Mark Brenneman
Assistant Professor

DNA repair and recombination and their roles in genome stability and tumor suppression

My lab's research interest is the repair of DNA damage via homologous recombination (homologous recombinational repair; HRR). and the critical roles this pathway plays in genomic stability and tumor suppression. That deficient DNA repair can predispose to tumorogenesis is well established in relation to other major DNA repair pathways. Defects in nucleotide excision repair underlie xeroderma pigmentosum. which confers extreme risk of skin cancer. Defects in mismatch repair cause hereditary non-polyposis colon cancer. The principle evidently extends to defects in HRR. which are strongly correlated with genomic instability at levels ranging from localized sequence rearrangement to gross chromosomal change.

This correlation is illustrated by the HRR gene XRCC3. Cells mutated for XRCC3 are hypersensitive to certain types of DNA damage and show extreme chromosomal instability. with high frequencies of chromosome breakage. rearrangements and loss [publication #8. below]. They are severely impaired for HRR of chromosomal breaks. showing not only reduced overall efficiency of repair [7]. but also a loss of fidelity such that rearrangements of chromosomal DNA often accompany repair [4]. Similar phenotypes of chromosomal instability and hypersensitivity to DNA damage have been seen for a growing list of genes with known or suspected involvement in HRR. These include other members of the RAD51 gene family (to which XRCC3 belongs). and genes linked to several cancer predisposition syndromes. including Nijmegen Breakage Syndrome (NBS1). Bloom Syndrome (BLM). Werner Syndrome (WRN). and familial breast cancer (BRCA1 and BRCA2).

Defective HRR has now been causally linked to tumorogenesis through BRCA1 and BRCA2; the first tumor suppressor genes shown unequivocally to function in HRR [reviewed in 6]. In mouse. complete gene knockout of BRCA2 is lethal. A milder mutation permits viability. but results in hypersensitivity to DNA crosslinking damage and frequent breakage or loss of chromosomes [3]. In human cells. disrupting functional interaction between the BRCA2 and RAD51 proteins also causes DNA damage hypersensitivity. and impaired HRR of chromosomal breaks [1]. Still unknown is why breast tissue should be especially susceptible to this defect. and whether loss of BRCA2 function represents a "weak link" in a chain of tumorogenic events common to non-familial ("sporadic") breast cancer as well. Answers to these questions may help us understand and combat the alarming increases in incidence of breast cancer seen over the past few decades.

New research directions include investigations of the molecular mechanisms by which BRCA2 and the RAD51 family proteins function in HRR. A particularly important aspect is the repair and/or bypass of DNA damage encountered by replication forks. and how mutations that impair this process. or environmental exposures that overwhelm it. might drive genomic instability and tumorogenesis. These studies will be extended to other tumor suppressor proteins (BRCA1. NBS1. BLM. and WRN). A parallel interest is exploiting new knowledge about HRR to develop techniques for high-efficiency gene targeting in human cells. This would enable the kind of fascile genetic analysis that is currently possible only in bacteria and yeast. and holds great promise for therapeutic intervention in genetic disease.

Selected Publications

Lo YC. Paffett KS. Amit O. Clikeman JA. Sterk R. Brenneman MA. Nickoloff JA. (2006) Sgs1 regulates gene conversion tract lengths and crossovers independently of its helicase activity. Mol Cell Biol. 26(11):4086-94.

Lio YC. Schild D. Brenneman MA. Redpath JL. Chen DJ. (2004) Human Rad51C deficiency destabilizes XRCC3. impairs recombination. and radiosensitizes S/G2-phase cells. J Biol Chem. 79(40):42313-20.
Bailey SM. Brenneman MA. Goodwin EH. (2004) Frequent recombination in telomeric DNA may extend the proliferative life of telomerase-negative cells. Nucleic Acids Res. 32(12):3743-51.

Bailey SM. Brenneman MA. Halbrook J. Nickoloff JA. Ullrich RL. Goodwin EH. (2004) The kinase activity of DNA-PK is required to protect mammalian telomeres. DNA Repair (Amst). 3(3):225-33.

Nickoloff JA. Brenneman MA. (2004) Analysis of recombinational repair of DNA double-strand breaks in mammalian cells with I-SceI nuclease. Methods Mol Biol. 262:35-52.

Brenneman. M.A.. Guo. X . Wagener. B.M. . Miller. C.A. . Shen. Z.. Chen. D.J. and Nickoloff; J.A. BRCA2 orchestrates homologous recombinational repair via multiple protein- and DNA-binding domains. (manuscript in preparation)

Bailey. S.M.. Brenneman. M.A.. Halbrook. J. . Ullrich. R.L.. Nickoloff. J.A. and Goodwin. E.H.; The kinase activity of DNA-PK is required to protect mammalian telomeres. (in press)

Donoho. G.. Brenneman. M.A. . Cui. T.X. . Donoviel. D.. Vogel. H.. Goodwin. E.H. . Chen. D.J. and Hasty. P. (2003) Deletion of Brca2 Exon 27 causes hypersensitivity to DNA crosslinks. chromosomal Instability. and reduced life span in mice. Genes. Chromosomes and Cancer 36(4): 317-331.

Brenneman. M.A.. Wagener. B.M. . Miller. C.A.. Allen. C.P. and Nickoloff. J.A. (2002) XRCC3 controls the fidelity of homologous recombinational repair: Roles for XRCC3 in late stages of recombination. Molecular Cell 10:387-95.

Allen. C.P.. Kurimasa. A.. Brenneman. M.A. . Chen. D.J. and Nickoloff. J.A. (2002) DNA-dependent protein kinase suppresses spontaneous and double-strand break-induced homologous recombination. Proceedings of the National Academy of Science. USA 99:3758-3763.

Brenneman. M.A. (2001) BRCA1 and BRCA2 in DNA Repair; in: DNA Damage and Repair. Volume III. J.A. Nickoloff and M.F. Hoekstra. eds. Humana Press.

Brenneman. M.A.. Weiss. A.E. . Nickoloff. J.A. and Chen. D.J. (2000) XRCC3 is required for efficient repair of chromosome breaks by homologous recombination. Mutation Research - DNA Repair 459: 89-97.

Cui. X.. Brenneman. M.A. . Meine. J.. Goodwin. E.H. and Chen. D.J. (1999) The XRCC2 and XRCC3 DNA repair genes are required for chromosome stability. Mutation Research - DNA Repair 434: 75-88.