Signalkaskade

Signalkaskade, or signal cascade, is a cellular communication process in which an extracellular signal is converted into a precise intracellular response through a sequential activation of signaling molecules. Most cascades are triggered by cell-surface receptors such as G protein-coupled receptors or receptor tyrosine kinases, though intracellular receptors can also initiate cascades. Upon activation, a receptor stimulates one or more downstream effectors, often kinases, that in turn activate additional enzymes and second messengers, propagating the signal to target molecules such as enzymes or transcription factors. This architecture commonly provides signal amplification, so a single ligand event can elicit a large response, as well as integration and specificity through modular components and scaffold proteins that organize enzymes in close proximity. Regulation occurs via feedback loops, both negative and positive, and by cross-talk with other pathways, shaping the duration, strength and spatial pattern of the response.

Common examples include the cAMP/PKA pathway, where adenylyl cyclase generates cAMP to activate PKA; calcium signaling, where Ca2+ waves regulate calmodulin and calcium-dependent kinases; the IP3/DAG pathway leading to PKC activation; and the MAPK/ERK cascade involved in growth, differentiation and stress responses. The JAK-STAT pathway is also part of the broader signaling network but operates with a distinct architecture.

Signalkaskade plays roles in development, immune responses, sensory perception, and homeostasis, and its dysregulation is linked to diseases such as cancer and autoimmune disorders. Because of its central role, signaling cascades are frequent targets for pharmacological intervention and systems biology modeling.