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A mutant strain of mouse FM3A cells defective in apoptotic DNA fragmentation
Y Yamauchi1, A Tanaka, F Hanaoka
1Cellular Physiology Laboratory, Institute of Physical and Chemical Research (RIKEN), Saitama, Japan.
Abstract:
A mutant strain of mouse FM3A cells was defective in apoptotic DNA fragmentation. Upon DNA damage by UV-radiation, the strain did not form DNA fragments, though it accumulated a large amount of p53 protein as did wild-type cells. No DNA fragmentation was observed when the strain was subjected to other kinds of DNA damaging agents such as X ray-radiation, or addition of etoposide to the culture medium. Other well-known biological stimulations inducing apoptosis, serum depletion or addition of TNF-alpha to the culture medium, also failed to cause DNA fragmentation in the cells. Using this apoptosis-deficient strain, we characterized another apoptotic reaction, export of phosphatidylserine to the cell surface. This molecule was exported onto the surface in both wild-type and the mutant cells when cells were treated with TNF-alpha and cycloheximide. Thus, the export of phosphatidylserine is suggested to be independent of the pathway for apoptotic DNA fragmentation.
Insights
This study identifies a mouse cell strain lacking apoptotic DNA fragmentation, even when exposed to DNA damage. This defect is separate from phosphatidylserine export, a key marker of apoptosis.
Area of Science:
- Cell Biology
- Molecular Biology
- Apoptosis Research
Background:
- Apoptosis, or programmed cell death, is a crucial biological process.
- DNA fragmentation is a hallmark of apoptosis, but its regulatory pathways are complex.
- Understanding the molecular mechanisms of apoptosis is vital for disease research.
Purpose of the Study:
- To investigate a mouse cell strain exhibiting a defect in apoptotic DNA fragmentation.
- To determine if this defect affects other apoptosis-related cellular events.
- To elucidate the relationship between DNA fragmentation and phosphatidylserine externalization.
Main Methods:
- Utilized a mutant mouse FM3A cell strain deficient in apoptotic DNA fragmentation.
- Exposed cells to various DNA damaging agents (UV, X-ray, etoposide) and apoptosis inducers (serum depletion, TNF-alpha).
- Assessed DNA fragmentation and phosphatidylserine export on the cell surface.
Main Results:
- The mutant cell strain failed to exhibit DNA fragmentation upon exposure to UV radiation, X-rays, or etoposide.
- Despite the lack of DNA fragmentation, p53 protein accumulated similarly to wild-type cells.
- Phosphatidylserine was exported to the cell surface in both mutant and wild-type cells when treated with TNF-alpha and cycloheximide.
Conclusions:
- The identified mouse cell strain is specifically defective in apoptotic DNA fragmentation.
- This defect is independent of p53 accumulation and other common apoptosis-inducing stimuli.
- Phosphatidylserine export is a distinct apoptotic event, not reliant on the DNA fragmentation pathway.