Dr. Mulligan completed her PhD in Medical Genetics at Queen’s University and went on to further training focusing on molecular genetics of rare cancer syndromes. Her research on the molecular mechanisms of inherited thyroid cancers led to the discovery of the role of the RET oncogene in endocrine tumours and its contributions to a number of cancers. Dr. Mulligan is a Professor of Pathology and Molecular Medicine, and a member of the Division of Cancer Biology and Genetics, Cancer Research Institute at Queens University. Her primary research interests are in understanding the molecular, cellular and clinical roles of the RET receptor tyrosine kinase in normal and cancer cells.
REGULATION OF THE RET RECEPTOR TYROSINE KINASE
EXPLORING POTENTIAL THERAPEUTIC TARGETS IN HUMAN CANCER
Receptor tyrosine kinases link extracellular signals with intracellular pathways that cause cells to move,grow, proliferate or differentiate. These roles are essential to normal development but can be hijacked in human cancers. The primary interest of our group is the relationship between these normal and neoplastic processes. We focus on the functions and regulation of the RET receptor tyrosine kinase and its roles in normal development and in the growth and spread of several challenging to manage human cancers. Mutations that inappropriately activate RET are found in multiple cancers including thyroid, adrenal, and lung tumours, but increases in normal RET expression are also associated with human disease including breas and pancreatic cancers. We focus on dissecting the mechanisms regulating normal RET function and how changes in regulation can lead to cancer growth and spread. Understanding these mechanisms will allow us to identify novel targets for future therapeutic interventions in RET-mediated cancers.
RECENT RESEARCH FROM OUR LAB:
Differential Roles of RET Isoforms in Medullary and Papillary Thyroid Carcinomas
Cells produce the RET protein in several different forms that have distinct roles in normal cells. In this study, we showed that one of these protein forms, called RET51, is the predominant form of RET contributing to human thyroid cancers. Using thyroid cancer cells, we showed that RET51 promotes growth, movement, invasiveness and survival of cancer cells, and notably, that reductions in RET51 expression dramatically lessened these undesirable cancer cell behaviours. Importantly, we also showed that RET51 expression was associated with more high-risk tumour behaviours in human thyroid cancers. Our study identifies an important protein involved in cancer spread that could also be a therapeutic target in combating human thyroid tumours, and potentially a number of other challenging human cancers.
Differential Recruitment of E3-Ubiquitin Ligase Complexes Regulates RET Isoform Internalization
The RET protein is regulated in many ways to maintain a proper functional balance in normal cells. An important aspect of this, is marking proteins for downregulation and degradation. In this study, we showed that the two RET protein forms are downreglated by recruiting unique protein complexes that help them move to the correct intercellular compartments. We showed that both RET9 and RET51 forms are “tagged” with ubiquitin and that this modification may be important both for degradation of the receptors, but also for guiding their intercellular trafficking.
Distinct Temporal Regulation of RET Isoform Internalization: Roles of Clathrin and AP2
The movement of proteins from the cell surface into compartments within the cell (endocytosis) is an important process regulating the duration and magnitude of the signals that cause cells to grow, mature or survive. Here, we explored the movement of RET proteins from the cell surface into these compartments that are important to regulating RET functions. We are the first to identify the molecules that interact with RET and promote its entry into the cell. These interactions are the key steps in controlling RET’s activity and, more importantly tell it when to signal and when to “turn off” these signals. Interestingly, our studies show that the activated form of RET51 rapidly enters the cell, while RET9 is recruited more slowly. These distinct rates of endocytosis may contribute to the functional differences between RET isoforms.
An Efficient and Flexible Cell Aggregation Method for 3D Spheroid Production
Traditional culture methods, where cells are grown in a flat 2D tissue culture plate, are not truly representative of cancer cell growth in the body. In situ growth of tumour cells occurs in 3D, where cells interact with each other and the surrounding environment to a greater extent. Here, we describe a rapid and flexible protocol for the formation of 3D cell spheroids through cell aggregation. This is easily adapted to multiple cell types and is suitable for use in a variety of applications including cell migration, invasion, or anoikis assays, and for imaging and quantifying cell-matrix interactions.