DNA VIRUSES Clinical features and replicatio Flashcards
Why are the life cycles of DNA viruses interesting?
- cause life-threatening human disease (oncogenic) e.g HBV and liver cancer and papilloma and cervical cancer)
- therapeutic agents (anti-cancer) e.g adenovirus to treat head and neck cancer. Herpes simplex to treat solid tumours
When do viruses cause cancer?
-when their life cycle goes wrong (not a usual part of life cycle as it is a dead end for the virus)
What is the role of immunosurvellience?
important in recognition and destruction of transformed cells before they grow into tumours and important in controlling DNA virus infections
How long does it usually take after a virus for a cancer to develop?
10 years
Where do DNA viruses replicate?
in the nucleus (except pox)
What are the requirements for DNA viral replication?
virus encoded immediate early and early protein can induce:
-polymerase plus other factors (thymidine kinase)
-access to nucleotides
OR induce the host cell to express the polymerase
Where do the replication proteins come from?
For small DNA viruses:
-do not encode a whole genome replication system
-encode proteins that orchestrate the host
Large DNA viruses
-encode proteins in their genome
What are the roles of the viral early proteins?
Affect host functions that regulate growth:
- stimulate cell proliferation
- block cell death
- orchestrate host cell so it supports virus genome replication
What is the role of early proteins E6 and E7?
- deregulate cell growth control
- deregulate host tumour suppressor (Rb and p53) pathways
What is the role of E7?
host cell cycle regulators (suppresses Rb and pushed cells through S phase)
What us the role of E6?
cell regulators of apoptosis (prevent apoptosis even when cells have been programmed for cell death)
How could HPV case cancer?
- E7 and E6 constantly targeting tumour suppressor genes so there is no way of monitoring genomic stability and preventing replication of cells with damaged DNA
- higher risk of acquiring mutations
What makes up the HPV vaccine?
HPV16 L1 protein expressed in insect cells
-assembled into empty particles to form virus like particles
Why does the HPV vaccine not cure women with cervical cancer?
-prophylactic and not therapeutic vaccines
What does the HPV vaccine do?
blocks infection with HPV16 and HPV18 neutralising antibiotics