Cell Signaling AP Chapter 11

Evolution of cell signaling Similarities in pathways in bacteria, protists, fungi, plants, and animals suggest an early evolution of signaling pathways Multicellular better due to coordination and control of pathways Boseman video

Bacteria communication “bacteria talking to each other” Quorum sensing- concentration of signaling molecules allows bacteria to sense their local density Ex- Vibrio – glowing bacteria (luciferase enzyme) give off auto inducers into their environment

autoinducers

Quorum sensing can lead to the formation of biofilms

Slime molds – chemical signaling Slime molds live as solitary amoebae. When slime mold cells begin to starve or dehydrate, they release a pheromone-like chemical called cyclic AMP. This messenger molecule alerts other slime mold amoebae. They detect the cAMP and follow the scent to join forces with the troubled amoebae forming a large mass of cells. Other slime mold amoebae detect the cAMP and follow the scent to join forces with the troubled amoebae.

cAMP is an important chemical word in the language of cells and seems to be understood and made by all cells, even our own.

Fruiting body formation in fungi chemical signaling

Local and long-distance signaling Direct cytoplasmic connections: - gap junctions in animal cells or plasmodesmata in plant cells - contact of surface molecules (cell-to- cell recognition via receptors

Plasmodesmata in plant cells

Gap junctions in animal cells

Immune cells – direct contact

Local regulators – nearby cells paracrine signaling – only includes cells of a particular organ synaptic signaling – between neurons

Long distance endocrine signaling nerve transmission

3 stages of cell signaling 1.Reception 2.Transduction 3.Response Boseman video on cell signaling pathways

Fig Reception 1 EXTRACELLULAR FLUID Signaling molecule Plasma membrane CYTOPLASM 1 Receptor

Fig EXTRACELLULAR FLUID Signaling molecule Plasma membrane CYTOPLASM Transduction 2 Relay molecules in a signal transduction pathway Reception 1 Receptor

Fig EXTRACELLULAR FLUID Plasma membrane CYTOPLASM Receptor Signaling molecule Relay molecules in a signal transduction pathway Activation of cellular response TransductionResponse 2 3 Reception 1

Ligand – the signal molecule, fits like a lock and key to receptor Most ligands bind to cell surface receptors; some bind to intracellular receptors Usually induces a shape change in receptor protein’s shape

Types of receptors Bind with water-soluble (hydrophilic) receptors on membrane: G-Protein-linked Receptor Protein Kinase Receptor Ligand-gated Ion Channel Bind with hydrophobic receptors: Intracellular Receptors

G- Protein-Linked Receptors 7 protein helices that span the membrane Binding of the ligand to the G-protein receptor, activates a specific G protein located on the cytoplasm side. How - GDP becomes GTP. The activated G-protein activates a membrane-bound enzyme which continues on its pathway. The GTP goes back to GDP. Animation: Membrane-Bound Receptors that Activate G Proteins

Fig. 11-7a Signaling-molecule binding site Segment that interacts with G proteins G protein-coupled receptor

Fig. 11-7b G protein-coupled receptor Plasma membrane Enzyme G protein (inactive) GDP CYTOPLASM Activated enzyme GTP Cellular response GDP P i Activated receptor GDP GTP Signaling molecule Inactive enzyme

How important is the G-protein system? Used by hormones, neurotransmitters, sensory reception, development…. Many bacteria produce toxins that interfere with G-protein systems Up to 60% of medicines influence G- protein pathways

Protein kinase receptors Tyrosine best understood Receptor tyrosine kinases (RTK) are enzyme membrane receptors that attach phosphates from ATP to tyrosines (Remember kinase…ATP.) Once the receptors are activated, relay proteins bind to them and become activated themselves. A receptor tyrosine kinase can trigger multiple signal transduction pathways at once

Fig. 11-7c Signaling molecule (ligand) Ligand-binding site  Helix Tyrosines Tyr Receptor tyrosine kinase proteins CYTOPLASM Signaling molecule Tyr Dimer Activated relay proteins Tyr P P P P P P Cellular response 1 Cellular response 2 Inactive relay proteins Activated tyrosine kinase regions Fully activated receptor tyrosine kinase 6 6 ADP ATP Tyr P P P P P P

Tyrosine Kinase Receptors Binding of the signal molecules causes the two polypeptides to join.

They are activated and act as enzymes to phosphorylate the tyrosines in the tails.

The receptor protein is now recognized by relay proteins, triggering different effects.

Ex of RTK: Insulin Signal Transduction Pathway Type 2 diabetes is accompanied by impaired insulin signal transduction.

Ligand-gated ion channel A ligand-gated ion channel receptor acts as a gate When a signal molecule binds as a ligand to the receptor, the gate allows specific ions, such as Na + or Ca 2+, through a channel in the receptor Ex- in neurotransmitters and nervous signal transmission

Fig. 11-7d Signaling molecule (ligand) Gate closed Ions Ligand-gated ion channel receptor Plasma membrane Gate open Cellular response Gate closed 3 2 1

Ligand-Gated Ion Channels

Intracellular Receptors Some receptor proteins are intracellular, found in the cytosol or nucleus of target cells Small or hydrophobic chemical messengers can readily cross the membrane and activate receptors Examples of hydrophobic messengers are the steroid and thyroid hormones of animals An activated hormone-receptor complex can act as a transcription factor, turning on specific genes

Fig Hormone (testosterone) EXTRACELLULAR FLUID Receptor protein Plasma membrane Hormone- receptor complex DNA mRNA NUCLEUS New protein CYTOPLASM

Intracellular Receptors

Signal Transduction Allow for amplification of signals Signal coordination and regulation Involves 1) second messengers (cAMP and Ca +2 ) 2) relay proteins such as protein kinases

How does epinephrine work?...an example of cAMP messenging

Epinephrine acts via cyclic AMP (cAMP) as a second messenger. An activated G protein activates the enzyme adenylyl cyclase (THINK CYCLING!) which turns ATP to cAMP. Then cAMP can activate other inactive molecules to reach the desired product. action of epinephrine Video | DnaTube.com - Scientific Video Site

Adenylyl cyclase Fig Pyrophosphate P P i ATP cAMP Phosphodiesterase AMP

First messenger Fig G protein Adenylyl cyclase GTP ATP cAMP Second messenger Protein kinase A G protein-coupled receptor Cellular responses

cAMP second messenger systems Membrane Structure

Calcium ions also act as second messengers. One example is activating an enzyme phospholipase C to produce two more messengers which will open Ca channels. The signal receptor may be a G protein or a tyrosine kinase receptor. Important in muscle contraction.

Fig G protein EXTRA- CELLULAR FLUID Signaling molecule (first messenger) G protein-coupled receptor Phospholipase C PIP 2 DAG IP 3 (second messenger) IP 3 -gated calcium channel Endoplasmic reticulum (ER) Ca 2+ CYTOSOL Various proteins activated Cellular responses Ca 2+ (second messenger ) GTP

RELAY PROTEINS Enzymes called protein kinases are also important links in transduction. A protein kinase catalyzes the transfer of PHOSPHATE GROUPS from ATP to another protein to activate it. Amplification is possible in these type of pathways.

Fig Signaling molecule Receptor Activated relay molecule Inactive protein kinase 1 Active protein kinase 1 Inactive protein kinase 2 ATP ADP Active protein kinase 2 P P PP Inactive protein kinase 3 ATP ADP Active protein kinase 3 P P PP i ATP ADP P Active protein PP P i Inactive protein Cellular response Phosphorylation cascade i

Mitogen-activated protein (MAP) kinases An example of a kinase cascade activated by a G Protein Mitogen – mitosis-generating A RTK receptor activates Ras – a G protein which sets off a cascade ultimately resulting in activating a transcription factor which manages genes for cell division and cell differentiation Ras is a cytoplasmic enzyme unlike the G protein connected to a GPCR.

Mutated Ras protein in cancer

This can get pretty complicated!

Cell Responses Alteration of metabolism Rearrangement of cytoskeleton Modulation of gene activity

Fig Growth factor Receptor Phosphorylatio n cascade Reception Transduction Active transcription factor Response P Inactive transcription factor CYTOPLASM DNA NUCLEUS mRNA Gene Modulating Gene Activity

Fig Reception Transduction Response Binding of epinephrine to G protein-coupled receptor (1 molecule) Inactive G protein Active G protein (10 2 molecules) Inactive adenylyl cyclase Active adenylyl cyclase (10 2 ) ATP Cyclic AMP (10 4 ) Inactive protein kinase A Active protein kinase A (10 4 ) Inactive phosphorylase kinase Active phosphorylase kinase (10 5 ) Inactive glycogen phosphorylase Active glycogen phosphorylase (10 6 ) Glycogen Glucose-1-phosphate (10 8 molecules) Alteration of Metabolism

Fig RESULTS CONCLUSION Wild-type (shmoos)∆Fus3∆formin Shmoo projection forming Formin P Actin subunit P P Formin Fus3 Phosphory- lation cascade GTP G protein-coupled receptor Mating factor GDP Fus3 P Microfilament Rearrangement Of cytoskeleton

Fine-Tuning of the Response Multistep pathways have two important benefits: –Amplifying the signal (and thus the response) –Contributing to the specificity of the response Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Specificity of Cell Signaling and Coordination of the Response Different kinds of cells have different collections of proteins which allow cells to detect and respond to different signals. Even the same signal can have different effects in cells with different proteins and pathways

Fig Signaling molecule Receptor Relay molecules Response 1 Cell A. Pathway leads to a single response. Response 2 Response 3 Cell B. Pathway branches, leading to two responses. Response 4 Response 5 Activation or inhibition Cell C. Cross-talk occurs between two pathways. Cell D. Different receptor leads to a different response. Pathway branching and “cross-talk” further help the cell coordinate incoming signals Same signal - different effects in cells with different proteins and pathways

Signaling Efficiency: Scaffolding Proteins and Signaling Complexes Scaffolding proteins are large relay proteins to which other relay proteins are attached Scaffolding proteins can increase the signal transduction efficiency by grouping together different proteins involved in the same pathway

Fig Signaling molecule Receptor Scaffolding protein Plasma membrane Three different protein kinases

Disruptions in cell signaling pathways Bacterial infections (cholera, anthrax, pertussis) Animal toxins Hormone imbalances (diabetes) Cancer Plant diseases BosemanBoseman video on disruptions

Apoptosis (programmed cell death) integrates multiple cell-signaling pathways Apoptosis is programmed or controlled cell suicide A cell is chopped and packaged into vesicles that are digested by scavenger cells Apoptosis prevents enzymes from leaking out of a dying cell and damaging neighboring cells Apoptosis is important in shaping an organism during embryonic development

Fig b (b) Death signal Death- signaling molecule Ced-9 (inactive) Cell forms blebs Active Ced-4 Active Ced-3 Activation cascade Other proteases Nucleases

Apoptotic Pathways and the Signals That Trigger Them Caspases are the main proteases (enzymes that cut up proteins) that carry out apoptosis Apoptosis can be triggered by: –An extracellular death-signaling ligand –DNA damage in the nucleus –Protein misfolding in the endoplasmic reticulum Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Apoptosis evolved early in animal evolution and is essential for the development and maintenance of all animals Apoptosis may be involved in some diseases (for example, Parkinson’s and Alzheimer’s); interference with apoptosis may contribute to some cancers Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig Interdigital tissue 1 mm