Proinflammatory cytokines were upregulated through activation of MAPK and NF-κB signaling pathways in HPS4-YC-infected STEC. A mRNA levels of cytokines IL-6, IL-8 and TNF-α were assessed through qRT-PCR assays. B Levels of the cytokines IL-6, IL-8 and TNF-α in culture supernatant of STEC were assessed by ELISA. C, D Activation of MAPK and NF-κB signaling pathways in STEC at 12 h and 24 h after HPS4-YC infection. The protein levels were determined by Western blot. E Expression of TNF-α was regulated by both MAPK and NF-κB signaling pathways. STEC were pretreated with DMSO or inhibitors for 1 h before HPS4-YC infection. The infection time of HPS4-YC was 12 h. SB203580, U0126, SP600125 and BAY11-7082 are inhibitors of p38, ERK, JNK and NF-κB, respectively. Data are shown as the mean ± SD of three independent experiments. Significant differences were determined using one-way ANOVA. *, P < 0.05; **, P < 0.01; ***P < 0.001.