title: Rac1 mediates STAT3 activation by autocrine IL-6.
abstract: The activity of the small GTPase, Rac1, plays a role in various cellular processes including cytoskeletal rearrangement, gene transcription, and malignant transformation. In this report constitutively active Rac1 (Rac V12) is shown to stimulate the activation of STAT3, a member of the family of signal transducers and activators of transcription (STATs). The activity of Rac1 leads to STAT3 translocation to the nucleus coincident with STAT3-dependent gene expression. The expression of Vav (Delta1-187), a constitutively active guanine nucleotide exchange factor for the Rho GTPases, or activated forms of Ras or Rho family members, leads to STAT3-specific activation. The activation of STAT3 requires tyrosine phosphorylation at residue 705, but is not dependent on phosphorylation of Ser-727. Our studies indicate that Rac1 induces STAT3 activation through an indirect mechanism that involves the autocrine production and action of IL-6, a known mediator of STAT3 response. Rac V12 expression results in the induction of the IL-6 and IL-6 receptor genes and neutralizing antibodies directed against the IL-6 receptor block Rac1-induced STAT3 activation. Furthermore, inhibition of the nuclear factor-kappaB activation or disruption of IL-6-mediated signaling through the expression of IkappaBalpha S32AS36A and suppressor of cytokine signaling 3, respectively, blocks Rac1-induced STAT3 activation. These findings elucidate a mechanism dependent on the induction of an autocrine IL-6 activation loop through which Rac1 mediates STAT3 activation establishing a link between oncogenic GTPase activity and Janus kinase/STAT signaling.
authors.affiliation: Department of Pathology, State University of New York, Stony Brook, NY 11794, USA.
authors.forename: T R
authors.initials: TR
authors.lastname: Faruqi
authors.forename: D
authors.initials: D
authors.lastname: Gomez
authors.forename: X R
authors.initials: XR
authors.lastname: Bustelo
authors.forename: D
authors.initials: D
authors.lastname: Bar-Sagi
authors.forename: N C
authors.initials: NC
authors.lastname: Reich
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D015850:Interleukin-6 / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D004268:DNA-Binding Proteins; D015850:Interleukin-6; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D015534:Trans-Activators; D020558:GTP Phosphohydrolases; D020830:rac1 GTP-Binding Protein