Fig. 9: The effect of TAK1 and AMPK inhibitors on S. Typhimurium growth.
a HeLa cells were left untreated or pretreated with CC (1 μM) or 5Z (0.5 μM) for 30 min. The cells were then infected with S. Typhimurium (10 MOI). After incubation for the indicated lengths of time, the cells were harvested and lysed. The colony formation units were analyzed by counting the number of bacterial colonies grown in the LB plates. The results represent the mean ± SD from the triplicate from one of three experiments with similar results. *p < 0.05, **p < 0.01, compared to uninfected control. b S. Typhimurium inoculated in LB medium (100 μl) was cultured in the absence or presence of CC (0.5 μM) or 5Z (1 μM) at 37 °C for 8 h with agitation. The OD600 values of triplicate cultures in LB medium were determined in the indicated intervals of indicated time. Gentamycin (100 μg/ml) was used as a positive control. c Schematic mode of Salmonella-induced autophagy. The binding of the TLR4-MD2 complex by LPS, which is abundantly present in the wall of the Gram-negative bacteria such as S. Typhimurium, activates TRAF6 through its two adaptor proteins, MyD88 and TRIF. In addition, the binding of TLR5 and TLR9 by flagelin and CpG, respectively, can also activates TRAF6 through MyD88. As a E3 ubiquitin ligase, TAFF6 induces TAK1 K63-ubiquitination and activation, leading to NF-kB and AMPK activation, the former regulates the expression of inflammatory cytokines, whereas the latter activates ULK1 and regulates autophagy. AKT activation by the sopB protein of S. Typhimurium would activate its downstream effector mTOR and subsequently suppress autophagy. In our model, AMPK activation by TAK1 circumvents the AKT-mediated mTOR activation by phosphorylating Raptor, a subunit in the mTORC1 complex. Inactivation of mTOR activity suppresses ULK1S757 phosphorylation and induces ULK1 activation and autophagy
