E1 ^∧ E4 Protein of Human Papillomavirus Type 16 Associates with Mitochondria

Abstract

The human papillomavirus (HPV) E1∧ E4 protein is the most abundantly expressed viral protein in HPVinfected epithelia. It possesses diverse activities, including the ability to bind to the cytokeratin network and to DEAD-box proteins, and in some cases induces the collapse of the former. E1∧ E4 is also able to prevent the progression of cells into mitosis by arresting them in the G 2 phase of the cell cycle. In spite of these intriguing properties, the role of this protein in the life cycle of the virus is not clear. Here we report that after binding to and collapsing the cytokeratin network, the HPV type 16 E1 ∧ E4 protein binds to mitochondria. When cytokeratin is not present in the cell, E1∧ E4 appears associated with mitochondria soon after its synthesis. The leucine cluster within the N-terminal portion of the E1 ∧ E4 protein is pivotal in mediating this association. After the initial binding to mitochondria, the E1 ∧ E4 protein induces the detachment of mitochondria from microtubules, causing the organelles to form a single large cluster adjacent to the nucleus. This is followed by a severe reduction in the mitochondrial membrane potential and an induction of apoptosis. HPV DNA replication and virion production occur in terminally differentiating cells which are keratin-rich, rigid squamae that exfoliate after completion of the differentiation process. Perturbation of the cytokeratin network and the eventual induction of apoptotic properties are processes that could render these unyielding cells more fragile and ease the exit of newly synthesized HPVs for subsequent rounds of infection.Papillomaviruses infect the skin and mucosa of many different hosts, including humans (1). In order to multiply in these tissues, these viruses have evolved and adapted their life cycle to the biology of the epithelium. Human papillomaviruses (HPVs) gain entry into the epithelium via microlesions, which allow them to infect the epithelial basal cells. While the viral episomes remain at a low copy number in basal cells, cellular proliferation leads to the generation of a pool of cells that contain viral DNA. Amplification of the HPV genome and the production of infectious virions do not occur until the infected cells undergo terminal differentiation (11,19). The amplification of papillomavirus DNA usually begins when infected keratinocytes differentiate into spinous cells (17). This is followed by the production of viral capsid proteins and the assembly of infectious particles. In order to replicate in differentiating cells, the E6 and E7 proteins of HPV stimulate the production of proteins required for DNA synthesis. This causes the differentiating cells to enter S phase (24, 26). The E6 and E7 proteins are able to do this largely because they can inactivate the p53 (32) and pRb (15, 27) proteins, respectively. It is noteworthy that in spite of inactivating two major tumor suppressor functions in the cell, normal productive HPV infections do not cause uncontrolled cellular proliferation leading to tumorigenesis. At most, hyp...

Genomic and phylogenetic analysis of two novel bovine papillomaviruses, BPV-9 and BPV-10

“…E1^E4 protein is abundantly expressed in the cytoplasm of terminally differentiated epithelial cells in the productive phase of the viral life cycle (Doorbar et al, 1997). E1^E4 has also been implicated in inducing apoptosis (Raj et al, 2004), causing G2 arrest in the cell cycle (Davy et al, 2005; Nakahara et al, 2002) and aiding successful virus replication (Roberts et al, 2003) or viral egress (Bryan & Brown, 2000;Wang et al, 2004). However, the role of E1^E4 in the PV life cycle is still speculative.…”

Mecanismo De Infección Y Transformación Neoplásica Producido Por Virus Papiloma Humano en El Epitelio Cervical

“…La proteína E1-E4 es la mayoritariamente expresada en epitelios infectados por VPH (aproximadamente el 30% del contenido proteico celular), se sintetiza como proteína mixta, involucrando regiones génicas E1 (primeros cuatro aminoácidos) y E4 (25,26). Forma complejos hexaméricos, capaces de unirse a la red de citoqueratina de la célula, a través de su región N-terminal produciendo su desestabilización.…”

“…Su región intermedia (aminoácidos 17 a 45) detiene el ciclo celular en G2, a través de la unión a ciclinas y kinasas dependientes de ciclinas y por bloqueo de E7. Por estos mecanismos, la célula pierde soporte estructural por la alteración del citoesqueleto, produciendo daño mitocondrial y del metabolismo energético, además de apoptosis (26). Es posible que durante esta etapa de amplificación del genoma viral, la inhibición de las oncoproteínas E6 y E7, el daño al citoesqueleto, el trastorno mitocondrial-energético y la apoptosis permitirían una mayor diseminación de la progenie viral, siempre que las proteínas de la cápside viral (L1 y L2) hayan sido sintetizadas, formando con el ADN viral nuevos viriones infectantes.…”

The Interaction between Human Papillomavirus Proteins and Cytoskeletal Filaments

“…HPV E1^E4 accumulates in differentiating cells of the upper epithelial layers. It is synthesized from a spliced mRNA, E1^E4, which encodes five amino acids from the E1 ORF spliced to the protein encoded by the E4 ORF , Doorbar et al, 1990, Nasseri et al, 1987 as cited in Raj et al, 2004). The first activity described for the 10-kDa HPV type 16 (HPV16) E1^E4 protein was its ability to bind and collapse the cytokeratin network (Doorbar et al, 1991 as cited in Raj et al, 2004).…”