The Role of BRCA1 in Nucleotide Excision Repair

Institution: Stanford University
Investigator(s): Anne-Renee Hartman, M.D. -
Award Cycle: 2001 (Cycle VII) Grant #: 7FB-0077 Award: $85,968
Award Type: Postdoctoral Fellowship
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease

Initial Award Abstract (2001)
Recent strides in breast cancer research have determined that mutations in two genes, BRCA1 and BRCA2, are responsible for 5-10% of all breast cancers. A significant portion of these cancers also harbor a mutation in p53, a tumor suppressor gene mutated in >70% of human cancers. This provides an important clue as to the linkage between the BRCA genes and p53. An important function of p53 is to regulate a type of DNA repair pathway; 'nucleotide excision repair', which corrects DNA damaged from many environmental toxins including cigarette smoke and ultraviolet radiation. However, the failure to correctly repair damaged DNA leads to the accumulation of genetic mutations which is a characteristic of cancer. One way that p53 affects nucleotide excision repair is through regulation of GADD45, a DNA damage response gene. BRCA1 also regulates the GADD45 gene, independent of p53.

The aim of this project is to understand the role of BRCA1 in the nucleotide excision repair pathway. We plan to develop genetically engineered mouse and human cell lines that either overexpress or lack the expression of the GADD45 or BRCA1 genes. We will then evaluate DNA repair properties in these cell lines after exposure to different DNA damaging agents. Finally, we plan to identify novel genes regulated by BRCA1 in the response to ultraviolet and ionizing radiation by using cDNA microarray technology recently developed at Stanford. The major locus of our work will be to incorporate the information on nucleotide excision repair from other cells into the p53 and BRCA1 context seen in breast cancer, where mutations in these two proteins are facilitators of the disease.

The planned research is significant because it aims to elucidate the role of the BRCA1 gene in an important DNA repair pathway, whose normal function is critical in preventing cancer. In addition to our interests in the initiation and progression of breast cancer, this research has a cancer treatment aspect, too. Since the cell-killing effects of chemotherapy drugs can be neutralized by breast cancer cells via DNA repair pathways, then our research could lead to the better application of treatment strategies.

Final Report (2003)
Note: The PI is continuing her postdoctoral research as a new faculty member at the Dana-Farber Cancer Institute in Boston.

Mutations in the BRCA1/2 tumor-suppressor genes are responsible for 5-10% of inherited breast cancer in the US. The majority of BRCA1-associated breast cancers also contain a mutation in the p53-tumor-suppressor gene. P53 regulates an evolutionarily conserved DNA repair pathway called nucleotide excision repair (NER), which repairs DNA damaged from many environmental carcinogens including ultraviolet-irradiation and tobacco smoke. NER is subdivided into two pathways; global genomic repair (GGR) that targets and removes lesions from the whole genome and transcription-coupled repair (TCR) that preferentially removes lesions from the transcribed strand of expressed genes. P53 affects GGR and not TCR through regulation of genes involved in DNA damage recognition, including GADD45, a DNA damage response gene that is also regulated by BRCA1.

In this research, we have addressed the question of whether BRCA1 affects NER and if this effect is independent of p53. In addition, I have evaluated the effect of BRCA1 on the expression of NER genes involved in DNA damage recognition. We found that BRCA1 plays a role in maintaining the nucleotide excision repair pathway in the cell. This effect is very significant when the p53 tumor suppressor gene is not functioning in the cell, which occurs in >50% of human cancers and 80% of BRCA1-associated breast cancers. We have found that similar to p53, BRCA1 affects only one subset of the NER pathway, GGR, and not TCR. BRCA1 exerts its effect on GGR repair through transcriptional activation of genes involved in the recognition of damaged DNA. Specifically, BRCA1 induces expression of three genes, XPC, p48, and GADD45 when p53 is absent in the cells, thus compensating for loss of p53 in maintaining expression of these genes and allowing DNA repair to occur in the cell. Thus, we have shown that BRCA1 affects NER, through transcriptional regulation of NER genes and believe this may be an important pathway in breast tumorigenesis. This work may impact breast cancer treatment for women who carry BRCA1 mutations by supporting the development of clinical trials using NER-targeted chemotherapy such as cisplatin, and incorporate their use in the treatment of breast cancers that certain genetic signatures. Future directions of this research are to translate laboratory results to the clinic and test the hypothesis that BRCA1-mutated breast tissue undergoes a temporal pattern of specific genetic alterations affecting the NER pathway that are associated with a multi-step carcinogenic progression of normal to pre-malignant to invasive breast cancer on breast tissue obtained from women who carry BRCA1 germline mutations that are undergoing breast cancer screeening. Using tissue obtained from MRI-screen detcted lesions and cells obtained from ductal lavage, we hope to show that genes involved in the NER pathway play a role in the transition of normal breast cells from atypia to invasive cancer.

BRCA1 induces DNA damage recognition factors and enhances nucleotide excision repair.
Periodical:Nature Genetics
Index Medicus: Nat Genet
Authors: Hartman AR, Ford JM
Yr: 2002 Vol: 32 Nbr: 1 Abs: Pg:180-4

Overexpression of Human BRCA1 enhances nucleotide excision repair and induces expression of DNA damage recognition factors
Periodical:Proceedings of the American Association for Cancer Research
Index Medicus: Proc Am Assoc Cancer Res
Authors: Hartman, AR, Haber D, and Ford JM
Yr: 2002 Vol: 43 Nbr: Abs: Pg:1688