Small DNA viruses: Papillomavirus, Polyomavirus and Adenovirus*

Polyomavirus

Papillomavirus Adenovirus

Collectively referred to as the small DNA tumor viruses *and perhaps a little parvovirus and hepatitis B virus for good measure

Replication: Small DNA viruses

• Reading material: – Field’s Virology (today’s lecture) • Chapter 5: Virus replication strategies – Expression and Replication of DNA Virus Genomes • Chapter 62: Papillomavirus • Chapter 63: Adenoviridae: the Viruses and Their Replication

– Field’s Virology (transformation lecture) • Chapter 8: Cell transformation by viruses

General features of DNA viruses

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Most DNA viruses replicate in the nucleus –

Exception?

• • •

Genome types: ssDNA, dsDNA, DNA with RNA intermediate Linear, circular, open circle

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Most DNA viruses are composed of dsDNA –

Exception?

• • • •

Virions: Enveloped Nonenveloped Icosahedral capsid

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Gene expression occurs in waves

Small DNA virus families •

Polyomaviridae – – – –

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Mouse polyomavirus SV40 JC, BK virus Merckel cell virus (MCV)

Papillomavirus – Human papillomavirus (HPV) – Bovine papillomavirus (BPV)

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Adenoviridae – Human adenovirus – Mouse adenovirus

Small DNA virus families (continued) •

Parvoviridae – Adeno-associated virus (AAV) • “dependovirus”

– B19

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Hepadnavirus – Hepatitis B virus

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Most are nonenveloped, icosahedral virions (HBV is enveloped)

Small DNA virus genomes •

Polyoma- and papilloma-viruses – Circular, dsDNA genomes – ~8 kbp

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Adenovirus – Linear dsDNA genome – ~36 kbp

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Parvovirus Linear ssDNA genome (usually minus strand) – ~5 kb

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Gene expression occurs in waves – Early (E) and Late (L)

Papillomavirus: Classification Species of origin (host restricted) DNA sequence homology in E6, E7, and L1 genes 100 defined human papillomavirus types, each give a number, HPV1, 2,….100, etc

Significance? Different HPV types are associated with different kinds of warts and cancer potential.

Papillomavirus Structure Virion-small, icosahedral, non-enveloped Composed primarily of L1 protein L1--major papillomavirus antigen L1 overexpression generates VLPs significance?

Genome

Papillomavirus capsids-computer reconstruction of cryo-EM images of papillovirus capsids. Capsomers (stars) are composed of L1 protein

Circular, dsDNA Approx. 8000 bp

Schematic diagram of the HPV genome

ORFs (Open Reading Frames) all on the same strand LCR-long control region

Papillomavirus Gene Expression Two classes of gene expression: Early

L genes

Late (similar in other small DNA tumor viruses)

E genes: Functional Transcription DNA replication Late: Structural Capsid

No DNA Polymerase! -Implications?-

E genes

Viral Gene Expression continued • • • • •

E gene expression controlled by LCR E2 regulates transcription from LCR E1 + E2 regulate viral DNA replication E5 may contribute to alteration of host environment E6 – ?

•

E7 – ?

• • •

L1 is the major capsid protein L2 is a minor capsid protein L1 overexpression is sufficient to generate VLPs – VLPs? – Significance?

Papillomavirus Replication

Not much detail, laboratory models are limited Species specific Bovine papillomavirus (BPV) serves as a model (grows in cell cultures) 1-3.

Attachment/absorption/nuclear translocation

Nuclear events 4-7. Uncoating/transcription/genome replication 10-13.

Particle maturation/egress/release

Cutaneous or mucosal epithelial tropism HPV only replicates in “skin” or skin-like rafts in culture

Infection of skin-like raft cultures of human keratinocytes with HPV. Left--uninfected Right--virus infected

Papillomavirus

Pathogenesis Induces the cell cycle Induces cell division

J. Clin. Invest. 116:5 doi:10.1172/JCI2860

Warts contain entire stratification pattern -albeit somewhat disorganized

Stratification is disrupted in HPVinduced carcinoma

Human Papillomaviruses (HPV) Warts = papillomavirus infection If there is a wart, there is a papillomavirus infection papillomas

Ano-genital papillomaviruses are among the most common sexually transmitted infections

Associated with most, if not all, cervical squamous cell carcinomas Recent evidence suggests an association with head and neck cancers (HPV 16)

Some Papillomavirus Diseases

Mucosal Genital Cervical carcinoma High risk HPV16, 18, 31, 45

Moderate risk

Low grade SIL. A. H&E stain. B. Stain for HPV capsid antigen. C. Cervical “Pap” smear. D. Cervical smear, stained for HPV capsid antigen.

HPV33, 35, 39, 51, etc

Low risk HPV6, 11, 26, 42, 43, 44

Head and neck cancers HPV16 J. Clin. Invest. 116:5 doi:10.1172/JCI28607

HPV-mediated cell transformation and cancer HPV is associated with all stages of cervical abnormalities >99% of cervical carcinomas have HPV sequences

BUT…..not all HPV infections of cervix, including high risk types, lead to cancer 50 human adenoviruses

(left and center) Electron micrographs of adenovirus particles. (right). Purified “spikes” from adenovirus.

Structure Complex icosahedral virion Non enveloped

Genome Linear, dsDNA 36,000 bp E & L gene expression Diagram of adenovirus replication cycle. Gene expression and replication more complex than HPV or polyomavirus

Encodes potent transforming proteins E1A--binds Rb E1B--binds p53

Human adenoviruses are not associated with human cancer

Adenovirus •

Important model for virology – Why?

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E and L gene expression from defined regions – Single, large L transcript • Significance?

– Bidirectional transcription • Advantages? • Disadvantages?

Electron micrograph of a nuclear inclusion showing array of adenovirus virions (can be as many as 10,000 particles per cell).

Some adenovirus genes • E1A – Functions?

• E1B – Functions?

• E2 – Functions?

• VA RNA – Structured RNAs – Functions?

• L genes – Functions?

Small DNA tumor viruses and the cell cycle

For adenovirus:??? For polyomavirus:???

Adenovirus

Disease (most common) Acute respiratory disease (ARD) Accounts for 5% of ARD in children Outbreaks in crowded living quarters Ex: Military barracks Most adults seropositive

Conjunctivitis

Clinical and research applications of adenoviruses Applications Transduction vehicles for cDNAs, shRNAs Gene therapy vectors Cancer therapy vectors Certain mutants selectively kill cancer cells “oncolytic”

Drawbacks Adenoviruses are quite antigenic Most adults seropositive for commonly used types Developing rare adenovirus types as vectors

Human Parvovirus Very small virions ssDNA genome Disease B19

Computer generated reconstruction of B19 parvovirus virion.

Erythema infectiosum “slapped cheek” syndrome “fifth” disease Febrile illness with facial rash

In utero infection Severe anemia Can be fatal

Adeno-associated virus (AAV) in development as gene therapy vectors

Hepatitis B genome structure Genome is partial dsDNA has an RNA genome stage viral RT converts RNA to genomic DNA for packaging

Papillomavirus

Pathogenesis

WARTS

Induces the cell cycle Induces cell division

J. Clin. Invest. 116:5 doi:10.1172/JCI2860

Warts contain entire stratification pattern -albeit somewhat disorganized

Stratification is disrupted in HPVinduced carcinoma