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IRF3 and Smad3 binding regions in a basal-like breast cancer cell line, BT549 transfected with polyI:C.

ABSTRACT: The activation of RIG-I-like receptor (RLR) signaling in cancer cells is widely recognized as a critical cancer therapy method. The expected mechanism of RLR ligand-mediated cancer therapy involves the promotion of cancer cell death and strong induction of interferon (IFN)-β that affects the tumor microenvironment. We have recently shown that activation of RLR signaling in triple-negative breast cancer cells (TNBC) attenuates TGF-β signaling, which partly contributes to the promotion of cancer cell pyroptosis. However, the consequences of suppression of TGF-β signaling by RLR ligands with respect to IFN-β-mediated tumor suppression are not well characterized. This study showed that cytosolic induction of a typical RLR ligand polyI:C in cancer cells produces significant levels of IFN-β, which inhibits the growth of the surrounding cancer cells. In addition, IFN-β-induced cell cycle arrest in surrounding cancer cells was inhibited by the expression of constitutively active Smad3 (caSmad3). caSmad3 suppresses IFN-β expression through the alleviation of IRF3 binding to the canonical target genes, as suggested by ChIP-seq analysis. Based on these findings, a new facet of the pro-tumorigenic function of TGF-β that suppresses IFN-β expression is suggested when exploiting RLR-mediated cancer treatment in TNBC.

ORGANISM(S): Homo sapiens

PROVIDER: GSE178830 | GEO | 2021/12/16

REPOSITORIES: GEO

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Project description:Background: Patients with Triple Negative Breast Cancer (TNBC) currently lack targeted therapies, and consequently face higher mortality rates when compared to patients with other breast cancer subtypes. The tumor microenvironment (TME) cytokine Oncostatin M (OSM) reprograms TNBC cells to a more stem-like/mesenchymal state, conferring aggressive cancer cell properties such as enhanced migration and invasion, increased tumor-initiating capacity, and intrinsic resistance to the current standards of care. In contrast to OSM, Interferon-β (IFN-β) promotes a more differentiated, epithelial cell phenotype in addition to its role as an activator of anti-tumor immunity. Importantly, OSM suppresses the production of IFN-β, although the mechanism of IFN-β suppression has not yet been elucidated. Methods: IFN-β production and downstream autocrine signaling were assessed via quantitative real-time PCR (qRT-PCR) and Western blotting in TNBC cells following exposure to OSM. RNA-sequencing (RNA-seq) was used to assess an IFN-β metagene signature, and to assess the expression of innate immune sensors, which are upstream activators of IFN-β. Cell migration was assessed using an in vitro chemotaxis assay. Additionally, TNBC cells were exposed to TGF-β1, Snail, and Zeb1, and IFN-β production and downstream autocrine signaling were assessed via RNA-seq, qRT-PCR, and Western blotting. Results: Here, we identify the repression of Toll-like Receptor 3 (TLR3), an innate immune sensor, as the key molecular event linking OSM signaling and the repression of IFN-β transcription, production, and autocrine IFN signaling. Moreover, we demonstrate that additional epithelial-mesenchymal transition (EMT)-inducing factors, such as TGF-β1, Snail, and Zeb1, similarly suppress TLR3-mediated IFN-β production and signaling. Conclusions: Our findings provide a novel insight into the regulation of TLR3 and IFN-β production in TNBC cells, which are known indicators of treatment responses to DNA-damaging therapies. Furthermore, strategies to stimulate TLR3 in order to increase IFN-β within the TME may be ineffective in stem-like/mesenchymal cells, as TLR3 is strongly repressed. Rather, we propose that therapies targeting OSM or OSM receptor (OSMR) would reverse the stem-like/mesenchymal program and restore TLR3-mediated IFN-β production within the TME, facilitating improved responses to current therapies.

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IRF3 and Smad3 binding regions in a basal-like breast cancer cell line, BT549 transfected with polyI:C.

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