Rapamycin suppresses TLR4-triggered IL-6 and PGE2 production of colon cancer cells by inhibiting TLR4 expression and NF-κB activation

Toll-like receptor 4 (TLR4) signaling in tumor cells can mediate tumor cell immune escape and tumor progression, being regarded as one of the mechanisms for chronic inflammation in tumorigenesis and progression. So, intervention of TLR4-mediated immune escape and metastasis has been proposed as one of the approaches to cancer prevention and treatment. Rapamycin, an immunosuppressant agent widely used for treatment of autoimmune diseases and transplantation rejection, is recently used for cancer therapy. However, the underlying mechanisms remain to be fully understood. In the present study, we demonstrate that rapamycin can significantly inhibit TLR4-triggered IL-6 and PGE2 production and invasion of colon cancer cells. Suppression of TLR4-induced IL-6 and PGE2 production is responsible for the rapamycin-mediated decrease of TLR4-evoked invasion of colon cancer cells. Furthermore, disruption of NF-κB pathway contributes to the inhibition of TLR4-induced IL-6, PGE2 production and invasion by rapamycin in colon cancer cells. Rapamycin can also downregulate TLR4 expression. Therefore, we demonstrate that rapamycin may abrogate TLR4-triggered tumor cell immune escape and invasion by downregulating TLR4 expression and inhibiting TLR4-activated NF-κB pathway, thus providing new mechanistic explanation for the antitumor effect of rapamycin.