Anti-inflammatory effects of nobiletin on TLR4/TRIF/IRF3 and TLR9/IRF7 signaling pathways in prostate cancer cells

Abstract

Background: Toll-like receptors (TLRs) are often expressed in natural immune cells as well as in tumor cells. TLR4 exhibits both tumor promoting and tumor-suppressing roles and higher TLR9 expression is an important marker of poor prognosis in prostate cancer (PCa). Nobiletin (NOB) is an O-methylated flavonoid and NOB has been proven to have anti-cancer effect in PCa cells. However, there is no study in the literature investigating the potential anti-inflammatory effects of NOB on the TLR signaling pathways in cancer. Therefore, we aimed to explore the potential anti-inflammatory effects of NOB on the TLR4/TRIF/IRF3 and TLR9/IRF7 signaling pathways in different types of PCa cell lines, for the first time.

Material and methods: In the current study, the cytotoxic effect of NOB PC-3 (hormone-independent and metastatic) and LNCaP cells (hormone-dependent) was evaluated by WST-1 assay. Furthermore, the inhibitory effects of NOB on TLR4/TRIF/IRF3 and TLR9/IRF7signaling pathway were determined by RT-PCR, western blotting and ELISA analysis.

Results: NOB demonstrated an inhibitory effect on PCa cell growth and LNCaP cells were more sensitive to NOB than PC-3 cells due to androjen receptor status. Furthermore, NOB alone could suppress TLR4/TRIF/IRF3 and TLR9/IRF7 signaling pathways through the downregulation of their associated pathways (mRNA and related protein levels) and the release of IFN-α and IFN-β compared to LPS or CpG-ODN stimulated PCa cells.

Conclusions: NOB potentially inhibited TLR4 and TL9-dependent signaling pathway in PCa cells. However, the efficacy of NOB was different in PCa cells due to the hormone status and aggressive features.

Keywords:

• Prostate cancer
• toll-like receptors
• flavonoid
• nobiletin
• inflammation

Acknowledgments

The authors thank Prof Dr. Murat Kasap and Assoc Prof Dr. Gurler Akpinar from the Department of Medical Biology, Kocaeli University and Assoc Prof Dr. Ozlem Aksoy from the Department of Biology, Kocaeli University for supporting our experiments.

Author contributions

A.D.O and S.K. originated and designed the research. H.I.O. and G.G.E advised on experimental design. A.D.O. and M.S. conducted experiments. A.D.O., A.K.Y., G.G.E. and M.A. analyzed and interpreted the data. All authors read carefully and approved the final version of the manuscript to be published.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Scientific and Technological Research Council of Turkey, [TUBITAK] under Grant [number 1002-116S102].