Glutamate activates PP125^FAK through AMPA/kainate receptors in Bergmann glia

Abstract

Glial glutamate receptors are likely to play a role in plasticity, learning, and memory and in a number of neuropathologies. An enhanced glutamate-dependent tyrosine phosphorylation has been detected in such processes. Using primary cultures of chick Bergmann glia cells and chick cerebellar slices, we addressed whether glial glutamate receptors can activate the nonreceptor tyrosine kinase pp125 focal adhesion kinase (pp125(FAK)). A dose- and time-dependent tyrosine phosphorylation of pp125(FAK) was found in both preparations upon glutamate treatment. This effect was mediated through alpha-amino-3-hydroxy-5-methyl-4-isoaxazolepropionate (AMPA)/kainate (KA) receptors, as shown by its inhibition by the specific antagonists 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7- sulfonamide (NBQX) and 6,7-dinitroquinoxaline-2,3-dione (DNQX) and the lack of effect of metabotropic agonists. FAK tyrosine phosphorylation was dependent on phosphatidylinositol 3-kinase activity. As expected, an increase in pp125(FAK) catalytic activity was found upon glutamate treatment. Immunprecipitation experiments demonstrated that FAK associates with ionotropic glutamate receptors. Taken together, these results suggest a role for glial glutamate receptors in cytoskeletal rearrengments and focal adhesion contact formation and provide new insight into the signaling transactions elicited by this neurotransmitter in glial cells.

α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptors signaling complexes in Bergmann glia

“…5A). It is important to mention that this time course matches perfectly with kinetics of pp125 FAK tyrosine phosphorylation in cultured BGC (Millan et al, 2001). When the dose dependence of the Glu effect was examined, an EC 50 of 138.2 Ϯ 11 M was obtained for cultured BGC and 141.6 Ϯ 9 M for cerebellar slices, again resembling to what has been determined for pp125 FAK tyrosine phosphorylation induced by Glu, in both systems (Fig.…”

“…4). It is important to note that, in the cerebellar slice preparation, a basal association of PI-3K of GluR1, -2, and -3 receptors is present, suggesting that indeed in neuronal cells PI-3K might be complexed to the AMPA receptors under basal conditions as reported for cultured hippocampal cells (Millan et al, 2001;Man et al, 2003). In any event, it is quite clear that Glu increases this interaction most possibly in the Bergmann glia cells present in the slice preparation.…”

“…After our preliminary observations that AMPA receptors interact with the nonreceptor tyrosine kinase pp125 FAK in BGC (Millan et al, 2001), we decided to characterize this issue further. Taking into consideration that pp125 FAK forms complexes with Src-related kinases, such as Lyn, Fyn, and Yes (Panetti, 2002), the reported interaction of GluR2/3 with Lyn (Hayashi et al, 1999) and that, in these complexes, tyrosine phosphorylation is involved, we evaluated the possibility that, in AMPA, receptors could become tyrosine phosphorylated as a result of Glu exposure.…”

“…B: Data were normalized after scanning of the autorradiograms of three independent experiments and are the mean Ϯ SD. Millan et al, 2001). Despite the fact that PI-3K has been reported to be constitutively associated with AMPA receptors in hippocampal neurons and that it becomes activated through the Ca 2ϩ /calmodulin complex (Man et al, 2003), this mode of activation is by no means the more common and better chararacterized mode of activation (Hiles et al, 1992) and, in fact, in such a scenario, the Ca 2ϩ /calmodulin complex has to compete with tyrosinephosphorylated proteins for binding to the SH2 domains of PI-3K (Joyal et al, 1997).…”

“…Cytoskeletal rearrangements as well as coordinated AMPA receptor signaling transactions might be the key features of this glial elongation. We have reported in this context that Bergmann glial AMPA receptors activate the focal adhesion kinase pp125 FAK , a nonreceptor tyrosine kinase (Millan et al, 2001). …”