Importin 7 and importin alpha/importin beta are nuclear import receptors for the glucocorticoid receptor.
The vertebrate glucocorticoid receptor (GR) is cytoplasmic without hormone and localizes to the nucleus after hormone binding. GR has two nuclear localization signals (NLS): NL1 is similar in sequence to the SV40 NLS; NL2 is poorly defined, residing in the ligand-binding domain. We found that GR displayed similar hormone-regulated compartmentalization in Saccharomyces cerevisiae and required the Sxm1 nuclear import receptor for NL2-mediated import. Two metazoan homologues of Sxm1, importin 7 and importin 8, bound both NL1 and NL2, whereas importin alpha selectively bound NL1. In an in vitro nuclear import assay, both importin 7 and the importin alpha-importin beta heterodimer could import a GR NL1 fragment. Under these conditions, full-length GR localized to nuclei in the presence but not absence of an unidentified component in cell extracts. Interestingly, importin 7, importin 8, and importin alpha bound GR even in the absence of hormone; thus, hormonal control of localization is exerted at a step downstream of import receptor binding.
Department of Cellular and Molecular Pharmacology, University of California-San Francisco, San Francisco, CA 94143-2280, USA.
Neal D
ND
Freedman
Keith R
KR
Yamamoto
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000502:physiology / Q000648:ultrastructure; D003907:Dexamethasone / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000032:analysis; D006801:Humans; D028884:Karyopherins; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D028901:alpha Karyopherins / Q000378:metabolism*; D028961:beta Karyopherins / Q000378:metabolism*
D028884:Karyopherins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D011965:Receptors, Glucocorticoid; C110035:SXM1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D028901:alpha Karyopherins; D028961:beta Karyopherins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D003907:Dexamethasone