Endoplasmic reticulum stress is involved in hydrogen peroxide induced apoptosis in immortalized and malignant human oral keratinocytes.
BACKGROUND
Although hydrogen peroxide may play an important role in the development of cancer, it can be an efficient inducer of apoptosis in cancer cells; the exact mechanism by which this action occurs is not completely understood in oral cancer cells.


METHODS
In this study, the mechanisms by which H(2)O(2) inhibited growth and induced apoptosis were differentially investigated using HPV-immortalized human oral keratinocytes (IHOK) and oral cancer cells (HN4).


RESULTS
H(2)O(2) treatment sensitively and dose-dependently induced growth inhibition and typical apoptosis in IHOK and HN4 cells, as demonstrated by a decreased level of cell viability, an increased population of cells in the sub-G(0)/G(1) phase, ladder formation of the genomic DNA, chromatin condensation and accumulation of Annexin V(+)/PI(+) cells. Furthermore, the expression of Bax, p53 and p21(WAF1/CIP1) increased, whereas the expression of Bcl-2 decreased in immortalized and malignant keratinocytes that were treated with H(2)O(2). In addition, cytochrome-c from the mitochondria was observed in H(2)O(2)-treated IHOK and oral cancer cells, and this was accompanied by the activation of caspase-3 and -9. Additionally, H(2)O(2) treatment induced upregulation of CHOP, GRP78 and several representative endoplasmic reticulum (ER) stress-responsive proteins, including heme oxygenase-1.


CONCLUSIONS
Overall, these results suggest that H(2)O(2) triggers apoptosis via the mitochondrial and ER stress pathway in IHOK and HN4 cells, and that increasing the cellular levels of H(2)O(2) sufficiently may lead to selective killing of oral cancer cells and therefore be therapeutically useful.
Min
Seung-Ki
SK
Department of Oral and Maxillofacial Surgery, College of Dentistry, Wonkwang University, Iksan, South Korea.
Lee
Sun-Kyung
SK
Park
Jae-Sang
JS
Lee
Jun
J
Paeng
Jun-Young
JY
Lee
Sang-Im
SI
Lee
Hwa-Jeong
HJ
Kim
Youngho
Y
Pae
Hyun-Ock
HO
Lee
Suk-Keun
SK
Kim
Eun-Cheol
EC
D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000187:drug effects; D053453:Caspase 9 / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002843:Chromatin / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000187:drug effects; D045304:Cytochromes c / Q000187:drug effects; D004247:DNA / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects*; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins / Q000187:drug effects; D051547:Heme Oxygenase-1 / Q000187:drug effects; D006801:Humans; D006861:Hydrogen Peroxide / Q000008:administration & dosage / Q000494:pharmacology*; D015603:Keratinocytes / Q000187:drug effects* / Q000473:pathology; D008928:Mitochondria / Q000187:drug effects; D018832:Molecular Chaperones / Q000187:drug effects; D009061:Mouth Mucosa / Q000187:drug effects* / Q000473:pathology; D009062:Mouth Neoplasms / Q000473:pathology*; D016877:Oxidants / Q000008:administration & dosage / Q000494:pharmacology*; D018384:Oxidative Stress / Q000187:drug effects*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects; D016192:Resting Phase, Cell Cycle / Q000187:drug effects; D051742:Transcription Factor CHOP / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects; D051028:bcl-2-Associated X Protein / Q000187:drug effects
C494826:BAX protein, human; C493956:CDKN1A protein, human; D002843:Chromatin; D050759:Cyclin-Dependent Kinase Inhibitor p21; C497249:DDIT3 protein, human; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D016877:Oxidants; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D051742:Transcription Factor CHOP; D045304:Cytochromes c; D004247:DNA; D006861:Hydrogen Peroxide; D051547:Heme Oxygenase-1; D053148:Caspase 3; D053453:Caspase 9