Nucleocytoplasmic shuttling of cytoskeletal proteins : molecular mechanism and biological significance

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In this study we focused on the communication between cytoskeleton and the nucleus, which is achieved by the dynamic shuttling of cytoskeletal components into the nucleus. Nuclear pore complex(NPC) serves as a hydrophobic selective gate of nucleocytoplasmic molecular transport, enabling small molecules(~ 40kDa) and nuclear transport receptors(e. g., importins and exportins) to pass through the nuclear membrane. However, the detailed selectivity property of NPC still remained unknown. First, we demonstrated the nucleocytoplasmic shuttling of several cytoskeletal proteins such as spectrin and actinin by immunostaining of cells treated with Leptomycin B, a selective inhibitor for CRM1-dependent nuclear export. Co-precipitation and quantitative PCR assays revealed their role in fundamental nuclear functions such as gene expression. In vitro nuclear transport assay using digitonin-treated cytoplasm-depleted cells clearly showed their interesting property to spontaneously migrate into the nucleus. Because these proteins possess a characteristic amphiphilic motif in their 3D structure, it was speculated that this amphiphilic motif plays an important role in the molecular passage through the hydrophobic barrier of the pore. Surface hydrophobicity measurement by using