Caspase-independent induction of apoptosis in human melanoma cells by the proapoptotic Bcl-2-related protein Nbk / Bik.
The proapoptotic BH3-only protein natural born killer / Bcl-2 interacting killer (Nbk/Bik) has been described to inhibit Bcl-2 and Bcl-xL, thereby supporting the death promoting ability of Bax. In order to evaluate its function in melanoma, we investigated the response after Nbk/Bik overexpression in cultured human melanoma cells and in a melanoma mouse model. Untransfected melanoma cell lines expressed Nbk/Bik only weakly at the mRNA and protein level. Conditional expression of Nbk/Bik by applying the inducible tetracycline-responsive expression system triggered apoptosis and enhanced sensitivity to proapoptotic stimuli as to agonistic CD95 activation and to chemotherapeutics etoposide, doxorubicin and pamidronate. For investigating the effects of Nbk/Bik in vivo, stably transfected melanoma cells were subcutaneously injected into nude mice. Significantly delayed tumor growth was the result when mice received doxycycline for induction of Nbk/Bik expression. By investigating the mechanism of Nbk/Bik-induced cell death, typical hallmarks of apoptosis such as DNA fragmentation and chromatin condensation were seen after induction. Interestingly, no indications for cytochrome c release and caspase processing were found, and selective caspase inhibition remained without effect. These data indicate the high potential of Nbk/Bik in regulating apoptosis in melanoma by a caspase-independent pathway and may corroborate the potency of novel antimelanoma strategies based on activation of BH3-only proteins such as Nbk/Bik.
Oppermann
Malte
M
Department of Dermatology and Allergy, Skin cancer center, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany.
Geilen
Christoph C
CC
Fecker
Lothar F
LF
Gillissen
Bernhard
B
Daniel
Peter T
PT
Eberle
Jürgen
J
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis; D020169:Caspases / Q000378:metabolism*; D002843:Chromatin / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D004164:Diphosphonates / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D005047:Etoposide / Q000494:pharmacology; D005260:Female; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D020287:In Situ Nick-End Labeling; D007279:Injections, Subcutaneous; D008545:Melanoma / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D000077268:Pamidronate; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D012867:Skin / Q000378:metabolism; D013752:Tetracycline / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D019014:fas Receptor / Q000378:metabolism
D000893:Anti-Inflammatory Agents; D000903:Antibiotics, Antineoplastic; D000972:Antineoplastic Agents, Phytogenic; C494772:BAK1 protein, human; D002843:Chromatin; D004164:Diphosphonates; D011500:Protein Synthesis Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D019014:fas Receptor; D005047:Etoposide; D004317:Doxorubicin; D045304:Cytochromes c; D020169:Caspases; D013752:Tetracycline; D000077268:Pamidronate