Lecture 10- Interferons Flashcards
The interferon phenomenon
Part of the innate immune response
Cell recognizes that it’s been infected by a virus, innate response is to produce a glycoprotein called interferon. This is technically an inducible innate response.
Induction of interferon mediated by presence of dsRNA, uncapped 5’ ends (5’ PPP-), and cytoplasmic dsDNA. mice without interferons have much more severe infections. 2 main signals are presence of ds dana and uncapped 5’ ends (only present in infected cells). cells only make interferon when infected with a virus. 1st line of defense. important to mute infection early on (important immediate response). TLR3 recognize certain pathogen patterns
(important sensors for presence of pathogens, each recognize different things). RIG-1 and mDA-5 are sensors in the cytoplasm. should know what they recognize?
Sources of dsRNA:
1) annealing fo plus and minus strands
2) reovirus dsRNA genome.
3) overlapping genes in dsDNA viruses
key take home: presence of ds RNA tells a cell BIG TROUBLE (universally)
source is the virus
Sources of uncapped 5’ ends:
1) antigenomes
2) other? don’t need to know
phosphorylated 5’ end
effect of interferon
Originally infected cell will die
interferons will protect others by creating antiviral state
receptors in cell membrane, interferons hit receptors of neighboring cell and antiviral state is established
1) if no infection, little effect
2) if infection occurs, cell dies before any virus can be produced
What are interferons?
Interferon is the prototype cytokine. Cytokines- small proteins or glycoproteins that are involved in cell to cell communication and growth regulation. They act by binding to cell surface receptors and they alter the pattern of gene expression in the target cell. Will mostly talk about type 1 and type 3, induced by viruses
type 1 alpha: produced by lymphocytes
type 1 beta: produced by fibroblasts and also macrophages and epithelial cells
type 3 lambda: three types, similar to type one IFNs
Activities of interferons:
1) induction of antiviral state (greater than 60 genes induced by IFN)
2) inhibition of cell growth
3) induction of MHC class 1 and 2 molecules
4) Activation of monocytes, macrophages, cytotoxic T lymphocytes and NK cells
5) other less well defined activities
characteristics of antiviral state
1) mx family of proteins are induced by interferon (GTPases involved in membrane remodeling)
a) mx1 inhibits transcription of neg strand viruses (best studied in influenza)
b) mx2 inhibits hiv1 infection by blocking nuclear import of sub viral particles
2) 2’5’ oligo A syntehtase induced by interferon
3) RNA activated protein kinase (PKR) induced by interferon
4) many other changes in gene expression
Induction of 2’5’ oligo a synthetase
not present in uninfected cell or cell that has not ben exposed to an interferon
gene induced at at least 1000 fold
interferon induces inactive 2’5’ oligo A synthetase. If cell infected, there will be dsRNA which will activate 2’5’…
binds and turns into active form. get signaling cascade.
atp plus active 2’5’ gives an oligonucleotide
Oligonucleotide pppA(2’p5’A)
Phosphodiester link in between 2’ and 5’, usually 3’ and 5’
range from 3-10
Induction of 2’5’ oligo A synthetase
interferon -> 1000 fold induced -> 2’5’ oligo A synthetase (inactive) -> dsRNA-> 2’5’ oligo A synthetase (active)
active 2’5’… plus ATP gives pppA(2’p5’A)n (n=3-10)
Inactive RNase L (always present in cell) plus oligonucleotide gives active RNase L
Active RNase L degrades RNA, protein synthesis inhibited, cell dies
kicks in soon enough that no new viruses are made
degrade RNA present in cell whether anti viral or not, poised to respond to this system
Induction and activation of PKR
Will phosphorylate a protein, activated by double stranded rna
this protein phosphorylates itself in the presence of ds RNA
for this to work, ds RNA has to be long enough that 2 PKRs can bind to the same piece (b/c A phos B, B phos A)
early in the initiation of protein synthesis
active all the time
to mediate protein synthesis in cell
when per becomes active, cells become infected
phosphorylates this eIF2alpha and that inactivates it
this prevents initiation of translation; cell dies
interferon-> 5 fold induced-> RNA-activated protein kinase (PKR) (inactive)
PKR is inactive, activated by ds RNA and atp (phosphorylation)
active/phosphorylated per plus atp and active eIF2alpha gives inactive phosphorylated eIF-2alpha
prevents initiation of translation, cell dies
How viruses antagonize the effects of interferon
1) Vaccinia E3L protein, HSV US11 protein, and reovirus sigma3 protein bind dsRNA
(sequesters ds rna so it can’t bind to other things like mda5 and rig 1 and TLR3)
2) influenza NS 1 protein blocks binding of Rig 1 to ds RNA
3) aden virus E1a protein, epstein barr virus EBNA-2 protein, and hep b terminal protein inhibit the signal transduction pathways that respond to binding of interferon to the cell surface receptor
block interferon from establishing anti viral state
often this is a race
4)Herpes virus simplex synthesizes 2’5’ oligo A analogs that block activation of RNase L
Not exactly like but similar enough that it interferes
prevents from binding to RNase 1 and activating it
protects cell against action of rnase L
analogs inhibit by stopping inactive rnase l from combining with with oligonucleotide to make active rnase l and kill the cell (continues to make viral proteins, etc.)
5) HIV tat and hep C Ns5A
proteins bind ot and inhibit PKR directly. polio protease cleaves PKR
6) aden virus VA1 RNA, epstein barr virus eber RNA, and HIV 1-TAR RNA
all small RNAs block activation of PKR by ds RNA
