Gastrin induces expression and promoter activity of the vesicular monoamine transporter subtype 2

Gastric enterochromaffin-like cells produce histamine in response to the an tral hormone gastrin and accumulate the biogenic amine in secretory organel les via vesicular monoamine transporter subtype 2. The putative effects of gastrin on vesicular monoamine transporter subtype 2 expression and promote r activity are poorly understood. In the present study we used highly enric hed rat enterochromaffin-like cells (purity, >90%) and rat pheochromocytoma cells stably transfected with a gastrin/cholecystokinin B receptor to inve stigate the expression and transcriptional regulation of vesicular monoamin e transporter subtype 2. Stimulation of vesicular monoamine transporter sub type 2 mRNA and protein expression was observed in isolated enterochromaffi n-like cells after 3- to 7-h incubation with gastrin (10(-7) M), forskolin (10(-5) m), or ionomycin (10(-5) m). Deletion analysis of the rat vesicular monoamine transporter subtype 2 promoter defined the minimal promoter sequ ence necessary for full basal activity as a -121 bp segment upstream of exo n 1 containing two Spl sites (-97 to -88 bp and -68 to -59 bp) and a cAMP-r esponsive element (-44 to -35 bp). Gastrin (10(-7) M) stimulated extracellu lar signal related kinase1/2 phosphorylation, activated Spl and cAMP-respon sive element-binding protein, and further induced activity of the complete rat vesicular monoamine transporter subtype 2 promoter (-800 bp) in gastrin /cholecystokinin B receptor cells. The -121-bp fragment was able to confer full gastrin responsiveness, and site-directed mutagenesis of the Spl and c AMP-responsive element motifs demonstrated their crucial importance for bas al and inducible activities. Comparison of promoter activity of histidine d ecarboxylase, chromogranin A, or vesicular monoamine transporter subtype 2 in transfected cell lines revealed significant differences in basal and gas trin-stimulated activities. Our current study provides the first evidence t hat gastrin directly stimulates the expression and promoter activity of ves icular monoamine transporter subtype 2. Sp1 and cAMP-responsive element-bin ding protein recognition motifs located within 121 bp upstream of exon 1 ap pear to be indispensable for full basal and inducible promoter activities. Diverging effects of gastrin on histidine decarboxylase, chromogranin A, an d vesicular monoamine transporter subtype 2 promoter may account for the co ordinated synthesis and storage of histamine in this neuroendocrine cell ty pe.