Zinc ions mediate gastrin expression, proliferation, and migration downstream of the cholecystokinin-2 receptor

Abstract

Gastrin, acting via the cholecystokinin-2 receptor (CCK2R), activates its own promoter in a positivefeed-forward loop that may result in hypergastrinemia. Activity of the gastrin promoter is also stimulated by exogenous Zn2β ions. Here, the role of intracellular zinc and calcium signaling in the gastrin positive-feed-forward loop was investigated. Gastrin promoter activity was measured in the human gastric carcinoma cell line AGS-CCK2R and in Jurkat cells transfected with various gastrin promoter-luciferase constructs after treatment with gastrin in the presence and absence of zinc-and calcium-chelating agents. The free intracellular zinc ion concentrations were measured in the same cells with the fluorescent indicator FluoZin-3. Cell proliferation and migration/invasion were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide cell proliferation assay and in Boyden chamber assays, respectively. The zinc chelator N,N,N,N-tetrakis-(2-pyridylmethyl)-ethylenediamine (TPEN) abolished gastrin-stimulated gastrin promoter activity, and the inhibition was completely reversed by exogenous Zn2β ions. In contrast, the calcium chelator 1,2-Bis(2-aminophenoxy)ethane-N,N,Nα,Nα-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTAAM) potentiated gastrin-stimulated gastrin promoter activity. Treatment with gastrin increased the intracellular concentration of free Zn2β ions, and the increase was blocked by TPEN, but not by BAPTA-AM. TPEN also inhibited the stimulation of cell proliferation and migration/invasion by gastrin, but BAPTA-AM had no effect. These results, which are the first report of the existence of Zn2β signaling downstream of CCK2R activation, suggest that zinc chelation therapies may be effective in counteracting gastrin-dependent tumor growth.