p27Kip1 accumulation by inhibition of proteasome function induces apoptosis in oral squamous cell carcinoma cells.
Ubiquitin-mediated proteolysis controls intracellular levels of various cell cycle regulatory proteins, and its inhibition has been shown to induce apoptosis in proliferating cells. In the present study, we examined induction of apoptosis in oral squamous cell carcinoma (OSCC) cells by treatment with specific proteasome inhibitors, carbobenzoxy-L-leucyl-L-leucyl-L-norvalinal and lactacystin. In all three OSCC cell lines examined, apoptotic changes such as apoptotic body formation and DNA fragmentation were observed at various degrees after 24 h of the carbobenzoxy-L-leucyl-L-leucyl-L-norvalinal or lactacystin treatment. HSC2 cells showed the most prominent apoptotic changes among the cell lines examined and demonstrated the highest level of accumulation of p27Kip1 protein after the treatment with proteasome inhibitor. Reduced expressions of cyclin D1 and phospho pRb were also observed after the treatment with proteasome inhibitor. Moreover, 12 h of treatment with the proteasome inhibitor inhibited cdk2/cyclin E kinase activity and increased the ratio of the cell cycle population at the G1 phase. The proteasome inhibitor led to inhibition of cell cycle progression. In addition, activation of CPP32 and reduced expression of Bcl-2 were observed. Because apoptosis induced by the proteasome inhibitor was inhibited by treatment with antisense p27Kip1 oligonucleotide, accumulation of the p27Kip1 protein might play an important role in the apoptosis induced by proteasome inhibitor. The present results suggest that inhibition of proteasome function may be used as a possible target of novel therapy for OSCC.
Kudo
Y
Y
Department of Oral Pathology, Hiroshima University, Faculty of Dentistry, Japan.
Takata
T
T
Ogawa
I
I
Kaneda
T
T
Sato
S
S
Takekoshi
T
T
Zhao
M
M
Miyauchi
M
M
Nikai
H
H
D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D002294:Carcinoma, Squamous Cell / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D053148:Caspase 3; D020169:Caspases / Q000096:biosynthesis / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D050760:Cyclin-Dependent Kinase Inhibitor p27; D003546:Cysteine Endopeptidases / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D008869:Microtubule-Associated Proteins / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D009061:Mouth Mucosa / Q000166:cytology / Q000187:drug effects; D009062:Mouth Neoplasms / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D009097:Multienzyme Complexes / Q000187:drug effects* / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex; D011498:Protein Precursors / Q000096:biosynthesis / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000187:drug effects; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000648:ultrastructure; D025521:Tumor Suppressor Proteins
D018797:Cell Cycle Proteins; D007976:Leupeptins; D008869:Microtubule-Associated Proteins; D009097:Multienzyme Complexes; D016376:Oligonucleotides, Antisense; D011480:Protease Inhibitors; D011498:Protein Precursors; D019253:Proto-Oncogene Proteins c-bcl-2; D025521:Tumor Suppressor Proteins; C089486:carbobenzoxy-leucyl-leucyl-norvalinal; C067713:lactacystin; D050760:Cyclin-Dependent Kinase Inhibitor p27; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000111:Acetylcysteine