Dr. Tracey Mason

Processing of DNA interstrand cross-links in-vivo; the influence of cell cycle
Student Researcher:  Ashley Pitti

My research is in DNA repair. Specifically, I am asking the question, how are interstrand DNA cross-links repaired by human cells? This is an issue because there are several very effective chemotherapeutics that are designed to deliver just this type of lesion to cancer cells when patients are undergoing chemotherapy. What is evident, however is that after cancer cells have been treated once with a therapy, they sometimes come back with a vengeance, and are no longer sensitive to the therapy that once killed them.

To study this question, a model cross-link has been prepared in collaboration with my post-doctoral mentor at Johns Hopkins University, Professor Paul Miller. It is a N4C-N4C cross-linked oligonucleotide which has been manipulated into a plasmid. This plasmid is then transfected into cells and the fate of the cell is determined through simple survival screens such as Trypan Blue Exclusion and MTT assay. This is the focus of the first Specific Aim.

I want to know if the survivability and repair of the cross-linked DNA is dependent on cell cycle progression. The second Specific Aim of the ORD grant asks if the introduction of an interstrand cross-link to DNA causes the cells to stall in their progression of the cell cycle and if so, in what phase of the cell cycle ? To make it more interesting, we will compare cells that are completely competent in repair to those that are diseased, i.e. deficient in repair due to a variety of mechanisms. This is important because cells have a variety of mechanisms available to repair damage. Depending on the type of damage and where in the cell cycle the damage is discovered, the cell may try one of several approaches to repair the damaged DNA.

This research will hopefully hint as to what pathway(s) is/are involved in repair of DNA interstrand cross-links and lead to more focused studies in this area.  Student contributions are very important to the success of this project; I mentor independent research students during the school year and summers from both Biology and Chemistry.