Photodynamic therapy (
PDT), a photochemotherapeutic regimen used to treat several diseases, including
cancer, exerts its effects mainly through induction of cell death. Using human
epidermoid carcinoma A431 cells as a model, we previously showed that distinct cell death types could be triggered by protocols that selectively delivered
Photofrin (a clinically approved
photosensitizer) to different subcellular sites (Hsieh et al. [2003] J Cell Physiol 194: 363-375]. Here, the responses elicited by
PDT in A431 cells containing intracellular organelle-localized
Photofrin were further characterized. Two prominent cell phenotypes were observed under these conditions: one characterized by perinuclear vacuole (PV) formation 2-8 h after
PDT followed by cell recovery or shrinkage within 48 h, and a second characterized by typical apoptotic features appearing within 4 h after
PDT.
DCFDA-sensitive
reactive oxygen species formed proximal to PVs during the response to
PDT, covering areas in which both endoplasmic reticulum (ER) and the Golgi complex were located. Biochemical analyses showed that
Photofrin-
PDT also induced JNK activation and altered the
protein secretion profile. A more detailed examination of PV formation revealed that PVs were derived from the ER. The alteration of ER structure induced by
PDT was similar to that triggered by
thapsigargin, an ER Ca(2+)-
ATPase inhibitor that perturbs Ca(2+) homeostasis, suggesting a role for Ca(2+) in the formation of PVs. Microtubule dynamics did not significantly affect PV formation. This study demonstrates that cells in which intracellular organelles are selectively loaded with
Photofrin mount a novel response to ER stress induced by
PDT.