scholarly journals Human Papillomavirus Oncoproteins E6 and E7 Independently Abrogate the Mitotic Spindle Checkpoint

1998 ◽  
Vol 72 (2) ◽  
pp. 1131-1137 ◽  
Author(s):  
Jennifer T. Thomas ◽  
Laimonis A. Laimins
Keyword(s):  
Human Papillomavirus ◽  
High Risk ◽  
Mitotic Spindle ◽  
Spindle Checkpoint ◽  
Human Keratinocytes ◽  
Mitotic Checkpoint ◽  
Cell Cycle Checkpoint ◽  
Checkpoint Control ◽  
Mitotic Spindle Checkpoint ◽  
E6 And E7

ABSTRACT The E6 and E7 genes of the high-risk human papillomavirus (HPV) types encode oncoproteins, and both act by interfering with the activity of cellular tumor suppressor proteins. E7 proteins act by associating with members of the retinoblastoma family, while E6 increases the turnover of p53. p53 has been implicated as a regulator of both the G1/S cell cycle checkpoint and the mitotic spindle checkpoint. When fibroblasts from p53 knockout mice are treated with the spindle inhibitor nocodazole, a rereplication of DNA occurs without transit through mitosis. We investigated whether E6 or E7 could induce a similar loss of mitotic checkpoint activity in human keratinocytes. Recombinant retroviruses expressing high-risk E6 alone, E7 alone, and E6 in combination with E7 were used to infect normal human foreskin keratinocytes (HFKs). Established cell lines were treated with nocodazole, stained with propidium iodide, and analyzed for DNA content by flow cytometry. Cells infected with high-risk E6 were found to continue to replicate DNA and accumulated an octaploid (8N) population. Surprisingly, expression of E7 alone was also able to bypass this checkpoint. Cells expressing E7 alone exhibited increased levels of p53, while those expressing E6 had significantly reduced levels. The p53 present in the E7 cells was active, as increased levels of p21 were observed. This suggested that E7 bypassed the mitotic checkpoint by a p53-independent mechanism. The levels of MDM2, a cellular oncoprotein also implicated in control of the mitotic checkpoint, were significantly elevated in the E7 cells compared to the normal HFKs. In E6-expressing cells, the levels of MDM2 were undetectable. It is possible that abrogation of Rb function by E7 or increased expression of MDM2 contributes to the loss of mitotic spindle checkpoint control in the E7 cells. These findings suggest mechanisms by which both HPV oncoproteins contribute to genomic instability at the mitotic checkpoint.

scholarly journals Different DNA damage and cell cycle checkpoint control in low- and high-risk human papillomavirus infections of the vulva

2011 ◽  
Vol 130 (12) ◽  
pp. 2874-2885 ◽  
Author(s):  
Lindy A.M. Santegoets ◽  
Romy van Baars ◽  
Annelinde Terlou ◽  
Claudia Heijmans-Antonissen ◽  
Sigrid M.A. Swagemakers ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Dna Damage ◽  
Human Papillomavirus ◽  
High Risk ◽  
Cell Cycle Checkpoint ◽  
Checkpoint Control ◽  
Papillomavirus Infections ◽  
Cycle Checkpoint

scholarly journals Roles of the E6 and E7 Proteins in the Life Cycle of Low-Risk Human Papillomavirus Type 11

2004 ◽  
Vol 78 (5) ◽  
pp. 2620-2626 ◽  
Author(s):  
Stephen T. Oh ◽  
Michelle S. Longworth ◽  
Laimonis A. Laimins
Keyword(s):  
Human Papillomavirus ◽  
Life Cycle ◽  
High Risk ◽  
Translation Termination ◽  
Human Keratinocytes ◽  
Low Risk ◽  
Hpv E6 ◽  
E6 And E7 ◽  
Substitution Mutations ◽  
E7 Proteins

ABSTRACT Many important functions have been attributed to the high-risk human papillomavirus (HPV) E6 and E7 proteins, including binding and degradation of p53 as well as interacting with Rb proteins. In contrast, the physiological roles of the low-risk E6 and E7 proteins remain unclear. Previous studies demonstrated that the high-risk E6 and E7 proteins also play roles in the productive life cycle by facilitating the maintenance of viral episomes (J. T. Thomas, W. G. Hubert, M. N. Ruesch, and L. A. Laimins, Proc. Natl. Acad. Sci. USA 96:8449-8454, 1999). In order to determine whether low-risk E6 or E7 is similarly necessary for the stable maintenance of episomes, HPV type 11 (HPV-11) genomes that contained translation termination mutations in E6 or E7 were constructed. Upon transfection into normal human keratinocytes, genomes in which E6 function was abolished were unable to be maintained episomally. Transfection of genomes containing substitution mutations in amino acids conserved in high- and low-risk HPV types suggested that multiple protein domains are involved in this process. Examination of cells transfected with HPV-11 genomes in which E7 function was inhibited were found to exhibit a more complex phenotype. At the second passage following transfection, mutant genomes were maintained as episomes but at significantly reduced levels than in cells transfected with the wild-type HPV-11 genome. Upon further passage in culture, however, the episomal forms of these E7 mutant genomes quickly disappeared. These findings identify important new functions for the low-risk E6 and E7 proteins in the episomal maintenance of low-risk HPV-11 genomes and suggest that they may act in a manner similar to that observed for the high-risk proteins.

scholarly journals Genetic Analysis of High-Risk E6 in Episomal Maintenance of Human Papillomavirus Genomes in Primary Human Keratinocytes

2002 ◽  
Vol 76 (22) ◽  
pp. 11359-11364 ◽  
Author(s):  
Regina B. Park ◽  
Elliot J. Androphy
Keyword(s):  
Human Papillomavirus ◽  
Dna Replication ◽  
High Risk ◽  
Viral Replication ◽  
Human Keratinocytes ◽  
Binding Motif ◽  
Primary Human Keratinocytes ◽  
Hpv16 E6 ◽  
E6 And E7 ◽  
Episomal Maintenance

ABSTRACT Papillomaviruses possess small DNA genomes that encode five early (E) proteins. Transient DNA replication requires activities of the E1 and E2 proteins and a DNA segment containing their binding sites. The E6 and E7 proteins of cancer-associated human papillomavirus (HPV) transform cells in culture. Recent reports have shown that E6 and E7 are necessary for episomal maintenance of HPV in primary keratinocytes. The functions of E6 necessary for viral replication have not been determined, and to address this question we used a recently developed transfection system based on HPV31. To utilize a series of HPV16 E6 mutations, HPV31 E6 was replaced by its HPV16 counterpart. This chimeric genome was competent for both transient and stable replication in keratinocytes. Four HPV16 E6 mutations that do not stimulate p53 degradation were unable to support stable viral replication, suggesting this activity may be necessary for episomal maintenance. E7 has also been shown to be essential for episomal maintenance of the HPV31 genome. A point mutation in the Rb binding motif of HPV E7 has been reported to render HPV31 unable to stably replicate. Interestingly, HPV31 genomes harboring two of the three p53 degradation-defective E6 mutations combined with this E7 mutation were maintained as replicating episomes. These findings imply that the balance between E6 and E7 functions in infected cells is critical for episomal maintenance of high-risk HPV genomes. This model will be useful to dissect the activities of E6 and E7 necessary for viral DNA replication.

scholarly journals High-Risk Human Papillomavirus E7 Alters Host DNA Methylome and Represses HLA-E Expression in Human Keratinocytes

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Louis Cicchini ◽  
Rachel Z. Blumhagen ◽  
Joseph A. Westrich ◽  
Mallory E. Myers ◽  
Cody J. Warren ◽  
...  
Keyword(s):  
Human Papillomavirus ◽  
High Risk ◽  
Human Keratinocytes ◽  
Dna Methylome

Characterization of MAD2B and Other Mitotic Spindle Checkpoint Genes

Genomics ◽  
1999 ◽  
Vol 58 (2) ◽  
pp. 181-187 ◽  
Author(s):  
Daniel P. Cahill ◽  
Luis T. da Costa ◽  
Eleanor B. Carson-Walter ◽  
Kenneth W. Kinzler ◽  
Bert Vogelstein ◽  
...  
Keyword(s):  
Mitotic Spindle ◽  
Spindle Checkpoint ◽  
Mitotic Spindle Checkpoint ◽  
Checkpoint Genes

High-Risk Human Papillomavirus Affects Prognosis in Patients With Surgically Treated Oropharyngeal Squamous Cell Carcinoma

2006 ◽  
Vol 24 (36) ◽  
pp. 5630-5636 ◽  
Author(s):  
Lisa Licitra ◽  
Federica Perrone ◽  
Paolo Bossi ◽  
Simona Suardi ◽  
Luigi Mariani ◽  
...  
Keyword(s):  
Human Papillomavirus ◽  
High Risk ◽  
Oropharyngeal Cancer ◽  
Clinical Results ◽  
Hpv Dna ◽  
Additional Information ◽  
Second Tumors ◽  
E6 And E7 ◽  
Second Tumor ◽  
P16 Expression

Purpose Human papillomavirus (HPV) DNA tumors actively integrating the E6 and E7 oncogenes have a distinct biologic behavior resulting in a more favorable prognosis. To which extent the viral integration by itself, and/or the associated wild-type (wt) TP53 status, and/or a functional p16 contribute to prognosis is unclear. Patients and Methods To clarify how the presence of high-risk (HR) -HPV, TP53, and p16INK4a status interact with clinical outcome, we considered a retrospective series of 90 consecutive oropharyngeal cancer patients treated primarily with surgery. Results Seventeen (19%) patients showed integrated HPV 16 DNA (HPV positive), wt TP53 in all but two patients, normal p16INK4a in 15 assessable patients, and p16 expression in all 17 patients. Thirty-five patients (39%), two of whom were HPV positive, harbored TP53 mutations. p16INK4a deletion and p16 null immunophenotype occurred in 28 and 58 patients, respectively, and was similarly distributed in both patients with mutated TP53 (48% and 82%, respectively) and in patients with wt TP53 (46% and 77%, respectively). Statistical analysis showed that HPV-positive status significantly affects all investigated end points: overall survival (P = .0018), incidence of tumor relapse (P = .0371), and second tumor (P = .0152), whereas TP53 and p16INK4a status and p16 expression were not prognostic by themselves. Conclusion Our molecular and clinical results are in agreement with previous findings but provide additional information into the biologic mechanisms involved in HR-HPV oropharyngeal cancer in comparison to HPV-negative tumors. According to the reduced risk of relapse and second tumors associated with HR-HPV positivity of oropharyngeal cancer, the therapeutic strategy and follow-up procedures should be reviewed.

scholarly journals Human Papillomavirus E6 Proteins Mediate Resistance to Interferon-Induced Growth Arrest through Inhibition of p53 Acetylation

2007 ◽  
Vol 81 (23) ◽  
pp. 12740-12747 ◽  
Author(s):  
Christy Hebner ◽  
Melanie Beglin ◽  
Laimonis A. Laimins
Keyword(s):  
Human Papillomavirus ◽  
Human Fibroblasts ◽  
Antiviral Agents ◽  
Growth Arrest ◽  
Physiological Role ◽  
Human Keratinocytes ◽  
Hpv E6 ◽  
E6 And E7 ◽  
E7 Proteins ◽  
Mutant Forms

ABSTRACT The high-risk human papillomavirus (HPV) E6 and E7 proteins act cooperatively to mediate multiple activities in viral pathogenesis. For instance, E7 acts to increase p53 levels while E6 accelerates its rate of turnover through the binding of the cellular ubiquitin ligase E6AP. Interferons are important antiviral agents that modulate both the initial and persistent phases of viral infection. The expression of HPV type 16 E7 was found to sensitize keratinocytes to the growth-inhibitory effects of interferon, while coexpression of E6 abrogates this inhibition. Treatment of E7-expressing cells with interferon ultimately resulted in cellular senescence through a process that is dependent upon acetylation of p53 by p300/CBP at lysine 382. Cells expressing mutant forms of E6 that are unable to bind p300/CBP or bind p53 failed to block acetylation of p53 at lysine 382 and were sensitive to growth arrest by interferon. In contrast, mutant forms of E6 that are unable to bind E6AP remain resistant to the effects of interferon, demonstrating that the absolute levels of p53 are not the major determinants of this activity. Finally, p53 acetylation at lysine 382 was found not to be an essential determinant of other types of senescence such as that induced by overexpression of Ras in human fibroblasts. This study identifies an important physiological role for E6 binding to p300/CBP in blocking growth arrest of human keratinocytes in the presence of interferon and so contributes to the persistence of HPV-infected cells.

scholarly journals The ESCRT protein Chmp4c regulates mitotic spindle checkpoint signaling

2018 ◽  
Vol 217 (3) ◽  
pp. 861-876 ◽  
Author(s):  
Eleni Petsalaki ◽  
Maria Dandoulaki ◽  
George Zachos
Keyword(s):  
Mitotic Spindle ◽  
Spindle Checkpoint ◽  
Metaphase Plate ◽  
Membrane Remodeling ◽  
Mitotic Progression ◽  
Mitotic Spindle Checkpoint ◽  
Checkpoint Signaling ◽  
Checkpoint Proteins ◽  
Endosomal Sorting ◽  
Anaphase Onset

The mitotic spindle checkpoint delays anaphase onset in the presence of unattached kinetochores, and efficient checkpoint signaling requires kinetochore localization of the Rod–ZW10–Zwilch (RZZ) complex. In the present study, we show that human Chmp4c, a protein involved in membrane remodeling, localizes to kinetochores in prometaphase but is reduced in chromosomes aligned at the metaphase plate. Chmp4c promotes stable kinetochore–microtubule attachments and is required for proper mitotic progression, faithful chromosome alignment, and segregation. Depletion of Chmp4c diminishes localization of RZZ and Mad1-Mad2 checkpoint proteins to prometaphase kinetochores and impairs mitotic arrest when microtubules are depolymerized by nocodazole. Furthermore, Chmp4c binds to ZW10 through a small C-terminal region, and constitutive Chmp4c kinetochore targeting causes a ZW10-dependent checkpoint metaphase arrest. In addition, Chmp4c spindle functions do not require endosomal sorting complex required for transport–dependent membrane remodeling. These results show that Chmp4c regulates the mitotic spindle checkpoint by promoting localization of the RZZ complex to unattached kinetochores.

Sign in / Sign up

Export Citation Format

Share Document