Nuclear factor-kappa B activation by the photochemotherapeutic agent verteporfin

The nuclear factor-kappa B (NF-kappa B) gene transactivator serves in the f ormation of immune, inflammatory, and stress responses. In quiescent cells, NF-kappa B principally resides within the cytoplasm in association with in hibitory kappa (I kappa B) proteins. The status of I kappa B and NF-kappa B proteins was evaluated for promyelocytic leukemia HL-60 cells treated at d ifferent intensities of photodynamic therapy (PDT), The action of the poten t photosensitizer, benzoporphyrin derivative monoacid ring A (verteporfin), and visible light irradiation were assessed. At a verteporfin concentratio n that produced the death of a high proportion of cells after light irradia tion, evidence of caspase-3 and caspase-9 processing and of poly(ADP-ribose ) polymerase cleavage was present within whole cell lysates, The general ca spase inhibitor Z-Val-Ala-Asp-fluoromethylketone (ZVAD.fmk) effectively blo cked these apoptosis-related changes. Recent studies indicate that I kappa B proteins may be caspase substrates during apoptosis, However, the level o f I kappa B beta was unchanged for HL-60 cells undergoing PDT-induced apopt osis, I kappa B alpha levels decreased during PDT-induced apoptosis, though ZVAD.fmk did not affect this change. At a less intensive level photosensit ization, cellular I kappa B alpha levels were transiently depressed after P DT. At these times, p50 and RelA NF-kappa B species were increased within n uclear extracts, as revealed by electrophoretic mobility supershift assays. HL-60 cells transiently transfected with a kappa B-luciferase reporter con struct exhibited elevated luciferase activity after PDT or treatment with t umor necrosis factor-or, a well-characterized NF-kappa B activator. Product ive NF-kappa B activation and associated gene transcription may influence t he phenotype and behavior of cells exposed to less intensive PDT regimens, However, I kappa B alpha is not subject to caspase-mediated degradation as a component of PDT-induced apoptosis, (C) 2000 by The American Society of H ematology.