Abstract
Breast cancer type 2, early onset susceptibility gene (BRCA2) is a major component of the homologous recombination DNA repair pathway. It acts as a tumor suppressor whose function is often lost in cancers. Patients with specific mutations in the BRCA2 gene often display discrete clinical, histopathological, and molecular features. However, a subset of sporadic cancers has wild type BRCA2 and display defects in the homology-directed repair pathway, which is the hallmark of ‘BRCAness.’ The mechanisms by which BRCAness arises are not well understood but post-transcriptional regulation of BRCA2 gene expression by microRNAs (miRNAs) may contribute to this phenotype. Here, we examine the post-transcriptional effects that some members of the six-miRNA cluster known as the miR-17/92 cluster have on the abundance of BRCA2’s messenger RNA (mRNA) and protein. We discuss two interactions involving the miR-19a and miR-19b members of the cluster and the 3′UTR of BRCA2’s mRNA. We investigated these miRNA:mRNA interactions in 15 cell lines derived from pancreatic, breast, colon, and kidney tissue. We show that over-expression of these two miRNAs results in a concomitant decrease of BRCA2’s mRNA and protein expression in a subset of the tested cell lines. Additionally, using luciferase reporter assays we identified direct interactions between miR-19a/miR-19b and a miRNA response element (MRE) in BRCA2’s 3′UTR. Our results suggest that BRCA2 is subject to a complex post-transcriptional regulatory program that has specific dependencies on the genetic and phenotypic background of cell types.
Highlights
The deoxyribonucleic acid (DNA) repair pathway functions to correct potential damages to the chromosomes that occur during DNA replication or upon insult by environmental factors
MiRNAs are involved in the DNA repair pathway: for example, miR-24, miR-421, and miR-21 modulate the expression of multiple DNA damage response (DDR) genes such as H2AX, ATM, and CDC25A, respectively (Hu and Gatti, 2011); miR-1245, miR-1255b, and miR-193b∗ were shown to target breast cancer 2 (BRCA2) (Song et al, 2012; Choi et al, 2014); and, we recently reported that the miR-15/107 group of miRNAs targets breast cancer 1 (BRCA1) (Quann et al, 2015)
Out of the five putative miRNA binding sites/miRNA response element (MRE) targeted by four members of the miR-17/92 cluster, wild type (WT) BRCA2 MRE-4 responded to transfections with miR19a and miR-19b exhibiting a concomitant statistically significant decrease of luciferase activity (P < 0.001)
Summary
The DNA repair pathway functions to correct potential damages to the chromosomes that occur during DNA replication or upon insult by environmental factors. Alterations of this pathway have been associated with many different diseases, most notably cancers (Gavande et al, 2016). Human BRCA2 has two known protein-coding transcripts with lengths of 11,986 and 10,984 nucleotides (nts), respectively. Both mRNAs code for a large protein (384,225 Da) that comprises 3,418 amino acids (Venkitaraman, 2002; Roy et al, 2012). Other tumor suppressors such as MSH, XPA, and TP53 are much better conserved with the human and mouse sequences exhibiting 92, 86, and 77% similarity, respectively (Jasin, 2002)
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