Pseudomonas aeruginosa exotoxin A reduces chemoresistance of oral squamous carcinoma cell via inhibition of heat shock proteins 70 (HSP70).
OBJECTIVE
Oral squamous carcinoma (OSCC) cells exhibit resistance to chemotherapeutic agent-mediated apoptosis in the late stage of malignancy. Increased levels of heat shock proteins 70 (HSP70) in cancer cells are known to confer resistance to apoptosis. Since recent advances in the understanding of bacterial toxins have produced new strategies for the treatment of cancers, we investigated the effect of Pseudomonas aeruginosa exotoxin A (PEA) on HSP70 expression and induction of apoptosis in chemoresistant OSCC cell line (YD-9).


METHODS
The apoptotic effect of PEA on chemoresistant YD-9 cells was confirmed by MTT, Hoechst and TUNEL stains, DNA electrophoresis, and Western blot analysis.


RESULTS
While YD-9 cells showed high resistance to chemotherapeutic agents such as etoposide and 5-fluorouraci (5-FU), HSP70 antisense oligonucelotides sensitized chemoresistant YD-9 cells to etoposide and 5-FU. On the other hand, PEA significantly decreased the viability of YD-9 cells by deteriorating the HSP70-relating protecting system through inhibition of HSP70 expression and inducing apoptosis in YD-9 cells. Apoptotic manifestations were evidenced by changes in nuclear morphology, generation of DNA fragmentation, and activation of caspases. While p53, p21, and E2F-1 were upregulated, cdk2 and cyclin B were downregulated by PEA treatment, suggesting that PEA caused cell cycle arrest at the G2/M checkpoint.


CONCLUSIONS
Therefore, these results indicate that PEA reduced the chemoresistance through inhibition of HSP70 expression and also induced apoptosis in chemoresistant YD-9 cells.
Park
Sang Rye
SR
Department of Oral Anatomy, School of Dentistry, Research Institute for Oral Biotechnology, Pusan National University, Yangsan, Korea.
Lee
Kyoung Duk
KD
Kim
Uk Kyu
UK
Gil
Young Gi
YG
Oh
Kyu Seon
KS
Park
Bong Soo
BS
Kim
Gyoo Cheon
GC
D036002:ADP Ribose Transferases / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001427:Bacterial Toxins / Q000494:pharmacology*; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D002853:Chromatography, Liquid; D019926:Cyclin B / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D050687:E2F1 Transcription Factor / Q000378:metabolism; D004586:Electrophoresis; D005098:Exotoxins / Q000494:pharmacology*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D020287:In Situ Nick-End Labeling; D009062:Mouth Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D053719:Tandem Mass Spectrometry; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D037521:Virulence Factors / Q000494:pharmacology*; D000097668:Pseudomonas aeruginosa Exotoxin A
D036002:ADP Ribose Transferases; D000970:Antineoplastic Agents; D001427:Bacterial Toxins; D019926:Cyclin B; D051357:Cyclin-Dependent Kinase 2; D050687:E2F1 Transcription Factor; D005098:Exotoxins; D018840:HSP70 Heat-Shock Proteins; D016159:Tumor Suppressor Protein p53; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A; C493753:E2F1 protein, human; C495894:CDK2 protein, human