Abstract 200: A transcribed BRCA1 pseudogene regulates gene expression and promotes breast cancer cell proliferation.
Authors: Han Yoo J. , Prat Aleix , Osborne Ruth A. , Perou Charles M. , Olopade Olufunmilayo I. 
Published: August 2012

Background: Pseudogenes, originally derived from protein coding genes, have generally been considered to represent non-functional artifacts of evolutionary processes due to degenerative features such as the absence of promoters or the presence of premature stop codons. Pseudogenes, however, account for a significant fraction of the human genome with an estimated number of ∼20,000 comparable to the number of protein-coding genes (∼27,000). Mounting evidence indicates potential biological functions for pseudogenes as regulators of gene expression by generating siRNA, sequestering microRNAs, or regulating RNA stability. Despite the abundance of pseudogenes in the human genome, the pathophysiological roles of pseudogenes remain poorly understood. Methods: qRT-PCR was performed in 15 breast cancer cell lines with custom-designed SYBR assays. Somatic copy number alterations (SCNAs) were measured in 44 normal and breast tumour tissues from patients recruited from the U of Chicago Breast SPORE using custom-designed TaqMan CNV assays. Cell proliferation and invasion assays were performed in bioengineered breast cancer cells with BRCA1P1 over-expression. Affymetrix GeneChip U133 and miRNA 2.0 microarrays were utilized for gene and microRNA profiling. Results: We analyzed the structure of a pseudogene of breast cancer susceptibility protein1 (BRCA1P1) duplicated from the functional gene (BRCA1) with only three exons (exon 1a, 1b & 2). Comparison of DNA sequences revealed that BRCA1P1 is a fusion pseudogene with 343 bp sequences of 60S acidic ribosomal protein (RPLP1) inserted in the exon 1a. Because of a point mutation in the translation start site of exon 2, BRCA1P1 expresses noncoding RNAs (ncRNA) that accumulate in nuclei. BRCA1P1 is ubiquitously transcribed in human normal tissues and highly expressed in breast cancer cell lines. Frequent BRCA1P1 amplification events (44%) were observed in breast tumor DNAs whereas no amplification occurred in normal breast tissues. The data indicate a potential contribution of BRCA1P1 amplification to an increase in BRCA1P1 expression in breast cancer. A significant increase in cell proliferation was observed in cells with BRCA1P1 over-expression (2.82 ± 0.32 fold) compared to cells transfected with control vectors. We are currently performing microarray as well as investigating the pseudogene interaction with BRCA1, RPLP1, or other miRNAs to elucidate mechanisms of cell proliferation regulation by BRCA1P1. Conclusion: This novel study of BRCA1P1 suggests that pseudogenes may play critical roles in neoplastic processes of human cancer. A better understanding of the function of pseudogenes and elucidation of pathways driven by BRCA1P1 pseudogene may advance the field of cancer biology and could provide novel targets for preventive and therapeutic intervention of human breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 200. doi:1538-7445.AM2012-200