Gastrin stimulates Ca2+ mobilization and clonal growth in small cell lung cancer cells

Gastrin has been postulated to be a physiological growth factor, but compelling in vitro evidence of this has been difficult to obtain. In the present study we investigated whether small cell lung carcinoma cell lines could provide a useful model system to study the effects of gastrin on signal transduction and cell proliferation in vitro. We found that the addition of gastrin to small cell lung cancer cells loaded with the fluorescent Ca2+ indicator fura 2-tetraacetoxymethylester causes a rapid and transient increase in the intracellular concentration of Ca2+ ([Ca2+]i) followed by homologous desensitization. The [Ca2+]i response was especially prominent in the small cell lung carcinoma cell line H510. In this cell line, gastrin I, gastrin II, cholecystokinin residues 26-33 (CCK-8), and unsulfated CCK-8 increased [Ca2+]i in a concentration-dependent fashion with half-maximum effects at 7, 2.5, 3, and 5 nM, respectively. The Ca(2+)-mobilizing effects of gastrin and CCK-8 were prevented by proglumide, benzotript, and the specific gastrin/CCKB receptor antagonist L365260. Gastrin stimulated the clonal growth of H510 cells in semisolid (agarose-containing) medium, increasing both the number and the size of the colonies. Gastrin and CCK agonists were equally effective in promoting clonal growth. The broad-spectrum neuropeptide antagonists [D-Arg1,D-Phe5,D-Trp7,9,Leu11] substance P and [Arg6,D-Trp7,9,MePhe8] substance P (6-11) markedly inhibited gastrin-stimulated Ca2+ mobilization and clonal growth. These results show that gastrin acts as a direct growth factor through gastrin/CCKB receptors and demonstrate, for the first time, that these peptides can stimulate the proliferation of cells outside the gastrointestinal tract.