Inositol phosphate signaling pathway (IP signaling)

The inositol phosphate–dependent second messenger pathway is a fundamental signal transduction system that translates extracellular stimuli into intracellular actions (KEGG: hsa04071). Upon activation of cell surface receptors, such as G protein-coupled receptors (GPCRs) or receptor tyrosine kinases (RTKs), the enzyme phospholipase C (PLC) hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into two key second messengers: inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) (StatPearls: Second Messengers). IP3 diffuses through the cytosol to bind IP3 receptors on the endoplasmic reticulum, triggering the release of sequestered calcium ions, while DAG remains membrane-bound to activate protein kinase C (PKC) (PubMed: PMC2883154). This dual signaling branch regulates diverse cellular processes including contraction, secretion, metabolism, and gene expression. Dysregulation of inositol phosphate signaling is linked to numerous pathologies, most notably bipolar disorder, where lithium's therapeutic effect is attributed to the inositol depletion hypothesis (PubMed: 12466457). Consequently, components of this pathway are significant targets for pharmacological intervention, though their widespread physiological roles present challenges for achieving tissue-specific therapeutic effects.

Other names

Phosphoinositide signaling pathwayIP3-DAG signaling pathwayPhosphatidylinositol signaling systemInositol phosphate-dependent second messenger pathways

Drugs targeting this pathway typically act by inhibiting key enzymes such as inositol monophosphatase (e.g., lithium) to deplete inositol levels, or by modulating phospholipase C (PLC) activity and inositol trisphosphate (IP3) receptor-mediated calcium release.