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Concomitant inactivation of p53 and Chk2 in breast cancer
Alexandra Sullivan1, Martin Yuille, Claire Repellin
1Ludwig Institute for Cancer Research, Imperial College Faculty of Medicine, St Mary's Campus, Norfolk Place, London W2 1PG, UK.
Abstract:
The structure and expression of the human Rad53 homologue Chk2 was analysed in breast cancer. The previously described silent polymorphism at nucleotide 252 in codon 84 (GAA>GAG) was observed in 5/141 cases. Somatic Chk2 coding mutations were detected in 7/141 cases, these occurring in 4/18 BRCA1-associated breast cancers, 1/78 sporadic breast cancers and 2/25 typical medullary carcinomas. Each of the BRCA1-associated cancers with Chk2 mutations also contained mutations in p53, whereas the single sporadic cancer with Chk2 mutation was wild-type for p53. Expression of Chk2 was ubiquitously detected in normal ductal epithelium of the breast, but there was loss of expression in a significant proportion of breast carcinomas, and this occurred in cancers both with and without p53 mutation. A CpG island was identified 5' of the Chk2 transcriptional start site, but there was no evidence of cytosine methylation in any of the cancers with down-regulated Chk2 expression. Analysis of the germ-line of 45 individuals with hereditary or early onset breast cancer revealed wild-type Chk2 sequence in all cases. Thus, despite the rarity of somatic mutations in Chk2 in sporadic breast carcinomas, our results nevertheless reveal that concomitant loss of function in Chk2 (via down-regulation of expression) and p53 (via mutation) occurs in a proportion of sporadic cases. However, consistent with other studies, we show that germ-line mutations in Chk2 are unlikely to account for a significant proportion of non BRCA1-, non BRCA2-associated hereditary breast cancers.
Insights
Somatic mutations and expression loss of Chk2 (a human Rad53 homologue) were analyzed in breast cancer. Concomitant loss of Chk2 and p53 function occurs in some sporadic breast cancers, but germline Chk2 mutations are rare in hereditary breast cancer.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- The cell cycle checkpoint kinase Chk2 is crucial for DNA damage response.
- Alterations in Chk2 function are implicated in various cancers, including breast cancer.
- Understanding Chk2's role in breast tumorigenesis is essential for developing targeted therapies.
Purpose of the Study:
- To investigate the structure and expression of human Chk2 in breast cancer.
- To determine the frequency and spectrum of Chk2 mutations in different subtypes of breast cancer.
- To explore the relationship between Chk2 alterations, p53 status, and breast cancer development.
Main Methods:
- Analysis of Chk2 coding mutations and polymorphisms in breast cancer tissues.
- Assessment of Chk2 protein expression levels in normal and cancerous breast tissues.
- Investigation of potential epigenetic regulation (CpG island methylation) of Chk2 expression.
- Germline mutation screening of Chk2 in hereditary and early-onset breast cancer cases.
Main Results:
- Somatic Chk2 coding mutations were found in 7/141 breast cancers, including BRCA1-associated and medullary carcinomas.
- Loss of Chk2 expression was observed in a significant proportion of breast carcinomas, independent of p53 mutation status.
- No germline Chk2 mutations were detected in 45 individuals with hereditary or early-onset breast cancer.
- Concomitant loss of function in Chk2 (expression loss) and p53 (mutation) was identified in sporadic breast cancers.
Conclusions:
- While somatic mutations in Chk2 are rare in sporadic breast cancer, its down-regulation contributes to tumorigenesis, often alongside p53 alterations.
- Germline Chk2 mutations are unlikely to be a major cause of hereditary breast cancer in non-BRCA1/BRCA2 families.
- Chk2 alterations represent potential therapeutic targets in specific breast cancer subtypes.