Photochemical destruction of the Bcl-2 oncoprotein during photodynamic therapy with the phthalocyanine photosensitizer Pc 4.
Photodynamic therapy (PDT), utilizing a photosensitizer and visible light, causes localized oxidative damage. With the mitochondrial photosensitizer Pc 4, PDT induces apoptosis, yet its molecular targets are not known. Here, the anti-apoptotic protein Bcl-2 is shown to be highly sensitive to PDT, as judged on Western blots by the disappearance of anti-Bcl-2-reactive material from the position of the native 26 kDa protein. The loss of Bcl-2 was PDT dose dependent and was observed for both endogenous and overexpressed Bcl-2 in several cell lines, immediately after PDT, and with chilled cells. It was accompanied by a trace of a 23-kDa cleavage product as well as high-molecular weight products that may result from photochemical crosslinking. PDT-induced Bcl-2 loss occurred in MCF-7 cells that do not express caspase-3 or in the presence of protease inhibitors, but was prevented, along with the induction of apoptosis, by the singlet oxygen scavenger L-histidine. Loss of FLAG-Bcl-2 was observed with both anti-FLAG and anti-Bcl-2 antibodies, indicating loss of native protein rather than simple BCL-2-epitope destruction. Photochemical damage was not observed in Bcl-x(L), Bax, Bad, the voltage-dependent anion channel, or the adenine nucleotide translocator. Therefore, Bcl-2 is one target of PDT with Pc 4, and PDT damage to Bcl-2 contributes to its efficient induction of apoptosis.
Xue
L Y
LY
Department of Radiation Oncology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA.
Chiu
S M
SM
Oleinick
N L
NL
D000230:Adenocarcinoma / Q000473:pathology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects; D001943:Breast Neoplasms / Q000473:pathology; D016466:CHO Cells / Q000187:drug effects / Q000528:radiation effects; D002294:Carcinoma, Squamous Cell / Q000473:pathology; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D016166:Free Radical Scavengers / Q000494:pharmacology; D006639:Histidine / Q000494:pharmacology; D006801:Humans; D007211:Indoles / Q000494:pharmacology / Q000627:therapeutic use*; D007425:Intracellular Membranes / Q000737:chemistry / Q000187:drug effects / Q000528:radiation effects; D007822:Laryngeal Neoplasms / Q000473:pathology; D008297:Male; D008565:Membrane Proteins / Q000187:drug effects / Q000528:radiation effects; D008970:Molecular Weight; D009363:Neoplasm Proteins / Q000187:drug effects / Q000528:radiation effects; D018384:Oxidative Stress; D010100:Oxygen / Q000378:metabolism; D010777:Photochemistry; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology / Q000627:therapeutic use*; D011471:Prostatic Neoplasms / Q000473:pathology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects / Q000528:radiation effects*; D026082:Singlet Oxygen; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000528:radiation effects
D016166:Free Radical Scavengers; D007211:Indoles; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D017319:Photosensitizing Agents; D019253:Proto-Oncogene Proteins c-bcl-2; C107448:phthalocyanine Pc 4; D026082:Singlet Oxygen; D006639:Histidine; D010100:Oxygen