Cytoplasmic and nuclear extracellular signal-regulated kinases are necessary for Campylobacter jejuni infection

Acute Campylobacter jejuni infection relies on effector proteins delivered from the flagellar apparatus to gut epithelial cells. While the C. jejuni Campylobacter invasion antigen D (CiaD) secreted protein has been linked to extracellular signal-regulated kinase (ERK) activation, the contribution of ERK in establishing acute bacterial infection has not been fully explored. We hypothesized that subcellular ERK could play distinct roles in C. jejuni proinflammatory cytokine production and bacterial invasion. The objective of this study was to determine the contribution of cytoplasmic and nuclear ERKs in response to C. jejuni infection with a wild-type isolate and effector mutants.

Epithelial cells were infected with C. jejuni in the presence of focal adhesion inhibitors that prevent extracellular signal-regulated kinases 1 and 2 (ERK1/2) activation and a peptide that disrupts ERK nuclear translocation. We measured markers of C. jejuni infection, including cell invasion and interleukin-8 (IL-8) cytokine secretion by gentamicin-protection assay and ELISA, respectively.

Our results demonstrate that inhibitors of ERK1/2 activation drastically reduce both the C. jejuni internalization and IL-8 secretion. Moreover, ERK1/2 activation was dependent upon its association with the focal adhesion protein paxillin, which is mediated by the C. jejuni CiaD effector. Blocking ERK nuclear translocation with a phosphomimetic peptide results in a significant reduction in IL-8 secretion, and surprisingly, bacterial invasion.

We conclude that nuclear ERK is required for C. jejuni-induced IL-8 secretion and that both cytosolic and nuclear ERK are necessary for C. jejuni maximal cell invasion. Targeting host ERK signaling represents a promising therapeutic strategy to reduce the severity of C. jejuni-mediated enteritis.