title: Lysosomal cathepsin initiates apoptosis, which is regulated by photodamage to Bcl-2 at mitochondria in photodynamic therapy using a novel photosensitizer, ATX-s10 (Na).
abstract: ATX-s10 is a novel and second-generation photosensitizer for photodynamic therapy (PDT). In order to conduct clinical trials of ATX-s10-PDT and/or extend its clinical applications, it is very important to elucidate the mechanisms of the action of ATX-s10-PDT. We examined the apoptic response against ATX-s10-PDT using a Bcl-2 or Bcl-2 mutant overexpressing cells. Using fluorescent microscopy, ATX-s10 localized not only to mitochondria but also to lysosomes and possibly other intracellular organelles, but not to the plasma membrane or the nucleus. These results suggest that ATX-s10-PDT can damage mitochondria and lysosomes. By Western blot analysis, ATX-s10-PDT damaged Bcl-2, which localized preferentially at mitochondrial membranes, and caused Bcl-2 to cross-link immediately after laser irradiation. However, ATX-s10-PDT was not able to rapidly induce morphologically typical apoptosis (i.e. chromatin condensation and fragmentation) as PDT using mitochondria targeted photosensitizers, such as phthalocyanine 4 (Pc 4). Pharmacological inhibitions of lysosomal cytokine protease cathepsins, such as cathepsin B and D, protected MCF-7c3 cells (human breast cancer cells expressing stably transfected procaspase-3) from apoptosis caused by ATX-s10-PDT. Overexpression of wild-type Bcl-2 or Bcl-2Delta33-54 resulted in relative resistance of cells to ATX-s10-PDT, as assessed by the degree of morphological apoptosis or loss of clonogenicity. We conclude that lysosomal damage by ATX-s10-PDT can initiate apoptotic response and this apoptotic pathway can be regulated by photodamage to Bcl-2 via mitochondrial damage.
authors.affiliation: Department of Thoracic Surgery, Tokyo Medical University, Tokyo, Japan.
authors.forename: Shuji
authors.initials: S
authors.lastname: Ichinose
authors.forename: Jitsuo
authors.initials: J
authors.lastname: Usuda
authors.forename: Takeshi
authors.initials: T
authors.lastname: Hirata
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Inoue
authors.forename: Keishi
authors.initials: K
authors.lastname: Ohtani
authors.forename: Sachio
authors.initials: S
authors.lastname: Maehara
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Kubota
authors.forename: Kentarou
authors.initials: K
authors.lastname: Imai
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Tsunoda
authors.forename: Yukari
authors.initials: Y
authors.lastname: Kuroiwa
authors.forename: Kimito
authors.initials: K
authors.lastname: Yamada
authors.forename: Hidemitsu
authors.initials: H
authors.lastname: Tsutsui
authors.forename: Kinya
authors.initials: K
authors.lastname: Furukawa
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Okunaka
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Oleinick
authors.forename: Harubumi
authors.initials: H
authors.lastname: Kato
mesh_terms: D017209:Apoptosis; D002403:Cathepsins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D006801:Humans; D008247:Lysosomes / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism* / Q000528:radiation effects; D009154:Mutation; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D011166:Porphyrins / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry*
chemical_list: C115550:ATX-S10; D017319:Photosensitizing Agents; D011166:Porphyrins; D019253:Proto-Oncogene Proteins c-bcl-2; D002403:Cathepsins