UPR was activated by <i>C</i>. <i>jejuni</i> infection.

(A-C) Western blotting of UPR signaling proteins, including phosphorylated eIF2α (Ser51), total eIF2α, ATF6, and CHOP, in lysates of Caco-2 cells treated with PBS or infected with C. jejuni was conducted at 3-h intervals for a 12-h period (A, C). Spliced XBP1 was detected by GFP expression. As a positive control, cells were treated with 2.5 μM thapsigargin, an inducer of ER stress, for 12 h. (D and E) Quantification of the relative CHOP expression and eIF2α phosphorylation levels were indicated by relative values, vs. no-infection group at 0 h. CHOP was normalized to the α-tubulin housekeeping protein expression, and phosphorylated-eIF2α was normalized to the total protein expression of eIF2α. Asterisks denote significant differences (*p < 0.05, **p < 0.01, by t-test, n = 5). Each experiment was repeated three times (A was repeated five times).