INVOLVEMENT OF PROTEIN-KINASE-C IN CA2-SIGNALING PATHWAYS TO ACTIVATION OF AP-1 DNA-BINDING ACTIVITY EVOKED VIA NMDA-GATED AND VOLTAGE-GATED CA2+ CHANNELS()

Stimulation of cultured cerebellar granule cells with N-methyl-D-aspar tate (NMDA) or kainic acid (KA) leads to activation of activator prote in-1 (AP-1) DNA-binding activity, which can be monitored by an increas e in 12-O-tetradecanoylphorbol 13-acetate (TPA)-responsive element (TR E)-binding activity, in concert with c-fos induction. For this increas e in TRE-binding activity, Ca2+ influx across the plasma membrane is e ssential. Treatment of cells with an intracellular Ca2+ chelator, BAPT A-AM, abolished this increase. Close correspondence between the dose-r esponse curves of Ca-45(2+) uptake and TRE-binding activity by NMDA or KA suggested that Ca2+ influx not only triggered sequential activatio n of Ca2+-signaling processes leading to the increase in TRE-binding a ctivity, but also controlled its increased level. Stimulation of non-N MDA receptors by KA mainly caused Ca2+ influx through voltage-gated Ca 2+ channels, whereas stimulation of NMDA receptors caused Ca2+ influx through NMDA-gated ion channels. The protein kinase C (PKC) inhibitors staurosporine and calphostin C inhibited the increase in TRE-binding activity caused by NMDA and KA at the same concentration at which they inhibited that caused by TPA. Furthermore, down-regulation of PKC inh ibited the increase in TRE-binding activity by NMDA and KA. Thus, a co mmon pathway that includes PKC could, at least in part, be involved in the Ca2+-signaling pathways for the increase in TRE-binding activity coupled with the activation of NMDA- and non-NMDA receptors.