Role of Myosin VI-DOCK7 interaction in neuronal cells
Myosin VI (MVI) is a unique unconventional myosin as unlike all other myosins it walks towards the minus (pointed) end of actin filaments. It is involved in many cellular functions related to intracellular transport and organization of the actin cytoskeleton. MVI involvement in a given function depends on its interactions with its tissue/cell specific partners. Several studies show that MVI plays a role in glutamate receptor internalization, synaptic transmission and synaptic vesicle recycling. Our search for MVI partners resulted in identification of DOCK7 as its potential partner in neuronal-lineage PC12 cells. Since DOCK7, a protein with GEF activity towards Rac1 and Cdc42, is crucial for axon formation, we aimed at characterization of physiological relevance of this novel interaction in neuronal cells, including neurosecretory PC12 cells and primary culture neurons. We confirmed that this interaction occurred also in neurons, and biochemically characterized MVI-DOCK7 binding sites. The presence of MVI was necessary for both DOCK7 localization and activity as well as for NGF-stimulated protrusion formation, as revealed for PC12 cells. Studies on primary culture neurons revealed that co-localization of both proteins was maintained during the culture time-course and was visible within cell body, neurites, dendritic spines and neurite growth cones. Also, lack or depletion of MVI affected the dendritic arbor formation and morphology of axonal growth cone. MVI-DOCK7 co-localization was also visible in the brain. Studies on brains of Snell’s waltzer mice (SV) that do not synthesize MVI also revealed a decrease of DOCK7 activity measured by the levels its own and its downstream effectors phosphorylation. Of note, SV mice exhibit several neuronal dysfunctions such as deafness, circling and head tossing behavior. Taken together, our data indicate that MVI-DOCK7 interaction plays important role in the neuronal system. FINANCIAL SUPPORT: The work was supported by a grant UMO-2012/05/B/NZ3/01996 from the National Science Centre and statutory funds for the Nencki Institute of Experimental Biology from Ministry of Science and Higher Education.