ER stress attenuated <i>C</i>. <i>jejuni</i> invasion.

(A and B) Caco-2 cells were treated with thapsigargin (0, 1.0, 2.5, or 5.0 μM) or tunicamycin (0, 1.0, 2.5, or 5.0 μg/mL) and collected after 12 h. UPR signaling was detected by Western blotting. (C-F) Caco-2 cells were pretreated with thapsigargin (2.5 μM), tunicamycin (5.0 μg/mL), or DMSO (as a control) for 12 h and infected with C. jejuni for 6 h. Then, bacterial invasion (C and D), adhesion (E), and intracellular survival (F) were assessed after 1 or 3 h using the gentamycin protection assay. (G and H) A selective assay of intracellular NA-resistant C. jejuni was performed. Caco-2 cells were infected with WT C. jejuni for 12 h, then washed with DMEM-FBS(-) three times to eliminate extracellular bacteria. After pre-infection, the cells were infected with NA-resistant C. jejuni for 6 h, and the number of intracellular NA-resistant bacteria was selectively estimated using the gentamycin protection assay. Asterisks denote significant differences (n.s., not significant, *p < 0.05, **p < 0.01, by t-test, n = 4). Each experiment was repeated four times.