Vesicular monoamine transporter type 2 (VMAT2) is crucial for accumulation of monoamine neurotranmitters into neuronal secretory vesicles and histamine into secretory granules of the enterochromaffin-like cell in the acid-secreting gastric mucosa. Gastric VMAT2 expression is regulated by the antral hormone gastrin acting at the CCK 2 receptor. We demonstrate a gastrin response element ؊56 ccgccccctc ؊47 in the proximal VMAT2 promoter that binds in a gastrin-sensitive manner to nuclear proteins from gastric epithelial cell lines. Mutations within this sequence prevented nuclear protein binding and significantly reduced gastrin-stimulated expression of VMAT2 promoter-reporter constructs in gastric epithelial cells. In a yeast one-hybrid screen of an AR42J cell cDNA library, using the gastrin response element as bait, we identified a beta subunit of the 20 S proteasome, PSMB1, as a potential binding partner. In supershift assays, antibodies to PSMB1 and other proteasome beta subunits disrupted gastrin sensitive nuclear protein binding to the VMAT2 promoter. Moreover, RNA interference of PSMB1 significantly inhibited gastrin-mediated VMAT2 transcription. These data suggest that elements of the 20 S proteasome interact with the VMAT2 promoter to enhance G-proteincoupled receptor-mediated transcription.The vesicular monoamine transporters (VMATs) 2 are responsible for the energy-dependent accumulation of biogenic amines into secretory vesicles of amine producing cells and thus play central roles in cellular physiology. The two members of this family, VMATs 1 and 2, have similar structures and mechanisms of action, but differ in their cellular localization and substrate specificity (1-4). VMAT2 (SLC18A2) is expressed in all monoaminergic neurones of the central nervous system, notably e.g. in dopaminergic neurones of the substantia nigra and histaminergic posterior hypothalamic neurones. Support for the idea that VMAT2 is important for neuronal function comes from studies in VMAT2 knock-out mice. Homozygotes have seriously disrupted patterns of feeding and locomotion and are poorly viable. Heterozygotes are grossly normal but have reduced central monoamine levels and are hypersensitive to the locomotor effects of cocaine and amphetamine and are more sensitive to the neurotoxin 1-methyl-(4-phenyl-1,2,3,6-tetrahydropyridine) (MPTP) and to 3,4-dihydroxyphenylalanine (L-DOPA) (5-7). VMAT2 is able to sequester from cytoplasm, toxins, and transmitters that cause Parkinson-like syndromes, and gain of function haplotypes have been reported to confer protection against Parkinson's disease (8). Transporter affinities for serotonin and the catecholamines are in the low micromolar range and are broadly similar for both VMATs. However, only VMAT2 has micromolar affinity for histamine (3). The ability of VMAT2 to accumulate histamine in secretory vesicles is consistent with its localization in central histaminergic neurones and in enterochromaffin-like (ECL) cells of the gastric epithelium, its only non-neuronal location (4). Hist...