chapter 22 papillomavirus

what does papillomavirus cause?

warts and causes cervical cancer

what is papillomavirus resistant to?

most disinfectants; even those used in hospitals

what is the structure of papillomavirus?

an icosahedral capsid surrounding a circular, double stranded DNA genome; capsid is made of two types of protein L1 and L2

how many genes does papillomavirus consist of?

8 genes

how does this virus duplicate?

a rolling mechanism

how are genes arranged in this virus?

all genes are on the same strand of DNA, while they overlap, the RNA transcript of one gene will not base pair with the transcript of another gene (becomes important for immune avoidance).

how is papillomavirus avoided by the immune system?

• since genes are arranged on one strand, transcripts don’t overlap, so they viruses don’t make dsRNA, so they can’t make interferon

• use cellular RNA polymerase, so that viral RNA is chemically like cellular RNA to the PAMPS

• don’t kill the cells they infect, so there is no cell death to cause inflammation or detection of the virus using DAMPS

• very few signals activating the innate immune system against it, so it stays in the body a very long time

True or false; parvoviruses show specific tropism, so that human parvoviruses will only infect humans, and tissue tropism, where they only infect the basal layer of the skin or mucous membranes.

True

true or false, immunity against one strain does not protect against others?

true

what is the cause of warts?

viruses infecting lower layers of the skin and then causing the cells to divide excessively; virus moves up the skin layers until it is shed on the outer surface

what is the infection pattern of papillomaviruses?

• scratch or tiny break in the skin that allows the virus access to the basal later; which is the layer where the stem cells are

• virus infects these stem cells but only replicates a small amount in these cells

• as the cell divides, they differentiate into the layers of the skin and the virus goes along for the ride

• during the differentiation process, the virus is triggered to reproduce

• the cells infected become karatinocytes and form the outer layer of the skin

what is the stability of papillomavirus like?

have to survive on surfaces for possibly a long time before they come in contact with another host (some are sexually transmitted)

why does it cause warts and cancer

they are small DNA viruses that use the cellular DNA replication machinery to copy themselves

what is the S phase?

The part of the cell cycle where DNA is replicated.

what does papillomavirus do to push the cell into the cell cycle?

two viral proteins E6, E7 (they inhibit the brakes on the cell cycle)

what is the mechanism of E6 and 7

E6 inactivates p53 and E7 inacticates Rb

p53

responsible for sensing DNA damage and shutting down the cell cycle to allow the damage to be repaired; also has the ability to kill the cell if DNA damage is sufficiently bad

Rb

an inhibitor of the cell cycle

what happens when E6 and E7 is inhibited?

the cell will undergo uncontrolled division; why warts which are small benign piles of cells form

what do E6 and 7 also cause

cervical cancer

what does a pap smear do?

looks for characteristic changes to cells caused by human papillomavirus and can detect dangerous cells before cancer develops