Term
| Where are insulin and glucagon hormones expressed? Where do they create metabolic changes? |
|
Definition
| The pancreas / Liver, muscles, and adipose cells |
|
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Term
| The range of paracrine signaling and examples... |
|
Definition
The signaling and responding cells
are very close to one another, often adjacent cells. This local signaling is seen with growth factors. For example, the growth factors produced in the prostate stromal cells can elicit growth of the neighboring prostate epithelial cells. The endothelial cells lining the blood vessels can induce smooth muscle relaxation. |
|
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Term
| The range of autocrine signaling and examples... |
|
Definition
| The receptors and the secreted signal are expressed from the same cell. As a result, the signaling cell and the responding cell are the same cell. Autocrine signaling is seen in many proliferating cell types, but can also become abrogated in cancer cells to induce uncontrolled proliferation. |
|
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Term
| G-Protein Coupled Receptor (GPCR) |
|
Definition
| They are characterized by seven membrane-spanning domains (shown as green cylinders). As the name implies, the receptor binds to and interacts with a G-protein |
|
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Term
|
Definition
| A G-protein binds to GTP, and hydrolyzes the GTP to GDP and inorganic phosphate. As we will see, there are two types of G proteins, monomeric and trimeric G-proteins. The G protein associated with GPCRs is the trimeric form. |
|
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Term
| What G Protein binds the GTP? |
|
Definition
|
|
Term
| What G proteins are in the cytoplasmic leaflet? |
|
Definition
|
|
Term
| What happens upon the initial binding of the receptor to the ligand hormone molecule? |
|
Definition
The receptor becomes activated upon binding to its ligand. This alters the
receptor’s conformation such that it can now bind to the Gα (GDP) subunit of the trimeric G protein. |
|
|
Term
| What happens once the G-alpha subunit binds to the the receptor? |
|
Definition
Upon binding, the active receptor
induces a conformational change in the Gα subunit, triggering dissociation of the GDP molecule. |
|
|
Term
| Upon unloading its GDP after binding to the receptor molecule, what does the G-alpha subunit do next? |
|
Definition
| Exchanges of the GDP for GTP. |
|
|
Term
| Once the exchange of GDP for GTP on the G-alpha subunit is accomplished, what happens next? |
|
Definition
The GTP-bound Gα subunit dissociates from the receptor, as well as from the Gβ and Gγ subunits. The GTP-bound Gα subunit then associates with and
activates the effector molecule. |
|
|
Term
| With the GTP bound G-alpha protein bound to the effector, what happens next? |
|
Definition
| The active effector can now generate a second messenger for the pathway inside the cell. |
|
|
Term
| What will GTP bound G-alpha do once it has successfully activated the effector? |
|
Definition
| GTP-bound Gα subunit hydrolyzes its GTP to GDP. This causes the GDP-bound Gα subunit to dissociate from the effector and to reassociate with the Gβ and Gγ subunits, resetting the signaling mechanism. |
|
|
Term
| Stimulatory versus Inhibitory G proteins |
|
Definition
| They follow the same mechanism except that stimulatory PRODUCE second messenger and inhibitors STOP PRODUCTION. Denoted by small "s" and "i" |
|
|
Term
| What is the most common 2nd messenger? |
|
Definition
|
|
Term
| How is 3ʹ,5ʹ-cyclic AMP (cAMP) generated? |
|
Definition
| The effector enzyme Adenylyl cyclase, which forms a phosphodiester bond between the 5ʹ phosphate and the 3ʹ-OH groups of AMP. |
|
|
Term
| What downstream pathway is activated by cAMP? |
|
Definition
| cAMP-dependent Protein Kinase, also referred to as the Protein Kinase A (PKA) pathway |
|
|
Term
| What does Guanylyl cyclase generate? What does that activate? What does that pathway do? |
|
Definition
| Guanylyl cyclase is the effector molecule that generates the cGMP second messenger. cGMP activates the downstream cGMP-dependent Protein Kinase (Protein Kinase G, PKG) pathway and opens cation channels in optical rod cells. |
|
|
Term
| What does Phospholipase C generate? What does that activate? What does that pathway do? |
|
Definition
Phospholipase C is the effector molecule that generates two second
messengers, Diacylglycerol (DAG) and Inositol 1,4,5-Trisphosphate (IP3). DAG can activate the downstream
Protein Kinase C (PKC), while IP3 can cause the release of Ca2+ from sequestered stores in the endoplasmic
reticulum. |
|
|
Term
| Simple description of the PKA? |
|
Definition
| PKA consists of four subunits, two catalytic and two regulatory. |
|
|
Term
| What happens to PKA in the presence of cAMP? |
|
Definition
cAMP binds to the PKA regulatory subunits, which causes the release and activation of the catalytic subunits. The active catalytic subunits will enter the nucleus and
phosphorylate the transcription factor cAMP Response Element Binding
(CREB) protein. |
|
|
Term
| What will a phosphorylated CREB protein do in the nucleus? |
|
Definition
It binds to cAMP response element
(CRE) DNA consensus sequences. CREB binding protein (CBP)/p300 transcription factors bind to CREB, and associate with the basal transcriptional machinery to mediate transcription of CRE containing genes. |
|
|
Term
| Other than CREB, what else does PKA phosphorylate? |
|
Definition
| Mitogen-Activated Protein Kinase (MAPK. |
|
|
Term
| What GPCR (and where) does epinephrine stimulate? What does it do? |
|
Definition
Epinephrine stimulates the β- Adrenergic stimulatory GPCR, causing an increase in cAMP levels and activation of PKA. In cardiac cells, PKA activity mediates an increase in heart rate. In liver and skeletal muscles, PKA activity mediates glycogen hydrolysis to increase glucose for energy. Triglyceride are also hydrolyzed in adipose cells
to provide fatty acids for energy. |
|
|
Term
| Explain the mechanism of cholera toxin... |
|
Definition
| Cholera toxin modifies a Gαs subunit (stimulatory) such that the subunit and Adenylyl cyclase remain active. This causes a continual increase in cAMP levels, PKA activity. Recall that PKA activates the CFTR channel in intestinal epithelial cells. This allows Cl- anions to flow into the intestinal lumen. H2O accompanies this anion flow. The chronic loss of H2O from intestinal epithelial cells causes the watery diarrhea associated with Cholera. |
|
|
Term
| Explain the mechanism of Bordatella pertussis aka Whooping Cough? |
|
Definition
| The Purtussis toxin modifies a Gαi subunit (inhibitory). This modification prevents GDP release from the inhibitory G protein. As a result, the inhibitory signal is continually inactivated. This causes the continual increase in Adenylyl cyclase activity and cAMP levels. In the lungs, this increased PKA activity activates the CFTR channel and results in fluid loss (as mucous secretion) into the lungs. |
|
|
Term
| Calcium, the heart, GPCR, and epinephrine in normal heart beats |
|
Definition
| Epinephrine activates GPCR. Makes cAMP, which activates PKA, which activates Ca2+ channels in SR and T-tubule. Cytosolic Cs2+ causes systolic heart muscle contraction. Ca2+ are restored in diastole. |
|
|
Term
| What happens if catecholamine levels become elevated in the heart? |
|
Definition
This causes chronic stimulation of the β-AR, and Adenylyl cyclase. The elevated cAMP levels cause chronic PKA stimulation and chronic release of SR Ca2+ stores. With a lessened relaxation, the Ca2+ stores are
not replenished. This leads to a decrease in the amplitude of the SR-sequestered:cytosolic Ca2+ stores. As a result, the muscle contractions are not as strong or regular. THINK BETA BLOCKERS! |
|
|
Term
| Give me an example of a beta blocker? |
|
Definition
|
|
Term
| What do beta blockers do? |
|
Definition
| Inhibit β-AR signaling. They are used to treat hypertension, cardiac arrhythmias, heart attacks and heart failure. They diminish the signaling of adrenaline and improve cardiac contractile function. Patients with heart failure due to chronic myofibril PKA activity have increased cytosolic Ca2+ stores. The amplitude of SR-sequestered:cytosolic Ca2+ stores is reduced. |
|
|
Term
| Explain the mechanism in which the phospholipase C / PKC produces it two 2nd messengers? |
|
Definition
| Thephospholipid Phosphatidylinositol (PI) is situated on the cytosolic leaflet of the plasma membrane. It can become phosphorylated on carbons 4 and 5 on the Inositol ring. The resulting molecule is PI 4,5-bisphosphate (PIP2). PIP2 can become cleaved by PLC (THIS IS THE EFFECTOR IN THIS REACTION) into 1,2-Diacylglycerol (DAG) in the membrane and Inositol 1,4,5-trisphosphate (IP3) in the cytosol. |
|
|
Term
|
Definition
IP3 activates a channel in the endoplasmic reticulum, releasing sequestered Ca2+ stores. The Ca2+ helps bring PKC to the plasma membrane surface where it becomes activated by DAG. Active PKC
can now function to phosphorylate target proteins to change cellular functions and processes. |
|
|
Term
| Smooth muscle relaxation: ligand? |
|
Definition
|
|
Term
| Smooth muscle relaxation: effector |
|
Definition
| PLC ==> IP3 (releases Ca2+) and DAG |
|
|
Term
| Smooth muscle relaxation: What does Ca2+ do? |
|
Definition
| Complexes with calmodulin |
|
|
Term
| Smooth muscle relaxation: What does calmodulin-Ca2+ complex do? |
|
Definition
| Activates NO synthase ==> NO |
|
|
Term
| Smooth muscle relaxation: What does the NO do? |
|
Definition
| The NO diffuses to the neighboring smooth muscle cells and binds to a NO receptor. This activated Guanylyl cyclase. An elevation in cGMP second messenger activates the cGMP-dependent protein kinase (also referred to as Protein Kinase G, PKG). PKG activity signals to cause relaxation of smooth muscle cells and dilation of the blood vessel. PARACRINE signaling. |
|
|
Term
| What are the three kinds of single pass receptors? |
|
Definition
| Cytokine receptors, Receptor Tyrosine Kinases (RTKs) and TGFβ receptors |
|
|
Term
| In what state of binding are the inactive single pass receptors? |
|
Definition
|
|
Term
| Once a single pass receptor is bound to its ligand, what will happen? |
|
Definition
| Form homodimers upon binding their specific ligand. Dimerization activates intracellular kinase function that transmits the signal internally. |
|
|
Term
| Which SPR have intrinsic kinases? |
|
Definition
|
|
Term
| Which SPR have extrinsic kinases? |
|
Definition
|
|
Term
| What is the protein kinase associated with cytokine receptors called? |
|
Definition
|
|
Term
| What activates the kinase protein? |
|
Definition
| The monomers dimerize, bringing together the two JAK proteins. Dimerization activates JAK by autotransphosphorylation. |
|
|
Term
| What residues are phosphorylated on JAK? |
|
Definition
|
|
Term
| What does phosphorylated JAK do? |
|
Definition
| It further phosphorylates more TYR on the intracellular domain and becomes a scaffold. |
|
|
Term
| What three domains have affinity for phosphotyrosine interactions? |
|
Definition
|
|
Term
| What is STAT protein? Mechanism? |
|
Definition
Signal Transducer and Activator of
Transcription (a transcription factor). It is phosphorylated by JAK, dimerizes via SH2 domains and Phy-TYR, tranlocates into nucleus nad affects gene expression. |
|
|
Term
| Examples of cytokine signaling... |
|
Definition
| Interferon, lactation, hematopoietic cell differentiation. |
|
|
Term
| Hematopoietic cell differentiation and Erythropoietin (Epo) |
|
Definition
Erythropoietin (Epo), which is produced in the kidneys, stimulates red blood cell (RBC) production (erythropoeisis) in the bone marrow through a cytokine-JAK/STAT pathway. Epo binds to the Epo receptor (a cytokine receptor), and this initiates a cascade of signaling that mediates both proliferation and
differentiation of the erythroid progenitor cell into mature RBCs. In
the absence of Epo, the progenitor cell would undergo apoptotic cell
death. |
|
|
Term
| What is the biggest structurally difference between RTK and JAK kinases? |
|
Definition
| RTK's are intrinsic (part of the ligand binding domain). JAK's are separate proteins from the ligand binding domain. |
|
|
Term
| When are monomeric G proteins active? |
|
Definition
|
|
Term
| What can dock on physpho-TYR residues on and RTK and how do they do it? |
|
Definition
| GRB2 and SOS (GEF) through SH2 and SH3 interactions. |
|
|
Term
| On an SOS-RTK complex, what will SOS often bind to? |
|
Definition
|
|
Term
|
Definition
|
|
Term
| What will an activated Ras protein do? |
|
Definition
| phosphoylates MAPK cascade (1st). Activates Raf by phosphorylation (2nd). Cleaves GTP to GDP (3rd). Disassociates from Raf and is inactivated (4th)... promotes cancer. |
|
|
Term
| What will activated Raf do? |
|
Definition
| Phosphorylates and activates Mek |
|
|
Term
| What will activated Mek do? |
|
Definition
| Phosphorylates and activates Erk |
|
|
Term
|
Definition
|
|
Term
| Examples of RTK families... |
|
Definition
| Epidermal Growth Factor Receptor (EGFR, aka ErbB receptor), Platelet Derived Growth Factor Receptor (PDGFR), Fibroblast Growth Factor Receptor (FGFR), Vascular Endothelial Growth Factor Receptor (VEGFR), RET receptor (Rearranged in Transfection), and the Ephrin receptor (EphR). Most RTKs function as growth factors and/or are required for the continuation of the specific cell lineage (by inhibiting apoptosis). EGFR and VEGFR are examples of such growth promoting signaling receptors. Because of their roles in growth, many of these signaling receptors are target for mutation that promote cancer. We will discuss EGFR in the next slide. RTKs are also involved in metabolism. The Insulin receptor is a RTK involved in glucose hemostasis, and can become inactive in diabetes. |
|
|
Term
| What is the HER (Human EGF Receptor) responsible for? |
|
Definition
|
|
Term
| What potential threat do HER's present to the the body? |
|
Definition
| Just as Ras pathway members are highly mutated in human cancers, many human cancers involve mutant HER forms that stimulate growth even in absence of the ligand. Additionally, amplification of HER2 in mammary epithelial cells occurs in ~25% of breast cancers, and patients have a worse prognosis. |
|
|
Term
| Treatment for HER2 breast cancer? |
|
Definition
HER2 monoclonal antibodies are effective in treating
HER2 positive breast cancers, and can reduce the recurrence of the cancer
by as much as ~50%. |
|
|
Term
| What is DIFFERENT about the TGFβ receptor? |
|
Definition
| It is phosphorylated and activated before the ligand binds. joy |
|
|
Term
| Once the ligand binds to the TGFβ receptor, what happens next? |
|
Definition
RII recruits co-receptor RI, and phosphorylates RI on its
intracellular domain. This activates RI. |
|
|
Term
| An activated RI co-factor will do what then? |
|
Definition
RI phosphorylates the transcription
factor Smad3, causes a conformational change in Smad3 that unmasks a
nuclear localization sequence |
|
|
Term
| Phosphorylated Smad4 (via RI)... so what? |
|
Definition
Two phosphorylated Smad3, and
one Smad4 are imported into the nucleus by a chaperone protein, Importin [Imp-β, (4-6)]. In the nucleus, Smad3/4 and other transcription factors facilitate changes in gene expression. |
|
|
Term
| BIG picture: what are some examples of TGFβ Signaling? |
|
Definition
| Secretion of extracellualar matrix proteins, serum proteases inhibitors, and anti-growth factors |
|
|
Term
| Example of serum protease inhibitor |
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
| suppress migration into tissues |
|
|
Term
| TGFβ Signaling and cancer |
|
Definition
Because of their antigrowth properties, inactivating TGFβ or Smad
mutations are found in many cancers. In pancreatic cancer, Smad4 is often deleted. Retinoblastoma, colon, and gastric cancers often are unresponsive to TGFβ antigrowth signals, because the TGFβ RI or RII receptors are often deleted. |
|
|
Term
|
Definition
| The steroids help to reduce inflammation associated with the damaged nerve cells. Interferons are ligands that signal through the cytokine JAK-STAT signaling pathway, mediating anti-inflammatory signals while inhibiting pro-inflammatory signals. |
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