Glutamate-stimulated activation of DNA synthesis via mitogen-activated protein kinase in primary astrocytes: Involvement of protein kinase C and related adhesion focal tyrosine kinase

Glutamate is the major excitatory neurotransmitter in the CNS. Although its role in neurons has been studied extensively, little is known about its fu nction in astrocytes. We studied the effects of glutamate on signaling path ways in primary astrocytes. We found that the tyrosine kinase related adhes ion focal tyrosine kinase (RAFTK) is tyrosine phosphorylated in response to glutamate in a time- and dose-dependent manner. This phosphorylation was p ertussis toxin (PTX) sensitive and could be attenuated by the depletion of Ca2+ from intracellular stores. RAFTK tyrosine phosphorylation was mediated primarily by class I/II metabotropic glutamate receptors and depends on pr otein kinase C (PKC) activation. Glutamate treatment of primary astrocytes also results in a significant increase in the activity of the mitogen-activ ated protein kinases [extracellular signal-related kinases 1/2 (ERK1/2)]. L ike RAFTK phosphorylation, ERK1/2 activation is PTX sensitive and can be at tenuated by the depletion of intracellular Ca2+ and by PKC inhibition, sugg esting that RAFTK might mediate the glutamate-dependent activation of ERK1/ 2. Furthermore, we demonstrated that glutamate stimulation of primary astro cytes leads to a significant increase in DNA synthesis. Glutamate-stimulate d DNA synthesis is PTX sensitive and can be inhibited by the MAP kinase kin ase inhibitor PD98059, suggesting that in primary astrocytes, glutamate mig ht signal via RAFTK and MAP kinase to promote DNA synthesis and cell prolif eration.