Paul J. Galardy, M.D., studies the role of the ubiquitin-proteasome system in the pathogenesis of cancer.
Ubiquitin (Ub), a small highly conserved protein, is attached to proteins in order to change their function or localization, or direct them to the proteasome for degradation. The specificity of Ub attachment is regulated by two large enzyme families called ubiquitin ligases and de-ubiquitinating enzymes (DUBs), with ligases responsible for attachment and DUBs catalyzing the removal of Ub. Many critical cellular events are under the control of this system, including those of cell division. It is therefore not surprising that a growing list of human cancers is associated with deregulated activity of these enzymes. Dr. Galardy's specific focus is on the involvement of DUBs in the development of cancer.
To accomplish this, Dr. Galardy's team uses techniques such as RNA interference, various protein analysis tools and advanced imaging techniques (e.g., live-cell video microscopy) to study the mechanisms of de-ubiquitinating enzymes in cell biology. They also use transgenic or knockout mouse models in which the expression of various de-ubiquitinating enzymes is manipulated to help understand the physiological relevance of the in vitro findings. The team also uses these cell- and animal-based models to explore the feasibility of targeting these enzymes in cancer therapy.
Dr. Galardy's research is funded through a number of sources, including the National Cancer Institute, the American Society of Hematology, the Howard Hughes Medical Institute and a number of other organizations charged with improving cancer cures.
- Role of UCH-L1 in the development of B-cell cancers. Using novel activity-based probes that detect active DUBs, Dr. Galardy and his team are developing activity signatures of DUBs in human cancer that may aid in the identification of cancer-related DUBs. Using this methodology, Dr. Galardy identified the enzyme UCH-L1 as highly active in several forms of human B-cell malignancies, including Burkitt lymphoma.
Using a transgenic mouse model that inappropriately expresses UCH-L1 in all tissues, Dr. Galardy's laboratory demonstrated that this enzyme is in fact an oncogene that drives the development of lung tumors and B-cell cancers (lymphoma and plasma cell tumors) and is required for the ongoing survival of cancers in which it is produced. Ongoing work centers on generating a deeper understanding of the molecular mechanism(s) behind the oncogenic activity of UCH-L1 and the feasibility of using UCH-L1 inhibition to target cancers in mice.
- Role of USP44 in ensuring accurate cell division and suppressing tumors. Cancer cells frequently contain abnormal numbers of chromosomes, a condition known as aneuploidy. Many mouse models that have increased numbers of aneuploid cells have an increased risk of cancer, suggesting that there is a direct link between the development of aneuploidy and the development of this disease. There are many cellular events that help to ensure that equal numbers of chromosomes are distributed to daughter cells upon cell division, and defects in any number of these can lead to aneuploidy. However, only a few of the genes involved in these processes have been found deregulated in human cancers.
USP44 regulates accuracy in mitosis by restraining cell division until all chromosomes are properly attached to the mitotic spindle that pulls the chromosomes toward opposing ends of the cell. To determine the physiological importance of this mechanism and determine if this is important in cancer, Dr. Galardy's team developed a mouse model that lacks the USP44 gene. They find that mice lacking this gene are very prone to cancer, especially that of the lung. They also find that reduced levels of this gene are commonly seen in adenocarcinoma of the lung in humans, and that patients who have tumors with reduced levels have a worse survival than others with normal levels. These results provide conclusive evidence that USP44 is an important gene in the development of tumors.
Cells from the mice lacking USP44 have many aneuploid cells. Dr. Galardy's group has identified a new important function of USP44 in regulating the formation of the mitotic spindle that is important for accurate chromosome movement in mitosis. Ongoing work centers on developing a deeper understanding of the molecular mechanism underlying this function and whether USP44 may be a candidate for genetic manipulation in cancer.
Significance to patient care
Although there has been great progress in the cure rates for childhood cancer, many children die each year of their diseases. Additionally, those that are cured often suffer severe side effects during treatment as well as some severe and life-threatening long-term effects of these treatments.
By developing a better understanding of tumor biology, Dr. Galardy's work seeks to uncover new treatments that will continue to increase cure rates while at the same time reducing the therapeutic burden on children to improve their overall health.