Ruth A. Gjerset, Ph.D., Associate Professor

Tumor Suppressor Research Program

Ruth A. Gjerset, Ph.D. (Associate Professor, Principle investigator)
Yinghui Huang, M.D., Ph.D., (Senior Research Scientist)
Keya Bandyopadhyay, Ph.D. (Senior Research Scientist)
Ming Zhao, B.S. (Technician)

Ruth Gjerset earned her Ph.D. in Biochemistry and Biophysics from the University of California, San Francisco Medical Center, and carried out post-doctoral training at the University of California San Francisco and San Diego, and at the Pasteur Institute in Paris, France, before establishing a tumor suppressor laboratory at the Sidney Kimmel Cancer Center. The laboratory focuses on the cellular and molecular mechanisms of cancer, particularly with regard to the regulation and function of the p53 and p14ARF tumor suppressors. These proteins are dormant in normal cells, but are induced in abnormal cells, where they shut down cell proliferation and provide a first line of defense against the development of cancer. The loss of one or the other of these two proteins is central to most cancers, and provides important opportunities for therapy and diagnosis. The long term perspective of the laboratory is to understand how deregulation of these tumor suppressors leads to cancer, and to develop novel biological approaches to cancer treatment and therapy sensitization based on the molecular interactions and functions of these tumor suppressors. The following projects are ongoing: (1) A study of novel activities and functions of the p14ARF tumor suppressor, including its interaction with topoisomerase I, an important target for chemotherapy. This study focuses on the role of the p14ARF-topoisomerase I complex in cancer and the opportunities it offers for anti-cancer therapy, and for detecting therapy resistant cancers. (2) Diagnostic profiling of cancer, based on alterations in p14ARF, topoisomerase I, and cellular stress response pathways. (3) Novel viral and cell-based strategies for gene delivery to localized and metastatic cancers.

Overview. There is an urgent need for efficient, non-toxic biological therapies for cancer, particularly for advanced disease, where current therapies are often inadequate. Loss of the p53 tumor suppressor pathway, usually through loss of p53 or p14ARF tumor suppressor function, is a key event in the development of all or most cancers. Restoration of this pathway specifically suppress the growth of cancer cells and is a promising approach for the development of safe, non-toxic, highly effective, therapeutic agents for cancer gene therapy.

The goal of our program is to better understand the activities and functions of these tumor suppressors and to develop novel, non-toxic biological approaches to cancer therapy based on p53 and p14ARF. Such approaches offer the perspective of cancer specific therapies with broad application for all or most cancers. We are also studying novel activities of p14ARF, independent of the p53 pathway, as well as epigenetic regulation of the p14ARF gene locus. These studies are providing a basis for the development of diagnostic assays for disease prognosis and therapy resistance.

Projects. To fully exploit the potential of p53 and p14 for cancer therapy and diagnosis, we are carrying out the following projects, fully funded through the National Cancer Institute, the Department of Defense Prostate Cancer Program, and the Joan Scarangello Lung Cancer Foundation:

1. Combination tumor suppressor gene therapy. p53 gene therapy using a viral-mediated gene delivery approach has reached an advanced stage of clinical development. We have found that co-delivery of p14ARF is needed to optimize p53 gene therapy and we have developed combination vectors that are some 20-fold more potent than the clinical grade p53 vectors presently in use. We are presently working on improved strategies for systemic gene delivery, in order to extend this approach to the broadest array of cancers.

2. Novel targets for drug development and diagnosis. p14ARF engages in interactions and functions beyond the p53 pathway that can be exploited therapeutically and diagnostically. We and others have identified a novel nucleolar complex involving the p14ARF tumor suppressor and topoisomerase I, an important chemotherapy target. The interaction involves a region of the p14ARF protein that is not required for its p53-dependent activity and results in activation of topoisomerase I. We have shown p14ARF sensitizes tumor cells to the topoisomerase I-target drug camptothecin, independently of p53, through complex formation with topoisomerase I and that complex formation requires casein kinase-mediated topoisomerase I serine phosphorylation. Furthermore, we have found that cancer associated defects in casein kinase activity, topoisomerase I serine phosphorylation, and p14ARF/topoisomerase I complex formation correlate with certain types of therapy resistance. We are presently developing ways to target the complex to enhance p14/p53 gene therapy, as well as ways to exploit the properties of the complex for diagnostic assays for therapy resistance.

3. Epigenomic regulation of p14ARF in esophageal cancer. Epigenetic changes at the p14ARF locus may be among the earliest occurrences in premalignancy and serve as markers for disease progression. Through a collaboration with Dr. Rebecca Fitzgerald at the University of Cambridge, U.K., Dr. Yinghui Huang is examining epigenetic changes in the p14ARF gene in Barrett's esophagus, a premalignant stage of esophageal adenocarcinoma. The identification of novel epigenetic markers could facilitate early detection and improve survival from this disease, whose incidence is increasing in western countries for unknown reasons.

Selected publications:

Huang, Y., Peters, C.J., Fitzgerald, R,C,, Gjerset, R.A. (2008) Progressive silencing of p14ARF in oesophageal adenocarcinoma. J Cell Mol Med in press.

Bandyopadhyay, K., Lee, C., Haghighi, A., Baneres, J. L., Parello, J., and Gjerset, R. A. (2007). Serine phosphorylation-dependent coregulation of topoisomerase I by the p14ARF tumor suppressor. Biochemistry 46, 14325-14334.

Huang, Y., Lee, C., Borgstrom, P., and Gjerset, R. A. (2007). Macrophage-mediated bystander effect triggered by tumor cell apoptosis. Mol Ther 15, 524-533.

Gjerset, R. A. (2006). DNA damage, p14ARF, nucleophosmin (NPM/B23), and cancer. J Mol Histol 37, 239-251.

Gjerset, R. A., and Bandyopadhyay, K. (2006). Regulation of p14ARF through subnuclear compartmentalization. Cell Cycle 5, 686-690.

Lee, C., Smith, B. A., Bandyopadhyay, K., and Gjerset, R. A. (2005). DNA damage disrupts the p14ARF-B23(nucleophosmin) interaction and triggers a transient subnuclear redistribution of p14ARF. Cancer Res 65, 9834-9842.

Huang, Y., Tyler, T., Saadatmandi, N., Lee, C., Borgstrom, P., and Gjerset, R. A. (2003). Enhanced tumor suppression by a p14ARF/p53 bicistronic adenovirus through increased p53 protein translation and stability. Cancer Res 63, 3646-3653.

Lebedeva, S., Bagdasarova, S., Tyler, T., Mu, X., Wilson, D. R., and Gjerset, R. A. (2001). Tumor suppression and therapy sensitization of localized and metastatic breast cancer by adenovirus p53. Hum Gene Ther 12, 763-772.

Haghighi, A., Lebedeva, S., and Gjerset, R. A. (1999). Preferential platination of an activated cellular promoter by cis-diamminedichloroplatinum. Biochemistry 38, 12432-12438.