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The p53 mutation which abrogates trans-activation while maintaining its growth-suppression activity
1Department of Biological Sciences, College of Natural Sciences, Chonnam National University, Kwangju, Korea. sjo@chonnam.chonnam.ac.kr
Abstract:
The p53 tumor suppressor protein functions as a transcription factor. It has, however, been previously reported that some p53 mutants are able to suppress cell growth independent of their transcriptional activity [Kaneuchi et al., (1999)]. In order to investigate the correlations between the trans-activation and growth-suppressive functions of p53, we have analyzed five p53 mutants by CAT reporter assay, colony formation assay, and growth-rate analysis. Five p53 mutants [Oh et al., (2000)]--199stop (Gly-->stop), 240ile (Ser-->Ile), 250ala (Pro-->Ala), 285lys (Glu-->Lys), and 291asn (Lys-->Asn)--were cotransfected with a reporter construct containing a p53-responsive element and then tested for their trans-activational activity in p53-null Saos-2 cells. As a result of a change in the protein structure, trans-activational activity was negated in 199stop, 240ile, 285lys, and 291asn, while 250ala retained its activity. Colony formation assay revealed that mutants 240ile and 250ala retained their growth suppression, while 199stop, 285lys, and 291asn did not. To study the features of these proteins, a group of isogenic cell lines that express mutant forms of p53 was generated from HeLa cells, and their growth rate was then examined: one group, containing 199stop, 285lys, and 291asn, showed a rapid growth rate, similar to that of the original HeLa cells; the other group, containing 240ile and 250ala, however, exhibited a slow growth rate. In conclusion, mutant p53 240ile, which completely lost its trans-activational activity, nevertheless continued to exhibit its growth-suppressive activity. Further work is required to understand how 240ile is involved in growth suppression.
Insights
Mutant p53 protein can suppress cell growth independently of its transcription factor role. The 240ile mutant lost trans-activation but retained growth suppression, indicating a novel mechanism for p53 in tumor suppression.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Biology
Background:
- The p53 protein is a crucial tumor suppressor that typically functions as a transcription factor.
- Previous studies suggest some p53 mutants can inhibit cell growth independent of transcriptional activity.
- Understanding the distinct functions of p53 is vital for cancer therapy development.
Purpose of the Study:
- To investigate the relationship between the trans-activation and growth-suppressive functions of p53.
- To analyze the specific roles of five distinct p53 mutants in cellular processes.
- To elucidate the mechanisms underlying p53-mediated tumor suppression.
Main Methods:
- Utilized CAT reporter assays to measure trans-activational activity of p53 mutants.
- Employed colony formation assays to assess the growth-suppressive capabilities of mutants.
- Generated isogenic cell lines expressing mutant p53 to analyze growth rates.
Main Results:
- The p53 mutant 250ala retained trans-activational activity, while mutants 199stop, 240ile, 285lys, and 291asn lost this function.
- Mutants 240ile and 250ala demonstrated retained growth suppression, unlike mutants 199stop, 285lys, and 291asn.
- Cell lines expressing 240ile and 250ala exhibited slower growth rates compared to those with non-functional mutants.
Conclusions:
- Mutant p53 240ile lost its trans-activational activity but maintained growth-suppressive properties.
- This finding highlights a potential non-transcriptional role for p53 in inhibiting tumor growth.
- Further research is needed to fully understand the growth-suppressive mechanisms of p53 mutant 240ile.