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Published on: January 11, 2019
Head and neck cancer cell lines are resistant to mitochondrial-depolarization-induced apoptosis
Ming Zhao1, Wojciech K Mydlarz, Shaoyu Zhou
1Department of Otolaryngology, Head and Neck Surgery, Johns Hopkins Medical Institution, Baltimore, MD 21287-0910, USA.
Purpose:
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.
Experimental Design:
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.
Insights
Head and neck cancer cells show impaired apoptosis due to mitochondrial defects. These cancer cells fail to release cytochrome c, a key protein in programmed cell death, even when their mitochondria are depolarized.
Area of Science:
- Cell Biology
- Cancer Research
- Mitochondrial Biology
Background:
- Mitochondrial dysfunction is implicated in cancer, particularly in apoptosis defects observed in head and neck squamous cell carcinoma (HNSCC).
- Loss of mitochondrial membrane potential (ΔΨm) is an early event in the mitochondrial apoptotic pathway.
Purpose of the Study:
- To investigate the apoptotic response of HNSCC cell lines to valinomycin, a mitochondrial membrane depolarizing agent.
- To determine if mitochondrial depolarization induces cytochrome c release in HNSCC cells.
Main Methods:
- HNSCC cell lines (JHU-011, -012, -019) and a leukemia control (HL-60) were treated with valinomycin.
- Mitochondrial membrane potential (ΔΨm) was measured using JC-1 dye.
- Apoptosis rates were assessed using annexin-V staining and FACS.
- Cytochrome c release was detected by Western blotting.
Main Results:
- HNSCC cell lines showed minimal ΔΨm loss initially, while HL-60 exhibited significant loss within 30 minutes.
- All cell lines achieved complete mitochondrial depolarization within 24 hours.
- Only the HL-60 control cell line underwent apoptosis and released cytochrome c.
- HNSCC cell lines did not release cytochrome c despite significant mitochondrial depolarization.
Conclusions:
- HNSCC cell lines display defects in apoptosis induction following mitochondrial membrane depolarization.
- Impaired cytochrome c release occurs in HNSCC cells even with substantial mitochondrial depolarization.
- Defects in the proximal mitochondrial apoptosis pathway are characteristic of HNSCC.
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