Complete switch from Mdm2 to human papillomavirus E6-mediated degradation of p53 in cervical cancer cells.
The E6 oncoprotein of human papillomaviruses (HPVs) that are associated with cervical cancer utilizes the cellular ubiquitin-protein ligase E6-AP to target the tumor suppressor p53 for degradation. In normal cells (i.e., in the absence of E6), p53 is also a target of the ubiquitin-proteasome pathway. Under these conditions, however, p53 degradation is mediated by Mdm2 rather than by E6-AP. Here we show in a mutational analysis that, surprisingly, the structural requirements of p53 to serve as a proteolytic substrate differ between E6 proteins derived from different HPV types and, as expected, between Mdm2 and E6 proteins in vitro and in vivo. Stable expression of such mutants in HPV-negative and HPV-positive cell lines demonstrates that in HPV-positive cancer cells, the E6-dependent pathway of p53 degradation is not only active but, moreover, is required for degradation of p53, whereas the Mdm2-dependent pathway is inactive. Because the p53 pathway was reported to be functional in HPV-positive cancer cells, this finding indicates clearly that the ability of the E6 oncoprotein to target p53 for degradation is required for the growth of HPV-positive cancer cells.
Hengstermann
A
A
Institute of Biochemistry I, Medical Faculty, University of Cologne, Joseph-Stelzmann-Strasse 52, 50931 Köln, Germany.
Linares
L K
LK
Ciechanover
A
A
Whitaker
N J
NJ
Scheffner
M
M
D005260:Female; D006207:Half-Life; D006801:Humans; D009687:Nuclear Proteins; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism*; D027383:Papillomaviridae / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity; D014162:Transfection; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D014452:Ubiquitins / Q000378:metabolism; D002583:Uterine Cervical Neoplasms
C118860:E6 protein, Human papillomavirus type 6; D009687:Nuclear Proteins; D009856:Oncogene Proteins, Viral; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D016159:Tumor Suppressor Protein p53; D014452:Ubiquitins; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2