What is the role of phospholipase C (PLC) in intracellular signaling?

• A. It cleaves PIP2 to produce IP3 and DAG, leading to increased intracellular Ca2+.
• B. It synthesizes cAMP from ATP.
• C. It directly phosphorylates target proteins.
• D. It inhibits IP3 formation.

Answer: (A)

Phospholipase C sets off a calcium and PKC signaling cascade by cleaving a membrane lipid (PIP2) to form two second messengers: IP3 and DAG. IP3 travels to the endoplasmic reticulum and triggers Ca2+ release into the cytosol, raising intracellular calcium levels that activate numerous Ca2+-dependent processes. DAG remains in the membrane and, together with the Ca2+ rise, activates protein kinase C, which then phosphorylates target proteins to propagate the signal. This pathway is commonly activated by Gq-coupled receptors or certain receptor tyrosine kinases that engage PLC-β or PLC-γ. By contrast, cAMP is produced by adenylyl cyclase, not PLC; PLC itself does not directly phosphorylate proteins—that role is carried out by PKC and other kinases after the second messengers are generated; and PLC promotes IP3 formation rather than inhibiting it.