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Status of the p53 tumor suppressor gene in human squamous carcinoma cell lines
M Reiss1, D E Brash, T Muñoz-Antonia
1Department of Medicine, Yale University School of Medicine, New Haven, CT 06510.
Abstract:
Dominant-negative and/or loss-of-function mutations of the p53 tumor suppressor gene are frequently found in squamous cell carcinomas of the skin and of the head-and-neck region. In order to identify the precise mechanisms of inactivation of p53 in tumors of this class, we examined the status of p53 RNA, protein and DNA in a panel of eight human squamous carcinoma cell lines (head-and-neck, 3; esophagus, 1; lung, 1; uterine cervix, 2; vulva, 1). Three lines (A253, CaLu-1, SqCC/Y1) failed to express any p53 mRNA. A253 cells contained a single p53 allele without mutations in exons 2-9, suggesting that the lack of transcription was the result of mutations in the regulatory region of the gene. Both p53 alleles were deleted in CaLu-1 cells, whereas the single allele present in SqCC/Y1 cells was rearranged and carried two missense mutations in exon 5. Two cell lines (A431, FaDu) expressed only 50% of the normal level of p53 mRNA, either because only one allele was present (A431), or because only one of the two alleles was transcribed (FaDu). The two cervical carcinoma lines (CaSki, C4-1) expressed normal levels of p53 mRNA, but no wild type protein, presumably as a result of accelerated degradation by the human papillomavirus 16 or -18 E6 oncoprotein present in these cells as previously described (Scheffner et al., Proc. Natl. Acad. Sci. USA 88:5523-5527; 1991). Three of the lines expressed only mutant p53 protein (A431, FaDu, CE-48) resulting from missense mutations in codons 248 and 273.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
p53 tumor suppressor gene mutations are common in squamous cell carcinomas. This study investigated p53 gene inactivation mechanisms across various cancer cell lines, revealing diverse alterations including transcriptional silencing, deletion, and mutations.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- The p53 tumor suppressor gene plays a critical role in preventing cancer.
- Loss-of-function or dominant-negative mutations in p53 are frequently observed in squamous cell carcinomas.
- Understanding p53 inactivation mechanisms is crucial for developing targeted therapies.
Purpose of the Study:
- To elucidate the precise mechanisms of p53 gene inactivation in human squamous carcinoma cell lines.
- To analyze the status of p53 RNA, protein, and DNA in a panel of cancer cell lines.
Main Methods:
- Analysis of p53 RNA expression levels via RT-PCR.
- Detection of p53 protein expression.
- Examination of p53 DNA for mutations, deletions, and rearrangements.
- Utilized a panel of eight human squamous carcinoma cell lines.
Main Results:
- Three cell lines showed no detectable p53 mRNA, attributed to regulatory mutations, allele deletion, or rearrangement with missense mutations.
- Two cell lines exhibited reduced p53 mRNA levels due to monoallelic presence or transcription from a single allele.
- Cervical carcinoma lines expressed normal p53 mRNA but lacked wild-type protein, likely due to HPV E6 oncoprotein activity.
- Three lines expressed only mutant p53 protein resulting from specific missense mutations.
Conclusions:
- p53 inactivation in squamous cell carcinomas occurs through diverse mechanisms, including transcriptional, post-transcriptional, and mutational alterations.
- The specific mechanism of p53 inactivation varies among different squamous cell carcinoma subtypes.
- Further research into these inactivation pathways can inform cancer treatment strategies.