Introduction to Signal Transduction Flashcards
How can signals be sent? (x4)
1) Endocrine: secreted into blood acting on distant target (hormones)
2) Paracrine ( acting on nearby cell, neurotransmitter)
3) autocrine ( secreted ligand acting on same cell (growth factor)
4) cell to cell signaling: plasma membrane attached proteins can signal to each other to affect dilation etc
what is signal transduction?
process of converting extracellular signals into intracellular responses
how do cells respond to signals? (2 ways)
1) fast: by changing activity of existing enzymes
2) slow: change levels of expression of enzymes vis gene regulation
what does signal amplification mean?
-at each step of signal transduction pathway, the number of activated participants increases
What does amplification cascade mean? Example of something that has it?
ex= hormone signaling pathways
- one epinephrine molecule leads to 1000s of cAMP final product. each step in process results in amplification
rate of responses to extracellular signals?
1) rapid:(seconds-minutes) phosphoryaltion, ion/glucose/aa transport
2) delayed: (hours) trxn/translation
3) prolonged: (hours-days) requires trxn of cell cycle genes, cell growth/proliferation
How are signals conveyed in the cell?
1) receptor mediated
2) non-receptor mediated
what is receptor mediated signaling?
- membrane receptors on cells respond to responsed to extracellular signals that bind to cell surface
- allows cells to respond to hormones etc
How do steroids signal?
-use nuclear receptors that are trxn factors capable of responding directly to steroid binding
Non receptor mediated signaling?
- cells sense contacts w/ the extracellular matrix or other cells by proteins etc
- cells turn on internal signals in response to situations such as poorly folded proteins
G-protein coupled receptors (GPCR)
- largest protein superfamily
- heptahelical (7 transmembrane)
- couples to one or two of the 20 known heterotrimeric G-proteins at one time to activate alpha subunit
What is a G-protein?
- heterotrimeric protein (alpha, beta gamma)
- activated/deactivated by many GEFs/GAPs
Alpha subunit of G-protein?
-GTP binding trimer with Beta and gamma
GEF & GAP?
1) GEF (guanine nucleotide exchange factor) activate reactions by exchanged GDP–>GTP
2) GAP (GTPase activating protein) cause hydrolysis of GTP–>GDP therefore terminating signaling
GPCR/G-protein steps?
- GPCR bound by ligand, activated (G-protein bound GDP inactive state)
- ligand binding/ conformational changes causes GDP–>GTP hydrolysis by GEFs activating G protein
- G-protein alpha subunit binds GPCR, dissociation from beta gamma subunits
a. Alpha subunit & some pieces of beta gamma cause downstream signaling - Downstream signaling activates kinases which dephosphorylate GPCR causing it to dissociate from G-protein alpha subunit
- RGS (regulator of G protein signals) are protein kinases that cause hydrolysis of GTPGDP therefore deactivating the G protein
a. GTP hydrolysis is the internal clock, controls G protein signaling - GPCR ONLY ACTIVE WHEN BOUND TO GPROTEIN no enzymatic activity on own
G alpha protein subunit?
- are G proteins
- 21 different versions encoded in human genome
- activated by different GPCRs, regulate variety of diff effector proteins that synthesize second messengers
cAMP and G alpha proteins?
- cAMP is a second messenger
- has stimulatory G alpha subunit activates it
- an inhibitory Galphai inhibits production
G(alpha)s
alpha–> adenylate cyclase (AC)–> cAMP–> protein kinase A (PKA)
G(alpha)i
alpha inhibits AC-> lower cAMP production
-actiavtes RhoGEFs & K+ channels
G(Alph)q
1) couples to phospholipase CB (PLCB) to hydrolyze PIP2 & produce inositol triphosphate (IPS) and diacylglycerol (DAG)
2) IP3 mobilizes Ca2+
3) DAG and Ca2+ activate PKC
-can activate RhoGEfs & K+ channels
G(alpha) 12/13
-couples to certain RhoGEfs to activate RhoA, PlC
Typical G(alpha)s signaling?
1) binds AC which, converts ATP–>cAMP, cAMP activates PKA
2) can activate K+ & Ca2+ channels
How cAMP made/deactivated?
1) made by conversion of ATP–>cAMP via Adenylate Cyclase
2) degraded by PDE (phosphodiesterase)
Typical G(alpha)I signaling?
1) inhibits AC, therefore inhibits cAMP production & PKA production
2) beta & gamma subunits can activate RAS
Typical G(alpha)q signaling?
1) couples to PLC(beta)
2) hydrolyzes PIP2
3) PIP2 makes DAG + IP3 which move calcium 4) DAG & Ca2+ activate PKC
What are Receptor Tyrosine Kinases?
- growth factor receptors
- 6 families
- some have intrinsic kinase activity
- some have kinase activity only after dimerization (growth factor families)
- cell surface receptors w/ into and extra cellular domains
intrinsic kinase activity?
insulin family
-is dimeric
How activate Receptor TK?
1) ligand binds extracellular domain, conformational change(dimerization) or autophosphoryaltion if is an intrinsic tyrosine kinase
2) RTK-P Phosphorylated sites recruit binding/adapter proteins
3) Proteins activated: Protein kinases, lipid kinases, Monomeric G protein
kinase activity only after dimerization?
-growth factor families: EGFR, PDGFR, FGFR
Extra cellular domain structure vs intracellular domain RTK?
extra: similar to IgG, fibronectin or cysteine rich repeats
intra: conserved w/ single tyrosine kinase domain or 2 tyrosine kinase repeats
Monomeric GTPases?
- Ras
- molecular switches for cell division, growth, gene expression
- are downstream of membrane receptors; bind & activate other proteins in signaling cascade
How are GEF’s activated?
1) y phosphorylation
2) active Tyrosine Kinase association
What is RAS-GEF called?
SOS
How monomeric GTPases (Ras) activated/deactivated? Where located?
- activated by exchange of GTP for GDP by GEFs
- deactived by GTP hydrolysis (Gap) which acts as intrinsic timer
2)RAS attach to membrane via farnesyl & myristoylation
ERK1/2 Cascade? (5 steps)
1) RAS activated by GTP, farnesylation RAF brings RAF to active RAS membrane. Phosphorylate it
2) Active RAF (MAPKKK) looses auto inhibition
3) RAF phosphorylates MEK1/2 (MAPKK) activating it
4) MAPKK (MEK1/2) phosphyrlates & activates ERK1/2
5) ERK1/2 phosphorylated can enter nucleus and effect early trxn factors that promote cell proliferation
What does the ERk1/2 cascade link?
Links external cues from the RTKs to internal processes (Ras) down to cell proliferation
PI3Kinase?
- is a lipid kinase that promotes cell survival, migration & glucose uptake
- alternative to RAS/RAF pathway
PI3 Kinase mechanism?
1) activated by RTK & GPCR
2) converts membrane lipids PIP2–> PIP3
3) PIP3 attracts proteins containing PH-domains
Downstream effects of PI3-Kinase?
1) Akt (protein kinase B)
^IMPORTANT
2)RhoA family GTPases
3) Glut 4
Examples of cellular oncogenes? How do they work?
1) src
2) Raf
3) Ras
4) Myc
* induce proliferation
- act on the mitogen activated protein kinase (MAPK) pathway
Akt?
- downstream effector of PI3 Kinase
- is a protein kinase B (ser-thre kinase)
- involved in mitogenic proliferation & survival
Jak/STAT pathway?
- JAK Family (Janus Kinase) = 3 JAK isoforms & tyrosine kinase 2 (TYK2)
- JAK inhibitors used to treat autoimmune diseases
Jak/stat pathway?
1) interferon ligand binds receptor, cytosolic cross phosphorylation of receptor
2) activates JAK, which phosphorylates tyrosine kinase
3) binding proteins activated by JAK phosphorylation become TF (Stats_ enter nucleus and effect immunity/inflammation gene
Non-receptor Tyrosine Kinases?
- some tyrosine kinases don’t have extracellular/membrane domains
- post translation modification allow them to attach to membrane
- unlike receptor TKs, intracellular domains are highly variable
- src=example
src?
1) first non-recepeptor tyrosine kinases
2) membrane localization =myristoylation
3) regulation= autoinhibition that suppresses kinase domain
4) phosphorylates: EGFR & cytosolic proteins
5) function: trxn cell cycle genes, proliferation, cell rounding
OVEREXPRESSED IN CANCER
