Phone: (949) 824-3053
Dr. Limoli’s research program is focused on understanding the molecular mechanisms that underlie the mammalian stress response and how disruptions to this tightly regulated process lead to genomic instability and cancer. Mammalian cells respond to cytotoxic and genotoxic agents by eliciting a series of signaling cascades that result in the activation of cell cycle checkpoints and DNA repair. Many of these events are error prone and can initiate biochemical and molecular changes that can compromise the integrity of cellular genomes over many cell divisions. Much of their work has focused on elucidating the types of DNA lesions that initiate genomic instability, the biochemical and molecular processes that perpetuate genomic instability, and the consequences associated with developing genomic instability. They have demonstrated that complex DNA lesions containing DNA double-strand breaks (DSBs) are critical determinants for the induction of genomic instability, and consequently, much of the present work is aimed at understanding how these lesions are recognized and processed in a variety of genetic backgrounds.
To this end they have identified a relatively new pathway in mammalian cells that leads to genomic instability and depends upon the formation of DSBs in response to replication blocks. Using a replication defective cell line derived from the xeroderma pigmentosum variant they have demonstrated that in response to replication arrest, stalled forks collapse and develop DNA DSBs that can be resolved by homologous recombination. These findings support past studies in lower organisms and provide an opportunity for dissecting the complex signaling and repair mechanisms that are activated during the intra-S-phase checkpoint. Further work is aimed at understanding how DSBs are formed at sites of stalled forks and how these lesions are shunted to homologous or nonhomologous repair pathways, a decision that influences the fidelity of repair and the likelihood of developing genomic instability. Related studies using a variety of checkpoint and repair mutants are being used in a genetic approach to further understand the pathways by which mammalian cells circumvent stalled replication forks.
Central to Dr. Limoli’s investigations is the identification of the mechanisms by which cells perpetuate genomic instability. Cells must retain a “memory” of past insult that is passed on to their progeny. One mechanism for maintaining prolonged phenotypic change is oxidative stress. They have shown that genomically unstable cells exhibit indications of oxidative stress, including elevated reactive oxygen species, mitochondrial dysfunction, lipid peroxidation, and DNA base damage. They have also determined that persistent oxidative stress can induce multiple endpoints of genomic instability including chromosomal destabilization. The details linking oxidative stress to specific changes in gene expression, sensitivity to environmental toxins, and karyotypic abnormalities are active areas of interest.
Dr. Limoli recently expanded his research into the rapidly growing field of neural stem cell biology. They are now exploring how DNA damage and oxidative stress might drive the progression of normal multipotent cells in the CNS to brain tumor stem cells. They have linked changes in redox state to many physiologic changes in marker expression, metabolism, proliferation, and radiosensitivity that suggest normal neural stem cells are prone to carcinogenic transitions. The working hypothesis is that changes in redox state alter the capability of normal neural stem and precursor cells to ward off genomic instability. This hypothesis predicts that any stem cell versus their immediate progeny (i.e., precursor/progenitor cells) will be more resistant to undergoing genomic instability, and work in their laboratory has thus far supported this idea. Ultimately, they expect that redox sensitive pathways in somatic stem cells throughout the body will prove critical in carcinogenesis.
Limoli, C. L., Giedzinski, E., Bonner, W. M., and Cleaver, J. E. (2002). UV-induced replication arrest in the xeroderma pigmentosum variant leads to DNA double-strand breaks, gamma -H2AX formation, and Mre11 relocalization. Proc Natl Acad Sci U S A 99(1), 233-8.
Limoli, C. L., and Giedzinski, E. (2003). Induction of chromosomal instability by chronic oxidative stress. Neoplasia 5(4), 339-46.
Limoli, C. L., Giedzinski, E., Morgan, W. F., Swarts, S. G., Jones, G. D., and Hyun, W. (2003). Persistent oxidative stress in chromosomally unstable cells. Cancer Res 63(12), 3107-11.
Thompson, L. H., and Limoli, C. L. (2004). Origin, recognition, signaling and repair of DNA double-strand breaks in mammalian cells. Eukaryotic DNA Damage Surveillance and Repair, 107-145.
Limoli, C. L., Giedzinski, E., and Cleaver, J. E. (2005). Alternative recombination pathways in UV-irradiated XP variant cells. Oncogene 24(23), 3708-14.