Cancer. BRCA1, everything but the RING?

The Breast Cancer Protooncogenes HER2, BRCA1 and BRCA2 and Their Regulation by the iNOS/NOS2 Axis

The expression of inducible nitric oxide synthase (iNOS; NOS2) and derived NO in various cancers was reported to exert pro- and anti-tumorigenic effects depending on the levels of expression and the tumor types. In humans, the breast cancer level of iNOS was reported to be overexpressed, to exhibit pro-tumorigenic activities, and to be of prognostic significance. Likewise, the expression of the oncogenes HER2, BRCA1, and BRCA2 has been associated with malignancy. The interrelationship between the expression of these protooncogenes and oncogenes and the expression of iNOS is not clear. We have hypothesized that there exist cross-talk signaling pathways between the breast cancer protooncogenes, the iNOS axis, and iNOS-mediated NO mutations of these protooncogenes into oncogenes. We review the molecular regulation of the expression of the protooncogenes in breast cancer and their interrelationships with iNOS expression and activities. In addition, we discuss the roles of iNOS, HER2, BRCA1/2, and NO metabolism in the pathophysiology of cancer stem cells. Bioinformatic analyses have been performed and have found suggested molecular alterations responsible for breast cancer aggressiveness. These include the association of BRCA1/2 mutations and HER2 amplifications with the dysregulation of the NOS pathway. We propose that future studies should be undertaken to investigate the regulatory mechanisms underlying the expression of iNOS and various breast cancer oncogenes, with the aim of identifying new therapeutic targets for the treatment of breast cancers that are refractory to current treatments.

A BRCA1 Splice Site Variant Responsible for Familial Ovarian Cancer in a Han-Chinese Family

OBJECTIVE

Ovarian cancer (OC) is one of the most common and most lethal gynecological malignancies. OC has an age-dependent incidence and occurs more commonly in females older than 50 years old. Most OC patients are diagnosed at an advanced stage and have a poor prognosis. Germline mutations in the BRCA1 DNA repair associated gene (BRCA1) and the BRCA2 DNA repair associated gene (BRCA2) account for 20%-25% of epithelial ovarian cancer (EOC). BRCA1 germline mutations are more common in Chinese EOC patients.

METHODS

This study reported a three-generation Han-Chinese family containing four EOC patients and a rectal adenocarcinoma patient. Whole-exome sequencing was performed on two EOC patients and an unaffected individual. Variant validation was also performed in all available members by Sanger sequencing.

RESULTS

A heterozygous splice site variant, c.4358-2A>G in the BRCA1 gene, was identified. Bioinformatic analysis showed that the variant may change the splicing machinery.

CONCLUSION

The BRCA1 splice site variant, c.4358-2A>G was identified as the likely genetic cause for EOC, and may also be associated with the increased risk of rectal adenocarcinoma in the family. The findings were beneficial for genetic counseling, helpful for cancer prevention in other family members, and may facilitate therapy decision-making in the future to reduce cancer lethality.

Breast cancer 1 (BRCA1)-deficient embryos develop normally but are more susceptible to ethanol-initiated DNA damage and embryopathies

The breast cancer 1 (brca1) gene is associated with breast and ovarian cancers, and heterozygous (+/−) brca1 knockout progeny develop normally, suggesting a negligible developmental impact. However, our results show BRCA1 plays a broader biological role in protecting the embryo from oxidative stress. Sox2-promoted Cre-expressing hemizygous males were mated with floxed brca1 females, and gestational day 8 +/− brca1 conditional knockout embryos with a 28% reduction in protein expression were exposed in culture to the reactive oxygen species (ROS)-initiating drug ethanol (EtOH). Untreated +/− brca1-deficient embryos developed normally, but when exposed to EtOH exhibited increased levels of oxidatively damaged DNA, measured as 8-oxo-2'-deoxyguanosine, γH2AX, which is a marker of DNA double strand breaks that can result from 8-oxo-2'-deoxyguanosine, formation, and embryopathies at EtOH concentrations that did not affect their brca1-normal littermates. These results reveal that even modest BRCA1 deficiencies render the embryo more susceptible to drug-enhanced ROS formation, and corroborate a role for DNA oxidation in the mechanism of EtOH teratogenesis.

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Heterozygous (+/−) brca1 conditional knockout (cKO) embryos develop normally.

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+/− brca1 cKO embryos have 28% less BRCA1 protein than wild-type (WT) littermates.

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Ethanol-exposed BRCA1-deficient mice have more oxidatively damaged DNA than WTs.

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Ethanol-exposed BRCA1 cKO embryos exhibit more embryopathies than WT littermates.

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BRCA1 protects the embryo from ethanol-enhanced oxidative stress—a novel role.

BRCA1 point mutations in premenopausal breast cancer patients from Central Sudan

Premenopausal breast cancer (BC) is one of the most common cancers of women in rural Africa and part of the disease load may be related to hereditary predisposition, including mutations in the BRCA1 gene. However, the BRCA1 mutations associated with BC in Africa are scarcely characterized. We report here 33 BRCA1 point mutations, among which 2 novel missense variants, found in 59 Central Sudanese premenopausal BC patients. The high fractions of mutations with intercontinental and uniquely African distribution (17/33, 51.5 % and 14/33, 42.4 %, respectively) are in agreement with the high genetic diversity expected in an African population. Overall 24/33 variants (72.7 %) resulted neutral; 8/33 of unknown significance (24.3 %, including the 2 novel missense mutations); 1 (3.0 %) overtly deleterious. Notably, in silico studies predict that the novel C-terminal missense variant c.5090G>A (p.Cys1697Tyr) affects phosphopeptide recognition by the BRCA1 BRCT1 domain and may have a pathogenic impact. Genetic variation and frequency of unique or rare mutations of uncertain clinical relevance pose significant challenges to BRCA1 testing in Sudan, as it might happen in other low-resource rural African contexts.

Structure-Function Of The Tumor Suppressor BRCA1

BRCA1, a multi-domain protein, is mutated in a large percentage of hereditary breast and ovarian cancers. BRCA1 is most often mutated in three domains or regions: the N-terminal RING domain, exons 11-13, and the BRCT domain. The BRCA1 RING domain is responsible for the E3 ubiquitin ligase activity of BRCA1 and mediates interactions between BRCA1 and other proteins. BRCA1 ubiquitinates several proteins with various functions. The BRCA1 BRCT domain binds to phosphoproteins with specific sequences recognized by both BRCA1 and ATM/ATR kinases. Structural studies of the RING and BRCT domains have revealed the molecular basis by which cancer causing mutations impact the functions of BRCA1. While no structural data is available for the amino acids encoded by exons 11-13, multiple binding sites and functional domains exist in this region. Many mutations in exons 11-13 have deleterious effects on the function of these domains. In this mini-review, we examine the structure-function relationships of the BRCA1 protein and the relevance to cancer progression.

BRCA1-directed, enhanced and aberrant homologous recombination: mechanism and potential treatment strategies

Despite intense studies, questions still remain regarding the molecular mechanisms leading to the development of hereditary breast and ovarian cancers. Research focused on elucidating the role of the breast cancer susceptibility gene 1 (BRCA1) in the DNA damage response may be of the most critical importance to understanding these processes. The BRCA1 protein has an N-terminal RING domain possessing E3 ubiquitinligase activity and a C-terminal BRCT domain involved in binding specific phosphoproteins. These domains are involved directly or indirectly in DNA double-strand break (DSB) repair. As the two terminal domains of BRCA1 represent two separate entities, understanding how these domains communicate and are functionally altered in regards to DSB repair is critical for understanding the development of BRCA1-related breast and ovarian cancers and for developing novel therapeutics. Herein, we review recent findings of how altered functions of these domains might lead to cancer through a mechanism of increased aberrant homologous recombination and possible implications for the development of BRCA1 inhibitors.