Current Research Interests

The major investigative focus of this laboratory is to explore the mammalian genetic determinants of the inducible response and cellular sensitivity to DNA damaging cytotoxic agents, focusing particularly on the effects of the p53 and BRCA1 gene products on DNA repair and apoptosis. We have found that loss of p53 and BRCA1 function results in defective nucleotide excision repair (NER) of DNA damage. Therefore, we are focused on identifying the molecular mechanisms that regulate DNA repair by these tumor suppressor genes, and how their deficiency impacts human cancer development. In addition, we are exploring ways to exploit the DNA repair deficiency of p53 and BRCA1 mutant cancer cells and to identify cytotoxic drugs that may specifically target these cancer cells. Current research projects include:

Mechanism of p53-dependent DNA repair:
We initially discovered that loss of activity of the p53 tumor suppressor gene results in defective global NER of UVC-induced DNA photoproducts from genomic DNA, but does not effect the preferential transcription-coupled DNA repair of the transcribed strand of expressed genes. These results suggest that mutations of the p53 gene lead to greater genomic instability due to reduced efficiency in DNA repair. A major current objective is to determine the mechanism for the effect of the p53 gene product on global NER. We have recently identified several p53 inducible genes that are involved in DNA repair, including XPE, XPC and GADD45. In addition, we are exploring how p53 may also effect the base excision repair pathway, and transcription-coupled repair following UVB-induced oxidative DNA damage. A number of approaches are being employed, including use of cell lines and animal models with defined genetic alterations in genes that may be involved in this DNA repair pathway, development of cell lines allowing inducible expression of these p53 regulated genes; cDNA microarrary analysis of p53 and DNA damage inducible gene expression, and novel genomics approaches.

DNA damage inducible response pathways: We have employed novel cDNA microarray analysis methods to explore the gene expression responses to various DNA damaging agents (UV, cisplatin, X-rays, etc.) and other cytotoxic drugs (Taxanes). These studies have identified a number of distinctive damage inducible gene expression patterns, as well as specific gene products whose functions we are currently exploring, including those involved in DNA damage induced apoptosis, proteosomal degradation and DNA repair.

Relationships between p53 function and cancer drug resistance:

The majority of cancer chemotherapeutic agents exert their cytotoxic effects through DNA damage, and p53 may effect cellular sensitivity to these drugs. We have shown that cells mutant for p53 function are resistant to the cytotoxic activity of DNA damaging drugs, but are more sensitive to the microtubule inhibitory drug Taxol, than are the same cells in which wild-type p53 expression is induced. Studies to determine the mechanism for this observation are underway, including analysis of the effect of p53 function on taxane induced apoptotic pathways, mitotic spindle checkpoints and regulation of tubulin dynamics. Additional approaches for the targeted elimination of genetically altered tumor cells are being explored, by searching for agents whose action is enhanced by cell cycle checkpoint defects.

DNA repair deficiencies in inherited genetic syndromes:
Specialized molecular techniques for the quantitative analysis of global NER and transcription-coupled DNA repair are being used to identify and characterize DNA repair deficiencies in human and animal tissues due to inherited genetic traits (e.g. xeroderma pigmentosum, Cockayne’s syndrome, Li-Fraumeni syndrome, HNPCC, Breast/Ovary Cancer etc.). Genotype-phenotype relationships between specific mutations and DNA damage response pathways and clinical outcomes will be established.