Signaalikaskadiin

Signaalikaskadiin, in Estonian, refers to a sequence of biochemical events by which an extracellular signal is transmitted through a cascade of intracellular signaling proteins to elicit a specific cellular response. The cascade typically begins with a receptor that detects a ligand at the cell surface or inside the cell and ends with changes in enzyme activity, gene expression, or cellular behavior.

Core components include receptors, adaptor and scaffolding proteins, protein kinases and phosphatases, and second messengers such as cyclic AMP, calcium ions, and diacylglycerol. Activation proceeds through sequential phosphorylation or other covalent modifications that propagate the signal and often amplify it at each step. Scaffold proteins help coordinate the timing and locality of signals, limiting cross-talk and ensuring specificity. Termination involves phosphatases, ubiquitination, receptor endocytosis, and GTPase inactivation.

Major types of signaling cascades involve receptor tyrosine kinases (RTKs), G protein–coupled receptors (GPCRs), and cytokine receptors, among others. Classic examples include the MAP kinase cascade (often ERK), the cyclic AMP–dependent protein kinase (PKA) pathway, and the IP3/DAG/Ca2+ pathway, which can converge on transcription factors or metabolic enzymes. Others include JAK-STAT and NF-κB pathways.

Dysregulation of signaalikaskadiin is associated with diseases such as cancer, inflammatory disorders, and metabolic syndromes. Because cascades integrate signals from multiple pathways, they are common targets for therapeutic intervention and are central to understanding cell biology and physiology.