BS21002 - Intracellular Signal Transduction Pathways (post-lecture version)
University of Dundee BS21002 Intracellular Signal Transduction Pathways
Instructor: Sharon Matthews (s.matthews@dundee.ac.uk)
Intended Learning Outcomes
Understanding Signal Transduction
Know how cell surface receptors relay signals from the external environment into cells.
Describe key intracellular signalling pathways (PKA, PLC, MAPK) and their roles in regulating cell function.
Discuss examples of how intracellular signalling pathways are influenced by amplification mechanisms, protein turnover, and feedback loops.
Intracellular Signalling Pathways
Definition
Intracellular signalling pathways process external and internal signals, integrating various agonist responses to achieve specific biological outputs.
Core Concepts in Intracellular Signalling
Environmental Sensing
Cells must sense changes in their environment (internal or external).
Activation/inhibition of signalling pathways leads to biological function changes.
Organizing pathways in 3D space allows rapid responses to environmental changes.
Amplification in signalling pathways filters out random fluctuations, ensuring reliability in cellular responses.
Feedback pathways (positive and negative) influence signalling pathway activity.
A single ligand can induce different biological outcomes in various cells.
A single receptor/ligand pair can activate multiple signalling pathways.
Signal Transmission Mechanism
Key Components
Extracellular signal molecules bind to receptor proteins on cell membranes.
Transduce signals through adaptor proteins, scaffolding proteins, second messengers, and effector proteins (metabolic, transcription, cytoskeletal).
Conformational Changes in Signalling Molecules
Mechanisms
Changes in protein-protein interactions, structure, stability, and generation of second messengers occur upon activation.
Example: Heterotrimeric G protein complexes undergo conformational changes upon receptor activation, leading to signalling.
Examples of Conformational Changes
Receptor Activation
Enzyme-coupled receptors undergo dimerization and activation, leading to active catalytic domains.
Post-Translational Modifications
Effects on Signalling
Modifications like phosphorylation, hydroxylation, and acetylation can alter protein interactions and stability, which impacts signalling outcomes.
Protein Kinase Activation Study
Highlight the roles of protein kinases and their regulatory scopes during cell division cycles, focusing on CDK/cyclin complexes.
Importance of Feedback Mechanisms
Feedback Types
Positive feedback enhances signal strength, while negative feedback reduces it, offering a balance in signalling pathway responses.
Specific Pathway Examples
Calcium Signalling
IP3 binding leads to calcium release from the endoplasmic reticulum, enhancing further calcium signals via CRAC channels.
Cyclin/CDK Activation
Positive feedback during the G2/M checkpoint amplifies the activation of mitotic processes.
Diverse Ligand Receptor Interactions
Varied Outcomes
The same ligand can lead to different cellular responses (e.g., adrenaline causes bronchodilation in bronchi smooth muscle and vasoconstriction in blood vessel smooth muscle).
Suggested Further Reading
Molecular Biology of the Cell (Alberts et al.) – Key chapters on Cell Signalling are recommended, available online for students.
University of Dundee BS21002 Intracellular Signal Transduction Pathways
Instructor: Sharon Matthews (s.matthews@dundee.ac.uk)
Intended Learning Outcomes
Understanding Signal Transduction
Comprehend how cell surface receptors relay signals from the external environment into the cell's interior, facilitating the communication between different cellular structures.
Describe key intracellular signalling pathways, specifically PKA (Protein Kinase A), PLC (Phospholipase C), and MAPK (Mitogen-Activated Protein Kinase), along with their specific roles and impacts on regulating cellular functions such as growth, differentiation, and metabolism.
Discuss examples of how intracellular signalling pathways are influenced by various mechanisms, including amplification strategies, protein turnover (the process of degrading and replacing proteins within cells), and feedback loops, which serve to stabilize cellular responses to external stimuli.
Intracellular Signalling Pathways
Definition
Intracellular signalling pathways are complex networks that process external (from the environment) and internal (from within the cell) signals, integrating a variety of agonist responses to generate specific biological outputs or cellular responses.
Core Concepts in Intracellular Signalling
Environmental Sensing
Cells must accurately sense and interpret changes in both their internal and external environments to adapt effectively. This sensing mechanism is critical for maintaining homeostasis and responding to physiological changes.
The activation or inhibition of signalling pathways results in significant changes in biological function, and proactive organization of signalling pathways in a three-dimensional space aids rapid responses to environmental changes.
Amplification in Signalling Pathways
Amplification mechanisms within signalling pathways are essential for filtering out random fluctuations in cellular contexts, ensuring that the cellular responses are reliable and consistent.
Feedback Mechanisms
Feedback pathways, both positive and negative, are integral as they modulate signalling pathway activity. For instance,
Positive feedback amplifies the signaling cascade, whereas negative feedback functions to downregulate it, achieving a balance in the cellular signaling responses.
Ligand Functionality
A single ligand can induce a diverse range of biological outcomes across different cell types. Similarly, a single receptor-ligand pair can simultaneously activate multiple signalling pathways, showcasing the complexity of cellular responses.
Signal Transmission Mechanism
Key Components
Extracellular signal molecules are crucial as they bind to specific receptor proteins located on the cell membrane, initiating the cascade of intracellular signalling.
Signals are transduced through various intermediaries, including adaptor proteins, scaffolding proteins, second messengers (e.g., cAMP and calcium ions), and effector proteins, which could be involved in metabolic processes, gene transcription, or cytoskeletal functions.
Conformational Changes in Signalling Molecules
Mechanisms
Upon activation, there are significant changes in protein-protein interactions, structural configurations, stability, and the generation of second messengers within the cell.
Example: Heterotrimeric G protein complexes, when activated through ligand-receptor interaction, undergo conformational changes that trigger the signal transduction cascade.
Examples of Conformational Changes
Receptor Activation
Enzyme-coupled receptors typically undergo dimerization and activate their respective catalytic domains, leading to downstream signalling events.
Post-Translational Modifications
Effects on Signalling
Various post-translational modifications such as phosphorylation, hydroxylation, and acetylation significantly alter protein interactions and stability, ultimately impacting signalling outcomes and pathways.
Protein Kinase Activation Study
This section emphasizes the pivotal roles of protein kinases, particularly in the regulation of the cell cycle. Attention is drawn to CDK (Cyclin-Dependent Kinase) and cyclin complexes, which are critical during cell division cycles, ensuring proper cell cycle progression and regulation.
Importance of Feedback Mechanisms
Feedback Types
Positive Feedback
Enhances and strengthens signal intensity, crucial for processes such as cell division.
Negative Feedback
Diminishes signal intensity, serving to counterbalance the signalling activity and avert overactivation.
Specific Pathway Examples
Calcium Signalling
The mechanism involves IP3 (Inositol trisphosphate) binding to its receptors, leading to calcium release from the endoplasmic reticulum (ER). This release amplifies further calcium signals via CRAC (Calcium Release-Activated Calcium) channels.
Cyclin/CDK Activation
At the G2/M transition in the cell cycle, positive feedback mechanisms amplify the activation process essential for entry into mitosis.
Diverse Ligand Receptor Interactions
Varied Outcomes
The same ligand can induce disparate cellular responses in different cell types; for example, adrenaline can trigger bronchodilation in smooth muscle of the bronchi while simultaneously causing vasoconstriction in smooth muscle of blood vessels, illustrating the context-specification of ligand-receptor interactions.
Suggested Further Reading
Molecular Biology of the Cell (Alberts et al.) – Recommended key chapters on Cell Signalling are available online, providing comprehensive insights and a deeper understanding of these fundamental concepts for students.