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Metabolically labeled cell membrane proteins in spontaneously and in SV40 virus transformed mouse fibroblasts
Abstract:
A family of mouse fibroblast cell lines in exponential phase of growth were compared in protein constitution of their cell membranes. In preparations from these cells enriched in cell-surface membrane we observed one protein component (apparent molecular weight about 250 000) consistently to be reduced or absent in an SV40 virus transformed cell line, when compared with the normal cell line. No such compositional difference was observed in a spontaneously transformed tumorigenic clonal derivative cell line, or in subclones of such a derivative cell line, with or without SV40 virus infection. However, in metabolic labeling experiments with 14C-labeled mixed amino acids, a consistent decrease also was demonstrated in the biosynthesis of the same protein in the SV40 virus infected subclone, as compared to an uninfected sister subclone, during exponential growth. This specific difference in biosynthesis is apparently related to the presence and functioning of the SV40 gene, and correlates with the ability of these cells to grow in viscous medium, but not with cellular tumorigenicity.
Insights
SV40 virus transformation reduces a specific cell surface protein in mouse fibroblasts. This protein reduction is linked to SV40 gene activity and affects cell growth in viscous media, not tumorigenicity.
Area of Science:
- Cell Biology
- Virology
- Biochemistry
Background:
- Cell surface proteins play crucial roles in cell adhesion and signaling.
- Viral transformation can alter cellular protein composition and function.
- SV40 virus is a well-characterized oncogenic virus used to study cellular transformation.
Purpose of the Study:
- To investigate differences in cell surface protein constitution between normal and SV40 virus-transformed mouse fibroblast cell lines.
- To determine if these protein differences correlate with cellular transformation, tumorigenicity, or viral gene expression.
- To examine the biosynthesis of specific cell surface proteins in response to SV40 infection.
Main Methods:
- Comparison of cell membrane protein profiles using biochemical techniques.
- Analysis of protein expression in normal, spontaneously transformed, and SV40-transformed mouse fibroblast cell lines.
- Metabolic labeling experiments using 14C-labeled amino acids to assess protein biosynthesis.
Main Results:
- A specific cell surface protein (approx. 250,000 MW) was reduced or absent in SV40-transformed cells compared to normal fibroblasts.
- No significant compositional difference was observed in spontaneously transformed cells or SV40-infected subclones.
- SV40 infection led to decreased biosynthesis of this specific protein in infected subclones.
Conclusions:
- The reduction and decreased biosynthesis of the 250,000 MW cell surface protein are directly related to SV40 gene activity.
- This protein alteration correlates with the ability of SV40-transformed cells to grow in viscous media.
- Cellular tumorigenicity was not found to correlate with this specific protein difference.