Signaltransduktionsprozess

Signal transduction is the process by which cells detect and respond to molecular cues from their environment. It begins when a ligand binds to a receptor on the cell surface or inside the cell, triggering a conformational change that transmits a signal across membranes and into the cytoplasm. The initial event is followed by a cascade of intracellular signaling proteins and often second messengers such as cyclic AMP, calcium ions, or IP3/DAG. These signals are propagated, amplified, and integrated to produce a precise cellular response, which may include altered metabolism, gene expression, secretion, movement, or differentiation.

Common receptor types include G protein-coupled receptors, receptor tyrosine kinases, and ligand-gated ion channels. G proteins couple receptors to enzymes or ion channels; RTKs phosphorylate themselves and downstream targets to activate pathways such as MAP kinase and PI3K-Akt. Second messenger pathways rapidly modulate enzymes and ion channels, creating fast responses, while transcriptional changes occur later. Signaling networks are highly regulated by feedback mechanisms, scaffolding proteins, localization within cellular compartments, and cross-talk between pathways. Desensitization and receptor endocytosis help terminate signals.

Signaling is fundamental to physiology and development and is a major focus in medicine. Dysregulation can contribute to cancer, metabolic diseases, and neurological disorders. Many therapeutics aim to modulate signaling pathways by targeting receptors, kinases, or downstream effectors.