Nuclear Import Strategies of High Risk HPV16 L1 Major Capsid Protein

Abstract

During the late phase of human papillomavirus (HPV) infection, the L1 major capsid proteins enter the nuclei of host epithelial cells and, together with the L2 minor capsid proteins, assemble the replicated viral DNA into virions. We investigated the nuclear import of the L1 major capsid protein of high risk HPV16. When digitonin-permeabilized HeLa cells were incubated with HPV16 L1 capsomeres, the L1 protein was imported into the nucleus in a receptor-mediated manner. HPV16 L1 capsomeres formed complexes with Kap ␣2␤1 heterodimers via interaction with Kap ␣2. Accordingly, nuclear import of HPV16 L1 capsomeres was mediated by Kap ␣2␤1 heterodimers, required RanGDP and free GTP, and was independent of GTP hydrolysis. Remarkably, HPV16 L1 capsomeres also interacted with Kap ␤2 and binding of RanGTP to Kap ␤2 did not dissociate the HPV16 L1⅐Kap ␤2 complex. Significantly, HPV16 L1 capsomeres inhibited the nuclear import of Kap ␤2 and of a Kap ␤2-specific M9-containing cargo. These data suggest that, during the productive stage of infection, while the HPV16 L1 major capsid protein enters the nucleus via the Kap ␣2␤1-mediated pathway to assemble the virions, it also inhibits the Kap ␤2-mediated nuclear import of host hnRNP A1 protein and, in this way, favors virion formation.Human papillomaviruses (HPVs) 1 are thought to be the primary causative agent in more than 90% of all cervical cancers, with HPV16 being the type most frequently found in these tumors. Approximately 500,000 new cases of cervical cancer are identified each year globally with nearly 300,000 deaths annually. About 85 genotypically distinct HPV genotypes have been isolated and characterized, with roughly half infecting the skin and the other half preferentially infecting oral/anogenital mucosal epithelial tissues. Mucosal HPVs have demonstrated varying degrees of oncogenic potential; high risk HPVs, such as types 16, 18, 31, and 45, are frequently detected in invasive cervical carcinomas, whereas the low risk types, such as types 6 and 11, are more often associated with benign exophytic condylomas (1).HPVs are small, nonenveloped, icosahedral DNA viruses that replicate in the nucleus of squamous epithelial cells. The virion particles (52-55 nm in diameter) consist of a single molecule comprising 8 kb of double-stranded circular DNA contained within a spherical capsid composed of 72 homopentameric L1 capsomeres and of L2 minor capsid protein. The number of L2 molecules per capsid has been estimated at 36 (2) or 12 (3). L1 protein is capable of self-assembly both in vivo and in vitro into capsid-like structures, referred to as virus-like particles (4 -9). L1 is stable in two oligomeric configurations: homopentameric capsomeres and capsids composed of 72 capsomeres. The capsids can be disassembled into capsomeres quantitatively by an agent that reduces disulfide bonds and reassembled by removing the reducing agent (10, 11). The L1 capsid proteins of HPVs seem to enter the nucleus of host cells twice during the virus life cycle: immediately after the vi...

Human Immunodeficiency Virus Type 1 (HIV-1) Induces the Cytoplasmic Retention of Heterogeneous Nuclear Ribonucleoprotein A1 by Disrupting Nuclear Import

“…Refs. [45][46][47]. This phenomenon has been attributed to a disruption in its nucleocytoplasmic shuttling activity.…”

The L2 Minor Capsid Protein of Human Papillomavirus Type 16 Interacts with a Network of Nuclear Import Receptors

“…Interestingly, bovine papillomavirus type 1 (BPV1) pseudovirions containing wild-type L1 without L2 protein or with mutant L2 protein lacking either an N-terminal or a C-terminal positively charged domain were noninfectious, despite efficient binding to the cell surface (20). This suggests that L2 also plays an essential role(s) in the infectious process via its N and C termini at a step after the binding of virions to the cells.We have previously established that the L1 major capsid proteins of both high-risk HPV16 and -45 and low-risk HPV11 form complexes with Kap␣ 2 ␤ 1 heterodimers via interaction with the Kap␣ 2 adapter and enter the nucleus via a classical Kap␣ 2 ␤ 1 -mediated import pathway (14,16,17). Virtually nothing is known about the nuclear import pathways for the L2 minor capsid proteins of different papillomaviruses.…”

“…We have previously established that the L1 major capsid proteins of both high-risk HPV16 and -45 and low-risk HPV11 form complexes with Kap␣ 2 ␤ 1 heterodimers via interaction with the Kap␣ 2 adapter and enter the nucleus via a classical Kap␣ 2 ␤ 1 -mediated import pathway (14,16,17). Virtually nothing is known about the nuclear import pathways for the L2 minor capsid proteins of different papillomaviruses.…”

Evaluation of the Association with Cervical Cancer of Polymorphisms in Syndecan-1, a Heparan Sulfate Proteoglycan Involved with Viral Cell Entry

“…Despite the lack of direct data on differential expression of SDC-1 in different types of cervical cells, it is possible that there might be specific localization that ties to disease risk. Alternatively, mechanisms of viral cell attachment and entry might vary between different HPV types (13)(14)(15)(16)(17). If so, and if HPV-18 infectivity is preferentially affected by the SDC-1 Pro-27 polymorphism, one might expect to observe an association between SDC-1 Pro-27 polymorphisms that are specific to cervical adenocarcinomas because HPV-18 accounts for a larger fraction of cervical adenocarcinomas compared with squamous cell carcinomas (18)(19)(20)(21)(22)(23)(24)(25).…”