12/15-Lipoxygenase Contributes to Platelet-derived Growth Factor-induced Activation of Signal Transducer and Activator of Transcription 3*

Abstract

Background: The small molecule indirubin-3′-monoxime (I3MO) inhibits activation of STAT3 in vascular smooth muscle cells, with an unresolved mechanism.

Results: Activation of 12/15-lipoxygenase (LO) is crucial for PDGF-induced Src and STAT3 activation and is impaired by I3MO.

Conclusion: I3MO interferes with PDGFR-Src-STAT3 signaling via impaired 12/15-LO activation.

Significance: 12/15-LO is an important signaling hub within the PDGF-STAT3 pathway.

Abstract

We showed previously that the small molecule indirubin-3′-monoxime (I3MO) prevents vascular smooth muscle cell (VSMC) proliferation by selectively inhibiting signal transducer and activator of transcription 3 (STAT3). Looking for the underlying upstream molecular mechanism, we here reveal the important role of reactive oxygen species (ROS) for PDGF-induced STAT3 activation in VSMC. We show that neither NADPH-dependent oxidases (Noxes) nor mitochondria, but rather 12/15-lipoxygenase (12/15-LO) are pivotal ROS sources involved in the redox-regulated signal transduction from PDGFR to STAT3. Accordingly, pharmacological and genetic interference with 12/15-LO activity selectively inhibited PDGF-induced Src activation and STAT3 phosphorylation. I3MO is able to blunt PDGF-induced ROS and 15( S)-hydroxyeicosatetraenoic acid (15( S)-HETE) production, indicating an inhibitory action of I3MO on 12/15-LO and consequently on STAT3. We identify 12/15-LO as a hitherto unrecognized signaling hub in PDGF-triggered STAT3 activation and show for the first time a negative impact of I3MO on 12/15-LO.