Cancer predisposing BARD1 mutations affect exon skipping and are associated with overexpression of specific BARD1 isoforms

Abstract

BARD1 is the main binding partner of BRCA1 and is required for its stability and tumor-suppressor functions. In breast cancer and other epithelial cell carcinomas, alternatively spliced isoforms of BARD1 are highly upregulated and correlated with poor outcome. Recent data indicate that germline mutations of BARD1 may predispose to breast and/or ovarian cancer. To evaluate the role of BARD1 germline mutations in predisposition to ovarian cancer we scanned a cohort of 255 patients for the presence of previously reported mutations located in exons 5, 8 and 10 using high-resolution melting analysis. Within this group we identified single-patients carrying mutation in exon 8 (c.1690C>T, p.Gln564Ter), two different variants in exon 10 (c.1972C>T, p.Arg658Tyr; c.1977A>G, p.=) and a carrier of novel missense mutation located in exon 5 (c.1361C>T, p.Pro454Leu). Three out of four identified mutations alter exonic splicing enhancing motives and result in expression of incorrect splicing skipping of exons 5, 8, and 2-9, respectively. Our data indicate that BARD1 variants may predispose to ovarian cancer in limited number of patients although based on actual data it is difficult to estimate its actual penetrance.

Antagonizing functions of BARD1 and its alternatively spliced variant BARD1δ in telomere stability

“…As described recently, specific BARD1 germline mutations promote expression of alternatively spliced BARD1 mRNAs and reduction of FL BARD1 mRNAs [46, 47]. We investigated the implication of these mutations in telomere integrity.…”

“…We conducted telomere FISH experiments using peripheral blood lymphocytes from breast and ovarian cancer patients with germline mutations in BARD1 or BRCA1 , namely BARD1 c.1690C > T, BARD1 c.1972C > T, BARD1 c.1977A > G, BRCA1 c.5266dupC [48], and the BRCA1 c.5266dupC and BARD1 c.1690C > T double mutation (Supplementary Figure S1B), as well as from healthy control subjects. The c.1690C > T mutation is a nonsense mutation that promotes alternative splicing [47] resulting in mRNAs that encode truncated proteins lacking the BRCT domains. The c.1972C > T mutation results in an arginine to cysteine substitution located between the two BRCT domains.…”

“…The c.1972C > T mutation results in an arginine to cysteine substitution located between the two BRCT domains. The c.1977A > G mutation promotes expression of a transcript lacking exons 2–9 [47]. The c.5266dupC mutation causes a frame shift in exon 20, a region that codes for the BRCT repeats in BRCA1 [48].…”

“…The BARD1 germline mutations predict a reduction of FL BARD1 expression [47], which might explain the genetic instability as described before [11, 12]. Loss of FL BARD1 was frequently found associated with expression of isoforms in many cancers [16].…”

“…This was confirmed by the genome wide association study for neuroblastoma, where SNPs in intron 1 of BARD1 were the most significantly associated with the disease (Carpasso et al, 2009). BARD1 SNPs and mutations that affect splicing were also reported for breast and ovarian cancers [46, 47]. …”