MEK inhibition enhances bleomycin A5-induced apoptosis in an oral cancer cell line: signaling mechanisms and therapeutic opportunities.
BACKGROUND
Bleomycin A5 is an anti-neoplastic glycoprotein antibiotic used for the treatment of various cancers. Previous work has shown that bleomycin A5 exerts its apoptotic effects on tumor cells. This was to study the signal transduction pathways that might exert the apoptotic effects of bleomycin A5 on tumor cells, as well as to examine the possibility of lower dosing of such drug in combinative treatment with other compounds in vitro.


METHODS
Bleomycin A5 was applied on a human oral epidermoid carcinoma cell line, human oral epidermoid carcinoma (KB), and the apoptotic activity was determined by the presence of DNA fragmentation and 4,6-diamidino-2-phenylindole (DAPI) nuclear staining. The signal transduction pathway was measured through Western blotting and in vitro kinase assay.


RESULTS
The apoptotic effect was associated with the sustained activation of c-Jun N-terminal kinases (JNK) and the inhibition of extracellular signal-regulated kinases1 (ERK1) and -2 activities, suggesting that JNK plays a positive role in the death process. ERK1 and -2 might exert a protection pathway from cell death. Here, it was determined that a combination treatment of bleomycin A5 and the MAP kinase-ERK kinase (MEK) inhibitor, PD98059, could lead to enhanced apoptosis. The activities of ERK1 and -2 are required for cell survival signaling using stable cell clones expressing MEK1. Upon bleomycin A5 treatment, cells expressing MEK1 exhibited significant delays in the onset of apoptosis, where the presence of MEK1 inhibitor enhanced cell death. Moreover, the increased activity of ERK1 and -2 coincided with cell survival. The survival signals exerted by MEK1 most likely result from the activation of ERK1 and -2.


CONCLUSIONS
The apoptosis enhancement through such combinative treatment in vitro has revealed new therapeutic opportunities and elucidated mechanisms contributing to the efficacy of existing anti-cancer treatments.
Yang
Li-Chiu
LC
Department of Dentistry, Chung Shan Medical University Hospital, and School of Dentistry, Chung Shan Medical University, Taichung, Taiwan.
Yang
Shyh-Hwang
SH
Tai
Kuo-Wei
KW
Chou
Ming-Yung
MY
Yang
Jaw-Ji
JJ
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001761:Bleomycin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002294:Carcinoma, Squamous Cell / Q000473:pathology*; D002467:Cell Nucleus / Q000648:ultrastructure; D002470:Cell Survival / Q000187:drug effects; D053938:DNA Fragmentation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D007624:KB Cells; D048670:MAP Kinase Kinase 4; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases / Q000037:antagonists & inhibitors*; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000494:pharmacology; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000494:pharmacology; D009062:Mouth Neoplasms / Q000473:pathology*; D015398:Signal Transduction / Q000187:drug effects*
D000903:Antibiotics, Antineoplastic; D004791:Enzyme Inhibitors; D005419:Flavonoids; D001761:Bleomycin; C025703:bleomycetin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases; C482576:MAP3K1 protein, human; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one