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Changes in gene expression and protein phosphorylation in murine cells, transformed or abortively infected with wild
Abstract:
The mechanism of SV40-induced cellular transformation was investigated by two-dimensional gel analysis of 35S- and 32P-labeled proteins of various cells. These included rat and mouse cells, either transformed or abortively infected by SV40 wild type, small t deletion mutants, and a large T temperature-sensitive mutant. Synthesis, turnover, or (de)phosphorylation of multiple protein spots was found to be reproducibly and quantitatively influenced by the transformed and/or infected status. Several of these alterations were attributable to the biological activity of either large T or small t antigen. Most changes in 35S-labeled proteins corresponded to a decreased intensity of the gel spots in transformed cells, while hyperphosphorylated proteins were more common than hypophosphorylated ones. About half of the polypeptide alterations in 35S-and 32P-labeled SV40-transformed rat cells, including a set of 35S-labeled small t-dependent changes were shared by Rous sarcoma virus-transformed cells. In contrast, small t-dependent (de)phosphorylation was rarely detected. Phosphoamino acid analysis of selected phosphoprotein spots of rat cells and alkaline hydrolysis of whole two-dimensional gels did not reveal any evidence for increased tyrosine-specific phosphorylation after SV40-induced transformation. Abortively infected mouse cells showed many protein alterations, also observed in stably transformed cells. However, the latter cells contained additional changes, also affecting several phosphoproteins and possibly related to the establishment of transformation. These findings are discussed in relation to the biological functions, known or presumed, for SV40 large T and small t antigens during transformation.
Insights
SV40 infection alters protein synthesis and phosphorylation, with large T and small t antigens playing key roles in cellular transformation. Some changes in SV40-transformed cells overlap with those in Rous sarcoma virus-transformed cells.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- SV40 (Simian Virus 40) is a well-characterized DNA tumor virus used to study cellular transformation.
- Understanding the molecular mechanisms of SV40-induced transformation is crucial for cancer research.
- The roles of SV40 large T and small t antigens in transformation are complex and not fully elucidated.
Purpose of the Study:
- To investigate the protein alterations associated with SV40-induced cellular transformation.
- To differentiate the effects of SV40 large T and small t antigens on cellular proteins.
- To compare protein changes in SV40-transformed cells with those transformed by other viruses.
Main Methods:
- Two-dimensional gel electrophoresis was employed to analyze 35S-methionine and 32P-orthophosphate labeled proteins.
- Various cell types were studied, including SV40-infected and transformed rat and mouse cells, as well as Rous sarcoma virus-transformed cells.
- Mutants of SV40, including small t deletion mutants and a temperature-sensitive large T mutant, were used.
Main Results:
- SV40 infection and transformation significantly altered the synthesis, turnover, and phosphorylation of multiple cellular proteins.
- Both large T and small t antigens were found to be responsible for specific protein modifications.
- SV40 transformation led to decreased protein synthesis and increased hyperphosphorylation, with some changes shared with Rous sarcoma virus transformation.
- No evidence of increased tyrosine-specific phosphorylation was found in SV40-transformed cells.
- Abortively infected cells showed protein alterations also seen in transformed cells, which had additional changes potentially related to transformation establishment.
Conclusions:
- SV40 large T and small t antigens induce distinct and overlapping protein expression and modification patterns during cellular transformation.
- The observed protein changes provide insights into the molecular pathways regulated by SV40 antigens.
- Comparison with Rous sarcoma virus transformation highlights both common and distinct mechanisms in viral oncogenesis.