13-14 mbb306 lecture 5 the herpesviruses - rj

8/13/2019 13-14 MBB306 Lecture 5 the Herpesviruses - RJ

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MBB 306 - 2013-2014

VIRUSES and INFECTIONS of

HUMANS

LECTURE:THE HUMAN HERPESVIRUSES

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CLASSIFICATION of the HUMAN HERPESVIRUSES

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ALPHAHERPESVIRUSES: --Epidermo-neurotropic viruses with a wide host range.

Type 1 herpes simplex virus (HSV-1) HHV-1Type 2 herpes simplex virus (HSV-2) HHV-2

Varicella-Zoster virus (VZV) HHV-3

BETAHERPESVIRUSES:-- Slow growing viruses with a narrow host range; grow in

T-lymphocytes and/or leukocytes.

Human cytomegalovirus (HCMV) HHV-5

Human herpesvirus 6 HHV-6

Human herpesvirus 7 HHV-7

GAMMAHERPESVIRUSES:-- These viruses have a predilection for B-lymphocytes.

Epstein-Barr virus (EBV) HHV-4

Kaposis sarcoma virus (KSHV) HHV-8

[Herpesviruses infecting very many vertebrate animals, including other primates, frogs andelephants have been identified].


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VIRUS

NUMBER

COMMON NAME DISEASE

HHV-1 Herpes simplex virus

type 1 (HSV-1)

Oropharyngeal herpes;

Encephalitis.

HHV-2 Herpes simplex virus

type 2 (HSV-2)

Genital herpes; Encephalitis

HHV-3 Varicella-Zoster virus

(VZV)

Chickenpox and shingles

HHV-4 Epstein-Barr virus

(EBV)

Glandular fever/Infectious

mononucleosis;

Burkittslymphoma

HHV-5 Human Cytomegalovirus

(HCMV)

Cytomegalic inclusion disease (CID) in

utero, in newborns and in the

immunocompromised.

DISEASES caused by the IMPORTANT

HUMAN HERPESVIRUSES


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4

SCHEMATICREPRESENTATION of

a HERPESVIRUS

PARTICLE

ELECTRON MICROGRAPH OF A

HERPESVIRUS PARTICLE

Viral nucleocapsid

containing the DNA

and ICP0 protein

Viral tegument containing

VP16 and ICP4 proteins

Lipid envelope ofthe virus


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CYTOPATHIC EFFECTPRODUCED by HERPES

SIMPLEX VIRUS (HSV) in CELL

CULTURE

THE

HSV GENOME

The linear 152kbp genome contains 3

origins of DNA replication and about 80ORFs.

HSV DNA replication is by a rolling circle

mechanism which takes place in discreet

HSV replication compartments.

Replication generates long progeny HSV

DNA concatamers which are cleaved and

packaged into progeny viral particles.


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HSV CAPSID

+ DNA

HSV

Glycoproteins

gB -

Fusogen

gH + gL -

Fusion Regulator

Host Cell

gDFusion Trigger

gB -

Receptors

gH + gL -

Receptors

gD

Receptors

ENTRY of HSV-1

into HOST CELLS

gBfusogen; essential

for cell entry

gD- essential for cellfusion and

penetration

gH+gLcomplexessential for

fusion and cell entry


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HSV PROTEINS regulating or operating against

HOST CELL METABOLISMImmediately after entering the cell the HSV-1 tegument protein, vhs, becomes free in the

cell cytoplasm.

The vhsprotein:-

a). accelerates decay of host cell mRNA

b). disrupts pre-existing host cell polysomes

Replication of the HSV genome commences with transcription and expression of the HSV IEproteins. Activation and accumulation of these proteins drives transcription of the other

viral genes and subverts host gene expression. In particular,

a). ICP0an E3 ubiquitin ligase destabilising specific cellular proteins that would

otherwise inhibit the HSV life cycle. Creates a cellular environment

favourable for HSV DNA transcription

b). ICP 27 - inhibits the host cell splicing of pre-mRNA

All the IE proteins contribute to a redirection of cell metabolism from synthesis of

host proteins to synthesis of viral proteins, and develop an active and robustenvironment.


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PROGRESSION of HSV and VIRAL DNA to CELL

NUCLEUS

After penetration into the cell cytoplasm, the viralenvelope is lost.

VP16 (500-1000 molecules) and the other tegument

proteins are freed into the cytoplasm.

The capsid containing the viral DNA and remnants of the

tegument is transported to the nuclear membrane along

the microtubule network.

The capsid docks at the nuclear pore and this facilites

release of the viral DNA into the nucleus.


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EMINTRACYTOPLASMIC HERPES SIMPLEX

VIRIONS


11/28THE NUCLEOSOME

Chromatin is a complex of DNA and histonesthe

nucleosome - through which DNA is structured and

manoeuvered in the cell nucleus.

Modifications of chromatin permit transcription

processes.

A nucleosome has a core of 8 histones, withDNA wrapped around the outside, and a single

molecule of histone H1 to stabilise the complex.

Two types of chromatin are recognised:-

Heterochromatin- highly condensed; DNAassociated with it is inaccessible and therefore

genetically inactive.

Euchromatin- much less condensed allowing

transcription of the associated DNA.

CHROMATIN and HSV DNA REPLICATION


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HCF is a co-activator unable to bind DNA alone. With activated

histone acetyl transferases (HATs), HCF causes chromatinmodifications that increase gene expression by binding to an

activator having a DNA binding domain such as HSV VP16.

The chromatin modifications involving HCF are acetylationandmethylationof the nucleosome histone core.

HCF/HAT activity opens the nucleosomes in the control regions of the

promoters close to the enhancers, by relaxing the connections

between the histones and associated DNA. High levels of acetylation

make the chromatin more active, allowing transcription.

With low or absent HCF, transcription is reduced as the promoters

and enhancers cannot be accessed by transactivating factors. 12

HOST CELL FACTOR (HCF-1), CHROMATIN

and HSV LYTIC INFECTION


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VIRAL GENE CASCADE in LYTIC HSV INFECTION

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The entire process of HSV replication takes 18-20h in fully permissive

cell cultures.

Immediate Early () - genes -- transcribed and expressed from input viral DNA, inducedby VP16 (-TIF) and responsible for synthesis of the 5 proteins (expressed 2-4h p.i.)

Early () and Late () - genes -- Only transcribed after expression of the genes.(Maximal expression at 5-7h p.i.)

Early () - genes -- Transcription and expression of the genes is notstimulated by viral DNA replication.

Late (-1 and -2)genes -- -1 genes are transcribed and expressed (at low levels) even in the absence of viral DNA replication, but are

greatly stimulated when viral DNA is replicating.

-- -2 genes are not transcribed or expressed in theabsence of viral DNA replication.


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INITIATION of LYTIC HSV INFECTION in

EPITHELIAL CELLSNUCLEUS

CYTOPLASM

TAATGARAT (R = purine) sequences-Immediate early promoterHSV DNA

HCF

Oct-1

VP16

HATs

Histone (H3K9) -

acetylation groupsform Euchromatin

around the HSV

DNA

Transcription of HSV DNA using

host cell RNA polymerase II

HCF

VP16

HATs HATsHATsHATs


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RELEASE of HERPES SIMPLEX

VIRUS FROM HOST CELLGolgi

Viral nucleic acidEmpty viral capsid

NUCLEUS

CYTOPLASM

Precursor viralglycoproteins

Endoplasmic

reticulum

Cytoplasmic

vesicle

Cytoplasmic

vesicle

EXTERIOR ENVIRONMENT

Nuclear membrane

Viral glycoproteins modified

and matured in the Golgi

Nucleocapsid +

tegument

Association of nucleocapsid

+ tegument with membrane

of vesicle bearing viral

glycoproteins

+Viral nucleocapsid

Cell membrane


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EMs showing BUDDING of IMMATURE HSV

PARTICLE from NUCLEAR MEMBRANE


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REGULATION of VIRAL GENE EXPRESSION

during LYTIC HSV-1 INFECTION

Viral entry to cellcytoplasm

Viral DNA

transported to

nucleus

VP16

transported

to nucleus

Immediate Early

gene expression

ICP4 ICP27 ICP0 ICP22/Us1.5 ICP47

X Immune evasion

Assembly of virions

and releaseX

Essential

in vitro

Non-essential

in vitro

Late geneexpression

Early gene

expression

Viral DNA replication

Viral structural proteins

Both ICP4 and ICP27

must be expressed for

the lytic cycle to proceed


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ACUTE PRIMARY HERPETIC


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ACUTE, PRIMARY HERPETIC

GINGIVISTOMATITIS RECURRENT HERPETICLESIONSCOLD SORES

HERPETIC WHITLOW


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NATURAL HISTORY of HERPES SIMPLEX VIRUS

INFECTIONS

PRIMARY INFECTION

PASIVE IMMUNITY

FROM MATERNALANTIBODY IN INFANCY

SOURCE OF VIRUS

SKIN LESIONS

SALIVA

(usually Type 1 virus)

SOURCE OF VIRUS

GENITAL LESIONS

GENITAL SECRETIONS

(usually Type 2 virus)

ASYMPTOMATIC

(90%-99%)

SYMPTOMATIC

(1%-10%)

NO IMMUNITY

ESTABLISHMENT OF

LATENT INFECTION

REACTIVATION OF

LATENT VIRUS AND

RECURRENT INFECTION

IMMUNE RESPONSES


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VARICELLA-ZOSTER VIRUS (VZV)

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Size120-250nm diameter;

typical herpesvirus structure

dsDNAlinear in virion,circular in the infected nucleus.

72 open reading frames (ORFs)

Latent infection in neurones.

Genetically stable

VIRAL PROPERTIESPatient with chickenpox


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VARICELLA-ZOSTER VIRUS (VZV)

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Highly infectious disease usually

occurring in children.

Virus spread from the upper

respiratory tract prior toappearance of rash.

Virus present in skin lesions (asmuch as 10101011virions/ml).

VZV causes severe infections in the

immunocompromised.

EPIDEMIOLOGYShingles in elderly patient


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The most common disease caused by EBV is

infectious mononucleosis (glandular fever).

About 70% of the worlds population are infected.

Often asymptomatic, but symptoms can include

sore throat, swollen cervical lymph nodes and mild

fever. May run a prolonged, episodic, course over 1-

2 years.

Associated with the cancer, BurkittsLymphoma in

some parts of the world.

THE EPSTEIN-BARR VIRUS (EBV)


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PATIENT with INFECTIOUS

MONONUCLEOSIS

(GLANDULAR FEVER)

EM of the EPSTEIN-

BARR VIRUS (EBV)


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END of LECTURE

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INITIATION f LYTIC HSV INFECTION i


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INITIATION of LYTIC HSV INFECTION in

EPITHELIAL CELLS

TAATGARAT sequences-Immediate early promoterHSV DNA

HATsHistone (H3K9) -

acetylation formingEuchromatin

SETs

Histone methylation

forming

Heterochromatin

Transcription of HSV DNA involvinghost cell RNA polymerase II

NUCLEUS

Oct-1

CYTOPLASM

HCF

VP16VP16

HCF

VP16HCF

Oct-1


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Oct-1

VP16

HCF

VP16HCF

SETs

Histone methylation

forming

Heterochromatin

13-14 mbb306 lecture 5 the herpesviruses - rj

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