Signal Transduction Pt. II Flashcards
What are the 3 major branches of signaling off tyrosine kinase
RAS-MAPK pathway
Phospholipase C-gamma pathway
PI-3 kinase/AKT pathway
What is the RAS-MAPK pathway
GRB2 (contains SH2 domain) interacts with tyrosine phosphorylated receptor, localizing it to the membrane
Sos is associated with GRB2 and becomes active
Sos stimulates Ras (a monomeric G-protein) to release GDP and bind GTP.
Ras is now active
Ras activates RAF (a MAPKKK)
RAF activates MEK (a MAPKK)
MEK activates ERK (a MAPK)
MAPKs phosphorylates transcription factors
Transcription factors induce cells to grow and divide
What is the phospholipase C-gamma pathway
PLC-γ has SH2 domains that associate with receptor protein-tyrosine kinases.
Tyrosine phosphorylation increases PLC- γ activity,
PLC- γ stimulates the hydrolysis of PIP2 to produce InsP3 and DAG.
InsP3 stimulates calcium release.
DAG stimulates PKC pathway
What is Calcineurin-NFAT pathway
Stimulated T cells trigger PLCg resulting in calcium being released
Calcium binds and activates calmodulin
Calmodulin binds and activates a phosphatase called Calcineurin
Calcineurin dephosphorylates NFAT allowing it to go to the nucleus
NFAT stimulates IL-2 gene expression.
What does Cyclosporin A do
Cyclosporin A bind to Calcineurin and inhibits its function
So NFAT can not bind to the nuclear membrane and there is no IL-2 gene expression
What is the PI 3-kinase/AKT pathway
- Ligand binds receptor, receptors aggregate and auto-phosphorylate each other
- PI 3 Kinase binds phosphorylated tyrosine on receptor and becomes active
- PI 3 Kinase phosphorylates PIP2 to become PIP3
- PDK and AKT (PKB) bind PIP3 molecules
- PDK and mTORC2 then phosphorylate and activate AKT (PKB)
- AKT then phosphorylates downstream targets
What is the role of PTEN
oThe role of PTEN is to dephosphorylate PIP3, acting as a negative control on PKB/Akt activation
oThis may result in the continued activation of PKB/Akt , which, in combination with other factors, could lead to increased cell growth and possible tumor development
What is FOXO and how is it regulated
- If growth factors are not present, Akt is not active, and FOXO travels to the nucleus where it stimulates transcription of genes that inhibit cell proliferation, or induce cell death.
- Akt phosphorylation of FOXO sequesters it in inactive form
What is Achrondroplasia
80% are new mutations, increased risk with increased PATERNAL age
Mutation in the FGF Receptor 3
characterized by dwarfism
failure of cartilage cell proliferation at the epiphyseal plate of long bones which causes shortened limbs
what is Noonan Syndrome
genes encoding for Ras/MAPK signaling proteins are mutated (PTPN11, KRAS, SOS, RAF1) AUTOSOMAL DOMINANT Characterized by short stature distinctive facial features congenital CV disease WEBBED NECK
What is Type I Diabetes
This type is an autoimmune attack of your BETA cells in the Islet of Langerhans in the pancreas
These patients ARE insulin dependent
HAVE a propensity to diabetic ketoacidosis
What is Type II Diabetes
This type is when the appropriate amount of insulin is being made by the body but the receptors have become RESISTANT
generally obese
results in end stage renal damage, peripheral arterial disease, and diabetic retinopathy
measure this by checking the HbA1c levels
strong genetic predisposition
What is the insulin production process
•gene encode for insulin are transcribed to mRNA in the nucleus
•translation of the mRNA is initiated on cytosolic ribosomes in cytosol
•but the translation is finished on the RER
•Further elongation directs the polypeptide chain into the lumen of the RER (Preproinsulin)
•The sequence is then cleaved to Proinsulin in the lumen
•Proinsulin is transported from RER to the golgi complex
In the golgi Proinsulin is cleaved to form insulin (cisternal space) and C-peptide
•Insulin and C-peptide are secreted in the form of secretory granules
•Secretory granules are secreted by exocytosis releasing insulin and C-peptide into the blood stream
Know insulin signaling pathways
•The insulin receptor is a dimer of two membrane-spanning α–β pairs.
The receptors auto-phosphorylate themselves
•The activated receptor binds insulin receptor substrates (IRS) and phosphorylates IRS at multiple sites
This forms binding sites for proteins with SH2 domains: there are 3 protein
Ras/MAPK, PLC-gamma, and PI 3 kinase
PI 3 kinase stimulates Akt
Akt activates Glut 4 to bring glucose into the membrane
Akt inhibits GSK which increases glycogen synthesis
Akt inhibits TSC1/TSC2 which increases protein translation
Akt causes FOXO phosphorylation which decreases glucose synthesis
Know TSC/mTOR signaling
A growth factor binds to a extracellular receptor
After bindinf that receptor activates Akt
Active Akt inhibits TSC2/TSC1 complex
This stops the inhibition of Rheb
The active Rheb activates mTOR/mTORC1 complex
This complex inhibits the eIF4E protein that was inhibiting eIF4E
EIF4E now activated
Rheb also activates S6 kinase
S6 kinase phophorylates ribosomal protein S6
Now S6 and eIF4E now both active it can increase cellular translation
Must know mechanism of action for rapamycin
A potent immunosupressant used to prevent transplant rejection
Binds to FK-binding protein 12 (FKBP12)
The rapamycin-FKBP12 complex binds and inhibits mTOR Complex 1 (mTORC1)
Must know Tuberous Sclerosis
Most are spontaneous mutations
The disorder results from a mutation in either TSC1 or TSC2 (more often TSC2)
inherited disorder whose key features include multiple facial angiofibromas, hypopigmented macules, periungual fibromas, seizures, Shagreen patch, cardiac rhabdomyoma, and renal lesions
Many patients also have ocular and neurologic manifestations, including mental retardation
Must know mechanism of action for metformin
Used to treat type 2 diabetes
Metformin stimulates the activation of AMPK
AMPK phosphorylates TORC2 and sequesters it in the cytoplasm
this decreases the synthesis of gluconeogenic enzymes
this also reduces hepatic output of glucose
Metformin reduces blood glucose levels by inhibiting hepatic gluconeogenesis
Metformin also reduces lipid synthesis in the liver
what are protein-tyrosine phosphatases and receptor guanylyl cyclases
Protein-tyrosine phosphatases remove phosphate groups from phosphotyrosine, counterbalancing the effects of protein-tyrosine kinases
(ex. CD45)
Receptor Guanylyl Cyclases
Ligand binding to receptors stimulates the cyclase activity of the receptor to synthesize cGMP
Know TGFb receptor signaling pathway
example of serine/threonine kinase
TGF ligand binds a complex of type I and II receptors
Type II receptor phosphorylates type I receptors
Type I receptors phosphorylates an R-Smad (Smad2 or Smad3)
R-Smad complexes with Smad4
In the nucleus, the Smad complex associates with transcription factors to modulate gene expression
Know JAK-STAT signaling pathway
Involved in the immune response.
Cytokine receptors activate the JAK-STAT signaling pathway
The receptor itself has no intrinsic kinase activity, but it binds the tyrosine kinase JAK (Janus kinase)
STAT proteins are located in the cytosol and are latent gene regulatory proteins because they only migrate into the nucleus and regulate transcription after they are activated
Know Notch signaling pathway
Notch signaling important during development
When individual epithelial cells begin to develop as neural cells, they signal to their neighbors not to do the same
They do this by having protein Delta bind receptor Notch
Upon binding Delta, Notch is cleaved on either side of the plasma membrane
The freed cytoplasmic tail of Notch then migrates to the nucleus
The tail then associates with other regulatory factors bound to promoter elements and modulates gene transcription
Know Wnt/b-catenin signaling pathway
Wnt proteins are secreted signal molecules that act as local mediators and morphogens to control many aspects of developments.
Wnt protein bind to Frizzled receptors and inhibit the degradation of b-catenin
APC is a key protein in the regulation of b-catenin
b-catenin accumulates and translocates to the nucleus
Once in the nucleus, b-catenin migrates to the nucleus, displaces Groucho and associates with coactivator
Hedgehog signaling
Binding of Hedgehog inhibits Patched (its receptor)
This leads to activation of Smoothened which initiates a signaling pathway leading to activation of a transcription Gli
Know NF-kB-dependent signaling pathway
TNF binds the receptor
IkB Kinase becomes active and phosphorylates IkB
IkB is ubiquitinated and degraded
NF-kB is no longer bound to IkB and it’s nuclear localization signal is now exposed
NF-kB is transported into the nucleus through the nuclear pores
NF-kB binds to promoter elements and modulates gene expression
Know integrin signaling via FAK
Binding of integrins to the extracellular matrix leads to activation of FAK ( focal adhesion kinase), a nonreceptor protein-tyrosine kinase.
Phosphorylation of FAK provides binding sites for several signaling molecules, including the Grb2-Sos complex,
This leads to activation of Ras, PI 3-kinase, and phospholipase C-γ.
Know the role of Rac, Rho & Cdc42 in actin remodeling
Rho family members are activated by integrin signaling and growth factor receptors
Rac - lamellipodia
Rho - Focal Adhesions and stress fibers
Cdc42 - filopodia
help with the organization of the actin cytoskeleton
What is signaling networks-crosstalk
Crosstalk is the interaction between signaling pathways, such as junctions between Ca2+ and cAMP signaling, between the cAMP and ERK pathways, and between integrin signaling and receptor protein-tyrosine kinases.
