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Early superoxide dismutase alterations during SV40-transformation of human fibroblasts
A Bravard1, F Hoffschir, L Sabatier
1CEA/DSV/DPTE/LCG, Fontenay aux Roses, France.
Abstract:
The expression of superoxide dismutases (SOD) 1 and 2 was studied in 4 clones of human fibroblasts after their infection by simian virus 40 (SV40), in parallel with the alterations of chromosomes 21 and chromosome 6q arms, carrying the genes that encode for SOD1 and SOD2 respectively. For all clones, a similar scheme with 2 main phases was observed for both chromosome and SOD variations. The first phase, defined as the pre-crisis phase, was characterized by chromosomal instability, but maintenance of normal numbers of chromosome 6q arms and chromosomes 21. The level of SOD2 mRNA was high, while SOD2 activity and immunoreactive protein were low. SOD1 protein and activity were decreased. In the second phase, defined as the post-crisis phase, the accumulation of clonal chromosomal rearrangements led to the loss of 6q arms, while the number of chromosomes 21 remained normal. SOD2 mRNA level was decreased and SOD2 immunoreactive protein and activity remained low. SOD1 protein and activity increased with passages, reaching values similar to those of control cells at late passages. As in established SV40-transformed human fibroblast cell lines, good correlation was found between SOD2 activity and the relative number of 6q arms. These results allow us to reconstruct the sequence of events leading to the decrease of SOD2, a possible tumor-suppressor gene, during the process of SV40-transformation of human fibroblasts.
Insights
Simian virus 40 (SV40) infection in human fibroblasts causes chromosomal changes and alters superoxide dismutase (SOD) expression. SOD2 levels decrease, potentially acting as a tumor suppressor during SV40 transformation.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Superoxide dismutases (SOD) are crucial enzymes for cellular defense against oxidative stress.
- Simian virus 40 (SV40) is a well-characterized DNA virus used to study cellular transformation.
- Chromosomal abnormalities are hallmarks of cancer and can be induced by viral infections.
Purpose of the Study:
- To investigate the relationship between SV40-induced chromosomal alterations and the expression of SOD1 and SOD2 in human fibroblasts.
- To elucidate the sequential events affecting SOD gene expression and activity during SV40 transformation.
- To determine if SOD2 functions as a tumor suppressor during SV40-induced cellular transformation.
Main Methods:
- Culturing of human fibroblast clones and infection with SV40.
- Monitoring of chromosomal changes, specifically chromosome 21 and 6q arms.
- Quantification of SOD1 and SOD2 mRNA levels, protein expression, and enzymatic activity.
Main Results:
- SV40 infection induced two distinct phases: pre-crisis (chromosomal instability, high SOD2 mRNA, low SOD2 activity/protein, decreased SOD1) and post-crisis (loss of 6q arms, decreased SOD2 mRNA, low SOD2 activity/protein, increased SOD1).
- A strong correlation was observed between SOD2 activity and the number of 6q arms in late passages.
- SOD1 levels recovered to control values in late passages, while SOD2 remained suppressed.
Conclusions:
- SV40 transformation of human fibroblasts involves a specific sequence of chromosomal and SOD expression changes.
- The decrease in SOD2, a potential tumor suppressor, is a key event during SV40-induced transformation.
- Chromosomal instability, particularly the loss of 6q arms, is linked to reduced SOD2 activity.