Importin alpha transports CaMKIV to the nucleus without utilizing importin beta.
Ca(2+)/calmodulin-dependent protein kinase type IV (CaMKIV) plays an essential role in the transcriptional activation of cAMP response element-binding protein-mediated signaling pathways. Although CaMKIV is localized predominantly in the nucleus, the molecular mechanism of the nuclear import of CaMKIV has not been elucidated. We report here that importin alpha is able to carry CaMKIV into the nucleus without the need for importin beta or any other soluble proteins in digitonin-permeabilized cells. An importin beta binding-deficient mutant (DeltaIBB) of importin alpha also carried CaMKIV into the nucleus, which strongly suggests that CaMKIV is transported in an importin beta-independent manner. While CaMKIV directly interacted with the C-terminal region of importin alpha, the CaMKIV/importin alpha complex did not form a ternary complex with importin beta, which explains the nonrequirement of importin beta for the nuclear transport of CaMKIV. The cytoplasmic microinjection of importin alpha-DeltaIBB enhanced the rate of nuclear translocation of CaMKIV in vivo. This is the first report to demonstrate definitely that mammalian importin alpha solely carries a cargo protein into the nucleus without utilizing the classical importin beta-dependent transport system.
Kotera
Ippei
I
Department of Cell Biology and Neuroscience, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan.
Sekimoto
Toshihiro
T
Miyamoto
Yoichi
Y
Saiwaki
Takuya
T
Nagoshi
Emi
E
Sakagami
Hiroyuki
H
Kondo
Hisatake
H
Yoneda
Yoshihiro
Y
D021581:Active Transport, Cell Nucleus; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D004734:Energy Metabolism; D007700:Kinetics; D051379:Mice; D008845:Microinjections; D046912:Multiprotein Complexes; D041681:NIH 3T3 Cells; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D028901:alpha Karyopherins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D028961:beta Karyopherins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D046912:Multiprotein Complexes; D011994:Recombinant Proteins; D028901:alpha Karyopherins; D028961:beta Karyopherins; D000255:Adenosine Triphosphate; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C517685:Camk4 protein, mouse
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