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Increased serine phosphorylation and activation of STAT1 by oncogenic Ras transfection

Ji-Hyun Song1, Eui-Young So, Choong-Eun Lee

  • 1Department of Biological Science and Institute for Basic Sciences, SungKyunKwan University, Suwon, Korea.

Molecules and Cells
|May 23, 2002
PubMed

Insights

Oncogenic Ras enhances interferon-gamma-induced STAT1 activation in fibroblasts. This involves increased serine phosphorylation of STAT1, mediated by the Ras/MAPK pathway, leading to improved DNA binding and nuclear translocation.

Area of Science:

  • Cellular signaling pathways
  • Oncogene-induced cellular transformation
  • Signal transducer and activator of transcription (STAT) family proteins

Background:

  • Interferon-gamma (IFN-γ) signaling activates Signal transducer and activator of transcription 1 (STAT1) primarily through tyrosine phosphorylation by Janus kinases (Jak1/Jak2).
  • Full STAT1 activation is believed to involve additional serine phosphorylation by unknown kinases.
  • Deregulation of STAT proteins is implicated in oncogene-driven cancers.

Purpose of the Study:

  • To investigate the effect of oncogenic Ras transformation on IFN-γ-induced STAT1 activation.
  • To elucidate the molecular mechanisms underlying enhanced STAT1 activation in Ras-transformed cells.

Main Methods:

  • Comparative analysis of STAT1 activation markers (DNA binding, nuclear translocation, tyrosine phosphorylation) in parental and Ras-transformed fibroblasts upon IFN-γ stimulation.
  • Transient transfection assays to assess the role of Ras and MAPK signaling.
  • Evaluation of STAT1 serine phosphorylation status and its correlation with MAPK and Akt activity.

Main Results:

  • Ras-transformed fibroblasts exhibited significantly enhanced IFN-γ-induced STAT1 activation compared to parental cells, evidenced by increased DNA binding, nuclear translocation, and tyrosine phosphorylation.
  • Ras transfection led to increased Erk MAPK activity and enhanced serine phosphorylation of STAT1.
  • Enhanced STAT1 serine phosphorylation was specifically linked to MAPK activation, not Akt activity.

Conclusions:

  • The Ras/MAPK signaling pathway positively regulates STAT1 activity in oncogenic Ras-transformed cells.
  • Ras-mediated MAPK activation promotes STAT1 serine phosphorylation, contributing to its enhanced tyrosine phosphorylation, nuclear translocation, and DNA-binding upon IFN-γ stimulation.
  • This crosstalk between Ras/MAPK and STAT1 pathways may play a role in oncogenesis.

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