This presentation includes information about DNA oncogenic viruses and latent and lytic replication of Herpes virus.

1. Femina Anjum
PhD Scholar (Animal Biotech.)
Deptt. Of Veterinary microbio. &Biotech.
Rajasthan university of Veterinary and Animal Sciences
Bikaner 1

2.  An oncovirus is a virus that can cause cancer and which induce
malignant transformation of cells on culture.
This term originated from studies of acutely transforming
retroviruses in the 1950–60s.
 Now refers to any virus with a DNA or RNA genome causing
cancer.
 The vast majority of human and animal viruses do not cause
cancer. 2

3.  Cancers are the result of a disruption of the normal
restraints on cellular proliferation.
 There are two classes of these genes in which altered
expression can lead to loss of growth control:
 Those genes that are stimulatory for growth and which
cause cancer when hyperactive.
 Those genes that inhibit cell growth and which cause
cancer when they are turned off.
 Viruses are involved in cancers because they can either
carry a copy of one of these genes or can alter
expression of the cell's copy of one of these genes.
3

4. oncogene
Tumor
suppressor

5.  Oncogenesis - Result of genetic changes that alter the expression or
function of proteins that play critical roles in the control of cell
growth and division
 Proto-oncogenes - normal (pre-mutation) (pre-diseased) genes
- present in normal cells
- conserved in their genomes
- code for proteins which regulate cell growth
&differentiation
 Oncogenes - mutated versions of proto-oncogenes

6. Activation of Cellular Oncogenes
Oncogene activation via insertional mutagenesis-the presence upstream
from a c-onc gene of an integrated provirus , with it’s strong promoter and
enhancer elements may enhance the expression of c-gene.
e.g. integrated avian leukosis provirus increase the synthesis of c-myc oncogene
product 30-100 fold.
Oncogene activation via transposition –
Transposition of c- onc may result in their enhanced expression by bringing
them under the control of strong promoter and enhancer elements.
E.g. Burkitt’s lymphoma
Oncogene activation via gene amplification-
Increase in gene copy number leads to corresponding amount of oncogene
products , thus producing cancer.
E.g. c- myc gene , c- ras gene
Oncogene activation via mutation-
Mutation alter the function of corresponding oncoprotein . it may be induced by
physical or chemical means or in course of recombination with integrated
retroviral DNA.

8. CELLULAR ONCOGENES
 Present in cancer cells
 Contains introns
 characteristic of eukaryotic
cells
 Encodes proteins triggering
transformation of normal
cells
VIRAL ONCOGENES
 Present in viruses
 Host cell origin
 Do not possesss introns
 Also called ‘cancer genes’
 Encodes proteins triggering
transformation of normal
cells into cancer cells

9. Introduction of new Alteration of expression of
‘Transforming gene’ preexisting cellular gene
into the cell
Loss of normal growth regulation processes
Affection of DNA repair mechanisms
Genetic instability
Mutagenic phenotype
DIRECT ACTING
INDIRECT
ACTING

10.  Worldwide, the WHO International Agency for Research on
Cancer estimated that in 2002, 17.8% of human cancers were
caused by infection, with 11.9% being caused by one of seven
different viruses.
 The importance of this is that these cancers might be
easily prevented through vaccination (e.g., papillomavirus
vaccines), diagnosed with simple blood tests, and treated with
less-toxic antiviral compounds.
1
0

11. 11

12. 12

13. Oncovirus
DNAoncogenic
viruses
RNAoncogenic
viruses
13

14. DNA VIRUSES RNA VIRUSES
VIRAL
ONCOPROTEIN
EXPRESSION
VIRAL
ONCOGENE
PROTO
ONCOGENE
CONVERSION
PROVIRAL
INSERTION NEAR
CELLULAR
ONCOGENE
TRANSFORMING NON
TRANSFORMING
INACTIVATION OF
TUMOR
SUPPRESSOR
GENES

15.  DNA tumor virus have a
DNA genome that is
transcribed into RNA which
is translated into protein.
 They have two life-styles:
 In permissive cells, all parts
of the viral genome are
expressed.
 In cells that are non-
permissive for replication,
viral DNA is usually, but
not always, integrated into
the cell chromosomes at
random sites. 15

16.  DNA oncoviruses typically impair two families of tumor
suppressor proteins: tumor proteins p53 and
the retinoblastoma proteins (Rb).
 While several DNA oncoviruses have been discovered,
three have been studied extensively.
 Adenoviruses can lead to tumors in rodent models but do not
cause cancer in humans.
 Simian virus 40 (SV40), a polyomavirus, can cause tumors in
rodent models but is not oncogenic in humans.
 The Human Papillomavirus-16 (HPV-16) has been shown to
lead to cervical cancer and other cancers, including head and
neck cancer.
 All three of these DNA oncoviruses are able to integrate
their DNA into the host cell, and use this to transcribe it
and transform cells by bypassing the G1/S checkpoint of
the cell cycle.
16

17.  Integration of viral DNA
 The DNA is believed to be inserted during
transcription or replication, when the two annealed
strands are separated.
 This event is relatively rare and generally
unpredictable; there seems to be no deterministic
predictor of the site of integration.
 After integration, the host’s cell cycle loses regulation
from Rb and p53, and the cell begins cloning to form a
tumor.
17

18.  The G1/S Checkpoint
 Rb and p53 regulate the transition between G1 and S
phase, arresting the cell cycle before DNA replication
until the appropriate checkpoint inputs, such as DNA
damage repair, are completed.
 p53 regulates the p21 gene, which produces a protein
which binds to the Cyclin D-Cdk4/6 complex. This
prevents Rb phosphorylation and prevents the cell
from entering S phase.
 In mammals, when Rb is active (unphosphorylated), it
inhibits the E2F family of transcription factors, which
regulate the Cyclin E-Cdk2 complex, which inhibits
Rb, forming a positive feedback loop, keeping the cell
in G1 until the input crosses a threshold.
18

19.  Inactivation of p53
 The adenovirus E1B protein (55K) prevents p53 from
regulating genes by binding to the site on p53 which binds
to the genome.
 In SV40, the large T antigen (LT) is an analogue; LT also
binds to several other cellular proteins, such
as p107 and p130, on the same residues. LT binds to p53’s
binding domain on the DNA (rather than on the protein),
again preventing p53 from appropriately regulating genes.
 The HPV protein E6 binds to a cellular protein called the
E6-associated protein (E6-AP, also known as UBE3A),
forming a complex which causes the rapid and
specific ubiquitination of p53.
19

20.  Inactivation of Rb
 Rb is inactivated (thereby allowing the G1/S transition
to progress unimpeded) by different but analogous
viral oncoproteins.
 The adenovirus early region 1A (E1A) is an
oncoprotein which binds to Rb and can stimulate
transcription and transform cells.
 SV40 uses the same protein for inactivating Rb, LT, to
inactivate p53.
 HPV contains a protein, E7, which can bind to Rb in
much the same way. 20

21.  Variations
 There may be many different mechanisms which have
evolved separately; in addition to those described
above, for example, the Hepatitis B virus (an RNA
virus) inactivates p53 by sequestering it in the
cytoplasm.
 SV40 has been well studied and does not cause cancer
in humans, but a recently discovered analogue
called Merkel cell polyomavirus has been associated
with Merkel cell carcinoma, a form of skin cancer. The
Rb binding feature is believed to be the same between
the two viruses.
21

22.  Small DNA tumor viruses  Complex DNA tumor viruses
S.
N
o.
Family Members
1 Papillomaviridae Papilloma virus
2 Polyomaviridae Polyomaviruses
Mouse
polymavirus
Simian virus 40
Human
polyomavirus
3 Adenoviridae Adenovirus
S.
No
.
Family Members
1 Herpesviridae Herpesviruses
Epstein barr
viruses (Human
Herpes virus 4)
Kaposi’s sarcoma
Herpes Viruses
(Human Herpes
Viruses 8)
Human
cytomegalovirus
(Human Herpes
Virus 5)
2 Hepadnaviridae Hepatitis B virus
22

23.  Oncogenic Papillomaviruses
 Papillomas are hyperplastic epithelial outgrowths that generally
regress spontaneously. Occasionally, however, infections by some
papillomavirus types may cause malignant cellular
transformation, resulting in the development of cancer.
 In warts, the papillomavirus DNA remains episomal.
 As the pattern of integration is clonal within cancers, each
cancer cell carries at least one, and often many incomplete copies
of the viral genome.
 The site of virus integration is random, and there is no consistent
association with cellular proto-oncogenes.
 For some papillomaviruses, integration disrupts one of the early
genes, E2, which is a viral repressor.
 These oncogenes alter normal cell growth and division and the
overexpression of E6 and E7 -critical step in malignant
transformation by a human papillomavirus.
 However, bovine papillomavirus type 1 -cause equine sarcoids
predominantly through changes in cell proliferation -mediated
by the E5 oncoprotein.
23

24.  Polyomavirus- or adenovirus-transformed cells do not
produce virus.
 Most of the integrated viral genomes are complete in the
case of the polyomaviruses, but defective in the case of the
adenoviruses.
 Only certain early viral genes are transcribed, albeit at an
unusually high rate.
 Their products, demonstrable by immunofluorescence,
used to be known as tumor (T) antigens.
 Virus can be rescued from polyomavirus-transformed
cells—that is, virus can be induced to replicate by
irradiation, treatment with certain mutagenic chemicals, or
cocultivation with certain types of permissive cells.
 This cannot be done with adenovirus-transformed cells, as
the integrated adenovirus DNA contains substantial
deletions.
24

25.  Oncogenic Herpesviruses
 Marek’s disease virus of chickens (gallid herpesvirus 2)
transforms T lymphocytes, causing them to proliferate to
produce a generalized polyclonal T lymphocyte neoplasm.
 The disease is preventable by vaccination with live-
attenuated virus vaccines that lack the retrovirus v-
onc genes that are present in Marek’s disease virus.
 The best characterized oncogene is the Meq protein, which
inhibits tumor suppressor genes and stimulates expression
of proteins important for cell growth (IL-2, Bcl-2, CD30).
 It also binds to the promoter of and stimulates the
expression of micro RNA21, which subsequently causes
expression of metalloproteinases required for tissue
invasion by tumor cells.
25

26.  Oncogenic Hepadnaviruses
 Mammalian, but not avian, hepadnaviruses are
associated strongly with naturally occurring
hepatocellular carcinomas in their natural hosts.
 Woodchucks that are chronically infected with
woodchuck hepatitis virus almost inevitably develop
hepatocellular carcinoma, even in the absence of other
carcinogenic factors.
 Ground squirrel and woodchuck hepatitis viruses
activate cellular oncogenes, the mode of action of
human hepatitis B virus is uncertain, as it apparently
has no consistent site of integration or oncogene
association. 26

27. 27
EHV2 HVS
HHV8
EBV
HSV1
HSV2
EHV1
PRV
HHV6
VZV
ALPHAHERPESVIRUSES
HCMV
BETAHERPESVIRUSES
HHV7

28. Herpes virus
type known
to infect
humans
HSV1 or
HHV1
HSV2
or
HHV2
VZV or
HHV3
HCMV
or
HHV5
HHV6AHHV6B
HHV7
EBV or
HHV4
KSHV
or
HHV8
28

29. Introduc
tion•Enveloped, spherical to
pleomorphic, 150-200 nm
in diameter, T=16
icosahedral symmetry.
• Capsid consists of 162
capsomers and is
surrounded by an
amorphous asymmetrical
tegument.
•Glycoproteins complexes
are embed in the lipid
envelope.
29

30.  Monopartite,
linear, dsDNA
genome of 120-
240 kb. The
genome contains
terminal and
internal reiterated
sequences.
30

31. GENE EXPRESSION
 Each viral transcript usually encodes a single protein and
has a promoter/regulatory sequence, a TATA box, a
transcription initiation site, a 5' leader sequence of 30-
300 bp, a 3' sequence of 10-30 bp, and a poly A signal.
 There are many gene overlaps. There are only few spliced
genes. Some of the expressed ORFs are antisense to each
other. Some ORFs can be accessed from more than one
promoter. Certain proteins are downregulated
translationaly by a leaky scanning from an upstream
ORF.
31

32. •replication of
circular viral
episome in
tandem with the
host cell DNA
using the host cell
replication
machinery.
Latent
replication
32

33. 33

34.  Adaptive immune response inhibition
 Herpesviruses have evolved different strategies
to inhibit the host adaptive immune response. For
example, Herpes simplex protein US12 binds
specifically to transporters associated with antigen
processing (TAP), blocking peptide-binding to
TAP and subsequent loading of peptides onto MHC
class I molecules. HCMV instead encodes a protein
termed US3 that directly binds and inhibits host
tapasin.
34

35.  Apoptosis modulation
 Apoptosis is very often modulated by herpesviridae.
The mechanisms used can be caspase-dependent such
as HCMV vICA that prevents host caspase-8
activation, or can involved the inhibition other cellular
proteins involved in apoptosis such as EBV protein
BHRF1, a viral homologue of the Bcl-2 that protect the
infected cell against apoptosis.
 Autophagy modulation
 Several herpesvirus are able to inhibit host cell
autophagy process, such as HHV-1 ICP34.5 that
interacts with Beclin-1 and stop autophagosomes
development. 35

36.  Cell-cycle modulation
The UL24 protein that is present in all herpesvirus
subfamilies induces a cell cycle arrest at G2/M
transition through inactivation of the host cyclinB/cdc2
complex .
 Innate immune response inhibition
Herpes viruses inhibit the cascade leading to
production of interferon-beta by mainly targeting the host
IRF3 protein. Thus, herpes simplex virus, varicella virus, or
HCMV all possess proteins to prevent IRF3 activation.
 Host splicing inhibition
HSV-1 ICP27 is an alternative splicing regulator of host
mRNA. This protein is conserved in several herpesviridae
genera. It has been shown to act as a splicing silencer at the
3' splice site of the PML intron 7a .
36

37. Name Synonym Subfamily
Primary
Target Cell
Pathophysiology
Site of
Latency
Means of
Spread
HHV-1
Herpes simplex
virus-1 (HSV-1)
α (Alpha) Mucoepithelial
Oral or genital
herpes (predominantly
orofacial), as well as
other herpes
simplex infections
Neuron
Close contact
(oral
or sexually
transmitted
infection)
HHV-2
Herpes simplex
virus-2 (HSV-2)
α Mucoepithelial
Oral or genital herpes
(predominantly genital),
as well as other herpes
simplex infections
Neuron
Close contact
(oral or
sexually
transmitted
disease)
HHV-3
Varicella zoster
virus (VZV)
α Mucoepithelial Chickenpox and shingles Neuron
Respiratory and
close contact
(including
sexually
transmitted
disease)
37

38. Name Synonym
Subfa
mily
Primar
y Target
Cell
Pathophysiology
Site of
Latency
Means of
Spread
HHV-4
Epstein–Barr
virus (EBV), lymphocryptovirus
γ
(Gamma
)
B
cells and
epithelial
cells
Infectious
mononucleosis, Burkitt's
lymphoma, CNS
lymphoma in AIDS patients,
post-transplant
lymphoproliferative
syndrome (PTLD), nasophary
ngeal carcinoma, HIV-
associated hairy leukoplakia
B cell
Close contact,
transfusions,
tissue
transplant, and
congenital
HHV-5 Cytomegalovirus (CMV) β (Beta)
Monocyte
s
and epithe
lial cells
Infectious mononucleosis-like
syndrome, retinitis
Monocyte
, and ?
Saliva, urine,
blood, breast
milk
HHV-6A
and 6B
Roseolovirus, Herpes
lymphotropic virus
β
T
cells and
?
Sixth disease (roseola
infantum or exanthem
subitum)
T cells
and ?
Respiratory
and close
contact?
38

39. Name Synonym Subfamily
Primary
Target Cell
Pathophysiology
Site of
Latency
Means of
Spread
HHV-7 β T cells and ?
drug-induced
hypersensitivity
syndrome,
encephalopathy,
hemiconvulsion-
hemiplegia-epilepsy
syndrome, hepatitis
infection, postinfectious
myeloradiculoneuropathy,
pityriasis rosea, and the
reactivation of HHV-4,
leading to
"mononucleosis-like
illness"
T cells and ? ?
HHV-8
Kaposi's sarcoma-
associated
herpesvirus
(KSHV), a type
of rhadinovirus
γ
Lymphocyte
and other cells
Kaposi's sarcoma, primary
effusion lymphoma, some
types of
multicentric Castleman's
disease
B cell
Close contact
(sexual), saliva?
39

40. Herpesviruses in which Vaccines are of
Significance
Herpesvirus Abbr Host Species Commercial
Vaccine
Marek disease virus MDV Chicken MLV, killed
Bovine herpesvirus 1 BHV-1 Cattle MLV, killed
Suid herpesvirus 1
(pseudorabies virus)
SHV-1 (PRV) Swine MLV, killed
Equine herpesvirus 1 EHV-1 Horse MLV, killed
Feline herpesvirus FHV-1 Cat MLV, killed

41. Evolution of Herpesvirus Vaccines
1st
Generation

- Conventional
killed-
-
Modified-live
e.g. PR-Vac,
Pseudo vax
2nd
Generation

3rd
Generation

4th
Generation

??
- Gene-deleted, i.e. virulence
genes
- e.g. Omni Vac-1
- Gene-deleted, i.e. differential
marker
- e.g. PRV-marker, Tolvid
Omnivac II
- Multiple marker genes
- e.g. PRV-Gold

42. Globally, almost 20% of cancers are related to infection
agents. Several viruses with oncogenic potential stimulate cell
proliferation and cause tumors and cancer in animals and
humans. They act with different mechanisms depending on
different factors.
The tumor viruses with small genomes integrate into host
cell chromosomal DNA and cause mutations and chromosomal
rearrangements that predispose to cancer. The oncogenic DNA
and RNA viruses that are carrying oncogenes encode
transforming proteins to stimulate tumor formation.
42

43.  Murat ŞEVİK, Laboratory of Molecular Microbiology, Veterinary Control Institute, Konya –
TURKEY, Oncogenic viruses and mechanism of oncogenesis, 2012; 36(4): pg. no.323-329.
 Parkin, Donald Maxwell (2006). "The global health burden of infection-associated cancers in the
year 2002". International Journal of Cancer, 118 (12): pg. no.3030–44.
 Oncovirus, from wikipedia, the free encyclopedia.
 Arbuthnot P, Kew M. 2001 Int. J. Exp. Path. 82: 77–100
 Astori G, Lavergne D, Benton C, Hockmayr B, Egawa K, Garbe C, de Villiers E-M. 1998 J.
Invest. Dermatol. 110: 752–755
 Bachmann A, Hanke B, Zawatzky R, Soto U, van Riggelen J, zur Hausen H, Rösl F. 2001 J.
Virol. in press
 Pathogenesis of Viral Infections and Diseases In Fenner's Veterinary Virology (Fifth Edition), 2017
 Dr Richard Hunt (Professor, Department of Pathology, Microbiology and Immunology), Virology -
Chapter Six (Part One), Oncogenic Viruses -DNA Tumor Viruses, University of South Carolina
School of Medicine
43

44. 44