Abstract
BackgroundThe Wnt/β-catenin signaling pathway is a prolific regulator of cell-to-cell communication and gene expression. Canonical Wnt/β-catenin signaling involves partnering of β-catenin with members of the TCF/LEF family of transcription factors (TCF1, TCF3, TCF4, LEF1) to regulate gene expression. IL-6 is a key cytokine involved in inflammation and is particularly a hallmark of inflammation in the brain. Astrocytes, specialized glial cells in the brain, secrete IL-6. How astrocytes regulate IL-6 expression is not entirely clear, although in other cells NFκB and C/EBP pathways play a role. We evaluated here the interface between β-catenin, TCFs/LEF and C/EBP and NF-κB in relation to IL-6 gene regulation in astrocytes.MethodsWe performed molecular loss and/or gain of function studies of β-catenin, TCF/LEF, NFκB, and C/EBP to assess IL-6 regulation in human astrocytes. Specifically, siRNA mediated target gene knockdown, cDNA over expression of target gene, and pharmacological agents for regulation of target proteins were used. IL-6 levels was evaluated by real time quantitative PCR and ELISA. We also cloned the IL-6 promoter under a firefly luciferase reporter and used bioinformatics, site directed mutagenesis, and chromatin immunoprecipitation to probe the interaction between β-catenin/TCFs/LEFs and IL-6 promoter activity.Resultsβ-catenin binds to TCF/LEF to inhibits IL-6 while TCFs/LEF induce IL-6 transcription through interaction with ATF-2/SMADs. β-catenin independent of TCFs/LEF positively regulates C/EBP and NF-κB, which in turn activate IL-6 expression. The IL-6 promoter has two putative regions for TCFs/LEF binding, a proximal site located at -91 nt and a distal site at -948 nt from the transcription start site, both required for TCF/LEF induction of IL-6 independent of β-catenin.ConclusionIL-6 regulation in human astrocytes engages a discordant interaction between β-catenin and TCF/LEF. These findings are intriguing given that no role for β-catenin nor TCFs/LEF to date is associated with IL-6 regulation and suggest that β-catenin expression in astrocytes is a critical regulator of anti-inflammatory responses and its disruption can potentially mediate persistent neuroinflammation.BnRUXdo6AhwiqE9HvUtiT7Video Graphical abstract
Highlights
The Wnt/β-catenin signaling pathway is a prolific regulator of cell-to-cell communication and gene expression
Results β-Catenin negatively regulates Interleukin 6 (IL-6) transcription in human astrocytes A previous study from our lab demonstrated that inhibition of β-catenin in human astrocytes leads to astrocyte senescence [41]
Given that IL-6 expression constitutes a Senescence Associated Secretory Phenotype (SASP) [75, 76], we assessed whether β-catenin regulates IL-6 gene expression
Summary
The Wnt/β-catenin signaling pathway is a prolific regulator of cell-to-cell communication and gene expression. Canonical Wnt/β-catenin signaling involves partnering of β-catenin with members of the TCF/LEF family of transcription factors (TCF1, TCF3, TCF4, LEF1) to regulate gene expression. How astrocytes regulate IL-6 expression is not entirely clear, in other cells NFκB and C/ EBP pathways play a role. Most resident CNS cells secrete IL-6, including astrocytes, neurons, microglia, and endothelial cells [20, 21]. Secreted IL-6 causes either inflammation or non-inflammatory effects based on whether IL-6 binds to the membrane bound IL-6 receptor (IL-6Rα) to activate the SHP2-MAPK or JAK-STAT signaling pathways or to the soluble form of the receptor for trans-signaling (enabling cells without IL-6Rα to respond to IL-6) [20, 21, 23]. C/EBP and NF-κB family members can heterodimerize and in some cases mediate inflammation [34, 38]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
