Bombesin receptor 2 (BB₂) is a member of a family of receptors that binds the 14 amino acid peptide, bombesin. Bombesin was first isolated from frog skin and it was later established that mammals express endogenous bombesin-like peptides such as gastrin-releasing peptide (GRP; a 27 amino acid homologue) and neuromedin B (NMB; a 10 amino acid homologue).

BB₂ is the preferred receptor for GRP and hence it is also referred to as GRP receptor or GRP-R.¹ BB₁ is the preferred receptor for NMB and therefore it is also known as NMB-R. A third member (called BB₃) of the bombesin receptor family has been recognized but the endogenous mammalian ligand for this receptor remains to be identified.

All three bombesin receptors are members of the seven-transmembrane domain, G protein-coupled receptor (GPCR) superfamily. BB₂ is coupled to a G_q/11 protein that activates phospholipase C (PLC) and leads to production of inositol 1,4,5-trisphosphate (InsP₃), intracellular Ca²⁺ mobilization, and cell growth.²

GRP (through its binding to BB₂) plays an essential role in the release of hormones in the intestinal tract, the regulation of smooth muscle contraction, and the secretion of pancreatic enzymes.² In the brain, BB₂ has been implicated in regulating feeding behavior, thermoregulation, and memory formation.³

Finally, BB₂ is overexpressed in several human tumors including breast, prostate, and lung, where it acts as a growth factor receptor inducing tumor growth. BB₂ is considered a potential target for the development of both diagnostics and anti-cancer therapies.⁴