Epigenetic Inactivation of the Chromosomal Stability Control Genes BRCA1, BRCA2, and XRCC5 in Non–Small Cell Lung Cancer

Abstract

Purpose: Lung cancer cells frequently exhibit marked chromosome instability. We postulated that alterations of the double-strand break repair genes (BRCA1, BRCA2, and XRCC5) might be involved in lung cancer. Patients and Methods: We examined the loss of protein and mRNA expression and the 5 ¶CpG hypermethylation and allelic imbalance of the BRCA1, BRCA2, and XRCC5 genes in 98 non^small cell lung cancer (NSCLC) samples. Anchorage-dependent growth after reexpression of these genes was examined in a lung cancer cell line that originally lacked BRCA1and BRCA2 expression. Results: The data indicated that low protein expression of BRCA1 and BRCA2 was frequent in lung adenocarcinomas (42-44%), whereas low XRCC5 protein expression was more prevalent among squamous cell carcinoma (32%). In addition, low BRCA1 expression was significantly associated with low RB expression, especially in lung adenocarcinoma. Concurrent alterations in XRCC5 and p53 were the most frequent profiles in smoking patients. Importantly, low mRNA and protein expressions of BRCA1, BRCA2, and XRCC5 were significantly associated with their promoter hypermethylation. 5-Aza-2 ¶-deoxycytidine treatment of NSCLC cells showed demethylation and reexpression of the BRCA1 and BRCA2 genes and reduced anchorageindependent growth. Conclusions: Our retrospective study provides compelling evidence that low mRNA and protein expression in the BRCA1/BRCA2 and XRCC5 genes occur in lung adenocarcinoma and squamous cell carcinoma, respectively, and that promoter hypermethylation is the predominant mechanism in deregulation of these genes. Alteration of the double-strand break repair pathway, perhaps by interacting with p53 and RB deregulation, is important in the pathogenesis of a subset of NSCLC.Lung cancer is one of the most common malignancies, making it very important to identify the associated gene(s) involved. We previously did a genome-wide loss of heterozygosity (LOH) study in 71 primary surgically resected non -small cell lung cancer (NSCLC) tumors in which a high mean LOH frequency was reported, indicating the presence of chromosome instability in NSCLC (1). Chromosome instability may be caused by failure in the repair of DNA double-strand breaks (DSB; ref. 2). Interestingly, the chromosome regions at 2q33-35 and 13q12.3, which included gene loci encoding the XRCC5 (Ku80) and BRCA2 (breast cancer 2) DSB repair proteins, respectively, showed a high frequency of LOH in NSCLC tumors (1). We therefore postulated that alterations of genes in chromosomal stability control pathways, such as DSB repair genes (BRCA1, BRCA2, and XRCC5), may be involved in NSCLC tumorigenesis.Two distinct and complementary mechanisms, homologous recombination and nonhomologous end joining, are involved in the repair of detrimental DSBs in mammalian cells (2, 3). The breast tumor suppressors BRCA1 and BRCA2 have been shown to interact with DNA damage -induced Rad51 protein to form foci on DSBs (4, 5). Mouse Brca1-and Brca2-deficient embryonic stem cells show a reduced efficiency ...

Epigenetic silencing of AXIN2/betaTrCP and deregulation of p53-mediated control lead to wild-type β-catenin nuclear accumulation in lung tumorigenesis

“…Reactions were carried out in a volume of 25 ml with 1 ml of cDNA and 0.25 pmol of primers in a DNA Thermal Cycler. The relative levels of gene expression were studied by multiplex RT-PCR assay as previously described (Wang et al, 2005;Lee et al, 2007).…”

Transcriptome sequencing of malignant pleural mesothelioma tumors

“…Its genetic basis is unknown but appears to involve multiple types of chromosomal abnormalities (5,(8)(9)(10)(11)(12)(13)(14). Central mechanisms underlying MPM are unclear, although MPM tumors evoke a strong inflammatory response thought to contribute to tumorigenesis (15).…”

Methylation of breast cancer susceptibility gene 1 (BRCA1) predicts recurrence in patients with curatively resected stage I non–small cell lung cancer

“…As described in previous studies, BRCA1 expression levels were associated with promoter hypermethylation status. 19,26 Correlation Between Disease Outcome and BRCA1 Methylation Status Demographics and clinical characteristics according to BRCA1 methylation status are shown in Table 2. There was no statistically significant relationship between BRCA1 methylation status and any of the clinicopathological features that we analyzed.…”

“…15 In addition, germline mutations in BRCA1 are a statistically significant risk factor in the prognosis of pancreatic and cervical cancers. 16 Several studies have investigated the clinical relevance of messenger RNA expression 17 and methylation of the BRCA1 promoter 18,19 in lung cancer, with emphasis primarily on responses to chemotherapy. 20 The relationship between epigenetic modifications of BRCA1 and the prognosis of curatively resected stage I NSCLC has not been elucidated.…”