The transcription factor NF‐κB orchestrates many pro‐inflammatory signals and its inhibition is considered a promising strategy to combat inflammation. Here we report the characterization of the natural product plumericin as a highly potent inhibitor of the NF‐κB pathway with a novel chemical scaffold, which was isolated via a bioactivity‐guided approach, from extracts of Himatanthus sucuuba, an Amazonian plant traditionally used to treat inflammation‐related disorders.

Rationale: Innate and adaptive immune responses alter numerous homeostatic processes that are controlled by nuclear hormone receptors. NR4A1 is a nuclear receptor that is induced in vascular pathologies, where it mediates protection. Objective: The underlying mechanisms that regulate the activity of NR4A1 during vascular injury are not clear. We therefore searched for modulators of NR4A1 function that are present during vascular inflammation. Methods and Results: We report that the protein encoded by interferon stimulated gene 12 (ISG12), is a novel interaction partner of NR4A1 that inhibits the transcriptional activities of NR4A1 by mediating its Crm1-dependent nuclear export. Using 2 models of vascular injury, we show that ISG12-deficient mice are protected from neointima formation. This effect is dependent on the presence of NR4A1, as mice deficient for both ISG12 and NR4A1 exhibit neointima formation similar to wild-type mice. Conclusions: These findings identify a previously unrecognized feedback loop activated by interferons that inhibits the vasculoprotective functions of NR4A nuclear receptors, providing a potential new therapeutic target for interferon-driven pathologies.

Objective—Our goal was to examine the influence of indirubin-3′-monoxime (I3MO), a natural product–derived cyclin-dependent kinase inhibitor, on vascular smooth muscle cell (VSMC) proliferation in vitro, experimentally induced neointima formation in vivo, and related cell signaling pathways. Methods and Results—I3MO dose-dependently inhibited platelet-derived growth factor (PDGF)–BB-induced VSMC proliferation by arresting cells in the G0/G1 phase of the cell cycle as assessed by 5-bromo-2′-deoxyuridine incorporation and flow cytometry. PDGF-induced activation of the kinases Akt, Erk1/2, and p38MAPK was not affected. In contrast, I3MO specifically blocked PDGF-, interferon-&ggr;-, and thrombin-induced phosphorylation of signal transducer and activator of transcription 3 (STAT3). Human endothelial cells (EA.hy926) responded to I3MO with increased endothelial nitric oxide synthase activity as assessed via [14C]l-arginine/[14C]l-citrulline conversion. The specific STAT3 inhibitor Stattic led to decreased VSMC proliferation, and transient expression of a constitutively active form of STAT3 overcame the I3MO-induced cell cycle arrest in mouse embryonic fibroblasts. In a murine femoral artery cuff model, I3MO prevented neointima formation while reducing STAT3 phosphorylation and the amount of proliferating Ki67-positive cells. Conclusion—I3MO represses PDGF- and thrombin-induced VSMC proliferation and, in vivo, neointima formation, likely because it specifically blocks STAT3 signaling. This profile and its positive effect on endothelial NO production turns I3MO into a promising lead compound to prevent restenosis.