It was previously shown that p38 mediates the sequential activation of p53 and caspase 3 to induce apoptosis in RAW 264.7 cells (Zhou et al., 2005a) . Suppression of DON-induced rRNA cleavage was observed here both for pifithrin-a (80 and 100 lM) (Fig. 6D) , which can reversibly inhibit p53-dependent transactivation of p53-responsive genes and apoptosis and for pifithrin-l (10 and 25 lM) (Fig. 6E) , which blocks p53 interaction with Bcl-2 family proteins and selectively inhibits p53 translocation to mitochondria. The caspase inhibitor Z-VAD-FMK also caused concentration-dependent inhibition of DON-induced rRNA cleavage (Fig. 6F) . Accordingly, both p53 and caspase activation are additional upstream elements in the signaling pathway leading to DON-induced rRNA cleavage.