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Novel roles of unphosphorylated STAT3 in oncogenesis and transcriptional regulation

Jinbo Yang1, Moitreyee Chatterjee-Kishore, Susan M Staugaitis

  • 1Department of Molecular Biology, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio, USA.

Cancer Research
|February 12, 2005
PubMed

Insights

Unphosphorylated Signal transducer and activator of transcription 3 (STAT3) drives gene expression through a novel mechanism, impacting cancer and cytokine responses. This finding reveals a new role for STAT3 beyond its dimer function.

Area of Science:

  • Molecular Biology
  • Cellular Signaling
  • Cancer Biology

Background:

  • Signal transducer and activator of transcription 3 (STAT3) is activated by phosphorylation at tyrosine 705, forming dimers that regulate gene expression.
  • STAT3 activation, often induced by cytokines like interleukin-6, leads to increased STAT3 protein levels due to a STAT3 binding site in the STAT3 promoter.
  • The role of unphosphorylated STAT3 in gene regulation is less understood, though unphosphorylated STAT1 is known to influence gene expression.

Purpose of the Study:

  • To investigate the potential role of unphosphorylated STAT3 in gene expression.
  • To explore whether non-phosphorylatable STAT3 can drive gene expression independently of its activated dimer form.
  • To understand the contribution of unphosphorylated STAT3 in cellular responses to cytokines and in cancer.

Main Methods:

  • Overexpression of either non-phosphorylatable Y705F STAT3 or wild-type STAT3 in human mammary epithelial cells and STAT3-null mouse cells.
  • Analysis of mRNA levels to identify genes affected by high STAT3 expression.
  • Comparison of gene expression changes induced by overexpressed STAT3 versus activated STAT3 dimers.

Main Results:

  • High levels of both wild-type and Y705F STAT3 significantly altered the expression of numerous mRNAs.
  • Expression of certain genes, including oncoproteins like MRAS and MET, was increased by overexpressed STAT3 but not by activated STAT3 dimers.
  • Unphosphorylated STAT3 was found to drive a significant late phase of gene expression in response to interleukin-6.

Conclusions:

  • Unphosphorylated STAT3 activates gene expression via a novel mechanism distinct from STAT3 dimers.
  • This unphosphorylated STAT3 pathway is likely crucial for oncogene expression in tumors with constitutive STAT3 activation.
  • Unphosphorylated STAT3 plays a significant role in both cancer development and cellular responses to cytokines.

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