Receptors & Cell Signaling Flashcards
Signaling hormone is transported in the blood. Name the hormone type. Give the relative half life as well.
Endocrine hormones
- short term, half life on minute scale
- act on far away signaling
This signaling hormone diffuses to neighboring target cell of a different cell type. Give the relative half life as well.
Paracrine hormones
-local signaling -short lived signal
What is type of hormone is testosterone?
Paracrine hormones
– Leydig cells synthesize and secrete testosterone induces spermatogenesis by acting on Sertoli and germ cells
Secreting cells express surface receptors for this signal hormone or release to cells of the same type. What types of proteins are they commonly found as?
Autocrine hormones
– Commonly found as chemokines
– Growth factors in cancer cells
What type of signaling hormone is interleukin-1?
What produces them and why?
Autocrine
Interleukin-1 is produced by T-lymphocytes which promote their own replication in immune response
– Growth factors in cancer cells
What type of hormone is heparin-binding epidermal growth factor? Where does it bind?
Justacrine
HB-EGF binds to EGF receptor in Immune cells
Hormone signals that cannot penetrate the cell membrane.
Hydrophilic Interact with cells at specific receptors.
Examples of hydrophilic signaling.
Epinephrine, insulin, glucagon etc
What are second messengers derived from? What is the half life?
Generally small and derived from AA, polypeptides or through lipid metabolism
Have short half-lives, about seconds to minutes.
What are two receptors involved in hydrophilic signaling?
Receptor tyrosine kinases (RTKs)
G protein - coupled receptors (GPCRs)
Hormone signals that pass through the membrane of the target cell.
Lipophilic signals
Examples of lipophilic signals.
Steroid hormones, thyroid hormone and retinoids.
What do lipophilic signals bind to?
Receptor proteins inside the cell. These can be in the nucleus or the cytosol.
Cytoplasmic receptors are what type of receptor?
Lipophilic
How do cytoplasmic receptors exist in an inactive state? By what mechanism are the activated
Bound to HSP 90.
Ligand binds -> HSP 90 dissociates -> hormone-receptor complex binds to hormone response element in promotor region of DNA
What are nuclear receptors in signaling? How are the acted upon by hormones?
Lipophilic signaling receptors, already present in nucleus and bound to DNA. Hormone allows for interaction with additional proteins and activates the complex.
What is the half-life of lipophilic signals?
Long half-lives (hours to days)
Name some examples of lipophilic signals.
Steroid hormones, thyroid hormones, and retinoids.
What are some ligand gated ion channels?
nAChR, GABAa, 5-HT3, GlyR
Name the components of a G Protein coupled receptor.
Extra cellular domain (ECD)
Trans Membrane domain- composed of 7 alpha helices
Intracellular Domain (ICD)
What does the Extracellular domain in a GPCR do?
Binds to the signal, this causes conformational change of GCPR, allowing the ICD to become active
What does the Intracellular domain in a GPCR do?
Interacts with G proteins, upon conformational change induced by ECD it activates G protein by triggering exchange between GDP and GTP.
Utilizes Gaunine Exchange Factor (GEF)
When is G-protein active? How does this occur?
When GDP is exchanged for GTP by the intracellular domain of GCPR. This occurs via the guanine nucleotide exchange factor (GEF).
What happens after activation of the trimeric G-protein?
The GTP-bound alpha subunit separates.
How does G-protein turn back to inactive state? How is this action accelerated?
The intrinsic GTPase activity of G protein hydrolyzes it’s bound GTP into GDP and phosphate.
Accelerated via the GTP-ase activating protein (GAP).
What does Gs do? Whats it bind to?
Gs stimulates adenylate cyclase through binding a signal molecule.
What does adenylate cyclase do once it becomes activated?
Activated Gs -> activates Adenylate cyclase -> up regulation of cAMP -> PKA becomes active -> target proteins have activity altered.
What does Gt do? Whats it bind to?
Stimulates cGMP phosphodiesterase. Light binds to it.
What does cGMP phosphodiesterase do?
Changes cGMP to 5’-GMP
What does Gi do? Whats it bind to?
Inhibits adenylate cyclase directly, through the binding of a signal molecule.
What does Gq do? Whats it bind to?
Activates phospholipase C.
What does phospholipase do?
PLC activates IP3 and DAG
IP3 -> Ca+ channel in ER/SR -> Ca+2 calmodulin -> Ca+2 calmodulin dependent proteins (CaM kinase, LC kinase)
DAG -> PKC -> phosphorylation of target proteins
Physiological effects of Epinephrin and Gs.
Relaxation of bronchial and intestinal smooth muscle
Contraction of heart muscle
Increased breakdown of triacylglycerides in adipose tissue
Increased breakdown of glycogen in liver and muscle
What does Epinephrine bind to on Gs-protein?
B-adrenergic receptor of Gs
It is a nonselective agonist of all adrenergic receptors (a1, a2, B1, B2, B3) and can undergo multiple GCPR pathways.
Physiological effects of Histamine and Gs.
Bronchoconstriction and symptoms of allergic reaction
What does Epinephrine/norepinephrine bind to on Gi-protein?
A-adrenergic receptor of Gi
Physiological effects of Epinephrine/norepinephrine and Gi
Constriction of smooth muscle
Physiological effects of Dopamine and Gi
Increased heart rate
Physiological effects of Acetylcholine and Gq
Bronchoconstriction and stimulation of salivary glands
Physiological effects of Light and Gt
Vision (binds to rhodopsin!)
Why are G-proteins responses so diverse in the context of epinephrine?
Epinephrine binds to the B-adrenergic receptor of the heart, the bronchial muscle, and intestinal smooth muscle.
All of which it up regulate cAMP, however produce different physiological responses.
What are the two cyclic nucleotide phosphodiesterases and what reactions do they catalyze?
cAMP Phosphodiesterase: hydrolyzes cAMP to AMP
cGMP Phosphodiesterase: hydrolyzes cGMP to 5’ GMP
Inhibitors of cGMP PDE do what? Name an example of one
Increase concentration of cGMP, causes smooth muscle relaction and vasodilation. (eg: Viagra, Levitra, and Cialis)
Inhibitors of cAMP PDE do what? Name an example of one.
Increase concentration of cAMP, leading to increased heart rate. (eg: Caffeine)
What effect does NO have on cGMP? What risks are there with NO?
Activates guanylate cyclase which increases cGMP. Active cGMP leads to smooth muscle relaxation and vasodilation. Taken by patients to lower blood pressure. Don’t take with erectile dysfunction drugs as combination can lead to extreme vasodilation and fatal drops in bp.
What does Cholera prevent from inactivating? How do you get it.
Gs alpha subunit of G-protein. Contaminated water
By what mechanism does cholera cause diarrhea?
Covalent modification of alpha subunits causes ADP ribosylation of Arg decreases GTPase activity. This leads to an overly active Gsa subunit which results in too much cAMP. Overabundance of cAMP cause Cl-channels to open and a loss of electrolytes and water => diarrhea.
What does pertussis prevent form activating? How do you get it.
Gi subunit of G-protein.
Whooping cough.
By what mechanism does pertussis cause whopping cough?
ADP ribosylation of Cys on Gia prevents activation and dissociation of a subunit from the G protein complex This causes less inhibition of AC and more cAMP Results in loss of fluids and excessive mucous in airway of epithelial cell.
What is the ability to turn off or ignore a signal known as?
Signal Desensitization
What are the types of signal desensitizations?
Hormone level drops (decreased adenylate cyclase activity)
Removal of signaling molecules (phosphordiesterase will remove cAMP/cGMP.)
Receptor sequestration: Endosomes
Receptor destruction: Endosomes + lysosomes
How do G protein Receptor Kinases (GRKs) inactivate GCPRs?
GRKs phosphorylate GPCRs, this causes arrestin to bind to the 3rd intracellular loop, preventing Ga subunit from interacting with third loop. Results in Ga-GDP that cannot become Ga-GTP.
What binds to the ECD of the Tyrosine Kinase Receptor?
Contains signal molecule binding site; signals tend to be growth factor. (EGF, NGF, PDGF)
Where is tyrosinase kinase activity of the Tyrosine Kinase Receptor located?
ICD
Binding of ligand to extracellular domain of the Tyrosine Kinase receptor causes what?
Dimerization occurs, dimerized receptor phosphorylates tyrosine residues.
What are proteins that recognize phospho-tyrosines and activate downstream signaling pathways? What are those pathways?
Adaptor and docking proteins
Triggers the phosphorylation of protein targets in the nucleus, plasma membrane and cytoplasm.
RAS-dependent (MAPK pathway) RAS-independent (other kinases)
Examples of adaptor and domains that recognize and bind to motifs on the receptor that contain phosphorylated Tyr.
Adaptor proteins GRB-2, IRS- 1
Domains known as SH2 or PTB
Signaling facilitated by mitogen-activated protein kinase (MAPK) family
Ras-depenent signaling
Examples of RAS Termination
Degradation of signaling molecules
Ligand-induced endocytosis followed by lysosomal degradation
Accelerated RAS inactivation
Dephosphorylation
Insulin signaling (RAS dependent)
IRS-1 => Binds GRB-2 => RAS => Alters gene transcription: increased transcription of glucokinase
Insulin signaling (RAS independent)
IRS-1 => PI3 => PKB => Alters protein and enzyme activity Increased GLUT4 movement to plasma membrane; activation of glycogen synthase
Overview of MAPK pathway
Binds Grb => Sos => Ras => Raf
% of pancreatic cancers and % lung cancers caused by point mutations in RAS
90% and 30-50%
Mutation in these locks RTK into active form.
Decrease in GTPase activity
Condition marked by growth of tumors from nerve tissue due to issues with RAS. Describe illness and mechanism of disease.
Neurofibromatosis Inactivating mutation in neurofibromin (NF-1) gene, which encodes a GAP for RAS; RAS uncontrollably
What are monomeric 20-25kb G proteins?
Small G Proteins which have intrinsic GTPase activity
What characterizes insulin resistance?
Loss of insulin stimulation of glucose uptake by GLUT4 transporters in adipose and skeletal tissue
Characterized by reduced activation of PKB
What is the molecular cause of insulin resistance?
Cytokines, free fatty acid and hyperinsulinemia stimulate the kinases involved in Ser/Thr phosphorylation of IRSs
Tyr phosphorylation of IRS-1/2 necessary for recruitment of PI-3 kinase
Ser/Thr phosphorylation inactivate IRSs and leads to degradation
