Human Papillomaviruses and Polyomaviruses

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Human Papillomaviruses and Polyomaviruses
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Introduction Features common to all
papillomaviruses Circular double stranded DNA
genome within an icosahedral capsid Limited
genetic capacity in 8kbp genome Encodes capsid
proteins, and non-structural proteins that
promote viral DNA replication, and inactivate
important cell cycle checkpoint proteins
retinoblastoma (RB) and p53 Causative agents of
papillomas on cutaneous skin and mucosal surfaces
(called warts when found on skin and chondylomas
on mucosal surfaces and genitalia) Some
serotypes are specifically associated with
cervical dysplasia and carcinoma (types 16, 18,
31, 35)
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Family name Papillomaviridae Closely related
morphologically to Polyomaviridae family with
whom they were originally grouped and
collectively called Papovaviridae, an acronym
derived from the three main branches of the
family papillomavirus, polyomavirus and simian
vaculating agent (SV40)
Polyomavirus and SV40 were studied extensively as
paradigms of tumor viruses The existence of
promoter/enhancer regions and of mRNA splicing
was first recognized in these viruses There are
two human polyomavirus BK and JC SV40-like
viruses have been isolated from human tumors
Cryo-EM reconstruction of HPV
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Classification gt120 human serotypes, with gt80
fully sequenced Numbered in order of
discovery Type designation indicates gt10
sequence divergence in three genes E6, E7 and
L1 all other genes are stable
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HPV genome - schematic representation
1 2 3
E7
E1
E5
L2
Open Reading Frames
E6
E2
L1
URR
E4
Poly - A
Poly - A
0 1 2 3
4 5 6
7 8
Kilobase
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Early region 6 E6 protein of oncogenic HPVs
binds to the p53 tumor suppressor gene product
and abrogates it activity by accelerating its
degradation
Noncoding Upstream Regulatory Region Contributes
to the control of DNA replication and
transcription of ORFs
Early region 7 E7 protein of oncogenic HPVs
bind to the tumor suppressor gene product
Retinoblastoma protein (RB) and related
proteins, thus inhibiting their function
Late region 1 L1 protein is the major capsid
protein
URR
E6
E7
Poly - A
Late region 2 L2 protein is the minor capsid
protein
L1
E1
Early region 1 E1 protein involved in viral
plasmid replication
Early region 5 E5 protein is located in the
cellular membrane, prevents acidification of
endosomes, and can stimulate the transformating
activity of epidermal growth factor receptor
and contribute to oncogenicity
Poly - A
L2
E2
E4 /
E5 /
Early region 2 E2 protein is an important
modulator of viral transcription and play a
role in viral replication
Early region 4 E4 proteins form filamentous
cytoplasmic networks and share the same cellular
distribution. They appear to play a role in
viral replication
HPV Genome Structure
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• Replication cycle
• The replication cycle of HPVs is intimately
  associated with the differentiation state of the
  epithelial cell
• following introduction of the virus into the
  basal squamous epithelial cell following breaks
  in the skin or mucous membrane, early viral gene
  expression (E1, E2, E5, E6 and E7) and
  steady-state viral DNA replication occurs,
  ensuring that as the basal cell divides, both
  basal and supra-basal daughter cells both contain
  viral DNA in the form of extra-chromosomal
  episomes
• as cells move upwards in the epithelium and
  differentiate (exemplified by keratin 1 and 10
  expression), late gene expression (E4, L1, L2)
  and vegetative viral DNA replication begins
• virion assembly occurs in the upper spinous
  layers, coincident with disintegration of nucleus
  and other cellular organelles, and virus is shed
  in the stratum corneum.
• little or no host cell death and inflammation
  associated with the replication cycle

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HPV infection and replication in cervical
epithelial cells
Columnar epithelial cell
Infection
Shedding
L1 L2 expression
Squamous epithelial cell
Transformation zone
Basement membrane
Basal epithelial cell
E1, E2, E4-E7 expression
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Malignant transformation of the cervix
E7
E7
E2F
RB
RB
E2F
E2F
E6
E6
P53
P53
P53
Cervical intraepithelial neoplasia (CIN)
HPV transformed epithelial cell
Invasive cervical cancer
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• Clinical manifestations
• breaks in epithelium necessary to gain access to
  basal epithelial cells
• incubation period may be from 2-6 months
  epithelial dysplasias (common warts on
  keratinized epithelium) can be found on hands and
  feet condylomas, on mucosal epithelium, in the
  larynx and oral cavity, as well as genitalia and
  anus
• expression of E5, E6 and E7 can drive
  hyper-proliferation and dysplasia of cells above
  the basal layer
• associated parakeratosis (persistence of the
  nuclei of keratinocytes as they rise into the
  stratum corneum) and hyperkeratosis (hypertrophy
  of the stratum corneum) which produces the
  papillomatous cytoarchitecture of warts or
  chondylomas
• except for those serotypes associated with
  cervical carcinoma, dysplasias eventually regress

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• Cutaneous warts (plantar, common and plane warts)
• single or clusters of slightly raised papules,
  1cm in diameter found on palms, fingers, soles,
  neck and face
• 50-90 spontaneously resolve within 1-5y
• Epidermodysplasia verruciformis
• autosomal recessive disease with flat crusty,
  wart appearance but covering areas of the face,
  torso and upper extremities
• usually appear in first decade of life, in 1/3
  of young adults, these undergo malignant
  transformation into invasive squamous cell
  carcinoma on sun-exposed areas

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• Anogenital warts
• hyperkaratotic papules either sessile or attached
  to skin by short, broad peduncle
• range in size from 1mm to several
• centimeters in areas when join together
• usually on the penile shaft of circumcised males
  and perianal in MSM
• in women usually on posterior vaginal
• orifice

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• Recurrent respiratory papillomatosis
• most common laryngeal neoplasm in children and
  usually results from vertical transmission of
  human papillomavirus at birth
• usually multiple, papillomas most commonly
• occur in the vocal cords and ventricular bands
• but can involve any part of the larynx
• most common in children between two and
• four years of age
• usual presenting symptom is hoarseness,
• but some patients have stridor and other
• signs of laryngeal obstruction.

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• Epidemiology
• transmission by direct contact with lesions of
  infected individuals or by contact with
  environmental surfaces harboring virus
• incidence of common warts is highest in older
  children and adults with 75 life time risk of
  infection with one or more strains first
  acquisition of HPV occurs with sexual debut (75
  of those who will be infected, were infected by
  age 18)
• approximately 75 of US population has
  experienced one or more HPV infections 60 of
  population are HPV antibody positive but DNA and
  lesion negative 10 of population is DNA
  positive but lesion negative, 4 of population
  are DNA positive and display sub-clinical
  changes, and 1 have genital warts
• 5 million new cases of genital infection per
  year, with 10 presenting with symptomatic
  genital warts
• increased incidence of genital warts in US
  predicted to result in increased incidence of
  cervical cancer 10-30 years in the future

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• Pathogenesis
• Low-grade intraepithelial lesions support
  productive viral replication an unknown number
  of high-risk HPV infections progress to
  high-grade cervical intraepithelial neoplasia
  (HGCIN)
• this progression of untreated lesions to
  microinvasive and invasive cancer is associated
  with the integration of the HPV genome into the
  host chromosomes with associated loss or
  disruption of E2, and subsequent upregulation of
  E6 and E7 oncogene expression
• E6 targets p53 cell cycle checkpoint protein
  for ubiquitylation and destruction in the
  proteosome, while E7 - binds Rb and promotes its
  proteosomal destruction
• consequently, normal cell cycle checkpoints are
  lost and unregulated DNA replication can lead to
  chromosomal damage, suppression of apoptosis, and
  cell proliferation
• Paradoxlow risk HPV strains also encode E6 and
  E7 proteins that can function to degrade p53 and
  Rb why is HPV16 high risk?

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• Pathogenesis, cont.
• Cervical cancer the most frequently diagnosed
  cancer of women, accounting for ¼ of all cancers
  in women 90 of cervical carcinomas contain HPV
  DNA squamous cell carcinoma represents the
  majority of cervical cancers and is associated
  with presence of high risk serotypes 16, 18, 31
  and, 35 cervical carcinoma rarely found in
  virgins, and its incidence increases with the
  number of sexual partners
• Head and neck papillomas includes laryngeal,
  recurrent respiratory and nasal papillomas are
  caused by low risk genital-mucosal strains
  HPV-6 and -11
• Oral cavity papillomas primarily with HPV-6,
  11, and 57
• Oral cancers 20 are HPV associated, risk
  factors for oral cancers include cigarette
  smoking and alcohol consumption a subset appear
  to be attributable to HPV mainly on tonsils,
  tonsillar fossa, base of the tongue, and soft
  palette HPV16 most frequent type isolated, types
  6, 11, and 57 less frequently

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• Diagnosis
• Pap smears identify cervical dysplasia specific
  strains are identified by PCR
• genital warts are diagnosed by visual inspection
• cervical cell changes (early signs of cervical
  cancer) can be identified by routine Pap tests.
  The HPV DNA test (PCR) can identify high-risk HPV
  types on a womans cervix
• Prevention
• Limiting number of sexual partners decreases
  incidence of infection, regular Pap smears main
  defense against invasive disease, followed by
  surgical intervention
• virus-like particle (VLP) vaccines
• Gardasil induces immune responses to L1 proteins
  of HPV 6, 11, and 16 and 18), which together
  cause 90 of genital warts and 90 of cervical
  cancer, respectively
• Cervarix only targets HPV 16 and 18
• Treatment
• ? surgery or cryotherapy for removal of warts,
  though recurrence is common

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• Human Polyomaviruses
• Introduction
• JCV and BKV are members of the polyomaviridae
  family
• dsDNA genomes within icosahedral capsids
  consisting of 72 pentameric capsomers
• first isolated in 1971 (JCV-brain tissue of
  patient with progressive multifocal
  leukoencephalopathy (PML) BKV from urine of
  renal transplant patient)
• Epidemiology
• BKV first acquired by age 3-4 JCV by age
• 10-14, 60-80 of adults are seropositive for
• both
• in pre-HIV era PML was seen in older adults
• with hematologic malignancies
• now seen in 5 of HIV/AIDS patients

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Virus replication BKV and JCV share 75
nucleotide sequence homology 70 with
SV40 smaller genome compared to
papillomaviruses (5 kbp v. 8 kbp genomes
divided into two regions, early and late,
transcribed from opposite DNA strands Early
proteins LT, MT and sT antigens expressed from
differentially spliced mRNAs Late, capsid
proteins VP1, VP2 and VP3 also expressed from
differentially spliced mRNAs
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Pathogenesis acquisition by inhalation or close
contact primary site of replication in
oropharynx, followed by viremia and seeding of
kidneys where clinical latent infection is
established DNA and capsid antigen detected in
mononuclear cells of patients with PML or
AIDS neuropathology of PML likely due to
infection of oligodendrocytes (viremic spread of
reactivated virus) leading to decreased myelin
production and de-myelination
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PML focal neurological defects due to
demyelination parieto-occipital brain
involvement associated with muscle weakness, gait
disturbance, speech defect, or visual blind
spot cerebellum involvement associated with
broadlegged gait and imbalance Diagnosis CT or
MRI lumbar puncture for JCV PCR Treatment none,
except for highly active antiretroviral therapy(
HAART) in AIDS patients
HE staining of PML brain biopsy black arrows
point out some of the reactive astrocytes blue
arrow points toward an oligodendrocyte nucleus
which has been markedly enlarged with viral
particles, giving it a magenta color
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• BK nephropathy
• no evidence that BKV causes
• disease in the immune competent
• population
• possible route of infection through
• contaminated food or water or
• respiratory spread
• remains latent in lymphocytes,
• urogenital tract, and brain but may
• be reactivated if the host becomes
• immunocompromised.
• especially associated with disease in renal
  transplant patients thought to cause graft
  failure in 2-5 of this population
• treatment is to decrease immunosuppression as
  much as possible without causing rejection
• Cidofovir appears to reduce BKV-associated
  nephropathy

viral inclusions and cellular changes in BK
nephropathy are seen in tubular epithelium of a
renal transplant case