Inhibition of nuclear import and cell-cycle progression by mutated forms of the dynamin-like GTPase MxB.
Mx proteins form a subfamily of the dynamin-like GTPases, which have well established roles in cellular trafficking. Some Mx proteins (e.g., human MxA) have antiviral activity and are tightly regulated by type I IFNs. Others (e.g., human MxB) lack antiviral activity and are thought to have normal cellular functions that remain undefined. Consistent with this hypothesis, we report that MxB is expressed without IFN treatment. MxB seems to be exclusively extranuclear and is concentrated at the cytoplasmic face of nuclear pores, suggesting a role in their regulation. We find that expression of dominant negative (GTPase-defective) MxB mutants efficiently blocks nuclear import and causes a delay in G(1)/S cell-cycle progression. MxB depletion using RNA interference (RNAi) leads to a similar cell-cycle defect but does not block nuclear import. MxB therefore seems not to be required for nuclear import per se but may instead regulate its efficiency and/or kinetics. These studies indicate an unexpected role for a dynamin-like protein in nucleocytoplasmic trafficking and suggest that a related function might be usurped by its antiviral relatives.
King
Megan C
MC
Department of Biochemistry and Biophysics and the Graduate Group in Biochemistry and Molecular Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. kingm@mail.med.upenn.edu
Raposo
Graça
G
Lemmon
Mark A
MA
D021581:Active Transport, Cell Nucleus / Q000235:genetics / Q000502:physiology; D019943:Amino Acid Substitution; D002453:Cell Cycle / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D015870:Gene Expression; D006160:Guanosine Triphosphate / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D016898:Interferon-alpha / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D064547:Myxovirus Resistance Proteins; D022022:Nuclear Pore / Q000378:metabolism; D028861:Nuclear Pore Complex Proteins / Q000378:metabolism; D034622:RNA Interference / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000502:physiology; D014162:Transfection
D016898:Interferon-alpha; C579071:MX1 protein, human; C579068:MX2 protein, human; D064547:Myxovirus Resistance Proteins; D028861:Nuclear Pore Complex Proteins; D011993:Recombinant Fusion Proteins; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins