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Protein Arginine Methyltransferase 6 dependent gene expression and splicing: Association with breast cancer outcomes

ABSTRACT: Protein arginine methyltransferase-6 (PRMT6) regulates steroid-dependent transcription and alternative splicing, and is implicated in endocrine system development and function, cell death, cell cycle, gene expression and cancer. Despite its role in these processes, little is known about its function and cellular targets in breast cancer. To identify novel gene targets regulated by PRMT6 in breast cancer cells, we used a combination of small interfering RNA (siRNA) and exon-specific microarray profiling in vitro, coupled to in vivo validation in normal breast and primary human breast tumours. This approach, which allows the examination of genome-wide changes in individual exon usage and total transcript levels, demonstrated PRMT6 knockdown significantly affected: (i) the transcription of 159 genes, and (ii) alternate splicing of 449 genes. Importantly, the levels of PRMT6 itself were significantly decreased in breast cancer, relative to normal breast tissue. The PRMT6 dependent transcriptional and alternative splicing targets identified in vitro, were validated in human breast tumours. Notably, expression of PRMT6 and the corresponding gene signature, correlated with decreased probability of relapse-free or distant metastasis free survival in ER+ breast cancer. These results suggest that dysregulation of PRMT6 dependent transcription and alternative splicing may be involved in breast cancer pathophysiology and the molecular consequences identifying a unique and informative biomarker profile.

ORGANISM(S): Homo sapiens

PROVIDER: GSE36542 | GEO | 2012/08/02

SECONDARY ACCESSION(S): PRJNA153415

REPOSITORIES: GEO

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Project description:MSI (Microsatellite Instability) colorectal cancer (CRC) show improved survival, are less prone to metastasis and show poor response to chemotherapy (compared to MSS tumors). The underlying reasons for these characteristics are still not understood and no specific therapeutic approach for MSI colon tumours (15% of CRC overall) has yet been developed. The MSI process is oncogenic when it affects DNA repeat sequences that have a functional role, e.g. Small Coding Repeats (SCR). MSI also frequently affects Long Non-Coding Repeats (LNCR) in tumour DNA. In contrast to SCR, only a few LNCR are endowed with biological activity. Consequently, this area has received very little attention. Our group recently identified HSP110 mutant chaperone protein in MSI CRC that was generated by somatic deletion of a LNCR. Of interest, HSP110 mutant (due to exon skipping) have anti-oncogenic properties and the survival of MSI CRC patients receiving chemotherapy is positively associated with HSP110 mutations in tumour DNA. The aim of the current project is to identify additional clinically relevant MSI-associated splicing aberrations due to mutations in LNCR located in splice acceptor sites. The four main steps are as follows: 1. To identify exon/intron sites affected by aberrant splicing events due to MSI in CRC . All RNASeq data will be exploited to identify recurrent splicing aberrations (mostly exon skipping) that occur specifically in MSI colon tumours; 2. To investigate for possible functional links between MSI and any detected aberrant splicing events . All specific aberrant splicing events detected by RNAseq in MSI CRC samples will be first confirmed (quantitative RT-PCR) in order to eliminate false positive cases. For validated exon candidates, the allelic profiles of adjacent intronic LNCR will be analysed (PCR and fluorescence genotyping) in CRC cell lines and primary tumours (MSI and MSS), as well as in matching normal mucosa samples in order to assess their polymorphic status; 3. To identify splicing events and LNCR mutations with clinical relevance in MSI CRC patients . All LNCR with a confirmed role in gene splicing in MSI CRC will be analysed. The clinical relevance of candidate genes will be assessed using multivariate survival regression models for Relapse- Free Survival, with interaction terms (response to chemotherapy); 4. To initiate functional studies on a limited number of clinically relevant, cancer-related genes whose splicing is perturbed in MSI cancer cells, and to develop biological tools to simplify screening in future clinical assays Similar to HSP110, we will focus on 4 or 5 mutant proteins that are promising drug therapeutic targets. Functional assays will be developed to further elucidate their role in the pathophysiology of MSI tumours. We also aim to develop biological tools for these candidate genes, such as the detection of wild-type or mutant proteins by immunohistochemistry.

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Protein Arginine Methyltransferase 6 dependent gene expression and splicing: Association with breast cancer outcomes

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