The pathways through which cells receive external signals and transmit, amplify, and direct them internally. The pathway begins with cell-surface receptors (q.v.) and may end in the cell nucleus with DNA-binding proteins that suppress or activate replication or transcription. Signaling pathways require intercommunicating chains of proteins that transmit the signal in a stepwise fashion. Protein kinases (q.v.) often participate in this cascade of reactions, since many signal transductions involve receiving an extracellular, chemical signal, which triggers the phosphorylation of cytoplasmic proteins to amplify the signal. See ABC transporter, cyclic AMP, gene-for-gene hypothesis, G proteins, polycystic kidney disease, transforming growth factor-β (TGF-β), Wnt.
Subjects: Genetics and Genomics.