DDIT3 and melanoma: Interestingly, we also observed that in the subtoxic range: XN dose-dependently induced the expression of the ER stress markers CCAAT-enhancer-binding protein homologous protein (CHOP) and heat shock protein family A (Hsp70) member 5 (HSPA5; also known as binding immunoglobulin protein (BiP)) in both human melanoma cell lines (Figure 2F,G, Figure S2F,G).