Unknown,Transcriptomics,Genomics,Proteomics

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The application of nonsense-mediated mRNA decay inhibition to the identification of breast cancer susceptibility genes

ABSTRACT: Identification of novel, highly penetrant, breast cancer susceptibility genes will require the application of additional strategies beyond that of traditional linkage and candidate gene approaches. Approximately one-third of inherited genetic diseases, including breast cancer susceptibility, are caused by frameshift or nonsense mutations that truncate the protein product [1]. Transcripts harbouring premature termination codons are selectively and rapidly degraded by the nonsense-mediated mRNA decay (NMD) pathway. Blocking the NMD pathway in any given cell will stabilise these mutant transcripts, which can then be detected using gene expression microarrays. This technique, known as gene identification by nonsense-mediated mRNA decay inhibition (GINI), has proved successful in identifying sporadic nonsense mutations involved in many different cancer types. However, the approach has not yet been applied to identify germline mutations involved in breast cancer. We therefore attempted to use GINI on lymphoblastoid cell lines (LCLs) from multiple-case, non-BRCA1/2 breast cancer families in order to identify additional high-risk breast cancer susceptibility genes. We applied GINI to a total of 24 LCLs,established from breast-cancer affected and unaffected women from three multiple-case non-BRCA1/2 breast cancer families. We then used Illumina gene expression microarrays to identify transcripts stabilised by the NMD inhibition. Total RNA obtained from the lymphoblastoid cell lines derived from 24 individuals.

ORGANISM(S): Homo sapiens

SUBMITTER: Julie Johnson

PROVIDER: E-GEOD-37210 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Use of DNA damaging agents and RNA pooling to assess expression profiles associated with BRCA1 and BRCA2 mutation status in familial breast cancer patients Background: A large number of rare sequence variants of unknown clinical significance have been identified in the breast cancer susceptibility genes, BRCA1 and BRCA2. Determining the functional effect of these variants as well as their role in breast cancer susceptibility can be challenging using current classification methods. Methodology/Principal Findings: To identify predictors of pathogenic mutation status in familial breast cancer patients, we explored the use of gene expression arrays to assess the effect of two DNA damaging agents (irradiation and mitomycin C) on cellular response in relation to BRCA1 and BRCA2 mutation status. A range of regimes were used to treat 27 lymphoblastoid cell-lines (LCLs) derived from affected women in high-risk breast cancer families (nine BRCA1, nine BRCA2, and nine non-BRCA1/2 or BRCAX individuals) and nine LCLs from healthy individuals. Using an RNA pooling strategy, we found that treating LCLs with 1.2 μM mitomycin C and measuring the gene expression profiles 1 hour post-treatment had the greatest potential to discriminate BRCA1, BRCA2 and BRCAX mutation status. A classifier was built using the expression profile of nine QRT-PCR validated genes that were associated with BRCA1, BRCA2 and BRCAX status in RNA pools. These nine genes could distinguish BRCA1 from BRCA2 carriers with 83% accuracy in individual samples, but three-way analysis for BRCA1, BRCA2 and BRCAX had a maximum of 59% prediction accuracy. Conclusions/Significance: Our results suggest that, compared to BRCA1 and BRCA2 mutation carriers, non-BRCA1/2 (BRCAX) individuals are genetically heterogeneous. This study also demonstrates the effectiveness of RNA pools to compare the expression profiles of cell-lines from BRCA1, BRCA2 and BRCAX cases after treatment with irradiation and mitomycin C as a method to prioritize treatment regimes for detailed downstream expression analysis.

Project description:We used a modification of GINI analysis to identify genes containing premature translation termination codons (PTC) generated by nonsense or frameshift mutations in prostate cancer cell lines. The analysis was performed in two steps. In the first step nonsense mediated mRNA decay (NMD) was inhibited in prostate cancer cell lines using incubation with medium containing caffeine for 4 hours. Gene expression analysis of caffeine treated or untreated cells after this step detects mRNA accumulation that takes place for genes containing PTC and as well as for genes that show induction of transciption due to stress caused by NMD inhibition. In the second step either both transcription and NMD or transcription only are blocked by incubating cell in a medium containing either both actinomycin D and caffeine or actinomacin D only for 4 hours. Gene expression analysis after this second step detects mRNA degradation for genes containing PTC as well as for genes that show induction of transciption due to stress caused by NMD inhibition. The efficiency of mRNA degradation for genes containing PTC during this step depends on whether NMD is inhibited or not. The efficiency of mRNA degradation for stress response genes does not depend on whether NMD is inhibited or not. Our modified GINI protocol allows efficient separation of genes containing PTC from the genes that show mRNA increases due to stress response to NMD inhibition. Experiment Overall Design: The LNCaP and 22Rv1 cells were seeded into four 60 mm tissue culture plates each. Caffeine (10 mM) was added to three plates and one plate was incubated without caffeine as a control. Following four hours? incubation, the medium was removed from one plate (with caffeine) and from the control plate and total RNA was prepared using TRIZOL reagent, according to manufacturer?s instructions, and used for an Affymetrix U133Plus2.0 oligonucleotide array hybridization. The caffeine-containing medium of the two remaining plates was removed, the cells were washed twice with phosphate-buffered saline and the medium with actinomycin D (2 mkg/ml) together with caffeine (10 mM) was added to one plate. Actinomycin D alone was added to the other plate. Following another four hours? incubation, the total RNA from both plates was prepared and used for an Affymetrix U133Plus2.0 oligonucleotide array analysis.

Project description:In more than 70% of families with a strong history of breast and ovarian cancers, pathogenic mutation in BRCA1 or BRCA2 cannot be identified, even though hereditary factors are expected to be involved. It has been proposed that tumors with similar molecular phenotypes also share similar pathophysiological mechanisms. Grouping into molecularly homogeneous subsets may therefore be of potential value for further genetic analysis in order to identify new high penetrance breast cancer genes. In the current study, the aim was to investigate if global RNA profiling can be used to identify functional subgroups within breast tumors from families tested negative for BRCA1/2 germline mutations and how these subgroupings relate to different breast cancer patients within the same family. By analyzing a collection of 70 breast tumor biopsies from 58 families, we show that distinct functional subgroupings, similar to the intrinsic molecular breast cancer subtypes, exist. The distribution of subtypes was markedly different from the distribution found among BRCA1/2 mutation carriers. From 11 breast cancer families, breast tumor biopsies from more than one affected family member were included in the study. Notably, in 8 of these families we found that patients from the same family shared the same tumor subtype, showing a tendency of familial aggregation of tumor subtypes (p-value = 1.7e-3). Our finding indicates involvement of hereditary factors in these families in which family members may carry genetic susceptibility not just to breast cancer but to a particular subtype of breast cancer. Using our previously developed BRCA1/2-signatures, we identified 7 non-BRCA1/2 tumors with a BRCA1-like molecular phenotype and provide evidence for epigenetic inactivation of BRCA1 in three of the tumors. In addition, 7 BRCA2-like tumors were found. This is the first study to provide a biological link between breast cancers from family members of high risk non-BRCA1/2 families in a systematic manner, suggesting that future genetic analysis may benefit from subgrouping families into molecularly homogeneous subtypes in order to identify new high penetrance susceptibility genes. Gene expression profiling of 253 breast tumor samples. Breast tumor tissue from 125 patients with germline mutations in BRCA1 (n = 33) or BRCA2 (n = 22) or with no detectable germline mutation in BRCA1 or BRCA2 (n = 70) were included in the study. Serving as a representative control group, primary breast tumor samples (n = 128) were randomly selected among available samples originating from the same department and time period as for the hereditary samples. The study was conducted using Agilent-029949 Custom SurePrint G3 Human GE 8x60K Microarray platform.

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The application of nonsense-mediated mRNA decay inhibition to the identification of breast cancer susceptibility genes

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