title: Signals that dictate nuclear localization of human papillomavirus type 16 oncoprotein E6 in living cells.
abstract: Human papillomavirus (HPV) type 16 E6 (16E6) is an oncogenic, multifunctional nuclear protein that induces p53 degradation and perturbs normal cell cycle control, leading to immortalization and transformation of infected keratinocytes and epithelial cells. Although it is unclear how 16E6 disrupts the epigenetic profile of host genes, its presence in the nucleus is a key feature. The present report describes intrinsic properties of 16E6 that influence its nuclear import in living cells. When the coding region of full-length 16E6 was inserted in frame into the C terminus of green fluorescent protein (GFP), it effectively prevented the 16E6 pre-mRNA from being spliced and led to the expression of a GFP-E6 fusion which localized predominantly to the nucleus. Further studies identified three novel nuclear localization signals (NLSs) in 16E6 that drive the protein to accumulate in the nucleus. We found that all three NLS sequences are rich in positively charged basic residues and that point mutations in these key residues could abolish the retention of 16E6 in the nucleus as well as the p53 degradation and cell immortalization activities of the protein. When inserted into corresponding regions of low-risk HPV type 6 E6, the three NLS sequences described for 16E6 functioned actively in converting the normally cytoplasmic HPV type 6 E6 into a nuclear protein. The separate NLS sequences, however, appear to play different roles in nuclear import and retention of HPV E6. The discovery of three unique NLS sequences in 16E6 provides new insights into the nuclear association of 16E6 which may reveal other novel activities of this important oncogenic protein.
authors.affiliation: HIV and AIDS Malignancy Branch. Experimental Immunology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Mingfang
authors.initials: M
authors.lastname: Tao
authors.forename: Michael
authors.initials: M
authors.lastname: Kruhlak
authors.forename: Shuhua
authors.initials: S
authors.lastname: Xia
authors.forename: Elliot
authors.initials: E
authors.lastname: Androphy
authors.forename: Zhi-Ming
authors.initials: ZM
authors.lastname: Zheng
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002472:Cell Transformation, Viral; D002522:Chlorocebus aethiops; D017353:Gene Deletion; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D019913:Nuclear Localization Signals / Q000737:chemistry* / Q000378:metabolism; D009856:Oncogene Proteins, Viral / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D027383:Papillomaviridae / Q000378:metabolism / Q000472:pathogenicity*; D012097:Repressor Proteins; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: C068651:E6 protein, Human papillomavirus type 16; D019913:Nuclear Localization Signals; D009856:Oncogene Proteins, Viral; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53