The effect of proteasome inhibition on p53 degradation and proliferation in tonsil epithelial cells.
OBJECTIVE
To determine whether proteasome inhibition could reverse E6-mediated p53 degradation, cause selective growth inhibition, and induce apoptosis in human papillomavirus E6-transformed primary tonsil epithelial cells.


METHODS
Primary human and mouse tonsil epithelial cell lines were transformed with a retrovirus containing human papillomavirus 16 oncogenes. MG132 was used to inhibit proteasome degradation in vitro and in vivo, and biochemical assays regarding p53 and apoptosis were performed.


RESULTS
In cells that express E6, proteasome inhibition with MG132 restored p53 protein levels and decreased proliferation in a dose-dependent fashion that was significantly more pronounced compared with controls. However, inhibition of proliferation occurred at a lower concentration than restoration of p53 protein expression. Also, wild-type and p53 knockout mouse tonsil epithelial cells that express E6 had near-identical inhibition of growth, suggesting that growth inhibition was p53 independent. In vivo studies did not demonstrate any growth inhibition.


CONCLUSIONS
The findings suggest that proteasome inhibition preferentially inhibits proliferation in cells expressing E6 through a p53-independent mechanism.
Harris
George F
GF
Department of Otolaryngology-Head and Neck Surgery, The University of Iowa, 200 Hawkins Dr, Iowa City, IA 52242-1078, USA.
Anderson
Mary E
ME
Lee
John H
JH
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3 / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000187:drug effects / Q000473:pathology*; D006258:Head and Neck Neoplasms / Q000821:virology*; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D014066:Palatine Tonsil / Q000166:cytology* / Q000821:virology; D011480:Protease Inhibitors / Q000494:pharmacology*; D061988:Proteasome Inhibitors; D012097:Repressor Proteins / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
C068651:E6 protein, Human papillomavirus type 16; D007976:Leupeptins; D009856:Oncogene Proteins, Viral; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53; D053148:Caspase 3; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde