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c-Src activates the DNA binding and transcriptional activity of Stat3 molecules: serine 727 is not required for

L K Schaefer1, S Wang, T S Schaefer

  • 1Department of Neurosurgery, Department of Molecular Genetics, University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030, USA.

Biochemical and Biophysical Research Communications
|December 22, 1999
PubMed

Insights

Signal transducer and activator of transcription 3 (Stat3) is activated by c-Src, influencing cell growth. Serine 727 phosphorylation is not essential for Stat3

Area of Science:

  • Cellular Biology
  • Molecular Oncology
  • Signal Transduction

Background:

  • Constitutive activation of Signal transducer and activator of transcription 3 (Stat3) proteins is observed in cells transformed by v-Src.
  • Stat3 directly interacts with v-Src and is crucial for v-Src-mediated NIH fibroblast transformation, indicating a role in aberrant cell growth.
  • Stat3 phosphorylation at tyrosine 705 is essential for dimer formation, while serine 727 phosphorylation is thought to enhance transcriptional activity.

Purpose of the Study:

  • To investigate the effect of c-Src on the DNA binding activity and transcriptional activity of Stat3alpha, Stat3beta, and specific Stat3 mutants.
  • To determine the role of serine 727 phosphorylation in Stat3's transcriptional activity when activated by c-Src.

Main Methods:

  • Co-transfection of COS-7 cells with c-Src and various Stat3 constructs (Stat3alpha, Stat3beta, Stat3alphaS727A, Delta48, Delta55).
  • Assessment of Stat3 DNA binding activity.
  • Measurement of tyrosine 705 phosphorylation levels.
  • Quantification of transcription from an alpha-2 macroglobulin reporter gene.

Main Results:

  • c-Src activates the DNA binding activity of Stat3alpha, Stat3beta, and Stat3 mutants (Stat3alphaS727A, Delta48, Delta55).
  • Co-transfection with c-Src leads to increased tyrosine 705-phosphorylated Stat3.
  • Stat3alphaS727A exhibits transcriptional activity comparable to wild-type Stat3alpha and Stat3beta in the presence of c-Src.

Conclusions:

  • Serine 727 phosphorylation is not required for Stat3's transcriptional activity when activated by c-Src in COS-7 cells.
  • These findings suggest that alternative pathways or mechanisms contribute to Stat3 transcriptional regulation independent of serine 727 phosphorylation in this context.
  • The study highlights the complex regulation of Stat3 activity by Src family kinases and identifies potential targets for therapeutic intervention in cancers with aberrant Stat3 signaling.

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