FIG. 8.

Stx1 treatment of macrophage-like THP-1 cells triggers the delayed activation of calpain, which requires toxin enzymatic activity. (A) Differentiated macrophage-like THP-1 cells were incubated without or with Stx1 for 0 to 24 h (left panel), or with Stx1 or Stx1A⁻ for 12 h (right panel). Cell lysates were prepared and subjected to SDS-PAGE. Calpain cleavage was detected by Western blotting with calpain-specific antibodies. (B) Undifferentiated (U) and differentiated (D) THP-1 cells were incubated with Stx1 for various times. At the indicated time points, cell lysates were prepared and subjected to Western blotting to assess calpain cleavage as described for panel A. C, control (untreated) cells. Representative gels from at least three independent experiments are shown. The bar graph (below in panel B) depicts results from at least three independent experiments with calpain activation (cleavage) as fold increase compared to control values (untreated cells).