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Transformation-sensitive protein with molecular weight of 45,000 secreted by mouse fibroblasts
Abstract:
The [35S]methionine-labeled proteins released in the medium conditioned by normal and transformed mouse fibroblasts have been analyzed by sodium dodecyl sulfate-polyacrylamide electrophoresis. Three major proteins, fibronectin, procollagens, and a protein with a molecular weight of 45,000 (45K protein) have been identified. The 45K protein, which has not yet been described, accounts for about 30% of the proteins released by control 3T3 fibroblasts or mouse embryo cultures. Quantitation of the radioactivity incorporated by the 45K protein indicated a 10- to 15-fold decrease in 3T3 fibroblasts transformed by Kirsten, Abelson, or Rous sarcoma viruses. The amounts of fibronectin and procollagens released in the medium by transformed cells were also reduced by factors of 3- and 5-fold, respectively. Pulse chase experiments have shown that the decreased level of the 45K protein in the medium of transformed cells cannot be explained by a reduced rate of secretion or by extracellular proteolytic degradation. It is not known, however, whether decreased synthesis is responsible for this alteration. The "tumor promoter" phorbol myristate acetate, which is known to induce many of the alterations associated with neoplastic cells, also induced 3T3 fibroblasts to release the 45K protein in amounts comparable to that of transformed cells. Thus, this protein represents a new molecular marker of oncoviral transformation.
Insights
A newly identified 45K protein is significantly reduced in virally transformed mouse fibroblasts. This protein, also affected by tumor promoters, serves as a novel molecular marker for oncoviral transformation.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Fibroblasts are crucial in tissue development and repair.
- Viral transformation of cells leads to significant molecular changes.
- Identifying molecular markers of transformation aids in understanding cancer progression.
Purpose of the Study:
- To identify and characterize proteins released by normal and transformed mouse fibroblasts.
- To investigate the role of a novel 45K protein in cellular transformation.
- To determine if the 45K protein can serve as a marker for oncoviral transformation.
Main Methods:
- Analysis of [35S]methionine-labeled proteins using sodium dodecyl sulfate-polyacrylamide electrophoresis.
- Quantitation of protein radioactivity in conditioned media from normal and transformed fibroblasts.
- Pulse-chase experiments to assess protein secretion and degradation rates.
Main Results:
- Identified fibronectin, procollagens, and a novel 45K protein in fibroblast-conditioned media.
- Observed a 10- to 15-fold decrease in the 45K protein in virally transformed fibroblasts.
- Found reduced levels of fibronectin (3-fold) and procollagens (5-fold) in transformed cells.
- Demonstrated that decreased 45K protein levels are not due to altered secretion or degradation.
- Showed that phorbol myristate acetate induces 45K protein release similar to transformed cells.
Conclusions:
- The 45K protein is a novel molecular marker associated with oncoviral transformation.
- Alterations in 45K protein levels are a characteristic feature of transformed cells.
- Further research is needed to determine if decreased synthesis causes the reduction of 45K protein in transformed cells.