Flashcards in MCM 2-7 Signalling II: Second Messenger Pathways of Cell Surface Receptors Deck (23)
Describe Trimeric G-Protein Coupled Receptors
seven pass receptors.
describe trimeric G-proteins
composed of membrane associated alpha and gamma subunits with an internal beta subunit
ligand binds TGPC, TGP interacts with TGPC. TGP swaps it's GDP bound to alpha subunit for GTP, alpha dissociates
beta-gamma activates - moves laterally across PM to interact with targets such as gated ion channnels to open them
once alpha-GTP hydrolyzes to alpha GDP - reassociates with beta:gamma subunit, closes the channel
describe how the alpha subunit can be involved in signal transduction
where is this type of signal transduction often found?
Gs (stimulatory G-protein family) use their alpha subunit to stimulate adenylate cyclase (converts ATP to cAMP)
cAMP activates protein kinase A, PKA, A-kinase, to phosphorlate specific aa residues on protein sequences
-often found in metabolic pathways, gene regulation, and other cellular processes
activation of Gi-linked G protein receptors
reverse the effects of Gs on adenylate cyclase.
Gi family members use their alpha subunit to inhibit adenylate cyclase (decrease concentration of camp, thereby decreasing concentration of PKA)
activation of Gq linked protein receptors
Gq family use alpha subunit to activate phospholiapse C which diffuses laterally to an inositol phospholipid in the membrane
phospholipace c cleaves (C as in cleaves) the inositol into a free IP3 and membrane bound DAG
IP3 diffuses into cytoplasm to the ER to open channels to release Ca+2
DAG activates Protein Kinase C by increasing its affinity for Ca+2
both DAG and IP3 give a strong activating signal to PKC
the released Ca+2 ions stimulate both activated PKC and calmodulin.
Calmodulin, after undergoing Ca+2 dependent conformation change, activates CAM kinases, such as myosin light chain kinase (MLCK is a major factor in the process of muscle contraction)
what does PKC do?
regulates cell division, growth, etc..
what does calmodulin do?
Calmodulin - small protein, its job is to bind calcium. Changes its conformation in response to the calcium concentration. Has 4 binding sites. As it changes its conformation, can interact with other proteins and regulate them
ex. Regulation of contraction of actin arrays in non-muscle and smooth muscle cells aka activates CAM kinases, such as myosin light chain kinase (MLCK, which is a major factor in the process of muscle contraction)
describe signal transduction by receptor tyrosine kinsases
inactive RTK exist as two separate receptor molecules
when ligand binds, they dimerize, and transphosphorylation of one another occurs, activating the RTK.
next, cellular proteins (SH2 Proteins) from within the cell bind to the cellular tails of the RTK and change their conformation to transduce the signal.
What types of events are controlled by receptor tyrosine kinases (RTKs)
can stimulate phospholipase Cgamma, which cleaves (C for cleaves) inositol phospholipid into IP3 (travels to ER to open Ca+2 Channels) and DAG (activates PKc and increases its Ca+2 affinity)
through the SH2 domains of SH2-SH3 adapter proteins, can activate RAS monomeric G-protein pathway
-adapter protein recruits GEF to bind GTP to RAS, activating it
example of RAS pathway (MAP kinase pathway)
-activated RAS activates MAP kinase kinase kinase, which activates Map Kinase Kinase, which activates Map Kinase.
Map kinase activates a number of proteins, including TF's and proteins that regulate other protein activities
these receptors are the kind that is most often affected when oncogenes are activated
what do SH2-SH3 adapter proteins do?
Sh2-sh3 adapter proteins can bind to the phosphorylated tyrosine- interact with and activates a GTP Exhange Factor GEF (ras activator) which activates RAS (monomeric G-protein), stimulates release of GDP and uptake of GTP by the RAS, causing onward transmission of signal
Some human receptor tyrosine kinase families have been implicated in
human malingnancies. Receptor tyrosine kinase families can stimulate cells to divide grow. Certain mutations in the receptor make it seem like a ligand is bound all the time, so always stimulated to divide/grow.
what is different about tyrosine kinase-linked receptors?
the receptor protein itself is not a kinase, it has a kinase associated with it.
When the tails become phosphorylated, STAT gene regulatory proteins bind, dimerize, and migrate to the nucleus where they along with other gene regulatory proteins bind DNA and influence transcription of target gene to RNA
gene regulation by Gs-linked receptors
Adrenaline activates GPCR, trimeric G-protein binds, Alpha swaps GDP for GTP, dissociates, activates adenylate cyclase. Cyclic AMP activates PKA which phosphorylates/activates a transcription factor (cyclic AMP response element binding protein) CREB binds to and increases transcription of genes that have cAMP response elements in their promoters (CRE)
PKA can activate
transcription of genes that are regulated by the cAMP response element binding protein (CREB)
phosphorylated form of CREB binds to CRE sequences in gene promoters
PKC, Calmodulin, and CAM Kinases
MAP kinases are mostly ______________ kinases with specificty for targets important in _______. Examples of targets?
targets important in growth control = including TF that regulate cyclin genes and cyclin dependent kinase inhibitors like p21 and p27
receptor tyrosine kinase is due to
diverse and unrelated EXTRAacellular ligand binding domains
the INTRAcellular kinase domains are all related
In both receptor tyrosine kinases and tyrosine kinase-linked receptors, the SH2 groups bind to
phosphorylated tyrosines in the tails (phosphotyrosines)
how is PKC activated?
by DAG through Gq.
Gq - alpha subunit - Phospholipase C - Inositol phospholipid - DAG + Ip3 = IP3 activates PKC by increasing its affinity for calcium
Gq = Phospholipase C, and PKC
how is PKA activated?
by cAMP generated from adenylate cyclase activation by alpha subunit of Gs
what is the functional use of transphosphorylation?
it passes the signal from the extracellular domain of the receptor to the cytoplasmic domain of the receptor
why have many tyrosine kinsae genes been identified as proto-oncogenes
because TKR genes are influential in cell growth and division. A mutation in them can make it appear like ligand it always bound, and they are always actiating growth pathways.