The lab studies cell polarity which is required for virtually all aspects of cell behavior including cell morphology, cell motility, and cell identity arising from asymmetric divisions (e.g., stem cells). In particular we are focused on how extracellular signals control metastatic behavior in melanoma by regulating cell polarity. Wnt5a is a non-canonical Wnt ligand that regulates cell polarity in developmental systems. We have found that Wnt5a induces the formation of a novel polarized structure (WRAMP structure) in melanoma cells that mediates membrane retraction and directional cell movement. We are using biochemistry and proteomics to identify the components of the WRAMP structure and live cell imaging to observe the temporal assembly of the components. Future work will determine the in vivo function of the WRAMP structure and regulated cell polarity during metastasis.

Our research is focused on the regulation of cell polarity in cancer and how it determines cell behavior during the transition from a non-metastatic to a metastatic state. We previously identified a novel polarized structure composed of an IgG family cell adhesion molecule named melanoma cell adhesion molecule (MCAM) forms in response to Wnt5a. We named this structure the "WRAMP (Wnt5a-induced, receptor, actin and myosin II polarity) structure", based on its recruitment of the MCAM cell adhesion receptor, Frizzled receptors, and an overlapping polarized complex of cytoskeletal proteins including F-actin and myosin IIB. Formation of the WRAMP structure led to rapid retraction of adjacent cell membrane, and moved the nucleus towards the side of the cell opposite from the WRAMP structure, leading to directional cell movement (Witze et al. Science 2008). Proteomic analysis has identified many proteins that localize to the WRAMP structure and many of these proteins are involved in cytoskeletal reorganization and/or membrane trafficking. This may suggest that Wnt signaling regulates polarity through the polarized trafficking of membrane compartments and proteins. 3D electron microscopy together with live imaging revealed that the endoplasmic reticulum also localizes to the WRAMP structure. This movement of the ER coincided with a localized elevation of calcium levels specifically in the WRAMP structure. These studies reveal a novel mechanism for the polarized distribution of cell structures that regulate calcium signaling spatially in response to Wnt5a in migrating cells.