Non-canonical Notch signaling activates IL-6/JAK/STAT signaling in breast tumor cells and is controlled by p53 and IKKα/IKKβ

Abstract

Notch signaling is frequently hyperactivated in breast cancer, but how the enhanced signaling contributes to the tumor process is less well understood. In this report, we identify the proinflammatory cytokine interleukin-6 (IL-6) as a novel Notch target in breast tumor cells. Enhanced Notch signaling upregulated IL-6 expression, leading to activation of autocrine and paracrine Janus kinase/signal transducers and activators of transcription signaling. IL-6 upregulation was mediated by non-canonical Notch signaling, as it could be effectuated by a cytoplasmically localized Notch intracellular domain and was independent of the DNA-binding protein CSL. Instead, Notch-mediated IL-6 upregulation was controlled by two proteins in the nuclear factor (NF)-κB signaling cascade, IKKα and IKKβ (inhibitor of nuclear factor kappa-B kinase subunit alpha and beta, respectively), as well as by p53. Activation of IL-6 by Notch required IKKα/IKKβ function, but interestingly, did not engage canonical NF-κB signaling, in contrast to IL-6 activation by inflammatory agents such as lipopolysaccharide. With regard to p53 status, IL-6 expression was upregulated by Notch when p53 was mutated or lost, and restoring wild-type p53 into p53-mutated or -deficient cells abrogated the IL-6 upregulation. Furthermore, Notch-induced transcriptomes from p53 wild-type and -mutated breast tumor cell lines differed extensively, and for a subset of genes upregulated by Notch in a p53-mutant cell line, this upregulation was reduced by wild-type p53. In conclusion, we identify IL-6 as a novel non-canonical Notch target gene, and reveal roles for p53 and IKKα/IKKβ in non-canonical Notch signaling in breast cancer and in the generation of cell context-dependent diversity in the Notch signaling output.

Interleukin 6 mediates selected effects of Notch in chondrocytes

“…However, concentration of Il6 in the supernatant of control cells was minimal and the neutralizing Il6 antibody had no impact on chondrocyte gene markers expression in the absence of Notch, suggesting that basal levels of Il6 are dispensable for chondrocyte function. Induction of Il6 by Notch is in agreement with previous studies carried out in bone marrow stromal cells, macrophages and breast cancer cells, and confirms that Il6 is a direct target gene of Notch signaling 26,48,49 .…”

HIF1α-induced PDGFRβ signaling promotes developmental HSC production via IL-6 activation

“…In contrast in glioma-initiating cells, a PDGF-driven signaling axis involving NO-dependent inhibitor of differentiation 4 (ID4) has been shown to promote JAGGED1–NOTCH activity [59]. Related, both direct and non-canonical regulation of IL-6 expression by Notch has been previously reported [60, 61]. As it is well established that generation of HSCs requires multiple Notch signaling inputs [62], it will be interesting to investigate whether Notch signaling may be a part of the Hif1α-PDGFRβ signaling axis in regard to the ability of IL-6 to enhance production of HSPCs.…”

Constitutive activation of STAT3 in breast cancer cells: A review

“…IL‐6 regulates cancer stem cell (CSC) self‐renewal and promotes breast CSC survival and proliferation when activated by the Notch, Wnt, Hedgehog and TGF‐β signaling pathways . A clinical study showed that IL‐6 is a novel Notch target gene in breast tumor cells and that hyper‐activated Notch signaling upregulates IL‐6 via the JAK/STAT3 pathway when p53 is mutated . High nuclear Notch1 ICD (intracellular domain of the Notch receptor) immunoreactivity, enhanced IL‐6 mRNA and pSTAT3 levels were observed in a panel of BC tissue samples from ER‐α and PR negative patients .…”