Signal Transduction Flashcards
which hormones pass through plasma membrane to intracellular receptors?
steroid hormones
another name for growth factors, function
mitogens, induce cellular proliferation and activate mitogen activated protein (MAP) kinase cascades
what is GDF-8?
myostatin (growth and differentiation factor), inhibits muscle growth a disruption would result in substantial increase in muscle mass
what is TGFbeta?
superfamily of transforming growth factor beta
what factors are considered TGF
bone morphogenetic proteins transforming growth factor beta glial derived neurotrophic factors growth and differentiation factors
4 examples of extracellular signaling molecules?
hormones survival factors growth factors/mitogens death signals
how does death signaling work?
FasL (ligand) on a T cell binds to Fas receptors induces apoptosis in Fas receptor expressing cell (there needs to be physical contact between cell receiving and giving signal)
what is the general reasoning for signal transduction?
detect, amplify and integrate external signals to generate responses such as changes in enzyme activity, gene expression or ion channel activity
steps of signal transduction
- stimulus induces a secretory cell to release a signaling molecule 2. the signaling molecule binds to its receptor on the target cell’s plasma membrane 3. binding of signaling molecule to its receptor initiates signaling cascade inside cell 4. signaling cascade induces a specific response in the cell
types of extracellular signaling
endocrine, paracrine
what are intracellular/nuclear receptors
receptors found in the cytoplasm/nucleus of the cell that respond to membrane-soluble ligands
4 major families of cell surface receptors
- ligand gated ion channel receptors 2. g protein coupled receptors 3. enzyme coupled receptors 4. cytokine receptors
where are ligand gated ion channel receptors usually found?
electrically excited cells like neurons and muscle cells
how do ions flow in ligand gated ion channel receptors?
enter or exit along their electrochemical gradients in a very fast response (miliseconds)
2 examples of ligand gated ion channel
GABA receptor, Nicotinic Acetylcholine receptors
what type of receptor is a GABA receptor
ligand gated ion channel receptor
what is GABA
gamma amino butyric acid, an inhibitory neurotransmitter
what does binding of specifically GABAa to GABAa receptors do?
opens Cl channel, allowing for influx of Cl- and resulting in hyperpolarization of the cell membrane, preventing neuron from firing
what to GABA receptor agonists do?
directly bind to GABA binding site, produce sedative effects
what are PAMs
GABA receptor positive allosteric modulators, enhance GABA-dependent activity of the receptor by holding them open longer
example of PAMs
alcohol (ethanol) barbiturates benzodiazepines (diazepam)
what receptor is a nicotinic acetylcholine receptor
ligand gated ion channel receptor
what goes binding of acetylcholine or nicotine do to a nicotinic acetylcholine receptor?
causes conformation change in receptor, resulting in the formation of a pore that allows Na to enter the cell ALLOWS propagation of action potentials is very important in the neuromuscular junction for depolarization and AP (postsynaptic cells)
how are signals terminated at the ligand gated ion channel receptors?
ligand is degraded by proteases (specific digestive enzymes) in the synaptic cleft ex. ACh degraded by acetylcholinesterase
pathology of myasthenia gravis
AUTOIMMUNE DISEASE, body makes antibodies against the nicotinic acetylcholine receptor to prevent signaling and NMJ, resulting in muscle weakness ACh activity works just not as much
treatment for myasthenia gravis
acetylcholinesterase inhibitors to decrease the breakdown of any produced ACh and increase likelihood of ACh binding
what is unique about the G protein coupled receptor through the membrane?
is a 7 pass trans membrane receptor
what external signals do GPCR receive?
adrenergic, somatostatin, muscarinic ACh, dopamine, histamine, serotonin, prostaglandin, olfactory, taste BOTTOM LINE, A LOT OF THINGS
composition of G protein complex
heterotrimeric complex, alpha, beta, gamma subunits
what does the alpha subunit of G protein complex bind to?
GTP/GDP because it contains GTPase activity
what occurs when the alpha subunit is bound to GTP?
g protein complex is ON (active)
what occurs when alpha subunit is bound to GDP?
g protein complex is OFF (inactive)
what is G-alpha-s
type of alpha subunit that Stimulates adenylyl cyclase and increases the production of cAMP
what is G-alpha-i
type of alpha subunit that Inhibits adenylyl cyclase and decreases the production of cAMP
what is G-alpha-q?
type of alpha subunit that activates phospholipase C that stimulates the production of inositol triphosphate (IP3) and diacylglycerol (DAG) (these are cleaved from the plasma membrane)
2 classes of second messengers?
hydrophobic (plasma membrane associated) and hydrophilic (cytoplasmic)
what are the hydrophobic second messengers?
DAG (diacylglycerol), works on things that are brought to the cell membrane
what are the hydrophilic second messengers?
cyclic AMP (cAMP) IP3 (inositol 1,4,5- triphosphate) calcium
explain of cAMP signaling works
- binding of ligand (adrenaline) to G protein coupled receptor results in activation (GTP binding) of G-alpha-S 2. GTP bound G-alpha-s stimulates adenylyl cyclase 3. membrane associated adenylyl cyclase synthesizes cAMP from ATP 4. cAMP activates protein kinase A (PKA) 5. PKA activates (through phosphorylation) phosphorylase kinase (PK) 6. PK activates glycogen phosphorylase 7. glycogen phosphorylase regulates breakdown of glycogen to release glucose
how is cAMP signaling terminated?
conversion of cAMP to 5’ -AMP via cAMP phosphodiesterase
explain how IP3 and DAG signaling works
- stimulation of GCPR by external signaling molecules, G-alpha-q protein activates phospholipase C
- inositol phospholipid (PIP3) is cleaved by activated phospholipase C to make DAG and IP3
- DAG serves as docking site on plasma membrane for protein kinase C (PKC)
- IP3 binds to ligand gated Ca channel receptor on ER membrane
- calcium channel opens, calcium released into cytoplasm
- together, DAG and Ca activate PKC, resulting in various signaling cascades in the cell
*IP3 and DAG 2nd messengers
*Ca is like 3rd messenger in this case
explain relationship between calcium and calmodulin (CaM)
Ca binding to calcium responsive proteins (calmodulins) mediates the effects of Ca signaling in the cytoplasm
i.e. binding of calcium to calmodulin results in conformation change in CaM that allows it to interact with other signaling proteins such as Ca/calmodulin dependent protein kinases (CaMKII) (binding of calcium to calmodulin allows it to wrap around CaMKII)
explain the process of Ca/calmodulin in smooth muscle contraction
- binding of ca/calmodulin moleules to the myosin light chain kinase (MLCK) turns on the kinase activity of MLCK
- active MLCK can then phosphorylate and activate myosin light chain (regulatory subunit of myosin) in the contractile units of the cell
- the activated myosin can walk along actin filaments and produce contraction
how is calcium reguated in the cells?
- plasma membrane uses Na/Ca exhanger antiports and Ca-ATPase pumps
- ER membrane (or sarcoplasmic reticulum) uses Ca ATPase pumps
what type of receptor is an adrenergic receptor?
GCPR
what do adrenergic receptors do in the cell?
regulate functions of the autonomic nervous system, they are the targets of epinephrine and norepinephrine
how are the types of adrenergic receptors modulated?
use different combinations of alpha and beta subunits
what do alpha 1 adrenergic receptors do?
stimulate production of IP3/DAG/Ca, associated with G-alpha-q, in the vascular smooth muscle, skin, renal, GI, spincters, bladder, iris
what do alpha 2 adrenergic receptors do?
decrease cAMP by inhibiting adenylyl cyclase via G-alpha-i
in the GI tract and presynaptic adrenergic neurons
what do beta 1 adrenergic receptors do??
increase cAMP via stimulation of adenylyl cyclase associated with G-alpha-S in the heart, salivary glands, adispose tissue, and kidney
what do beta 2 adrenergic receptors do?
increase cAMP by stimulating adenylyl cyclase associated with G-alpha-S, in the vascular smooth muscle of skeletal muscle, Gi tract, bladder, and bronchioles
explain the process of beta/gamma complex signaling
- ACh binds to muscarininc ACh receptor, Galpha AND Gbeta/gamma are activated
- only the G-beta/gamma is functional
- activated G-beta/gamma binds to intracellular domain of a K+ channel, causing it to open
***NO SECOND MESSENGERS
difference between muscarinic ACh receptor and nicotinic ACh receptor?
muscarininc is GPCR
nicotinic is ligand gated ion channel receptor
what happens to ACh in the heart muscle?
binds to GPCR (muscarinic) leading to opening of K channels via G-beta/gamma proteins, outflow of K and DECREASED muscle contraction
what happens to ACh in skeletal muscle?
binds to ligand gated ion channel (nicotinic) which directly opens Na channel, causing influx of Na and INCREASING muscle contraction
how are GPCR terminated?
alpha subunit of G proteins INACTIVATES ITSELF via GTP hydrolysis, then reassembles with beta/gamma to make inactive G protein
TAKES TIME so acts as an internal timer
explain when Wnt is absent
in the absence of Wnt, beta-catenin is held in an inactive state by association with a complex that includes GSK-3 and APC.
the GSK-3 phosphorlyates beta-catenin, resulting in degradation of beta-catenin.
without beta-catenin, the Wnt responsive genes are off
explain when Wnt is present
Wnt ligand binds to Frizzled (its receptor), signaling cascade is initated inside the cell, resulting in the inactivation of APC, which allows for the accumulation of beta-catenin inside the cell.
Beta-catenin then translocates into the nucleus, where it binds to complex of transcription factors called TCF complex.
when beta-catenin binds to TCF complex, TCF complex is activated resulting in transcription of responsive genes, leading to proliferation of gut stem cells
where are PTCH receptors found?
cell surface of many cell types, including keratinocytes
what is the ligand for PTCH?
sonic hedgehog (SHH)
what occurs when SHH is absent?
PTCH associates with SMO (smoothin), a GPCR and this association keeps SMO in an INACTIVE state
what occurs when SHH is present?
SHH binds to PTCH, SMO dissociates from PTCH and is now active.
the activated SMO turns on signaling cascade that leads to increased gene expression through the activity of the GLI1 transcription factor, is very important for transcription factor activated cellular proliferation
what 3 AA are major targets for phosphorylation?
serine, threonine, tyrosine
what is a kinase
adds phosphate to another protein
what is a phosphatase
removes phosphate from another protein
what is the response time for enzyme coupled receptors?
hours - slow response
what is the largest class of enzyme coupled receptors? and what do those do?
receptor tyrosine kinases (RTKs), most extracellular signals for growth, survival and proliferation act through these, initates signaling cascade via phosphorylation
what is SH2 domain
src homology 2 domain, specifically recognizes phosphorylated tyrosines, is important for signal transduction processes mediated by RTK and cytokine receptors
what are the steps for activating RTK’s
- ligand binds, inactive RTK monomers dimerize (come together to form dimer)
- contact between the adjacent receptor tails activates kinase function, and each receptor unit phosphorylates the other on specific tyrosines
- the phosphorylated tyrosines serve as docking sites for adaptor proteins that have SH2 domains
- signal is relayed inside the cell
what is RAS
small GTP binding protein with GTPase activity, like the alpha subunit of g protein
more than 20% of all human tumors contain what ?
an activating RAS mutation
what occurs when GTP is bound to RAS? GDP?
Ras is active when GTP bound, inactive when GDP bound
what is Mitogen Activated Protein kinase pathway important for
important signal transduction pathway involved in cell growth and proliferation, and gene expression/protein activity
what can occur if there is a mutation in an RTK?
unregulated cell proliferation, usually due to ligand-independent firing (activation of receptors)
what is EGFR, what does it do, and why is it important
receptor for epidermal growth father (EGF), stimulates cell growth, proliferation and differentiation. some cancers activate mutations in the EGF pathway (lung cancers, glioblastoma multiforme)
example of a RTK
insulin receptor
what is the process of insulin receptor RTK signaling
- insulin binds to insulin receptor, which phosphorylates itself and creates a docking site for Insulin Receptor substrate (IRS)
- the active IRS activates PI-3 kinase
- IR-3 kinase phosphorylates PIP2 to make PIP3
- PIP3 acts as docking site for phosphoinositide dependent kinase 1 (PDK-1) and protein kinase B (PKB)
- PDK1 and PKB come together and PDK1 phosphorylates PKB
- activated PKB acts to increase glucose uptake and glycogen synthesis
what is unique about PIP2?
it is a component of both RTK signaling and G-protein signaling
what is the difference between RTK and receptor serine or threonine kinases?
- serines or threonines are phosphorylated
- SMAD docks at the intracellular tail of the receptor.
- SMAD is phosphorylated by the activated receptor
- phosphorylated SMAD forms compled with regulatory proteins and translocates to the nucleus where it serves as a regulator of gene expression
how are cytokine receptors different than RTK?
receptors DO NOT have intrinsic kinase activity, so they have to associate with other proteins that DO have tyrosine kinase activity
what is the end result of the JAK-STAT pathway
transcriptional regulators for expression of specific genes
what type of receptors does the JAK-STAT pathway have
cytokine
explain JAK-STAT signaling pathway
- ligand binds to the cytokine receptor subunits, which have an associated JAK tyrosine kinase
- JAK is activated and phosphorylates specific tyrosine sites on the intracellular tail
- phosphorylated tyrosines serve as docking sites for SH2 domain containing proteins (STATs)
- STATs are phosphorylated and dimerize, and translocate to the nucleus, acting as transcriptional regulators for the expression of specific genes
how are enzyme coupled and cytokine receptor signals terminated?
dephosphorylation of the downstream components of the enzyme coupled pathway
what is adaptation/desensitization
if a receptor is repeatedly exposed to a particular signaling molecule, the cell adapts its sensitivity to that molecule by
- inactivating the receptor
- internalization of receptor
- downregulating the receptor
how are receptors inactivated?
structural modification of receptor, leading to its inactivation
how are receptors internalized?
receptor/ligand complexes are incorporated into endosomes
RESULTS IN FEWER RECEPTORS ON THE MEMBRANE AT A GIVEN TIME
how are receptors downregulated?
receptor/ligand complexes are incorporated into endosomes, which fuse with lysosomes, which degrade the receptor and ligand (in the lysosome)
what is synaptic signaling
when neurons release NT that act on postsynaptic target cells
how does signaling occur through membrane diffusible molecules
small hydrophobic signaling molecules can directly pass through plasma membrane
what is juxtacrine signaling, what 3 methods can it use?
cell cell communication that does not involve extracellular diffusion of molecules.
can use:
- notch signaling or Fas
- integrins
- gap junctions
how are integrins used for juxtacrine signaling
ligands in the extracellular matrix secreted by one cell interact with receptors on neighboring cells
how are notch/Fas used for juxtacrine signaling
protein on one cell surface interacts with a receptor on an adjacent cell
how are gap junctions used for juxtacrine signaling
direct transmission of signals from cytoplasm of one cell to cytoplasm of adjacent cell
what is notch signaling and notch protein
notch signaling is an important mode of signaling in organogenesis (neurogenesis)
notch protein is a single pass transmembrane protein
how is notch activated?
binding to delta, serrate, or jagged (which are transmembrane proteins found on the surface of adjacent cells, and are “ligand” for notch receptor)
pathway of notch signaling
- binding of notch to its ligand (delta, serrate, jagged) on adjacent cell
- conformational change in cytoplasmic domain of notch
- cleavage of notch’s cytoplasmic domain by membrane associated protease
- cleaved domain of notch translocates to the nucleus and induces transcription of target genes
what is lateral inhibition
cell cell interaction where a cell that adopts a particular fate INHIBITS its immediate neighbors from also adopting that fate, this is mediated by notch delta interaction
example of lateral inhibition
during neurogenesis, a cell that has committed to be a neuron expresses delta on its surface. notch binds that protein, and that signaling inhibits neighboring cells that express notch on their surface from becoming neurons
what is the function of Fas signaling
death receptor initiated apoptosis
mechanism of Fas signaling
death ligand FasL that is expressed on a surface of one cell interacts with another cell that expresses a plasma membrane associated death receptor FasR (on plasma membrane).
the cell that has the receptor undergoes apoptosis
what are integrins, what do they bind to extracellularly and intracellularly
transmembrane heretodimers
extracellularly: bind to fibronectin
intracellularly: bind to actin via adaptor proteins
what occurs when tension is felt between the cell and the matrix through the integrin transmembrane heterodimer?
integrin is activated and initiates strong binding to the ECM and cytoskeleton
AKA activation of integrin dimers on ONE side of the membrane causes activation on the OTHER side of the membrane
what can be the outcome of integrin signaling
influence on cell proliferation, cell survival and cell migration
pathway of integrin signaling
- ligand is deposited in the ECM
- ECM side of integrin from neighboring cell binds to ligand
- binding causes conformational change in the cytoplasmic side of the integrin
- intracellular signaling cascade is initated
what are allowed to pass through gap junctions, and how are they controlled?
small water soluble molecules and ions, can be opened and closed in response to extracellular signals
what forms gap junctions?
connexons made of 6 subunits that form a central channel are aligned end to end to create the larger channel
what is a common site and function for gap junctions
cardiac muscle to help propagate the AP to cause synchronized muscle contractions
what is the purpose of having a high concentration of NT in the synaptic cleft?
this allows for the NT receptors to have LOW AFFINITY for their ligand, that ensures that the NT can be rapidly dissociated from their receptors. ALLOWS FOR RAPID TERMINATION OF NEUROTRANSMISSION
what molecules can readily pass through lipid bilayers
O2, CO2, nitrogen, water, ethanol
what molecules CANNOT readily pass through lipid bilayers
AA, glucose, nucleosides, charged ions
what is the pathway of nitric oxide signaling?
- Ach released from nerve terminal of activated neuron
- ach binds ach receptor on surface of endothelial cell
- binding causes signal transduction cascade that releases Ca into the endothelial cell
- increase in Ca activates NOS (nitric oxide synthase) that uses arginine to make NO
- produced NO diffuses out of the cell and through the plasma membrane of a smooth muscle cell (adjacent to it)
- in the smooth muscle cell cytoplasm, NO binds to guanylyl cyclase and activates it
- activated guanylyl cyclase produces cyclic GMP, and this causes smooth musce cells to relax = vasodilate
which hormones can bind to intracellular receptors in the cytoplasm, how, and what do they do
STERIOD HORMONES cortisol, estradiol
because they are lipophilic, they are able to pass through plasma membrane unaided and bind themselves to intracellular receptors
hormone receptor complex translocates to nucleus where induce expression of specific response genes
