Polycomb Proteins

Question 1

Where do polycomb proteins bind

Answer 1

At genomic loci of developing genes

They generally target cis-elements known as Polycomb Response Elemetns PREs

Question 2

What are the components and functions of PRC1

Answer 2

CBX - binds H3K27
PH1,2 - Protein - protein interactions
Ring1A/B - E3 ubiquitin ligase activity for H2AK19
BMI2, MEL18, NSPC1 - cofactos for the E3 ubiquitin ligase

Question 3

What are the components and fucntions of PRC2

Answer 3

EZH1/2 - H3K27 methylase
SUZ12 and EED - required for HMT activity
RBAP46, 48 - histone binding - the histone chaperones

Question 4

How are PRCs recruited to PREs

Answer 4

Possibly by ncRNAs

Question 5

What are the target genes of PcG in ESC

Answer 5

50% of genes had H3K4me2 –> increased gene expression involved in metabolism and pluripotency
2% had H3K27me3
10% had both of the prior –> these had low gene expression levels and were generally involved in development –> these are known as bivalent domains

Question 6

What happens to bivalent domains as development occur

Answer 6

Lose the H3K27me3 due to UTX activity

Monovoalent domain resolves into H3K methylation

Question 7

How is PcG needed for X-inactivation

Answer 7

Xist recruits PcG and HDACs to cause silencing of the X chromsome in an X-ist dependent manner
Then once chroamtin modifications occur repression is in an Xist independent manner

Question 8

What ncRNA regulates KNQ1

Answer 8

KCNQOT1 gene is an antisense to the KCN1 gene and is paternally expressed under the control of the ICR
KCN1 recruits PRC2 and G9a histone methyltransferase to the KCNq1 locus

Question 9

What cancers is EZH2 often expressed in

Answer 9

Breast , prostate and melanoma

Levels are inversely asociated with survival

Question 10

What haematological malignancies is EZH2 mutated in

Answer 10

lymphomas and myeloid malignancies

Question 11

Where may you see UTX mutations

Answer 11

leukaemias, colon, lung, kindye and bladder carcinomas

Question 12

Which genes may be targeted by PcG proteins in cancer

Answer 12

Liekly that many genes that are DNA methylated in cacner are those that were bivalent in early development –> instructive DNA methylation whcih can revert expression back to an spigenetic stem cell signature

Question 13

Name some additional polycomb proteins

Answer 13

AEB2
JARID2
PCL

Question 14

WHAT IS THE FUNCTION OF AEB2 AND PRC

Answer 14

both increases the enzymatic activity of PRC2

Question 15

What are the proportions of H3K27 methylation

Answer 15

15% mono
50% di
15%

Question 16

What is the problem with monomethylation

Answer 16

Still occurs even in non functional PRC mutations –> what is doing it?

Question 17

How is PRC recurited

Answer 17

JARID2 and AEBP2 interact with dNA –> histone chaperones interact with H3 and H4 –> interaction of EED with H3K27me3 –> interactin of PRC2 with lncRNA

Question 18

What is the 3rd PRC complex that has been seen

Answer 18

Been seen in D. melangoster PHORC –> pleihomeotic Repressive Complex

Question 19

What is the additional function of PHORC

Answer 19

Also can recognise methylated histones

Question 20

Why might PcG targets change in cancer

Answer 20

PRC2 genes may chagne due to formation of PRC-2 like complexes with different EED isorforms
For example in prostate cancer there is the formation of a PRC-2 like compex with EED isoform 2

Question 21

What are PcG targets normally

Answer 21

Homeobox containing TF

Question 22

What is also at the PREs in genes

Answer 22

OCt4, Sox2, Nanog –> these generally are associated with inducing pluripotency and therefore are though to potentially recruit PcG to the target genes

Question 23

Role of PcG in wounds

Answer 23

Wounds activate JNK signalling –> JNK inhibits PCg –> transdifferentiaton