Toll‐like receptor‐9 agonists increase cyclin D 1 expression partly through activation of activator protein‐1 in human oral squamous cell carcinoma cells

Increasing evidence suggests that malignant transformation can result from chronic infection, and T oll‐like receptors ( TLR s) may play an important role in this process. We have previously reported that the increased expression of TLR ‐9 is associated with tumor cell proliferation in oral cancer. However, the mechanisms involved have not been elucidated. The aim of this study was to investigate whether C p G ‐oligodeoxynucleotides ( C p G ‐ ODN ), a special TLR ‐9 agonist, is able to exert the proliferation‐promoting effect in human oral squamous cell carcinoma ( OSCC ), and to explore the possible underlying molecular mechanism. Flow cytometry, MTT , and colony formation assay were used to evaluate cell proliferation and cell cycle distribution. The m RNA and protein levels were analyzed by quantitative RT ‐ PCR and W estern blot assay. Luciferase reporter gene, EMSA , and C h IP assays were used to detect the activity of activator protein‐1 ( AP ‐1) and nuclear factor‐κ B ( NF ‐κ B ) in HB cells. Results showed that C p G ‐ ODN could stimulate proliferation of HB cells in a dose‐ and time‐dependent manner with a promoted G 1 / S cell cycle progression. Increased cyclin D 1 expression was detected in the nuclear region after C p G ‐ ODN treatment. Moreover, C p G ‐ ODN promoted nuclear translocation and activation of AP ‐1, which appeared to be required for TLR ‐9‐mediated cyclin D 1 expression and subsequently cell proliferation, but seemed to have little impact on NF‐κB activity. Our results indicate that C p G ‐ ODN stimulates tumor cell proliferation through TLR ‐9‐mediated AP ‐1‐activated cyclin D 1 expression in OSCC HB cells. Pharmacologic inhibition of the TLR ‐9/ AP ‐1/cyclin D 1 pathway may be a new therapeutic approach for prevention as well as treatment of OSCC .