Head and neck cancer cell lines are resistant to mitochondrial-depolarization-induced apoptosis.
OBJECTIVE
Mitochondrial dysfunction has been linked to defects in the apoptotic pathway, and solid tumors, including head and neck squamous cell carcinoma (HNSCC), exhibit defects in apoptosis. Loss of mitochondrial membrane potential (DeltaPsim) is an early initiating event in the mitochondrial apoptotic pathway. We investigated the apoptotic response of 3 head and neck cancer cell lines treated with a mitochondrial-membrane-depolarizing agent, valinomycin, and studied the ability of depolarization to induce release of cytochrome c in these cell lines.


METHODS
HNSCC cell lines JHU-011, -012 and -019, and a leukemia control cell line HL-60 were assayed for DeltaPsim after valinomycin treatment by staining with mitochondrial-membrane-potential-specific probe JC-1 and stained with apoptosis-specific probe annexin-V to measure their rate of apoptosis by FACS. Western blotting was also applied to detect cytoplasmic cytochrome c release.


RESULTS
DeltaPsim in head and neck cell lines started to show slight loss of DeltaPsim, while HL-60 showed significant loss of DeltaPsim after 30 min of treatment. All cell lines demonstrated complete mitochondrial depolarization within 24 h, however, only the control cell line HL-60 underwent apoptosis. In addition, HNSCC cell lines did not demonstrate cytoplasmic cytochrome c release despite significant mitochondrial membrane depolarization, while HL-60 cell initiated apoptosis and cytochcrome c release after 24 h of treatment.


CONCLUSIONS
Head and neck cancer cell lines exhibit defects in mitochondrial-membrane-depolarization-induced apoptosis as well as impaired release of cytochrome c despite significant mitochondrial membrane depolarization. Proximal defects in the mitochondrial apoptosis pathway are a feature of HNSCC.
Zhao
Ming
M
Department of Otolaryngology, Head and Neck Surgery, Johns Hopkins Medical Institution, Baltimore, MD 21287-0910, USA.
Mydlarz
Wojciech K
WK
Zhou
Shaoyu
S
Califano
Joseph
J
D017209:Apoptosis / Q000502:physiology*; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D045304:Cytochromes c / Q000096:biosynthesis; D005434:Flow Cytometry; D006258:Head and Neck Neoplasms / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D053078:Membrane Potential, Mitochondrial / Q000502:physiology*; D008928:Mitochondria / Q000378:metabolism* / Q000473:pathology
D045304:Cytochromes c