N-Acetylcysteine enhances UV-mediated caspase-3 activation, fragmentation of E2F-4, and apoptosis in human C8161 melanoma: inhibition by ectopic Bcl-2 expression.
Redox imbalance due to oxidative stress or excessive antioxidant levels can alter apoptotic responses. Recently, antioxidants like N-acetylcysteine (NAC) were reported to inhibit H(2)O(2)-mediated necrotic cell death, although they were inactive against apoptosis induced by other agents like etoposide. NAC was also found to kill preferentially tumor cells compared to normal fibroblasts at 20-50mM, but these concentrations are lethal to normal splenocytes. We now demonstrate that 10mM NAC, a non-toxic concentration, can enhance the UV radiation-mediated apoptosis of human C8161 melanoma cells. Compared to treatment with UV radiation alone, combination treatment with NAC doubled the ratio of activated caspase-3 to pro-caspase-3 and produced greater fragmentation of the retinoblastoma protein and the E2F-4 transcription factor without affecting the E2F-1 protein. These effects of joint NAC-UV radiation treatment were counteracted by the overexpression of the bcl-2 gene. To our knowledge, this report is the first to: (i) demonstrate a synergy between DNA-damaging agents, like UV radiation, and antioxidants, like NAC, and (ii) show that a Bcl-2-inhibitable E2F-4 fragmentation occurs concurrently with caspase-3 activation and apoptosis.
Rieber
Manuel
M
IVIC, Tumor Cell Biology Laboratory, CMBC, Apartado 21827, Caracas 1020 A, Venezuela. mrieber@ivic.ve
Rieber
Mary Strasberg
MS
D000111:Acetylcysteine / Q000494:pharmacology*; D017209:Apoptosis; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D004247:DNA / Q000187:drug effects / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D050704:E2F4 Transcription Factor; D004789:Enzyme Activation / Q000528:radiation effects; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D008545:Melanoma / Q000473:pathology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000494:pharmacology*; D014157:Transcription Factors / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D014466:Ultraviolet Rays
D004268:DNA-Binding Proteins; D050704:E2F4 Transcription Factor; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D004247:DNA; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D000111:Acetylcysteine