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Regulation of STAT1 nuclear export by Jak1

K Mowen1, M David

  • 1Department of Biology, University of California at San Diego, La Jolla, California 92093, USA.

Molecular and Cellular Biology
|September 13, 2000
PubMed

Insights

Signal transducer and activator of transcription 1 (STAT1) requires Jak1 for nuclear localization after tyrosine phosphorylation. This nuclear export signal (NES) regulation is crucial for STAT1 function in gene expression.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Gene Regulation

Background:

  • Signal transducer and activator of transcription 1 (STAT1) is a key mediator of gene expression, activated by cytokines and growth factors.
  • STAT1 activation involves tyrosine phosphorylation, primarily mediated by Janus tyrosine kinases (Jak).

Purpose of the Study:

  • To investigate the role of Jak1 in STAT1 nuclear localization and function.
  • To identify the molecular mechanisms regulating STAT1 nuclear import and export.

Main Methods:

  • Analysis of STAT1 localization in Jak1-deficient and Tyk2-deficient cells.
  • Treatment with leptomycin B, a nuclear export inhibitor.
  • Site-directed mutagenesis to identify a nuclear export signal (NES) within STAT1.
  • Assessment of CBP binding to STAT1.

Main Results:

  • STAT1 phosphorylation on Y701 is insufficient for nuclear localization in the absence of Jak1 or its kinase activity.
  • STAT1 nuclear accumulation is preserved in Tyk2-deficient cells.
  • Leptomycin B restores nuclear presence of tyrosine-phosphorylated STAT1 in Jak1-deficient cells.
  • A leucine-rich nuclear export signal (NES) between amino acids 197-205 was identified in STAT1.
  • Mutation of the NES (L-->A) restores nuclear retention of STAT1 in Jak1-deficient cells.
  • Impaired binding of CBP to tyrosine-phosphorylated STAT1 from Jak1-deficient cells suggests a regulatory model.

Conclusions:

  • Jak1 is essential for the nuclear localization of tyrosine-phosphorylated STAT1, independent of Tyk2.
  • A novel NES within STAT1 regulates its nuclear export, influenced by Jak1 activity and CBP binding.
  • This finding provides insights into the intermolecular regulation of STAT1 nuclear transport and its role in signal transduction.

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