Fig. 7

Caspase and proteasome pathway involvement in c-IAP1 expression. (A) Etoposide-initiated (c-IAP1) loss is not prevented by caspase or (cdk2) inhibitors. K562 cells incubated for 16 hr in the presence of dimethylsulfoxide (DMSO) vehicle (−) or etoposide (100 µM) as indicated. Caspase inhibitors (DEVD; 80 µm) or (ZVAD; 80 µm) and cdk2 inhibitor, roscovitine (8 µg/ml), were added 2 hr prior to etoposide. (B) Increase in c-IAP1 levels by proteasome inhibitors. K562 cells were exposed for 24 hr to proteasome inhibitors (LNLL; 75 µM) or (MG132; 40 µM). The specific proteasome inhibitor lactacystin (lact) also enhanced c-IAP1 expression. Equal loading is demonstrated by blotting for Stat 3. (C) Mimosine does not protect against etoposide-mediated c-IAP1 loss. K562 cells were exposed to etoposide for 48 hr in the presence or absence of pre-incubation with p21WAF1 inducer (IPTG), 250 µM mimosine (MIM), 5 µg/ml β clasto-lactocystin (LACT), or lactocystin and IPTG combined, as shown. Protein loading was equivalent by Ponceau S staining. The membrane was sequentially probed with c-IAP1 and with cyclin A antibodies.