory enhancer region, based on the observed differences between the mutants selected at different stages of differentiation in neuroblastoma and previously described mutants selected in undifferentiated cells, is discussed
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