Figure 4.

Stx1 and Stx2 activation of stress-associated MAPKs in RPE cells. ARPE-19 cells were stimulated with Stx1 (100 ng/mL), Stx1A⁻ (100 ng/mL), Stx2 (10 ng/mL) or Stx2A⁻ (10 ng/mL). After washing, cell lysates were collected at the indicated time points. Phosphorylation of p38MAPK (p-p38), Jun N-terminal kinase (p-JNK), and extracellular signal-regulated kinase (p-ERK) were examined by Western blotting. β-Actin was used as a control for equal protein loading. The results are from one representative experiment of three independent experiments. The data supports the necessity of Stx A₁-fragment retro-translocation and action on the ribosomal peptidyl transferase center for activation of p38 and JNK, but not ERK. The bar graphs show the mean ± SEM of fold changes in band densities normalized to β-Actin in comparison to untreated control cell values (right panel). Asterisks indicate significant differences between Stx1 vs. Stx1A⁻ or Stx 2 vs. Stx2A⁻; * = p < 0.05; ** = p < 0.01; *** = p < 0.001.