Determinants of the nucleocytoplasmic shuttling of muscle glycogen synthase.
Muscle glycogen synthase (MGS) presents a nuclear speckled pattern in primary cultured human muscle and in 3T3-L1 cells deprived of glucose and with depleted glycogen reserves. Nuclear accumulation of the enzyme correlates inversely with cellular glycogen content. Although the glucose-induced export of MGS from the nucleus to the cytoplasm is blocked by leptomycin B, and therefore mediated by CRM1, no nuclear export signal was identified in the sequence of the protein. Deletion analysis shows that the region comprising amino acids 555-633 of human MGS, which encompasses an Arg-rich cluster involved in the allosteric activation of the enzyme by Glc6P, is crucial for its nuclear concentration and aggregation. Mutation of these Arg residues, which desensitizes the enzyme towards Glc6P, interferes with its nuclear accumulation. In contrast, the known phosphorylation sites of MGS that regulate its activity are not involved in the control of its subcellular distribution. Nuclear human MGS co-localizes with the promyelocytic leukaemia oncoprotein and p80-coilin, a marker of Cajal bodies. The subnuclear distribution of MGS is altered by incubation with transcription inhibitors. These observations suggest that, in addition to its metabolic function, MGS may participate in nuclear processes.
Cid
Emili
E
Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Spain.
Cifuentes
Daniel
D
Baqué
Susanna
S
Ferrer
Juan C
JC
Guinovart
Joan J
JJ
D016475:3T3 Cells; D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D001120:Arginine / Q000235:genetics; D022003:Cell Nucleus Structures / Q000378:metabolism; D002478:Cells, Cultured; D006003:Glycogen / Q000378:metabolism; D006006:Glycogen Synthase / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D028884:Karyopherins / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D000071156:Promyelocytic Leukemia Protein; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013347:Subcellular Fractions; D014157:Transcription Factors / Q000378:metabolism; D025521:Tumor Suppressor Proteins; D000097606:Exportin 1 Protein
D001120:Arginine; D006003:Glycogen; D006006:Glycogen Synthase; D049452:Green Fluorescent Proteins; D028884:Karyopherins; D009363:Neoplasm Proteins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D000071156:Promyelocytic Leukemia Protein; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D000097606:Exportin 1 Protein; C513293:Pml protein, mouse; C068921:p80-coilin; C070576:PML protein, human