Human Pailloma and Polyoma Viruses Flashcards
Papillomaviruses Structure
- ds DNA circular
- icosohedral, naked
- Genomic diversity among papillomaviruses
- More than 100 genotypes of human papillomaviruses (HPVs) have been identified
- Viral components can be detected in infected cells
Papillomaviruses encode [] and [] proteins.
Papillomaviruses encode early (E1-E8) and late (L1-L2) proteins.
[] proteins are required for replication and [] proteins form the structure of the virus.
Early proteins are required for replication and late proteins form the structure of the virus.
Papillomavirus Replication
- Entry (viropexis) ——>Transcription (host RNA polymerase)——>Early viral protein synthesis (E1-E8)——>DNA replication (host DNA polymerase)——>Late viral protein synthesis (L1, L2)——>virus assembly in the nucleus——>virus release by cell destruction
- Close contact allows virus entry
- Early transcription/replication in lower portion of epidermis
- Vegetative DNA (genome) replication occurs in more differentiated cells of epidermis
- No cellular DNA synthesis
- Burst of viral DNA synthesis to generate viral genomes for packaging of progeny viruses
Papillomavirus Transmission
- Public showers/swimming pool suspected
- Occupational exposure
- Meat and fish handlers are prone to hand warts
- Sexually (20 to 60% females in the U.S. are infected)
- Genital warts ~65% of sexual contacts develop an infection
- Perinatally
Papillomavirus Incubation
•1-8 months (average 3 months)
Papilloma Virus Infection - Type 6 and 11
- low risk
- cause most common (about 90%) benign genital warts in males and females with some cellular dysplasia of the cervical epithelium, rarely becomes malignant.
-External genital HPV infection occurs as exophytic genital warts (condylomata acuminata)
- Can be transmitted through oral sex (7% of teens and adult carry oral HPV, risk of mouth and throat cancer)
- HPV types 6 and 11 have been associated with nasal, oral, conjunctival, and laryngeal warts, although high-risk genotypes (type 16 and 18) are associated with oropharyngeal cancer
- Can be perinatally transmitted from mother-to-child and cause infantile laryngeal papillomas
Papillomavirus Infection - Types 16,18,31,33,45,52,58
- high risk
- may cause lesions of the vulva, cervix, and penis
- Several others types have also been implicated such as 35, 39, 56, 59, 66, and 68 in dysplasia and carcinoma.
- Development of cervical cancer and its precursor lesion, cervical intraepithelial neoplasia (CIN)
- Infections with these viral types, especially type 16 and 18, may progress to malignancy
- HPV-16 is probably the most carcinogenic genotype because of its association with 60% of cervical cancers, whereas HPV-18 association is about 10-15%
- HPV is the major cause of most carcinomas of the cervix
Papillomavirus Pathogenesis
- First DNA viruses linked to malignancy
- HPV genome can be detected in the nuclei of both benign and malignant tumors
- Mechanism of oncogenicity not understood
Which viral genes are involved in transformation?
E7, E6 and E5 of higher HPV genotypes
E7 interacts with [] to abrogate cell cycle regulation mediated by [].
E7 interacts with pRB to abrogate cell cycle regulation mediated by pRB.
E6 accelerate the degradation of [] and reduces stability.
E6 accelerate the degradation of p53 and reduces stability.
E5 more functional in [].
E5 more functional in benign papillomas.
DOes the viral genome integrate into cellular genome in tumors?
Viral genome exists as multiple copies and does not integrate into cellular genome in benign tumors but may integrate in malignant tumors.
How does the host cell try and prevent tumor formation?
- Host cell produces a protein that inhibits the HPV transforming genes expression
- But this can be inactivated by products of the virus allowing malignant transformation