Purpose: Toll-like receptor 4 (TLR4) was found to be aberrantly expressed in bladder cancer, inducing some genes expression and facilitating tumor progression. Recent data suggest that tumor associated Interleukin-6 (IL-6) correlates with tumor size and grade in bladder cancer. However, the molecule mechanisms of the induction of IL-6 response in bladder cancer cells are not well elucidated. In this study, we manage to find out whether TLR4 signaling is involved in the production of IL-6 by human bladder cancer cells, and the detailed molecule mechanisms by which IL-6 is up-regulated.
Methods: We selected human bladder cancer T24 cell line in the present study, and examined its expression of TLR4 and CD14 by using flow cytometry. TLR4 signaling was activated by lipopolysaccharide (LPS) and IL-6 secretion in culture supernatants was tested by using ELISA kit. The expression of p38, ERK, JNK and Akt were determined by western-blot analysis using specific antibodies.
Results: Our study demonstrated that CD14 and TLR4 were constitutively expressed in T24 cells and activation of TLR4 signaling by LPS resulted in phosphorylation of MAPK and PI3K pathways and up-regulation of IL-6 in dose- and time-dependent manner. Pretreatment of cells with SB203580 (inhibitor of p38) and PD98059 (inhibitor of ERK) attenuated LPS-induced IL-6 expression, whereas LY294002 (inhibitor of PI3K) markedly amplified the LPS-stimulated synthesis of IL-6.
Conclusions: Our results demonstrate that activation of TLR4 signaling in bladder cancer cells induces tumor-associated IL-6 expression via activation of p38 and ERK, whereas activation of PI3K/Akt exerts an opposing action.