Premium
Importin α transports CaMKIV to the nucleus without utilizing importin β
Author(s) -
Kotera Ippei,
Sekimoto Toshihiro,
Miyamoto Yoichi,
Saiwaki Takuya,
Nagoshi Emi,
Sakagami Hiroyuki,
Kondo Hisatake,
Yoneda Yoshihiro
Publication year - 2005
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1038/sj.emboj.7600587
Subject(s) - importin , nuclear transport , microbiology and biotechnology , nuclear localization sequence , biology , cytoplasm , cell nucleus
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 α is able to carry CaMKIV into the nucleus without the need for importin β or any other soluble proteins in digitonin‐permeabilized cells. An importin β binding‐deficient mutant (ΔIBB) of importin α also carried CaMKIV into the nucleus, which strongly suggests that CaMKIV is transported in an importin β‐independent manner. While CaMKIV directly interacted with the C‐terminal region of importin α, the CaMKIV/importin α complex did not form a ternary complex with importin β, which explains the nonrequirement of importin β for the nuclear transport of CaMKIV. The cytoplasmic microinjection of importin α‐ΔIBB enhanced the rate of nuclear translocation of CaMKIV in vivo . This is the first report to demonstrate definitely that mammalian importin α solely carries a cargo protein into the nucleus without utilizing the classical importin β‐dependent transport system.