postreceptor

Postreceptor refers to the intracellular events triggered by activation of a cell-surface receptor. Following ligand binding, the receptor undergoes conformational changes that initiate signaling cascades within the cell, converting an extracellular message into a coordinated cellular response. Postreceptor signaling encompasses diverse pathways and is a key determinant of the specificity, magnitude, and duration of the response.

Two broad themes are common across receptors. Second messengers such as cyclic AMP, inositol trisphosphate, diacylglycerol, and calcium ions propagate signals that modulate enzyme activity and gene expression. Protein kinase cascades relay and amplify signals, including PKA, PKC, Ca2+-dependent kinases, and mitogen-activated protein kinase (MAPK) pathways, as well as lipid kinases and phosphoinositide kinases. In receptor tyrosine kinases, adaptor proteins recruit signaling modules that activate small GTPases such as Ras and downstream kinases, leading to transcriptional responses via factors such as CREB or AP-1.

Postreceptor signaling is tightly regulated and subject to termination and feedback. Desensitization and receptor internalization limit responsiveness; regulatory proteins such as arrestins, phosphatases, and phosphodiesterases reduce signal strength and duration. Cross-talk between pathways, spatial organization within signaling microdomains, and receptor downregulation shape the cellular outcome. Pharmacological modulation of postreceptor components—by altering second messengers, kinase activity, or transcriptional programs—underpins many therapeutic strategies.

Examples include the beta-adrenergic receptor signaling via Gs to increase cAMP and activate PKA, affecting metabolism and heart rate; insulin receptor signaling through IRS and PI3K-AKT to promote glucose uptake and growth; GPCRs involving arrestins that mediate desensitization and can initiate alternative signaling; and receptor tyrosine kinase pathways such as Ras-MAPK that regulate gene expression.