Nuclear Receptors

Question 1

Plasma membrane associated receptor

Answer 1

signal outside cell covered to signal inside cell without signaling molecule entering the cell

Question 2

nuclear receptors vs GPCR and tyrosine kinase receptors

Answer 2

nuclear receptors 99% of their role is the regulate transcription; GPCR and tyrosine kinase receptors eventually will talk to genome but not main existence

Question 3

nuclear receptors

Answer 3

directly affect transcription since they are essentially ligand regulated transcription factors (ligand has to get into cell, it is hydrophobic so it can passively cross membrane); directly interact with DNA

Question 4

what do GPCRs affect

Answer 4

go through complicated pathway to affect transcription, also have global affect on cell

Question 5

Regulation of gene transcription by enzyme-linked receptors

Answer 5

Direct or indirect activation of tyrosine kinase -> cascasde protein interactions -> changes gene transcription

Question 6

How do nuclear receptors work

Answer 6

ligand passively crosses membrane, binds specifically to receptors in cytoplasm or nucleus to induce conformation change in receptor

Question 7

steroid recepor family

Answer 7

Reside in cytoplasm; bind to DNA as homodimers so need 2 binding to DNA;
- adrenal cortical receptors (glucocorticoids, mineralocorticoids)
- sex hormone receptors (progestins, estrogens, androgens)
Family= NR3

Question 8

RXR heterodimer receptor family

Answer 8

already associated with DNA; sometimes with corepressors; bind as heterodimers

• thyroid hormone receptor (T3)
• Vitamin D receptor
• Retinoic acid receptors
• Retinoid X receptors (RXR)
• Others including PPAR, LXR, FXR

Question 9

ligand-receptor complex

Answer 9

bound to DNA can -> activation (via coactivator association) or -> inhibition (association with corepressors) of gene transcription

Question 10

nuclear receptor famillies

Answer 10

numbered NR0-NR6
NR3- steroid receptor family
NR1 and NR2- rxr heterodimeric receptor family

Question 11

NR0, NR4-NR6

Answer 11

Most are orphan receptors (no endogenous ligands identified)

Question 12

Ligand structures sex hormones

Answer 12

very similar structure which is why it is important to have highly specific binding site

Question 13

Receptor domains

Answer 13

1. Regulatory domain
2. DNA binding domain
3. Hinge domain
4. Ligand Binding domain

Question 14

Regulatory domain

Answer 14

binds coregulators (coactivators or corepressors) and is responsible for most effects on gene transcription, may also contain phosphorylation sites for kinase mediated modulation

Question 15

DNA-Binding domain

Answer 15

contains two zinc fingers; binds to specific response elements determining which genes will be influenced and also contributes to dimerization

Question 16

hinge domain

Answer 16

involved in nuclear localization and dimer formation

Question 17

ligand binding domain

Answer 17

determines binding specificity and can also bind coregulators

Question 18

Estrogen and progesterone receptors

Answer 18

DNA and hinge receptors v similar variations in regulatory and ligand binding domain (most differences in regulatory bit some in ligand binding domain)

Question 19

mechanism of steroid receptor action

Answer 19

homodimers; receptors found in cytoplasm not nucleus; usually associated with hsp; take final shape when ligand binds to receptor; when ligand binds releases hsps exposes nls so receptor bound to ligand -> nucleus -> binds to DNA and recognizes palindromic sequence in DNA -> binding transactivation factors communicating with transcription apparatus

Question 20

Steroid receptors and dimers

Answer 20

bc hormone response elements are generally palindromic 2 monomers of receptor can bind to 1 surface of response element making extensive dimer interface; dimers face head to head so identical DNA binding domains contact different strands DNA in opposite directions

Question 21

RXR dimers

Answer 21

heterodimersl not same; not looking for palindromic sequence; bound to DNA in absence of ligand attached to corepressors, hormones or ligand come in and activate receptor-> release corepressor and binding of coactivator; receptors generally reside in nucleus

• • corepressor doesn’t require ligand**
• • binding of ligand and activation of receptor induces release of corepressor and binidng of coactivator, can occur in absence of ligand for RXR

Question 22

transactivation

Answer 22

effect of nuclear receptor on transcription; binding of ligand-bound dimeric receptor to response element will activate transcription at distant core promotor site

Question 23

early response

Answer 23

secondary gene expressions

Question 24

late response

Answer 24

initial gene expression

Question 25

coactivators

Answer 25

mediate transactivation; these bind to ligand-receptor complex and preinitation complex to initiate activation of transcription (short distance mediation between activated receptor and initiation complex); huge amount of protein scaffolding and communication with activation complex

Question 26

coactivators and chromatin structure

Answer 26

coactivators can have intrinsic histone acetyltransferanse (HAT) activity (loosens chromatin via histone acetylation on lysin residues on amino terminus of histone)

Question 27

Transcriptional inhibitors

Answer 27

antagonists and corepressors

Question 28

antagonists

Answer 28

ligand that binds to receptor preventing interaction of coactivators with the receptor or recruits binding of corepressors rather than coactivators -> active repression of transcription (via active antagonists)

Question 29

how do corepressors work

Answer 29

may bind to free receptor or antagonist-receptor complex and preinitation complex to inhibit transcription; binding of this complex -> HDAC activity or enzyme recruitment -> tightening of chromatin

Question 30

HAT transcription

Answer 30

activates it

Question 31

HDAC transcription

Answer 31

suppresses it

Question 32

other actions of nuclear receptors

Answer 32

• can have effects outside of effects on genome
• can effect enzyme activity with in cell
• can involve interactions with and effects on cytoplasmic proteins

Question 33

Examples of nuclear receptors and effects on cytoplasmic proteins

Answer 33

1. progesterone receptor interacts with cytoplasmic kinases -> activation in ligand dependent manner
2. glucocorticoid receptor can directly interact with cellular signaling factors inhibiting them
3. estrogen receptor can interact directly with PI3K to increase its activity
4. Growing evidence for “membrane associated” steroid hormone receptors (variants of nuclear receptors or unrelated proteins)

Question 34

hormones and drugs that are ligands for nuclear receptors

Answer 34

can directly regulate transcription of specific genes

Question 35

regulation of gene expression by response elements

Answer 35

cell specific; dependent on receptor expression, avaliblity of coregulators, presence of TFs and phosphorylation state of many proteins involved