Paeoniflorin inhibits glioblastoma growth in vivo and in vitro: A role for the Triad3A-dependent ubiquitin proteasome pathway in TLR4 degradation

Abstract

Background: Paeoniflorin, a polyphenolic compound derived from Radix Paeoniae Alba (Paeonia lactiflora), has exhibited anticancer activity in various human cancers, including glioblastoma. However, the mechanisms underlying the effects of this compound have not been fully elucidated. Toll-like receptor 4 (TLR4) plays an important role in the regulation of cancer cell proliferation and progression, and high TLR4 expression in glioblastoma specimens is associated with a poor prognosis. The present study aimed to investigate whether paeoniflorin suppresses glioblastoma via inhibition of TLR4 expression. Methods: CCK-8 experiments and clone formation assay were performed to detect the cell proliferation. Western blotting was used to analyze protein expression levels. Detection of Triad3A binding with TLR4 was assessed by the immunoprecipitation. Orthotopic xenograft mouse model was used to evaluate the effect of paeoniflorin in vivo. MST was used to analyze the interaction between paeoniflorin and TLR4 protein. Results: In our study, we found that paeoniflorin effectively inhibited glioblastoma growth and suppressed TLR4 protein levels, as well its downstream effectors both in vivo and in vitro. Moreover, when overexpressed TLR4 in glioblastoma abolished the effects of paeoniflorin on cell proliferation, migration, and invasion. Furthermore, we found that paeoniflorin decreased TLR4 protein through ubiquitination proteasome pathway (UPP)-mediated degradation in glioblastoma cells. Mechanistically, paeoniflorin promoted Triad3A to conjugate with TLR4, resulting in degradation. In addition, Triad3A-shRNA abolished paeoniflorin-enhanced UPP-mediated TLR4 degradation. Finally, we found that paeoniflorin could directly bind with TLR4 protein as assessed by MST assay. Conclusion: Our study is the first to identify a novel mechanism for the antitumor activity of paeoniflorin, specifically: it decreases tumor growth by directly targeting TLR4 and modulating the TLR4/Triad3A-dependent axis, leading to TLR4 protein degradation and inhibition of glioblastoma cell progression in vitro and in vivo. Our current findings indicate that paeoniflorin is a potential glioblastoma therapeutic agent due to its Triad3A-dependent ubiquitin degradation of TLR4.