Figure 1.

General view of intercellular messengers’ receptors and their downstream signaling pathways. (1) Intracellular ligand-regulated transcription factor. (2)–(5) Plasma membrane receptors: (2) protease-cleavable receptor with intracellular domain exhibiting transcriptional activity; (3) enzyme receptors (Tyr, Ser/Thr, His kinases, GMPcyclase, phosphatase); (4) non-enzymatic receptors recruiting cytoplasmic partners (kinases, G proteins, scaffolding proteins); and (5) channel receptors (ionotropic). For details, see also Table 1.