Structure of the human M₂ muscarinic acetylcholine receptor gene and its promoter

The M₂ muscarinic receptor inhibits the release of acetylcholine from cholinergic fibers in the lungs and elsewhere. In airway parasympathetic neurons, M₂ receptor expression is decreased by viral infections and by interferon-γ, increasing actylcholine release. Dexamethasone increases M₂ receptor expression, decreasing acetylcholine release. We carried out 5′ rapid amplification of cDNA ends beginning with mRNA from human heart and IMR32 human neuroblastoma cells. This demonstrated a 5′ UTR of 100 BP, corresponding to two sequences on chromosome 7, separated by a 22.6 kB intron. The splice acceptor site is at -45 relative to the initiating atg. The 3000 BP upstream of 5′ RACE product were subcloned into a pGL3 luciferase reporter vector. Deletional constructs were expressed in IMR32 cells. These demonstrated that 412 BP provided full expression of the reporter gene, and suggested a repressor element between -1848 and -1510.