ExtrazellulärLiganden

ExtrazellulärLiganden are molecules that exist outside the cell and bind to specific receptors on the cell surface or in the extracellular environment to elicit cellular responses. They include a broad range of entities, such as soluble proteins, peptides, hormones, growth factors, cytokines, chemokines, neurotransmitters, and extracellular matrix components that act as ligands for receptors like receptor tyrosine kinases, G protein–coupled receptors, integrins, and ion channels. Some ligands are freely diffusible, while others are immobilized within the extracellular matrix and presented to cells in a context-dependent manner.

ExtrazellulärLiganden mediate signaling through different modes. Endocrine ligands are released into the bloodstream and act on distant cells, while paracrine ligands affect neighboring cells, and autocrine ligands influence the cell that secretes them. Juxtacrine ligands remain attached to the producing cell surface and signal to adjacent cells. Binding of a ligand to its receptor triggers a conformational change that propagates signals inside the cell, often via second messengers, phosphorylation cascades, or transcriptional changes, leading to altered gene expression, metabolism, differentiation, or cell behavior.

Regulation of extracellular signaling involves ligand availability, receptor expression, and the presence of decoy receptors or proteolytic processing that modulates ligand activity. Spatial and temporal dynamics, such as gradients and signaling duration, shape developmental processes, immune responses, tissue homeostasis, and repair. Dysregulation of ExtrazellulärLiganden signaling is implicated in diseases including cancer, inflammation, and metabolic disorders.