Department of Neuroscience, Neurobiology, Uppsala University, Box 587 Biomedical Center, S-75123 Uppsala, Sweden.
The ERM protein family members ezrin, radixin, and moesin are cytoskeletal effector proteins linking actin to membrane-bound proteins at the cell surface. Here we report on the cloning of myosin regulatory light chain interacting protein (MIR), a protein with an ERM-homology domain and a carboxyl-terminal RING finger, that is expressed, among other tissues, in brain. MIR is distributed in cultured COS cells, in a punctuated manner as shown using enhanced green fluorescent protein (EGFP)-tagged MIR and by staining with a specific antibody for MIR. In the yeast two-hybrid system and in transfected COS cells, MIR interacts with myosin regulatory light chain B, which in turn regulates the activity of the actomyosin complex. Overexpression of MIR cDNA in PC12 cells abrogated neurite outgrowth induced by nerve growth factor (NGF) without affecting TrkA signaling. The results show that MIR, a novel ERM-like protein, affects cytoskeleton interactions regulating cell motility, such as neurite outgrowth.