Biochemistry: Signal Transduction

Endocrine Signlaing

Long distance signaling

Estrogen is a steroid hormone using what type of signaling

Endocrine

Paracrine Signaling

Short distance signaling (between cells)

Autocrine Signaling

Self signaling (cell produces something that feeds back on itself)

Overall mechanism of signal transduction

1. Initiation

2. Diffusion

3. Transduction

4. Primary effector

5. 2nd messenger

6. Amplification

6. Secondary effector

7. Response

Neuromuscular junctions use what type of signaling

Paracrine

Acetylcholine uses what type of signaling and where

Paracrine at the neuromuscular junction

Myastania Gravis

A neurotransmitter disease where you produce antibodies against Ach receptor, so muscle doesn't respond to Ach

2 Main types of receptors

1. PM

2. Intracellular

Types of PM receptors

1. Ion channels

2. Enzymatic activity receptors (kinases and GTPases)

Type of Intracellular receptor

Steroid Hormone receptor

Structure of TK receptor

1. EXC domain that contacts ligand

2. Transmembrane domain that changes conformation and induces signal from outside to inside

2. Intracellular domain with TK domain

Steps in TK receptor transduction

1. Ligand Binds

2. Dimerization which induces conformational change

3. Cross phosphorylation

4. Binding of SH2 domain-containing proteins

Two key proteins in Ras signaling pathway

1. Ras

2. MAPK (Mitogen Associated Protein Kinase)/ERK

Ras

Small GTP-binding protein (GTPase) that is bound to PM

GDP-bound Ras

Inactive

GTP-bound Ras

Active

MAPK/ERK

Serine/Threonine Kinase that activate changes in protein activity and gene expression

GTPase Activating Proteins (GAP)

Activate hydrolysis of GTP on GTP-bound proteins

Guanine Nucleotide EXchange Factor (GEFs)

Exchange GDP for GTP on proteins

Steps in Ras Signaling Pathway

1. Ligand binding

2. Dimerization

3. Cross phospohrylation

4. Binding of GRB2

5. Binding of SOS

6. Activation of Ras

7. Activation of MAPK cascade (activates MAPKKK)

GRB2

SH2 domain-containing protein

SOS

GEF that activates Ras

Secondary messengers

Molecules that greatly amplify signals and convey source to target

3 types of secondary messengers

1. hydrophilic

2. hydrophobic

3. gases

Examples of Hydrophilic 2nd messengers

cAMP, cGMP, Ca2+, and IP3

Examples of hydrophobic 2nd messengers

DAG and phosphatidylinositols

Examples of gases 2nd messengers

Nitric oxide, carbon monoxide, and hydrogen sulphide

Properties of secondary messengers

1. rapidly synthesized and degraded

2. Can be stored and released when needed

3. Localized signal

Calcium

Secondary messenger with high concentrations found outside the cell (EXC space) and in the ER

Role of calcium

Cell death, cell division, and neurotransmitter release

Phospholipase C Signaling (PLC) Pathway

1. Signal binds to receptor

2. Receptor dimerizes

3. Cross phosphorylation

4. Binding and activation of PLC-Gamma

5. PLC-G cleaves PI 4,5 BP (PIP2) into DAG and IP3

DAG (Diacylglycerol)

Messenger that stays in the membrane and can stimulate PKC

IP3 (Inositol 1,4,5, Trisphosphate)

Cyyoplasmic messenger that acts on ca2+ channels in the ER to release calcium, which activates PKC

PI3 Kinase Signaling

1. Insulin binds to receptor

2. Receptor dimerizes

3. Cross phosphorylation

4. Binding of IRS 1 (insulin receptor substrate 1)

5. IRS1 activates PI3K

6. PI3K phosphorylated PIP2 to PIP3 (PI 3,4,5 Trisphosphate)

7. PIP3 binds and activates PDK1

8. PDK1 activates PKB/AKT

PKB/AKT Effects

leads to GLUT4 being activated and brought to the membrane

Type II diabetes

Insulin-resistance, so PI3K pathway is not activated and GLUT4 not brought to the membrane

Cytokines

Small secreted proteins that control growth and differentiation of tissues and are important in inflammation and immune system response

Cytokine receptors

Receptors that lack intrinsic TK activity, so they associate with non-receptor TK proteins in the cytoplasm

JAK/STAT pathway purpose

Links cytokine receptors to direct transcriptional activity

JAKs (Janus Kinases)

Non-receptor TK proteins that are attached to cytokine receptors

STATs

Phosphoproteins that act as transcription factors

JAK/STAT pathway steps

1. cytokine binding

2. dimerization of receptor

3. attachment and cross/autophosphorylation of JAKs

4. STATs bind to active JAKs and are phosphorylated

5. STATs dimerize and go to nucleus

What do drugs target in cancer cells?

receptors to inhibit their activity

When won't receptor-inhibiting drugs work?

If there is a mutant protein downstream in the pathway that's always active

What do Serine/Threonine Kinases use for signaling?

SMADs

Protein Tyrosine Phosphatases

Dephosphorylate receptors to turn them off

G Protein Receptors (GPR)

Activate adenylyl cyclase

Adenylyl Cyclase

Membrane-bound protein that turns ATP into cAMP

cAMP

Secondary messenger that activates PKA and binds to CREB in the nucleus to change gene transcription

cAMP phosphodiesterase

Hydrolyzes cAMP to 5' AMP to turn off singal

Guanylyl cyclase

Turns GTP into cGMP

2 forms of Guanylyl Cyclase

1. Membrane Bound

2. Soluble

What can soluble guanylyl cyclase be activated by?

Nitric Oxide

cGMP

Secondary messenger that activates PKG

What protein kinase does calcium activate?

PKC

Structure of GPRs

Single polypeptide with 7 transmembrane domains bound to a heterotrimeric complex (alpha, beta, and gamma)

GDP-bound Galpha

Bound to GPR, Gbeta, and Ggamma complex

Steps in GPR signaling pathway

1. Ligand Binds

2. GDP exchanged for GTP

3. GTp-Galpha dissociates from Gbeta/gamma

4. GTp-Galpha activates adenylyl cyclase

5. GTp hydrolyzed and reassociation of complex

Galpha (s)

stimulates adenylyl cyclase

Galpha (i)

Inhibits adenylyl cyclase

Galpha (t)

stimulates cGMP phosphodiesterase

Galpha (q/11)

activates PLC-Beta

Galpha (12/13)

Activates GEF-Rho

Cholera Toxin

Activates ADP ribosylation of Galpha (s), inhibiting its GTPase activity (it'll always be active) and leading to high levels of cAMP

Pertussis Toxin

Activates ADP ribosylation of Galpha (i), inhibiting it's inhibitory action of adenylyl cyclase, so cAMP levels are high and desruction of respiratory epithelium

Ways to terminate signal

1. Remove ligand

2. Receptor-ligand internalization

3. Activate phosphatases, kinases, GTPases, and phosphodiesterases (anything that opposes signal)