UNIVERSITY OF MASSACHUSETTS
Rapid cell movement is important for the normal functioning of the immune system and for the spread of metastatic tumor cells. Migrating cells extend surface protrusions at their front edges, bind to the external matrix at focal adhesions, and then disassemble rear focal adhesions as they retract their back ends. The Luna laboratory has identified a group of proteins at the interface between the membrane and the cytoskeleton that is found in both immune and cancer cells. Supervillin is the cytoskeletal protein in this membrane skeleton that is the most tightly bound to the membrane. Supervillin regulates each step of cell motility. It also promotes matrix degradation under cancer cells, associates with rapidly moving internal membranes, increases turnover of focal adhesions, and increases the rate of undirected motility of carcinoma cells. One mechanism by which supervillin regulates these processes is by increasing myosin II contractility stimulated by light chain phosphorylation by the long form of myosin light chain kinase (L-MLCK). The supervillin amino-terminus binds directly to both the myosin II heavy chain and to L-MLCK, and forms clusters with L-MLCK and activated myosin II. The working hypothesis is that the supervillin-associated proteins regulate membrane-associated myosin II contractility by assembling scaffolds at membranes that include L-MLCK. Myosin II also is involved in every step of the motility cycle, including membrane trafficking, and a role in regulating when and where myosin II is activated could underlie most of the functions associated with supervillin. The goal of this ARRA Supplement is to deepen our understanding of the intracellular role played by supervillin in the regulation of myosin II contractility and to facilitate the publication of a proteomics-based study carried out in the current funding period that describes 29 supervillin-binding proteins and an initial characterization of their roles in motile processes.