Brad Preston

My laboratory studies the causes and consequences of mutation in human disease. We are particularly interested in how organisms maintain their genomic integrity and how this integrity may be perturbed during disease progression. A central theme of our research is understanding mechanisms that govern faithful DNA synthesis with a focus on defining the biologic significance of replication fidelity in nature. Diseases impacted by fidelity that we are studying in the lab include cancer, AIDS and aging. We are currently pursuing three related projects:

GENOME STABILITY, CANCER & AGING

It is increasingly clear that cancer results from the accumulation of mutations in genes that affect cellular and tissue homeostasis. We do not know, however, how these mutations arise and propel the transformation of normal cells to cancer. We are studying the origins of cancer- and age-related mutations using molecular genetic approaches in mice and in tissue culture.

We have developed gene-targeted mouse systems to study causative links between mutation, cancer and aging in whole animals. This approach allows us to examine disease phenotypes in "mutator" mice that contain defects in genes important for DNA replication fidelity. We recently generated a series of novel mouse lines that are deficient for polymerase proofreading, and we are using these mice to characterize the biologic consequences of mutator phenotypes. Our goal is to understand the molecular origin of mutations that cause cancer and aging and to thereby identify pathways and potential susceptibility genes in humans.

HIV MUTATION, EVOLUTION & DRUG RESISTANCE

The AIDS virus (HIV) is a highly variable retrovirus that continuously mutates during the course of infection. This propensity for mutation underlies the alarmingly adaptive nature of HIV, which leads to evasion of the immune system, drug resistance, virus spread and ultimately AIDS. We want to understand how HIV mutates and evolves.

Past studies in our laboratory show that HIV mutates every time it multiplies and that the virus-encoded reverse transcriptase (RT) is a major player in HIV mutagenesis. We are currently using genetic, molecular biology and biochemical approaches to investigate the mechanisms and roles of virus- and host cell-encoded accessory proteins in retroviral replication, mutation and evolution. We are also examining pathways that confer drug resistance in HIV-1 and HIV-2 in vitro and in vivo. Our goal is to understand the biochemistry of HIV replication and to thereby identify means to exploit the mutation process, slow disease progression, and increase the effectiveness of antiviral therapies.

MOLECULAR DETERMINANTS OF POLYMERASE FIDELITY

Comparisons of DNA polymerases from a variety of organisms suggest that protein structure is a critical determinant of faithful DNA replication. Some DNA polymerases (e.g., TLS pols) incorporate and extend the wrong nucleotide with relative ease, while others (e.g., pols delta, epsilon and gamma) have intrinsic proofreading activity and are highly accurate. Structural elements in these polymerases determine base selection, primer*template recognition, processivity, proofreading and thus fidelity. Moreover, there appears to be an interplay among polymerases involving accessory replication factors that govern replication fork progression during the cell cycle. We are using genetic strategies to study the effects of polymerase alleles and mutant accessory proteins on substrate recognition and fidelity in yeast and mouse model systems.