Invasive Fusobacterium nucleatum activates beta-catenin signaling in colorectal cancer via a TLR4/P-PAK1 cascade

The underlying mechanism of Fusobacterium nucleatum (Fn) in the carcinogenesis of colorectal cancer (CRC) is poorly understood. Here, we examined Fn abundance in CRC tissues, as well as beta-catenin, TLR4 and PAK1 protein abundance in Fn positive and Fn negative CRCs. Furthermore, we isolated a strain of Fn (F01) from a CRC tissue and examined whether Fn (F01) infection of colon cancer cells activated alpha-catenin signaling via the TLR4/P-PAK1/P-beta-catenin S675 cascade. Invasive Fn was abundant in 62.2% of CRC tissues. TLR4, PAK1 and nuclear alpha-catenin proteins were more abundant within Fn- positive over Fn-negative CRCs (P < 0.05). Fn and its lipopolysaccharide induced a significant increase in TLR4/P-PAK1/P-beta-catenin S675/C-myc/CyclinD1 protein abundance, as well as in the nuclear translocation of beta-catenin. Furthermore, inhibition of TLR4 or PAK1 prior to challenge with Fn significantly decreased protein abundance of P-beta-catenin S675, C-myc and Cyclin D1, as well as nuclear beta-catenin accumulation. Inhibition of TLR4 significantly decreased P-PAK1 protein abundance, and for the first time, we observed an interaction between TLR4 and P-PAK1 using immunoprecipitation. Our data suggest that invasive Fn activates beta-catenin signaling via a TLR4/P-PAK1/P-beta-catenin S675 cascade in CRC. Furthermore, TLR4 and PAK1 could be potential pharmaceutical targets for the treatment of Fn-related CRCs.