Cytoprotective Signaling Associated with Nitric Oxide Upregulation in Tumor Cells Subjected to Photodynamic Therapy-like Oxidative Stress

► 5-Aminolevulinic acid (ALA)-induced protoporphyrin IX in mitochondria sensitizes tumor cells to apoptotic photokilling, which is suppressed by stress-upregulated iNOS and NO. ► Investigation of underling signaling activity revealed that stress NO positively effects survivin induction/activation, but negatively effects pro-apoptotic JNK and p38α activation and pro-survival p38β deactivation. ► These results provide insights into how tumor cell NO can antagonize photodynamic therapy.