title: Expression of human BRCA1Δ17-19 alternative splicing variant with a truncated BRCT domain in MCF-7 cells results in impaired assembly of DNA repair complexes and aberrant DNA damage response.
abstract: Alternative pre-mRNA splicing is a fundamental post-transcriptional regulatory mechanism. Cancer-specific misregulation of the splicing process may lead to formation of irregular alternative splicing variants (ASVs) with a potentially negative impact on cellular homeostasis. Alternative splicing of BRCA1 pre-mRNA can give rise to BRCA1 protein isoforms that possess dramatically altered biological activities compared with full-length wild-type BRCA1. During the screening of high-risk breast cancer (BC) families we ascertained numerous BRCA1 ASVs, however, their clinical significance for BC development is largely unknown. In this study, we examined the influence of the BRCA1Δ17-19 ASV, which lacks a portion of the BRCT domain, on DNA repair capacity using human MCF-7 BC cell clones with stably modified BRCA1 expression. Our results show that overexpression of BRCA1Δ17-19 impairs homologous recombination repair (sensitizes cells to mitomycin C), delays repair of ionizing radiation-induced DNA damage and dynamics of the ionizing radiation-induced foci (IRIF) formation, and undermines also the non-homologous end joining repair (NHEJ) activity. Mechanistically, BRCA1Δ17-19 cannot interact with the partner proteins Abraxas and CtIP, thus preventing interactions known to be critical for processing of DNA lesions. We propose that the observed inability of BRCA1Δ17-19 to functionally replace wtBRCA1 in repair of DNA double-strand breaks (DDSB) reflects impaired capacity to form the BRCA1-A and -C repair complexes. Our findings indicate that expression of BRCA1Δ17-19 may negatively influence genome stability by reducing the DDSB repair velocity, thereby contributing to enhanced probability of cancer development in the affected families.
authors: Institute of Biochemistry and Experimental Oncology, First Faculty of Medicine, Charles University in Prague, U Nemocnice 5, CZ-128 53 Prague 2, Czech Republic. jsevc@lf1.cuni.cz
authors: Jan
authors: J
authors: Sevcik
authors: Martin
authors: M
authors: Falk
authors: Libor
authors: L
authors: Macurek
authors: Petra
authors: P
authors: Kleiblova
authors: Filip
authors: F
authors: Lhota
authors: Jan
authors: J
authors: Hojny
authors: Lenka
authors: L
authors: Stefancikova
authors: Marketa
authors: M
authors: Janatova
authors: Jiri
authors: J
authors: Bartek
authors: Jana
authors: J
authors: Stribrna
authors: Zdenek
authors: Z
authors: Hodny
authors: Lucie
authors: L
authors: Jezkova
authors: Petr
authors: P
authors: Pohlreich
authors: Zdenek
authors: Z
authors: Kleibl
mesh_terms: D017398:Alternative Splicing; D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D004249:DNA Damage / Q000528:radiation effects; D004260:DNA Repair; D004706:Endodeoxyribonucleases; D006801:Humans; D061986:MCF-7 Cells; D009687:Nuclear Proteins / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011839:Radiation, Ionizing
chemical_list: C520310:ABRAXAS1 protein, human; D019313:BRCA1 Protein; D002352:Carrier Proteins; D009687:Nuclear Proteins; D004706:Endodeoxyribonucleases; C410741:RBBP8 protein, human