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A mutation in the p53 tumor suppressor gene of AHH-1 tk+/- human lymphoblastoid cells
S M Morris1, M G Manjanatha, S D Shelton
1Division of Genetic Toxicology, Food and Drug Administration, Department of Health and Human Services, Jefferson, AR 72079, USA. smorris@nctr.fda.gov
Abstract:
Loss-of-function mutations in the p53 tumor suppressor gene result in an altered response to DNA-damaging agents. Included in the mutant p53 phenotype are the loss of the G1 checkpoint and delayed apoptotic cell death, characteristics we have consistently observed in the AHH-1 tk+/- cell line following exposure to DNA-damaging agents. In order to determine the functional status of p53 in the AHH-1 tk+/- cell line, molecular analysis (single-strand conformational polymorphism [SSCP] and sequence analysis) was performed on exons 5-9 of the p53 gene. In addition, the status of the p53 gene in the closely related lymphoblast line, MCL-5, which, in our hands, has a much higher spontaneous rate of apoptosis than AHH-1 tk+/-, was also determined by molecular analysis. Initial SSCP analysis of AHH-1 tk+/- revealed an abnormal migration pattern of exon 8 when compared to a wild-type control. Subsequent sequence analysis indicated that a base-pair substitution (CGG-->TGG) mutation had occurred at codon 282, a reported "hot spot' for 5-methylcytosine mutations in the human p53 gene. Neither SSCP nor sequence analysis of exons 5-9 of MCL-5 indicated any differences from wild-type DNA. These results suggest that the lack of a G1 arrest and the delayed entrance into apoptosis observed in chemically-exposed AHH-1 tk+/- cells are, at least partially, accounted for by a loss-of-function mutation in the p53 gene.
Insights
Loss-of-function mutations in the p53 tumor suppressor gene disrupt DNA damage response. AHH-1 tk+/- cells exhibit a p53 mutation, explaining their impaired G1 checkpoint and delayed apoptosis after DNA damage.
Area of Science:
- Molecular Biology
- Cancer Genetics
Background:
- Loss-of-function mutations in the p53 tumor suppressor gene alter cellular responses to DNA-damaging agents.
- The AHH-1 tk+/- cell line exhibits a loss of the G1 checkpoint and delayed apoptotic cell death upon exposure to DNA-damaging agents, suggesting a potential p53 defect.
Purpose of the Study:
- To determine the functional status of the p53 gene in the AHH-1 tk+/- cell line.
- To investigate the p53 gene status in the related MCL-5 lymphoblast line for comparison.
Main Methods:
- Molecular analysis, including single-strand conformational polymorphism (SSCP) and sequence analysis, was performed on exons 5-9 of the p53 gene.
- Comparison of p53 gene status between AHH-1 tk+/- and MCL-5 cell lines against wild-type controls.
Main Results:
- SSCP analysis of AHH-1 tk+/- cells revealed an abnormal migration pattern in exon 8.
- Sequence analysis identified a base-pair substitution (CGG-->TGG) at codon 282 in the p53 gene of AHH-1 tk+/- cells, a known mutation hotspot.
- No mutations were detected in exons 5-9 of the p53 gene in the MCL-5 cell line.
Conclusions:
- The observed p53 mutation in AHH-1 tk+/- cells likely accounts for the impaired G1 arrest and delayed apoptosis following chemical exposure.
- These findings highlight the critical role of functional p53 in maintaining genomic stability and mediating cellular responses to DNA damage.