Antisense Inhibition of BRCA1 Expression and Molecular Analysis of Hereditary Tumors Indicate That Functional Inactivation of the p53 DNA Damage Response Pathway Is Required for BRCA-Associated Tumorigenesis

RAP80 binds p32 to preserve the functional integrity of mitochondria

RAP80, a member of the BRCA1-A complex, is a well-known crucial regulator of cell cycle checkpoint and DNA damage repair in the nucleus. However, it is still unclear whether Rap80 localizes to another region outside the nucleus and plays different roles with its partners. Here, we found mitochondrial p32 as a novel binding partner of RAP80 by using yeast two-hybrid screening. RAP80 directly binds the internal region of p32 through its arginine rich C-terminal domain. Based on the interaction, we showed that a subset of RAP80 localizes to mitochondria where p32 exists. Loss of function study revealed that RAP80 deficiency reduces the protein level of p32 and p32 dependent mitochondrial translating proteins such as Rieske and COX1. As a result, mitochondrial membrane potential and oxygen consumption are reduced in RAP80 knockdown cells, indicating mitochondrial dysfunction. Our study identifies a novel interaction between RAP80 and p32, which is important for preserving intact mitochondrial function.

BRCA1 and p53 tumor suppressor molecules in Alzheimer's disease

Tumor suppressor molecules play a pivotal role in regulating DNA repair, cell proliferation, and cell death, which are also important processes in the pathogenesis of Alzheimer’s disease. Alzheimer’s disease is the most common neurodegenerative disorder, however, the precise molecular events that control the death of neuronal cells are unclear. Recently, a fundamental role for tumor suppressor molecules in regulating neurons in Alzheimer’s disease was highlighted. Generally, onset of neurodegenerative diseases including Alzheimer’s disease may be delayed with use of dietary neuro-protective agents against oxidative stresses. Studies suggest that dietary antioxidants are also beneficial for brain health in reducing disease-risk and in slowing down disease-progression. We summarize research advances in dietary regulation for the treatment of Alzheimer’s disease with a focus on its modulatory roles in BRCA1 and p53 tumor suppressor expression, in support of further therapeutic research in this field.

Early preinvasive lesions in ovarian cancer

Faced with the catastrophic prognosis for ovarian cancer due to the fact that it is most often diagnosed late at the peritoneal carcinomatosis stage, screening and early detection could probably reduce the mortality rate. A better understanding of the molecular characteristics of the different ovarian cancer subtypes and their specific molecular signatures is indispensable prior to development of new screening strategies. We discuss here the early natural history of ovarian cancer and its origins.

Family History of Cancer Rather Than p53 Status Predicts Efficacy of Pegylated Liposomal Doxorubicin and Oxaliplatin in Relapsed Ovarian Cancer

Background:

The aim of the study was to assess the efficacy of pegylated liposomal doxorubicin (PLD) and oxaliplatin in patients affected by relapsed epithelial ovarian cancer with a family history of BRCA and p53 mutations.

Methods:

Seventy-two women received a median of 7.5 courses of PLD at 30 to 35 mg/m2 plus oxaliplatin at 70 mg/m2, and associations between BRCA1/2 and TP53 status and overall survival (OS) were determined. Thirty-eight had a short platinum-free interval (PFI; <12 months), and 34 had a long PFI (≥12 months).

Results:

Nine patients had BRCA1 mutations, and 1 had a BRCA2 mutation. Platinum sensitivity was associated with OS (P = 0.0001). At a median follow-up of 9.3 months, objective response rate, median time to progression, and OS were 47.3%, 5.8 months, and 12.9 months, respectively, in short PFI compared with the 76.5%, 11.5 months, and 47.7 months in long PFI. p53 status did not correlate to these parameters. The median time to progression was 11.5 months for high-risk patients versus 6.5 months for patients with sporadic cancer (P = 0.0188), and the median OS from the start of treatment was 48.7 and 16.2 months (P = 0.0032), respectively. Toxicity was mostly grade 1 or 2.

Conclusions:

High response rates in the long-PFI patients indicate that this treatment is beneficial and well tolerated. Platinum sensitivity and positive family history and/or a BRCA1/BRCA2 mutation are a useful predictor of response.

Sporadic epithelial ovarian cancer: clinical relevance of BRCA1 inhibition in the DNA damage and repair pathway

Among the most promising pathways for molecular targets in sporadic epithelial ovarian cancer (SEOC) are those involving the BRCA1 protein. Because somatic mutations in BRCA1 are rare in SEOC, it was originally postulated that BRCA1 plays a limited role in the pathogenesis of this disease. However, inactivation of BRCA1 through various mechanisms is a relatively frequent event in ovarian cancer. This is important because BRCA1 is involved in the cellular response to DNA damage and repair and has an essential role in the maintenance of genomic stability. The BRCA1 tumor suppressor protein is known to interact with genes and proteins known collectively as the BRCA1 pathway, and defects in this pathway are believed to be a driving force for cancer progression. As a result, there is compelling evidence to suggest that the dysfunction of BRCA1 may be a central mechanism in all ovarian carcinogenesis, and this has clinical and molecular significance beyond the management of patients with hereditary ovarian cancer. The aim of this review is to evaluate the evidence for BRCA1 dysfunction in SEOC and to link this dysfunction to a defective DNA repair pathway and ultimately the promotion of genomic instability and tumorigenesis. Furthermore, we advocate the continued need to study BRCA1 and its pathway by prospectively correlating clinicopathologic data with molecular aberrations. This will determine whether BRCA1 has relevance as a predictive and prognostic marker in SEOC and whether aberrations in the BRCA1 pathway warrant further study as potential therapeutic targets.

Gene expression profiles of luteal phase fallopian tube epithelium from BRCA mutation carriers resemble high-grade serous carcinoma

PURPOSE

To identify molecular alterations potentially involved in predisposition to adnexal serous carcinoma (SerCa) in the nonmalignant fallopian tube epithelium (FTE) of BRCA1/2 mutation carriers, given recent evidence implicating the distal FTE as a common source for SerCa.

EXPERIMENTAL DESIGN

We obtained and compared gene expression profiles of laser capture microdissected nonmalignant distal FTE from 12 known BRCA1/2 mutation carriers (FTEb) and 12 control women (FTEn) during the luteal and follicular phase, as well as 13 high-grade tubal and ovarian SerCa.

RESULTS

Gene expression profiles of tubal and ovarian SerCa specimens were indistinguishable by unsupervised cluster analysis and significance analysis of microarrays. FTEb samples as a group, and four individual FTEb samples from the luteal phase in particular, clustered closely with SerCa rather than normal control FTE. Differentially expressed genes from these four samples relative to other FTEb samples, as well as differentially expressed genes in all FTEb luteal samples relative to follicular samples, were mapped to the I2D protein-protein interaction database, revealing a complex network affecting signaling pathways previously implicated in tumorigenesis. Two candidates, disabled homolog 2 mitogen-responsive phosphoprotein (DAB2) and Ski-like (SKIL), were further validated by real-time reverse transcription-PCR and tissue arrays. FTEb luteal and SerCa samples expressed higher levels of oncogenic SKIL and decreased levels of tumor suppressor DAB2, relative to FTEb follicular samples.

CONCLUSIONS

These findings support a common molecular pathway for adnexal SerCa and implicate factors associated with the luteal phase in predisposition to ovarian cancer in BRCA mutation carriers.

Is there more to BARD1 than BRCA1?

It has been over a decade since mutations in BRCA1 and BRCA2 were found to be associated with a small number of familial breast cancer cases. BRCA1 is a large protein that interacts with many other proteins that have diverse functions, so it has been a challenge to determine how defects in its function could lead to cancer. One particular protein, BARD1, seems to be an important regulator of the tumour-suppressor function of BRCA1, as well as acting as a tumour suppressor itself. BARD1 is indispensable for cell viability, so loss-of-function mutations are rare, but mutations and truncations that alter its function might be involved in the pathogenesis of breast cancer.

p53 inactivation is a rare event in familial breast tumors negative for BRCA1 and BRCA2 mutations

Germline mutations at BRCA1 or BRCA2 genes result in susceptibility to breast and ovarian cancers. BRCA1- and BRCA2-associated tumors have distinct histologic and molecular phenotypes, as compared to sporadic breast tumors. Typically, a higher grade of malignancy is observed in BRCA-associated cancers. A number of studies have suggested that BRCA1 and BRCA2 proteins are of importance in DNA repair and maintenance of genome integrity, bringing about molecular models of tumor pathogenesis. In particular, alterations at p53 gene have been suggested to be a necessary step in the tumorigenesis of BRCA-associated carcinomas. In fact, BRCA-associated breast cancers have higher p53 mutation frequencies than sporadic ones. At present, very little is known regarding BRCA non-associated familial tumors (termed BRCAx tumors). To our knowledge no data is available on p53 alterations in this sub-group of familial tumors. In this study p53 alteration frequencies were evaluated in 13 BRCA1, 11 BRCA2 and 55 BRCAx breast tumors. Tumor samples were analyzed for p53 gene mutations by PCR-SSCP/direct sequencing, and for p53 protein overexpression by immunohistochemistry (IHC). Altogether, p53 alterations were detected in 54% of BRCAI tumors compared with 5% of BRCAx tumors. No p53 alteration was found in BRCA2 tumors. While loss of p53 checkpoint control is likely to be an important step in the molecular pathogenesis of BRCA1-associated cancers, our data seem to indicate a p53-independent molecular mechanism underlying BRCAx neoplastic transformation.

Improved survival in women with BRCA-associated ovarian carcinoma

BACKGROUND

The objective of this study was to determine the clinical characteristics, treatment response, and frequency of p53 overexpression in Ashkenazi Jewish women with hereditary ovarian carcinoma.

METHODS

Seventy-one Jewish women with epithelial ovarian carcinoma (EOC) were tested for the three BRCA founder mutations using single-strand conformation polymorphism analysis, heteroduplex analysis, and protein truncation testing. Clinical and histopathologic data were reviewed retrospectively. In vitro chemoresistance was analyzed in 32 patients. Mutations of p53 were studied using immunohistochemical detection of p53 overexpression.

RESULTS

Thirty-four of 71 Jewish patients with EOC (48%) had germline BRCA mutations (BRCA heterozygotes), including 22 BRCA1 mutations and 12 BRCA2 mutations. BRCA heterozygotes were younger compared with Jewish patients who had EOC without mutations (sporadic carcinoma; 50 years vs. 59 years, respectively; P = 0.01). BRCA1 heterozygotes were younger compared with BRCA2 heterozygotes (48 years vs. 57 years, respectively; P = 0.01). Histopathologic tumor features were similar; however, tumors with low malignant potential were seen only in women with sporadic carcinoma. Both groups had equivalent rates of surgical cytoreduction and similar median follow-up (72 months). BRCA heterozygotes had higher response rates to primary therapy compared with patients who had sporadic disease (P = 0.01). In vitro chemoresistance predicted tumor response to platinum chemotherapy correctly in BRCA heterozygotes (P = 0.0096). BRCA heterozygotes with advance-stage disease had improved survival compared with patients who had advanced stage sporadic carcinoma (91 months vs. 54 months, respectively; P = 0.046) and had a longer disease free interval (49 months vs. 19 months, respectively; P = 0.16). p53 overexpression was common in BRCA heterozygotes (80%).

CONCLUSIONS

BRCA1 heterozygotes developed EOC at a younger age compared with BRCA2 heterozygotes and women who had sporadic ovarian carcinoma. BRCA heterozygotes had a better response to platinum chemotherapy compared with women who had sporadic disease, which may have contributed to their improved prognosis.

Identification of BARD1 as mediator between proapoptotic stress and p53-dependent apoptosis

The BRCA1-associated protein BARD1 is a putative tumor suppressor. We suggest that BARD1 is a mediator of apoptosis since (1) cell death in vivo (ischemic stroke) and in vitro is accompanied by increased levels of BARD1 protein and mRNA; (2) overexpression of BARD1 induces cell death with all features of apoptosis; and (3) BARD1-repressed cells are defective for the apoptotic response to genotoxic stress. The proapoptotic activity of BARD1 involves binding to and elevations of p53. BRCA1 is not required for but partially counteracts apoptosis induction by BARD1. A tumor-associated mutation Q564H of BARD1 is defective in apoptosis induction, thus suggesting a role of BARD1 in tumor suppression by mediating the signaling from proapoptotic stress toward induction of apoptosis.