HPV 5 and 8 E6 abrogate ATR activity resulting in increased persistence of UVB induced DNA damage.
The role of the E6 oncoprotein from high-risk members of the α human papillomavirus genus in anogenital cancer has been well established. However, far less is known about the E6 protein from the β human papillomavirus genus (β-HPVs). Some β-HPVs potentially play a role in non-melanoma skin cancer development, although they are not required for tumor maintenance. Instead, they may act as a co-factor that enhances the carcinogenic potential of UV damage. Indeed, the E6 protein from certain β-HPVs (HPV 5 and 8) promotes the degradation of p300, a histone acetyl transferase involved in UV damage repair. Here, we show that the expression of HPV 5 and 8 E6 increases thymine dimer persistence as well as the likelihood of a UVB induced double strand break (DSB). Importantly, we provide a mechanism for the increased DNA damage by showing that both extended thymine dimer persistence as well as elevated DSB levels are dependent on the ability of HPV 8 E6 to promote p300 degradation. We further demonstrate that HPV 5 and 8 E6 expression reduces the mRNA and protein levels of ATR, a PI3 kinase family member that plays a key role in UV damage signaling, but that these levels remain unperturbed in cells expressing a mutated HPV 8 E6 incapable of promoting p300 degradation. We confirm that the degradation of p300 leads to a reduction in ATR protein levels, by showing that ATR levels rebound when a p300 mutant resistant to HPV 8 mediated degradation and HPV 8 E6 are co-transfected. Conversely, we show that ATR protein levels are reduced when p300 is targeted for degradation by siRNA. Moreover, we show the reduced ATR levels in HPV 5 and 8 E6 expressing cells results in delayed ATR activation and an attenuated ability of cells to phosphorylate, and as a result accumulate, p53 in response to UVB exposure, leading to significantly reduced cell cycle arrest. In conclusion, these data demonstrate that β-HPV E6 expression can enhance the carcinogenic potential of UVB exposure by promoting p300 degradation, resulting in a reduction in ATR levels, which leads to increased thymine dimer persistence and increased UVB induced DSBs.
Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America.
Nicholas A
NA
Wallace
Kristin
K
Robinson
Heather L
HL
Howie
Denise A
DA
Galloway
D064007:Ataxia Telangiectasia Mutated Proteins; D052686:Betapapillomavirus / Q000378:metabolism*; D059447:Cell Cycle Checkpoints / Q000528:radiation effects; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D053903:DNA Breaks, Double-Stranded; D006801:Humans; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011740:Pyrimidine Dimers; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering; D012878:Skin Neoplasms / Q000821:virology; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D014466:Ultraviolet Rays; D050880:p300-CBP Transcription Factors / Q000235:genetics / Q000378:metabolism*; D000099224:p300-CBP-Associated Factor
D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins; D009856:Oncogene Proteins, Viral; D017346:Protein Serine-Threonine Kinases; D011740:Pyrimidine Dimers; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D050880:p300-CBP Transcription Factors; D000099224:p300-CBP-Associated Factor; C466081:E6 protein, Human papillomavirus type 8; C487708:E6 protein, human papillomavirus type 5; C576597:ATR protein, human