Cell Signaling I - Principles of Cell Signaling - F24 - PDF

1 CELL SIGNALING I – PRINCIPLES OF CELL SIGNALING 11/4/2024 Tobias Weinrich, PhD School of Integrative Biological and Chemical Sciences  2 Student Learning Outcomes ▪ Describe the principal modes of ce...

1 CELL SIGNALING I – PRINCIPLES OF CELL SIGNALING 11/4/2024 Tobias Weinrich, PhD School of Integrative Biological and Chemical Sciences  2 Student Learning Outcomes ▪ Describe the principal modes of cell signaling. ▪ Explain the three stages of a general signaling cascade. ▪ Identify and describe the different types of molecules involved in signaling pathways. ▪ Relate the location of receptors to the type of signaling molecule. ▪ Distinguish among specificity, amplification, adaptation, integration and distribution steps in a signaling cascade. ▪ Describe different types of response timings to extracellular ligands. ▪ Identify mechanisms by which signaling pathways are deactivated. ▪ Correctly interpret schematic representations of signaling cascades.  3 Lecture Structure 1. Types of Cell Signaling 5. Characteristics 2. Stages of Cell Signaling A. Specificity 3. Types of molecules B. Integration and Coordination A. Extracellular signaling molecule C. Dynamics (ligand) ▪ Speed B. Receptor proteins ▪ Deactivation C. Intracellular signaling proteins D. Sensitivity, adaptation, and signal ▪ Enzymes Amplification ▪ Molecular switches E. Optimization D. Second messengers E. Effector proteins 4. Signal transduction  4 1. Types of Cell Signaling 1) DIRECT CELL-CELL CONTACT (JUXTACRINE) ▪ Membrane-bound signaling molecule ▪ Does not involve secreted molecules 2) SIGNALING BY SECRETED MOLECULES – distance over which signal is transmitted ▪ Endocrine (long distance, blood stream) – hormones ▪ Paracrine (neighbouring cells) – local mediators ▪ Neuronal (synaptic) – neurotransmitter ▪ Autocrine (signaling and target cell is the same cell)  5 2. Stages of Cell Signaling ▪ [Signal transmission – synthesis and release of signal molecule] 1. Signal reception – ligand and receptor 2. Signal transduction ▪ Interpretation of the signal 3. Cellular response ▪ Altered metabolism ▪ Altered cell shape ▪ Altered gene expression 3. Cellular response 1. Signal reception 2. Signal transduction  6 3. Types of Molecules A. Ligand (primary messenger) ▪ Extracellular signaling molecule B. Receptor protein ▪ Cell surface ▪ Intracellular C. Proteins – enzymes INTRACELLULAR SIGNALING MOLECULES D. Non-proteins – second messenger E. Effector/target proteins ▪ Metabolic Enzyme ▪ Transcription Factor ▪ Cytoskeletal protein  7 3.A. Signal Molecules – Primary Messenger ▪ Extracellular signal molecule ▪ Non-chemical ▪ Photons ▪ Mechanical force ▪ Chemical - Ligand ▪ Odorants Membrane-bound signaling molecule ▪ Macromolecules – proteins, lipids, carbohydrates, nucleic acids ▪ Neurotransmitters  8 Nuclear receptors 3.B. Receptor proteins ▪ Ligand binds to receptor on target cell, inducing: ▪ Conformational change (change in 3D structure) ▪ Activation of receptor 1) Intracellular – hydrophobic ligands ▪ Enzyme EXAMPLE: NO receptor (guanylyl cyclase) ▪ Transcription Factors – nuclear receptors Guanylyl cyclase NO NO  9 3.B. Receptor proteins 2) Cell surface – hydrophilic ligands ▪ Transmembrane proteins – ligand binding domain (extracellular domain) i. Ion-cannel coupled receptors ii. G-protein-coupled receptors – trimeric G protein iii. Enzyme-coupled receptors ▪ Intrinsic enzymatic activity ▪ Associated enzymatic activity  10 3.C. Intracellular Signaling Molecules – Enzymes ▪ Kinases - PKA, PKC, receptors ▪ Tyrosine or Serine/Threonine Molecular Switches ▪ Phosphatases ▪ Monomeric G proteins (small G proteins, GTPases) ▪ Adenylyl Cyclase ▪ Convert ATP to cyclic AMP (cAMP) ▪ Guanylyl Cyclase ▪ Convert GTP to cyclic GMP (cGMP) ▪ Phospholipases ▪ Cleave phospholipids in the cell membrane ▪ Proteases ▪ Precursor proteins → active proteins ▪ Example: pro-caspases → caspases  11 3.C. Intracellular Signaling Molecules – Enzymes ▪ Small G proteins – proteins bound to GTP/GDP ▪ G activating protein (GAP) promotes hydrolysis of GTP → GDP + P ▪ Guanosine Exchange Factor (GTP) exchanges GDP → GTP  12 3.C. Intracellular Signaling Molecules – Enzymes Multiple receptors have intrinsic or associated kinase activity.  13 3.C. Intracellular Signaling Molecules – Second messengers Second messengers: ▪ Small, non-protein intracellular molecules ▪ Cyclic AMP (cAMP), DAG, IP3, Ca2+, ▪ Short half-life Function: ▪ Relay and amplify the signal of the “first messenger” (ligand) ▪ Pass information to other signaling proteins  14 4. Signal Transduction SIGNAL TRANSDUCTION ▪ Ability of a cell to translate a receptor-ligand interaction to changes in its behavior or gene-expression ▪ Relay – signal is transmitted from one molecule to another within a cell → cascade ▪ Amplification ▪ Integration ▪ Feedback – modulate the response ▪ Distribution – spatial and temporal dissemination of signal → appropriate response  15 5.A. Specificity ▪ All signaling molecules act by binding to receptor on the target cell → interaction is specific Same ligand causes different changes in cell behaviour based on target cell: ▪ Different receptors ▪ Different intracellular proteins  16 5.B. Integration and Coordination In the cell, all different signaling pathways interact enabling each cell type to produce the appropriate response to a combination of extracellular signals. In the absence of signals ↓ cell dies (apoptosis)  17 5.B. Integration and Coordination Proteins may have multiple phosphorylation sites. ▪ The net outcome will depend both on the numbers of signaling molecules and the strengths of their connections.  18 5.B. Integration and Coordination  19 5.C. Dynamics - Speed Response timing: ▪ Fast – function on preexisting proteins ▪ Activation or inhibition of a protein ▪ Opening/closing ion channel ▪ Slow ▪ Change in gene expression ▪ Duration of ligand exposure may also affect cell behaviour  20 5.C. Dynamics ▪ Ca2+ release upon egg fertilization ▪ cAMP production after serotonin stimulation  21 5.C. Dynamics – deactivation of signaling pathway ▪ Receptor sequestration - receptor endocytosis ▪ Receptor down-regulation – receptor endocytosis and digestion ▪ Receptor inactivation ▪ Phosphorylation of receptor ▪ Inactivation or proteolysis of signaling molecule ▪ Production of inhibitory protein  22 5.D. Sensitivity, adaptation and amplification AMPLIFICATION ▪ At each step in the cascade, the number of activated products can be much greater than in the preceding step.  23 5.D. Sensitivity, adaptation and amplification SENSITIVITY: ▪ Receptors may detect very small amount of ligand associated with a change in cell behaviour ▪ Achieved by signal amplification ADAPTATIONN (desensitization): ▪ Signal pathways adapt to amount of ligand ▪ Allows cells to respond to small changes in the concentration of ligand  24 5.E. Optimization i. Scaffold proteins – organize complexes of signaling molecules ii. Membrane domains ▪ Lipid rafts ▪ Regions rich in specific lipids ▪ Phosphoinositiddes  25 5.E. Optimization iii. Activated receptor ▪ Recruitment of signaling proteins to activated receptor ii iii i