Hormone action Flashcards
steps in GPCR singling through IP3 and Ca (7)
- hormone binds to specific receptor
- occupied receptor causes GDP to be replaced by GTP on Gq-alpha
- Gq-alphae bound to GTP moves to phospholipase C (PLC) and activates it [membrane bound]
- activated PLC cleaves PIP2 into IP3 (inositol triphosphate) and diacylglycerol (DAG)
- IP3 binds to a specific receptor-gated calcium channel, releasing sequestered calcium
- DAG and Ca activate protein kinase C at the surface of the plasma membrane
- phosphorylation of cellular proteins by PKC produces some of the cellular responses to the hormone
what are the 2 products of PIP2 cleavage?
IP3 and DAG
what molecule cleaves PIP2?
PLC
which G-alpha subunit activates PLC?
Gq-alpha
where is DAG located?
membrane bound
where is IP3 found?
free in cytoplasm
hormones may use more than one G-protein. true or false?
true
why is singling through GPCR complex?
use can change during development and use can change depending on hormone concentration or in different tissues
what are the two types of receptors involved with tyrosine kinase?
- receptors with an integrated (intrinsic) kinase activity
2. receptors that recruit a kinase
what is a tyrosine kinase?
kinase that specifically phosphorylates tyrosine residue on a protein
which are the most studied RTK?
insulin receptor and IGF-1 receptor
which type of RTK are the insulin receptors and IGF-1 receptors?
receptors with intrinsic tyrosine kinase activity
what is the structure of the insulin receptor?
hetero-tetrameric structure 2 alpha and 2 beta chains held together by disulphide bonds
=> 2 types of subunits, 4 subunits in total
how is the insulin receptor synthesized?
from a single precursor protein
where are insulin receptors most abundant?
adipocytes and hepatocytes
what is the series of events after insulin binding? (3)
- autophosphorylation (intrinsic kinase activity) of intracellular domain of receptor (carboxylic end)
- docking and phosphorylation of IRS-1 or IRS-2 (insulin receptor substrate)
- activation of 2 major signal pathways MAPK and PIP3
which signaling pathways does insulin binding trigger?
MAPK and PIP3
steps involved in Insulin receptor signaling through MAPK pathway (7)
- insulin receptor binds insulin and undergoes autophosphorylation on its carboxyl-terminal Tyr residues
- insulin receptor phosphorylates IRS-1 on its tyrosine residue
- SH2 domain of Grb2 binds to phosphorylated-Tyr of IRS-1, Sos binds to Grb2, then to Ras, causing GDP release and GTP binding to Ras
- activated Ras binds and activates Raf-1
- Raf-1 phosphorylates MEK on two Ser residues, activating it. MEK phosphorylates ERK on a Thr and a Tyr residue, activating it
- ERK moves into the nucleus and phosphorylates nuclear transcription factors such as Elk1, activating them
- phosphorylated Elk1 joins SRF to stimulate the transcription and translation of a set of genes needed for cell division
what are adaptor proteins? give examples (4)
1 protein comes and adapts to a multiprotein conglomeration complex
ex: Grb2, Sos, Ras, Raf-1
Ras acts like a G protein, why?
GDP replaced by GTP
role of Raf-1
kinase that activates MEK
1st protein of MAPK pathway
what is the cellular response of the MAPK pathway
changes in gene expression - targets are transcription factors
steps involved in Insulin receptor signaling through PIP3 pathway (5)
- IRS-1, phosphorylates by the insulin receptor, activates PI3K by binding to its SH2 domain. PI3K converts PIP2 to PIP3
- PKB bound to PIP3 is phosphorylated by PDK1. Thus activated, PKB phosphorylates GSK3 on a Ser residue, inactivating it
- GSK3, inactivated by phosphorylation, cannot convert glycogen synthase (GS) to its inactive form by phosphorylation, so GS remains active
- synthesis of glycogen from glucose is accelerated
- PKB stimulates movement of glucose transporter GLUT4 from internal vesicles to the plasma membrane, increasing the uptake of glucose
PIP2 is involved in 2 signaling pathways. which are they?
GPCR pathway and IRS through PIP3 pathway
what is the difference between PIP2 in GPCR and PIP3 pathway?
in GPCR: PIP2 converted to DAG and IP3 by PLC
in PIP3: PIP2 is phosphorylated by PI3-K into PIP3
what is the difference between IP3 and PIP3
in IP3 - 1st carbon is phosphorylates
in PIP3 - PIP2 isn’t cleaved, a phosphate is just added to 3rd carbon
+ IP3 is cleaved off into cytoplasm where as PIP3 is still membrane bound
what is the distinct feature of GSK3 and Glycogen synthase involved in PIP3 signaling pathway
GSK3 and GS are active when it is NOT phosphorylated
=> when phosphorylated by PKB -> inactivation
=> when phosphorylated by GSK3 -> inactivation
when can glycogen synthesis happen?
when GSK3 is phosphorylated because this will inactivate GSK3 and prevent phosphorylation (inactivation) of GS rendering GS active -> glycogen synthesis
which hormones have receptors with recruited tyrosine kinase activity?
growth hormone
prolactin
leptin
characteristics of GH signaling pathways
- GH has 2 binding sites and binds sequentially to 2 receptor molecules forming a dimeric complex
- > dimerization of the cytoplasmic regions initiates signal transduction
what are the 2 first steps of GH signaling pathway?
- binding of GH and dimerization
2, recruitment of JAK-2 [tyrosine kinase]
what are the 3 branches possible when recruiting JAK protein?
- activation of the transcription regulatory proteins STAT
- activation of the MAPK pathway (as insulin, but JAK2 plays role of IRS1)
- activation fo PIP3 pathway (instead of IRS we have JAK2)
what kind fo activity does JAK have?
intrinsic kinase activity -> phosphorylates itself, the receptor and other proteins
what are STAT proteins?
transcription regulatory proteins - transcription factors that translocate from membrane to nucleus -> change in gene expression
steps in JAK-STAT pathway (5)
- binding of interferon cross-links adjacent receptors, and JAKs cross-phosphorylate each other on tyrosine (intrinsic tyrosine kinase activity)
- activated JAKs phosphorylate receptors on tyrosine residues
- After STATs dock on specific phosphotyrosines on the receptor, the JAKs phosphorylate them
- STATs dissociate from receptor and dimerize via their SH2 domain
- STATs translocate to nucleus where they act as transcription factors (bind to DNA and other gene regulatory proteins)
which hormones bund to a family of intracellular receptors?
steroid hormones and thyroid hormones
where are intracellular receptors located?
in cytoplasm or nucleus
what is the function of the intracellular receptors?
transcription factors
Response of intracellular receptors is fast since transcription and translation of proteins is necessary. True or false?
False! SLOW response
for intracellular receptors to have a typical function, what must their nuclear receptor domain have? (3)
- DNA-binding domain (DBD)
- Nuclear localization signal (NLS) - for translocation into nucleus
- ligand binding domain (LBD)
once the hormone binds to the nuclear receptor and is activated, which sequence does it recognize on the DNA?
hormone response element
if the nuclear receptor is a homodimer, what is the particularity of their HRE?
HRE sequence is the same for both
what are co-repressors?
involved in repression of gene transcription
associated with nuclear receptor bound to DNA but not bound to ligand - inhibitory to transcription
histone acetylation is involved with …..
gene expression
histone deacetylation is involved with ….
repressed/lowered gene expression
