Stimulation of group I metabotropic glutamate receptors evokes calcium signals and c-jun and c-fos gene expression in human T cells

Abstract

To study if the activation of group I mGlu receptors in human T cells modifies intracellular Ca 2+ concentration ([Ca 2+] i) and cell function, we measured [Ca 2+] i on cell suspensions (spectrofluorimetric method) or single cell (digital Ca 2+ imaging system) using fura-2 as indicator. Early-inducible gene ( c-jun and c-fos) expression was studied by reverse transcriptase-polymerase chain reaction assay as representative of Ca 2+-sensitive gene expression. (1 S,3 R)-ACPD (100 μM), the selective mGlu receptor agonist, evoked a significant increase (34.1 ± 4.9%) of [Ca 2+] i, pharmacologically characterized as mediated by group I mGlu receptors, since both ( S)-3,5-DHPG (100 μM), a selective group I mGlu receptor agonist and CHPG (1 mM), the specific mGlu 5 receptor agonist, reproduced the effects, that were abolished by AIDA (1 mM), a selective group I mGlu receptor antagonist. ( S)-3,5-DHPG-induced a rapid [Ca 2+] i rise (initial phase) followed by a slow decrease (second phase) to the baseline. Both extracellular Ca 2+ and Ca 2+ released from intracellular stores contribute to the [Ca 2+] i increase which depend on PLC activation. In a Ca 2+-free buffer, the second phase rapidly return to the baseline; LaCl 3 (1–10 μM), an inhibitor of extracellular Ca 2+ influx, significantly reduced the second phase only; thapsigargin (1 μM), by discharging intracellular Ca 2+ stores, U 73122 (10 μM) and D609 (300 μM), by inhibiting PLC activity, prevented both phases. In our system, PTX pre-treatment increased ( S)-3,5-DHPG effects, demonstrating that PXT-sensitive G i/o proteins are involved. Finally, specific stimulation of these receptors in Jurkat cells upregulates c-jun and c-fos gene expression, thus activating multiple downstream signalling regulating important T cell functions.