Fig. 4.

Increased CHOP is a biomarker of poor survival in RMS patients after chemotherapy. (A) 120 RMS samples were divided by median expression of DDIT3 (CHOP) from Affymetrix U133A microarrays (36). P value for survival was calculated by log-rank test. (B) Immunoblot of RMS13 cells treated with 10 μM MAL3-101, 5 nM vincristine, 5 nM actinomycin D, 5 μg/mL 4-hydroperoxy-cyclophosphamide, or 1 μM doxorubicin for the indicated times. (C) A model for HSP70 dependence in RMS. Cytosolic HSP70s degrade or refold unfolded proteins (1) that back up in the ER after MAL3-101 treatment (2), thereby activating PERK to phosphorylate eIF2α (3). When CHOP mRNA is abundant, eIF2α phosphorylation leads to rapid translation of CHOP protein (4), activating a lethal program culminating in caspase 8 activation.