title: Glutamate involvement in calcium-dependent migration of astrocytoma cells.
abstract: BACKGROUND
  Astrocytoma are known to have altered glutamate machinery that results in the release of large amounts of glutamate into the extracellular space but the precise role of glutamate in favoring cancer processes has not yet been fully established. Several studies suggested that glutamate might provoke active killing of neurons thereby producing space for cancer cells to proliferate and migrate. Previously, we observed that calcium promotes disassembly of integrin-containing focal adhesions in astrocytoma, thus providing a link between calcium signaling and cell migration. The aim of this study was to determine how calcium signaling and glutamate transmission cooperate to promote enhanced astrocytoma migration.
  
  
  METHODS
  The wound-healing model was used to assay migration of human U87MG astrocytoma cells and allowed to monitor calcium signaling during the migration process. The effect of glutamate on calcium signaling was evaluated together with the amount of glutamate released by astrocytoma during cell migration.
  
  
  RESULTS
  We observed that glutamate stimulates motility in serum-starved cells, whereas in the presence of serum, inhibitors of glutamate receptors reduce migration. Migration speed was also reduced in presence of an intracellular calcium chelator. During migration, cells displayed spontaneous Ca(2+) transients. L-THA, an inhibitor of glutamate re-uptake increased the frequency of Ca(2+) oscillations in oscillating cells and induced Ca(2+) oscillations in quiescent cells. The frequency of migration-associated Ca(2+) oscillations was reduced by prior incubation with glutamate receptor antagonists or with an anti-β1 integrin antibody. Application of glutamate induced increases in internal free Ca(2+) concentration ([Ca(2+)]i). Finally we found that compounds known to increase [Ca(2+)]i in astrocytomas such as thapsigagin, ionomycin or the metabotropic glutamate receptor agonist t-ACPD, are able to induce glutamate release.
  
  
  CONCLUSIONS
  Our data demonstrate that glutamate increases migration speed in astrocytoma cells via enhancement of migration-associated Ca(2+) oscillations that in turn induce glutamate secretion via an autocrine mechanism. Thus, glutamate receptors are further validated as potential targets for astrocytoma cancer therapy.
authors.affiliation: Laboratoire de Biophotonique et Pharmacologie, CNRS, UMR 7213, Université de Strasbourg, Illkirch 67401, France.
authors.forename: Abdelkader
authors.initials: A
authors.lastname: Hamadi
authors.affiliation: Interdisciplinary Institute for Neuroscience and UMR CNRS 5297, University of Bordeaux, Bordeaux 33000, France.
authors.forename: Grégory
authors.initials: G
authors.lastname: Giannone
authors.affiliation: Laboratoire de Biophotonique et Pharmacologie, CNRS, UMR 7213, Université de Strasbourg, Illkirch 67401, France.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Takeda
authors.affiliation: Laboratoire de Biophotonique et Pharmacologie, CNRS, UMR 7213, Université de Strasbourg, Illkirch 67401, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Rondé
keywords: Calcium spikes; Glutamate release; Migration; U-87MG cell