Inhibition of TLR9 signaling stimulates apoptosis and cell cycle arrest and alleviates angiogenic property in human cervical cancer cells

Abstract

Aims: The aim of the study was to assess the effect of blocking TLR9 signaling on the proliferation of cervical cancer cells and its angiogenic property. Background: Toll-like receptors (TLRs) have been implicated for their crucial role in not only cervical cancer but also in other malignancies. TLR9 is expressed on an array of cells such as macrophages, dendritic cells, melanocytes, and keratinocytes. It is reported to modulate oncogenesis along with tumorigenesis by augmenting NF-κB mediated inflammation within the tumor environment. TLR9 has also been reported to positively regulate oncogenesis within the cervix and as a marker to evaluate malignant remodeling of cervical squamous cells. Therefore, this study was designed to explore the functional relevance of blocking the TLR9 signaling pathway in cervical cancer cells. Objective: The objective of the current study was to investigate the effect of human TLR9 antagonist, ODN INH-18, on apoptosis and cell cycle regulation and angiogenic property of human cervical cancer Caski cells. Method: MTT assay was performed to measure cell viability, and flow cytometry analysis was performed to assess cell cycle arrest. Quantitative real-time PCR (qRT-PCR) analysis was performed to measure fold change in the gene expression of various markers of apoptosis, cell cycle regulation, and angiogenesis. Result: The qRT-PCR results showed a higher expression level of TLR9 mRNA in Caski cervical cancer cells as compared to normal cervical keratinocytes. The apoptotic, angiogenic, and cell cycle regulatory factors were also deregulated in Caski cells in comparison to normal keratinocytes. The MTT assay demonstrated that treatment of TLR9 antagonist, ODN INH18, significantly reduced the proliferation of Caski cells in a dose-dependent manner. Treatment of ODN INH18 led to substantial cell cycle arrest in Caski cells at G0/G1 phase. Moreover, the qRT-PCR results demonstrated that ODN INH18 treatment led to suppressed mRNA expression of Bcl-2 and enhanced expression of Bax, signifying induction of apoptosis in Caski cells. Moreover, the expression of cyclin D1, Cdk4, and Cdc25A was found to be reduced, whereas expression of p27 was increased in ODN INH18-treated Caski cells, indicating G0/G1 phase arrest. Interestingly, expression of VEGF and VCAM-1 were found to be significantly inhibited in ODN INH18-treated Caski cells, substantiating alleviation of angiogenic property of cervical cancer cells. Conclusion: The results of our study suggest that inhibiting TLR9 signaling might be an interesting therapeutic intervention for the treatment of cervical cancer.