Mislocalization of the exitatory amino-acid transporters (EAATs) in human astrocytoma and non-astrocytoma cancer cells: effect of the cell confluence

Abstract

BackgroundAstrocytomas are cancers of the brain in which high levels of extracellular glutamate plays a critical role in tumor growth and resistance to conventional treatments. This is due for part to a decrease in the activity of the glutamate transporters, i.e. the Excitatory Amino Acid Transporters or EAATs, in relation to their nuclear mislocalization in astrocytoma cells. Although non-astrocytoma cancers express EAATs, the localization of EAATs and the handling of L-glutamate in that case have not been investigated.MethodsWe looked at the cellular localization and activity of EAATs in human astrocytoma and non-astrocytoma cancer cells by immunofluorescence, cell fractionation and L-glutamate transport studies.ResultsWe demonstrated that the nuclear mislocalization of EAATs was not restricted to astrocytoma and happened in all sub-confluent non-astrocytoma cancer cells we tested. In addition, we found that cell-cell contact caused the relocalization of EAATs from the nuclei to the plasma membrane in all human cancer cells tested, except astrocytoma.ConclusionsTaken together, our results demonstrated that the mislocalization of the EAATs and its associated altered handling of glutamate are not restricted to astrocytomas but were also found in human non-astrocytoma cancers. Importantly, we found that a cell contact-dependent signal caused the relocalization of EAATs at the plasma membrane at least in human non-astrocytoma cancer cells, resulting in the correction of the altered transport of glutamate in such cancer cells but not in astrocytoma.

Visualization of Implanted GL261 Glioma Cells in Living Mouse Brain Slices Using Fluorescent 4-(4-(dimethylamino)-styryl)-N-Methylpyridinium Iodide (ASP + )

“…Gene expression analyses identified a high expression of SOX2 in high-grade glioma cultures [14] except glioma cultures of mesenchymal origin. Some reports indicate that during tumor development glioma cells may lose or translocate some of their surface transporters [15, 16], and our data demonstrating strong ASP + uptake in cultured and implanted GL261 glioma cells during the first two weeks after implantation in mouse brain and significant reduction of ASP + uptake in older tumors support these findings. Thus OCT family transporters are initially overexpressed in many gliomas and ASP + can be used as a fast and effective glioma marker.…”

Glioblastoma Development in Mouse Brain: General Reduction of OCTs and Mislocalization of OCT3 Transporter and Subsequent Uptake of ASP<SUP>+</SUP> Substrate to the Nuclei

“…This suggests that the mislocalized transporter remains active in the nucleus, pumping fluorescent substrate to the inside of the nucleus of migrating glioma cells. The functionality of transporters has not been studied for other transporters reportedly also mislocalized in gliomas [23]. The only study describing functional mislocalization to the nucleus is the case of CXCR4 mislocalization in prostate-cancer cells [24].…”

“…Recently, numerous reports have emerged that some important transporters, receptors and channels, normally presented in the plasma membrane can be mislocalized in gliomas and, generally, in cancer cells, to the nuclei. It was shown that glutamate transporters became mislocalized to the nucleus in glioma cells that depends upon cellular confluence or the amount of cells in the tumor (tumor size) [25, 23]. Also, potassium inward-rectifying channels Kir 4.1 and Kir 2.3 in glioma cells are found almost exclusively in either the cell nucleus or endoplasmic reticulum/Golgi apparatus (Kir 3.1) [26].…”

From the Gut to the Brain: Journey and Pathophysiological Effects of the Food-Associated Trichothecene Mycotoxin Deoxynivalenol

“…Surprisingly and contrarily to what we found with another mycotoxin, ochratoxin A [148], such inhibition is associated to a massive increase in the membrane expression of EAAT1/2 through an unidentified mechanism. Inhibition induced by DON of the glutamate uptake by astrocytes may have major consequences since this activity prevents neuronal damage caused by high excitotoxic extracellular glutamate concentrations [149] and that perturbation of glutamate clearance by astrocytes could also contribute to brain tumor progression [150], pain hypersensitivity [151] and to alterations in learning and memory consolidation [152]. Although very interesting, these in vitro data showing the perturbation of glial cells by DON now need to be confirmed by in vivo studies.…”