Alexander J.R. Bishop, Ph.D.Assistant Professor
Dr. Bishop joined the Department of Cellular and Structural Biology January 2005 and his laboratory is housed in the Greehey Children's Cancer Research Institute.
The research of the laboratory is aimed at understanding the contribution of different genes to genomic instability and the role of such instability in development, aging and carcinogenesis. Strategies used include RNAi knockdown, transgenic over-expression and both constitutive and conditional knock-out models in a variety of systems including Drosophila tissue culture, mammalian tissue culture and mouse models. The central question addressed in the laboratory is what is the effect on genomic stability of modulating a gene particularly after exposure to a carcinogenic agent. We assess genomic instability by measuring homologous recombination (HR) or following the machinery involved in this process. HR repair is a significant component of the cellular repair process in a replicating cell, and most importantly, responds to the widest variety of DNA damages, from oxidative stress, alkylation damage, bulky adducts on DNA as well as cross-links and ionizing radiation.
Homologous recombination is an important process of genetic alteration in the generation of cancers. Certain genetic deficiencies result in higher than normal levels of genomic instability during development, including a higher frequency of HR and a higher probability of developing cancers. In addition, environmental exposures to carcinogenic agents result in genomic instability, in particular deletion by HR. In the last decade several researchers have demonstrated that spontaneous deletions can be mediated by HR between repeated DNA fragments and that the frequency of such events are elevated following exposure to carcinogens. Conversely, a higher level of HR can result in a greater resistance to certain chemotherapeutic agents, making some cancers refractory to these treatments.
Over the last few years we have established several systems to begin to ask key questions in the field of DNA damage response. Similar systems were previously established and characterized, such as a murine HR assay system (Mutation Research (2000), 457; Carcinogenesis (2001), 22(4)) and the demonstration that both the endogenous level of HR and carcinogen induced HR were dependent upon components of the p53 damage response pathway (Carcinogenesis (1999) 20; Cancer Research (2000) 60; Cancer Research, (2003) 63). Information and experience gained from these studies directed the hypothesis that there are other cellular components that affect genomic stability through development and over age. These components are also likely to play a part in cellular damage response. It is these modulators of genomic stability that we are trying to determine and would like to characterize.
To determine novel factors involved in DNA repair and damage response we are taking advantage of an available Drosophila genome library of RNAi at Harvard University, Boston, MA. We are using this library to determine which genes are determine survival following exposure to particular forms of DNA damage. We are hoping to establish interactome maps to mine this data, elucidating commonalities between different damage exposures as well as similarities. As the major interest of the laboratory is to find genetic modulators of spontaneous HR we will examine the frequency of HR following RNAi knockdown and later in combination with particular DNA damaging agents. These results will be compared with survival information gained from the screens currently being performs with just the DNA damaging agents. In addition, epistatic effects will provide further insight, by specifically removing particular components of DNA repair, such as Rad54, and central component of the homologous recombination machinery.
The main aim of the laboratory is to examine the role of various components of the DNA damage response pathway on development, aging and cancer propensity. To facilitate this, the laboratory has and continues to develop novel HR assays for both mouse tissue culture and in vivo. The longterm goal is to identify and confirm functional homologues of any identified Drosophila genes of interest. Secondly, we are taking a candidate approach to examine a number of genes of interest. We are taking advantage of BAC modification tools to introduce specifically modified genes under their correct promoter, inserting mutations, splice variations and introducing fluorescent tags. Information gained from these studies, together with the novel tools established, should open up a wealth of research opportunities.