Interferon-gamma-dependent nuclear import of Stat1 is mediated by the GTPase activity of Ran/TC4.
In response to interferon-gamma (IFN-gamma), Stat1 enters the nucleus, where it activates transcription. In order to better understand the mechanism of the extracellular signal-induced protein import into the nucleus, we have established an in vivo assay system that uses recombinant Stat1 protein as a model transport substrate. Using this system, we found that Stat1 is actively transported through the nuclear pores in an IFN-gamma-dependent manner and tyrosine (Tyr701) phosphorylation of Stat1 is actually required for its nuclear import. When the antibody against Ran, which was identified as an essential factor for active nuclear protein transport, was injected, the IFN-gamma-dependent nuclear transport of Stat1 was completely inhibited. Furthermore, nuclear import of Stat1 was suppressed by microinjection of two mutant Ran proteins, one defective in GTP hydrolysis (G19V) and the other with little or no binding to GTP (T24N), both of which are known to act as dominant negative inhibitors of nuclear import. These results indicate that the conditional nuclear import of Stat1 requires GTP hydrolysis by Ran.
Sekimoto
T
T
Department of Anatomy and Cell Biology, Biomedical Research Center, Osaka University Medical School, 2-2 Yamada-oka, Suita, Osaka 565, Japan.
Nakajima
K
K
Tachibana
T
T
Hirano
T
T
Yoneda
Y
Y
D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism*; D008845:Microinjections; D009687:Nuclear Proteins / Q000008:administration & dosage / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D050794:STAT1 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D020931:ran GTP-Binding Protein
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D015534:Trans-Activators; D007371:Interferon-gamma; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020931:ran GTP-Binding Protein