L20 - Intracellular Receptors Flashcards
Describe the strcuture of the signal if it is to act intracellualrly
Must be hydrophobic enough and must be small enogh
What are the two main types of receptor
Cell surface receptor
Intracellular receptor
What are the two types of an intracellular receptor
Gases and nucelar receptor
What two substances to intracellular gas receptors bind
NO and CO
What types of molecules do nuclear receptors bind
Steroid hormones
Thyroid hormones
Retinoids
Vit D
What are the properites of nitric oxide
Gaseous
Free radical
Very reactive
What is the hlaf life of nitric oxide
5-10s
The fact NO is a free radical means what
That it has an unpaired electron in its outer shell
What is NO2
Nitrogen dioxide
What is N2O
Nitrous oxide
What is NO
Nitric oxide
What is NO synthesisded from
L-arginen
L-argine undergoes a ___________ to form _______
An oxidation
Forms N-hydroxyarginine
N-hydroxyargine undergoes a _________ to form ______________ and ______
Oxidation
L-citrulline and NO
So it can be said NO is synthesised by ___
Two successive oxidations
What molecule is produces as waste from NO syntheseis (how many)
2 molecules of water - produced at each oxidaition reaction
What enzyme catlayses the synthesis of NO
NOS
Nitric oxide synthease
The two oxidations in NO synthesis are analgous to the
NADPH dependent cytochrome P450 oxidorectuctase
What is cNOS
Consitutive NOS
cNOS
Enzymatic activity
Expression
Activity
How much NO
Enyzmatic act. induced by Ca/Calmodulin
Expression is constitutive
Activity is short lived
Picomoles of NO are produced
What are the two types of cNOS
eNOS and nNOS
What is eNOS
Endothelial
where is eNOS found within the cell
Bound at the cell membrane
Which cells express eNOS
Endothelium, cardiac myocytesm renal mesangial cells, oesteoblasts/fibroblasts and platelets
What is nNOS
Neural
Where is nNOS found within the cell
Cytosol
what cells express nNOS
CNS
NANC neurones
ENS
Retina
What is iNOS
Inducible
iNOS
Enzymatic activity
Expression
Activity
How much NO
Enxymatic activity is constitutive
Expression is inducible
Long lasting
Nanomoles of NO are produced
What induces the transcription of iNOS
Pathological stimuli - LPS, IFN-g and IL-1
What cells express iNOS
Macrophages and Kupfferr cells
Neutrophils
Fibroblasts
Vascular smooth muscle and endothelila cells
What is the main effect of NO in the vasculature
Vasodilaiton
Describe how NO causes vasodilation in the vasculature
ANS release Ach whuch acts on endothelial cells containing eNOS
Endothelila cells release NO which causes the surrounding smooth muscle to relax
What are the other effects of NO in the vasculature
These properties make NO a
Inhibition of platelet aggregation and vascular smooth muscle proliferations
Termed an anti-atherisclerotic
Describe the process of NO induction
Ach from the NAS Activation of eNOS Acts on argine --> NO Rapid diffusion of NO away NO activates guanylyl cyclase GTP --> cGMP Causes a rapid relaxation of the smooth muscle
Describe how increased cGMP leads to the relaxtion of the smooth muscle
cGMP
Activates cGMP dependent protein kinase (PKG)
Myosin light chain phosphatase
Acts on the myosine light chain
Describe the location of nNOS in the brain
Tethered to NMDA type glutamate receptors
What can nNOS in the brain respond to
Ca increase near the open channels
What effect does Ca have on nNOS
Activates - causes the production of NO
NO produced by nNOS in the brain does what
Diffuses back to the presynaptic terminal where it activayes glutamate production
At the presynaptic terminal what is the effect of NO
Increase the production of glutamate
Thus creating a state of long term potentiation
What is the effect of NO in the immune system
Kills bacteral and parasites
Induces programmed cell death
How is the NO produced in inflammatory cells used as
Cytostatic and cytotoxic agent - involving muchhigher amounts of NO
What dieseas can be caused by overproduction of NO iin the lungs and intestines
Rheumatoid arthritus
Crohns
Asthma
Describe the composition of synamite
Nitroglycerine and fine clay as the stabiliser
What is nitroglycerine used as a treatment for
How does this work?
100 year treatment for angina
It is rapidly broken down into NO which causes the relaxation of the blood vessels reducing the load on the heart
What is the main symptom and cause for angina
Pain resulting from inadequet blood flow to the heart
What enzyme does NO act on
Guanylyl cyclase
NO causes the build up of what molecule
cGMP
Build up of cGMP is counteracted by
Phospho-diesterase 5
What does PDE-5 prevent
Build of of cGMP
How does viagra act
Inhibits phosphodiesterase-5
What is the mechanism for viagra actions
Inhib of PDE-5
Less breakdown of cGMP so more cGMP produced
Smooth muscles constricting the blood vessles relax
So more blood flow
Steroid hormones made from
Cholesterol
Thyroid hormones made from
Tyrosine
Retinoids like RA are made from
Vitamin A
What do retinoids act as
Local mediators in vertebrate developement
What is the solubility of retinoids, and steriod hormone
Poorly soluble
How do poorly soluble molecules - steroid and theyroid hormones become soluble so that they can travel in the blood
Bind to specific carrier proteins from which they can disociate from before entering a target cell
How are nuclear receptors kept in the inactive state
By inhibitory proteins
Describe what happens when a ligand binds to a nuclear receptor
Binding of the ligand removes the inhibitor leading to a conformational change
The receptors now interact with coactivtor to direct trnascriptipn
What dos the DNA bidning domain of each nuclear receptor contain
Two repeats of C4 zince fingers
What is a C4 zinc finger
Where the zinc is bound by four conserved cyteinines
What are the domains of the oestrogen receptor
N terminal domain DNA binding Hinge region Ligand binding C-terminal domain
What does the DNA binding domain of the oestrogen receptor consist of
Zinc fingers - each of which binds to specific DNA sequences
Describe the binidng of nuclear receptors as homorodimers
Bind as symmetric homodierms to an inverted repeat (so head to head)
Examples of intraceullualr receptors which bind as homodimers
Glucocorticoid receptesos and oestrogen receptors
Describe the binding of intracellular receptors as heterodimers
Bind as heterodimers with RXR to direct repeat sides (head-tail)
What nuclear receptors bind as heterodimers
VitaminD, thyroid hormone and RA receptors
What is RXR (what does it stand for)
Retinoid X receptor
Head to head binding of nuclear recptors seen in
Symmetrical homodimers binding to an inverted repeat
Receptors that bind with RXR bind as ___________ to __________________
Heterodimers
Direct repeat
In the absence of ligand where are homodimeric receptors found
In the cytoplasm
What causes the translocation of the receptor to the nucelus
Hormone binding to the receptor
How are homodimeric receptors kept in the cytoplasm when there is no lignd bound
Anchored in the cytoplasm buy inhibitor proetins including Hsp90
What is Hsp90 a relative of
Hsp70
What does hormone bidning cause for homodimeric receptors
Release of the inhibitor proteins allowing them to enter the nucleus
Where are heterodimeric receptors always found
In the nucleus - with or without the ligand present
How do heterodimeric receptors act in the absense of a ligand
Recruitment of histone deacetylases
How do heterodimeric receptors act in presence of a ligand
Acts as an activator by the recruitment of histone acetylases
Describe the early primary response to steroid hormone
Steriod hormone - receptor complex activates primary response genes
Induces synthesis of a few proteins
What is the time frame of the early prmary response
1-6 hours
Describe the secondary response
A primary response protein shuts off the primary response genes
A primary response protein turns on secondary response genes
Induces synthesis secondary response proteins
What is the time frame for delayed secondary response
6-48 hours
