BRCA1 Interacts with Poly(A)-binding Protein

Abstract

BRCA1 has been implicated in a number of cellular processes, including transcription regulation, DNA damage repair, cell cycle control, and apoptosis. We identified poly(A)-binding protein 1 (PABP) as a novel BRCA1-interacting protein in a yeast two-hybrid screen and confirmed the interaction by in vitro assays and coimmunoprecipitation in mammalian cells. Endogenous interaction between BRCA1 and PABP was also observed. This interaction was abolished by BRCA1 cancer-associated mutations, suggesting that it may be physiologically relevant. Deletion mapping demonstrated that the RNA recognition motifs 1-4 region of PABP is required to mediate the interaction with BRCA1. To understand the biological function of the BRCA1-PABP complex, we sought to determine whether BRCA1 is a modulator of translation. We showed here that inhibition of endogenous BRCA1 using a small interfering RNAbased approach decreased protein synthesis. Conversely, overexpression of BRCA1 activated translation. Using a RNA transfection approach, we clearly showed that BRCA1 modulates translation, independently of any transcriptional activity. The data presented here suggest that BRCA1 modulates protein synthesis via its interaction with PABP, providing a novel mechanism by which BRCA1 may exert its tumor suppressor function.The breast cancer susceptibility gene breast cancer 1 (BRCA1) acts as a tumor suppressor gene (1). Germ-line mutations of BRCA1 are found in about 40% of patients with inherited breast cancer and up to 90% of families with breast and ovarian cancer (2). The decreased BRCA1 expression found in approximately one-third of sporadic breast tumors may also play a role in these cancers (3, 4). Several lines of approach tend to define the biochemical function of BRCA1 protein. BRCA1 has thus far been involved in regulation of cell cycle checkpoints, apoptosis, DNA damage repair, transcription, and ubiquitination (5). Although the implication of BRCA1 in these cellular processes has been demonstrated, the exact mechanism of BRCA1 function remains unclear.The BRCA1 protein contains a RING finger at its N-terminal region (1), two nuclear export signals near its N terminus (6, 7), two nuclear localization signals in the central portion of the protein (8), and a tandem of two BRCT domains at its C-terminal region (9 -11). The majority of cancer-associated BRCA1 mutations affect the BRCT tandem, resulting in truncated products lacking one or two BRCT domains (2). These findings together with the observation that deletion of the Brca1 BRCT domains is responsible for tumor development in mice (12) demonstrate that BRCT domains play a central role in the BRCA1 tumor suppressor function.Several proteins interact with this region and collaborate functionally with BRCA1. For example, BRCA1 interacts with proteins implicated in transcriptional regulation such as RNA polymerase holoenzyme, CtIP (13-15), and histone deacetylases (16), with BACH1 implicated in response to DNA damage (17) and with acetyl-CoA carboxylase ␣ implicated in fatty acid syn...

BRCA1-Dependent Translational Regulation in Breast Cancer Cells

“…We showed that the global translation was diminished in BRCA1-depleted cells and increased in BRCA1-overexpressing cells [14]. Because BRCA1 is clearly not a canonical factor of translation, our findings suggested that the effect on global translation results from the targeting of a subset of mRNAs by BRCA1, rather than an effect on all cellular mRNAs.…”

“…The sequences of the siRNAs against BRCA1 were Si-BRCA1 5′-GGAACCUGUCUCCACAAAG-3′ and Si-control 5′-CACGAUGUGACAGUGAUAU-3′ [14]. For transfection, cells were plated at 1.8×10 6 cells per 10 cm diameter dish 24 h before transfection.…”

Nuclear relocalisation of cytoplasmic poly(A)-binding proteins PABP1 and PABP4 in response to UV irradiation reveals mRNA-dependent export of metazoan PABPs

“…In metazoans, PABP1 interacts with several nucleo-cytoplasmic proteins (e.g. Dizin et al, 2006; Nagaoka et al, 2006) but only the cytoplasmic functions of these interactions have been investigated. Our results indicate that neither PABP1 nor PABP4 is important for bulk RNA export (Fig.…”

Potential Excess Mortality in BRCA1/2 Mutation Carriers beyond Breast, Ovarian, Prostate, and Pancreatic Cancers, and Melanoma

“…Premature aging with decreased life-span has been observed in animal studies using mice that were homozygous for a hypomorphic mutation Brca1 allele and heterozygous for wild-type p53 ( Brca Δ11/ Δ 11 p53 +/− ) [29]; however, the mechanism by which BRCA genes exert their affect on mortality is not known. In vivo studies and mice model studies have suggested that BRCA1/2 is involved in translation regulation and the Insulin-Like Growth factor signaling axis [30], [31], but whether these pathways are directly related to premature aging is not clear.…”