Galanin stimulates Ca2+ mobilization, inositol phosphate accumulation, and clonal growth in small cell lung cancer cells.
Addition of the neuropeptide galanin to small cell lung cancer (SCLC) 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. Galanin increased [Ca2+]i in a concentration-dependent fashion with half-maximum effect (EC50) at 20-22 nM in H69 and H510 SCLC cells. Galanin mobilized Ca2+ from intracellular stores since its effects on [Ca2+]i were not blocked by chelation of extracellular Ca2+. Pretreatment with pertussis toxin (200 ng/ml for 4 h) did not prevent galanin-induced Ca2+ mobilization. In contrast, direct activation of protein kinase C with phorbol esters attenuated the Ca2+ response induced by galanin. The effects of galanin could be dissociated from changes in membrane potential: galanin did not increase membrane potential in SCLC cells loaded with bis(1,3-diethyltiobarbiturate)-trimethineoxonol and induced Ca2+ mobilization in depolarized SCLC cells, i.e., in cells suspended in a solution containing 145 mM K+ instead of Na+. Galanin also caused an increase in the formation of inositol phosphates in a time- and dose-dependent manner (EC50 10 nM). A rapid increase in the inositol trisphosphate fraction was followed by a slower increase in the inositol monophosphate fraction. Galanin stimulated clonal growth of both H69 and H510 cells in semisolid (agarose-containing) medium. This growth-promoting effect was sharply dependent on galanin concentration (EC50 20 nM) and markedly inhibited by [Arg6,D-Trp7,9,MePhe8]substance P, a recently identified broad spectrum neuropeptide antagonist. The results show for the first time that galanin receptors are coupled to inositol phosphate and [Ca2+]i responses in SCLC cells and, in particular, that this neuropeptide can act as a direct growth factor for these human cancer cells.
Sethi
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Imperial Cancer Research Fund, London, United Kingdom.
Rozengurt
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D002118:Calcium / Q000378:metabolism*; D018288:Carcinoma, Small Cell / Q000378:metabolism / Q000473:pathology*; D002455:Cell Division / Q000187:drug effects; D004533:Egtazic Acid / Q000494:pharmacology; D019004:Galanin; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D008175:Lung Neoplasms / Q000378:metabolism / Q000473:pathology*; D008564:Membrane Potentials; D010455:Peptides / Q000494:pharmacology*; D037342:Pertussis Toxin; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000187:drug effects; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D007295:Inositol Phosphates; D010455:Peptides; D010566:Virulence Factors, Bordetella; D015240:Phorbol 12,13-Dibutyrate; D004533:Egtazic Acid; D019004:Galanin; D037342:Pertussis Toxin; D002118:Calcium