title: Brd4 regulation of papillomavirus protein E2 stability.
abstract: The papillomavirus (PV) E2 protein is an important regulator of the viral life cycle. It has diverse roles in viral transcription, DNA replication, and genome maintenance. Our laboratory has previously identified the cellular bromodomain protein Brd4 as a key interacting partner of E2. Brd4 mediates the transcriptional activation function of E2 and plays an important role in viral genome maintenance in dividing cells. E2 interacts with the C-terminal domain (CTD) of Brd4, and the CTD functions in a dominant-negative manner through binding E2 and interfering with E2's interaction with the full-length Brd4 protein. Previous studies have shown that PV E2 proteins are short lived; however, the mechanisms regulating their stability and degradation have not yet been well established. In this study, we explored the role of Brd4 in the regulation of bovine PV 1 (BPV1) and human PV 16 (HPV16) E2 stability. Expression of the Brd4 CTD dramatically increases E2 levels. Both BPV1 E2 and HPV16 E2 are regulated by ubiquitylation, and Brd4 CTD expression blocks this ubiquitylation, thus stabilizing the E2 protein. Furthermore, we have identified the cullin-based E3 ligases and specifically cullin-3 as potential components of the ubiquitylation machinery that targets both BPV1 and HPV16 E2 for ubiquitylation. Expression of the Brd4 CTD blocks the interaction between E2 and the cullin-3 complex. In addition to Brd4's role in mediating E2 transcription and genome tethering activities, these data suggest a potential role for Brd4 in regulating E2 stability and protein levels within PV-infected cells.
authors: Department of Pathology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA.
authors: Gang
authors: G
authors: Zheng
authors: Michal-Ruth
authors: MR
authors: Schweiger
authors: Gustavo
authors: G
authors: Martinez-Noel
authors: Leon
authors: L
authors: Zheng
authors: Jennifer A
authors: JA
authors: Smith
authors: J Wade
authors: JW
authors: Harper
authors: Peter M
authors: PM
authors: Howley
mesh_terms: D000818:Animals; D052688:Bovine papillomavirus 1 / Q000502:physiology*; D002417:Cattle; D018797:Cell Cycle Proteins; D044842:Cullin Proteins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D052162:Human papillomavirus 16 / Q000502:physiology*; D006801:Humans; D009687:Nuclear Proteins / Q000502:physiology*; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D055550:Protein Stability; D014157:Transcription Factors / Q000502:physiology*; D054875:Ubiquitination; D014764:Viral Proteins / Q000378:metabolism*; D000092468:Bromodomain Containing Proteins
chemical_list: D018797:Cell Cycle Proteins; D044842:Cullin Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D009856:Oncogene Proteins, Viral; D014157:Transcription Factors; D014764:Viral Proteins; C441289:BRD4 protein, human; D000092468:Bromodomain Containing Proteins; C503645:CUL3 protein, human; C051550:E2 protein, Bovine papillomavirus; C076036:oncogene protein E2, Human papillomavirus type 1