Transduction Systems for Peptide Hormones, Growth Factors, and Cytokines
Signal Transduction Overview:
Signal transduction is the process by which a cell responds to molecules (such as peptide hormones, growth factors, and cytokines) outside the cell and converts that signal into a functional change inside the cell. These signalling molecules bind to specific receptors on the cell surface.
Transduction Systems for Peptide Hormones, Growth Factors, and Cytokines
Types of Molecules Involved:
- Peptide Hormones: Small proteins that regulate a variety of physiological functions (e.g., insulin, glucagon).
- Growth Factors: Proteins that stimulate cell proliferation and differentiation (e.g., EGF - Epidermal Growth Factor).
- Cytokines: Small proteins important in cell signalling, particularly in immune responses (e.g., interleukins, interferons).
Transduction Systems for Peptide Hormones, Growth Factors, and Cytokines
Receptors:
These molecules bind to receptors on the cell surface, which then initiate intracellular signalling cascades. The main types of receptors involved include:
- G-Protein Coupled Receptors (GPCRs): Activate G-proteins, which then trigger various downstream signalling pathways.
- Receptor Tyrosine Kinases (RTKs): Undergo autophosphorylation upon ligand binding, leading to activation of downstream signalling proteins.
Lipid Second Messengers
Second messengers are small molecules that propagate a signal within the cell after activation by a receptor.
1. Phosphatidylinositol Bisphosphate (PIP2): PIP2 is a membrane phospholipid that can be cleaved by the enzyme phospholipase C (PLC) into two important second messengers:
- Diacylglycerol (DAG): Remains in the membrane and activates Protein Kinase C (PKC).
- Inositol Triphosphate (IP3): Diffuses through the cytoplasm to the endoplasmic reticulum (ER), where it triggers the release of calcium ions (Ca²⁺) into the cytoplasm.