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Rac1 mediates STAT3 activation by autocrine IL-6

T R Faruqi1, D Gomez, X R Bustelo

  • 1Department of Pathology, State University of New York, Stony Brook, NY 11794, USA.

Proceedings of the National Academy of Sciences of the United States of America
|July 27, 2001
PubMed

Insights

The small GTPase Rac1 activates signal transducer and activator of transcription 3 (STAT3) signaling. Rac1 induces STAT3 activation indirectly via an autocrine interleukin-6 (IL-6) loop, linking oncogenic GTPase activity to JAK/STAT signaling.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Oncology

Background:

  • The small GTPase Rac1 is crucial for cellular processes like cytoskeletal rearrangement, gene transcription, and malignant transformation.
  • Signal transducers and activators of transcription (STATs), particularly STAT3, are key mediators in cellular signaling pathways.
  • Dysregulation of Rac1 and STAT3 signaling is implicated in various cancers.

Purpose of the Study:

  • To investigate the mechanism by which constitutively active Rac1 (Rac V12) influences STAT3 activation.
  • To elucidate the role of autocrine signaling and specific molecular players in Rac1-mediated STAT3 activation.
  • To establish a link between oncogenic GTPase activity and the Janus kinase/STAT signaling pathway.

Main Methods:

  • Utilized constitutively active Rac1 (Rac V12) and Vav (Delta1-187) expression systems.
  • Assessed STAT3 activation through translocation, gene expression, and tyrosine phosphorylation at residue 705.
  • Employed neutralizing antibodies against IL-6 receptor, and expression of IkappaBalpha S32AS36A and suppressor of cytokine signaling 3 to inhibit signaling pathways.

Main Results:

  • Constitutively active Rac1 (Rac V12) stimulates STAT3 activation, leading to nuclear translocation and STAT3-dependent gene expression.
  • Rac1-induced STAT3 activation is mediated indirectly through the autocrine production and action of IL-6.
  • Rac V12 expression upregulates IL-6 and IL-6 receptor genes; inhibition of IL-6 signaling or nuclear factor-kappaB blocks Rac1-induced STAT3 activation.

Conclusions:

  • Rac1 activates STAT3 through an autocrine IL-6 signaling loop, involving IL-6 and IL-6 receptor gene induction.
  • The mechanism requires tyrosine phosphorylation of STAT3 at residue 705 and is dependent on nuclear factor-kappaB activation.
  • This study establishes a novel link between oncogenic GTPase activity (Rac1) and the JAK/STAT signaling pathway via IL-6.

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