Role of protein kinase Cβ in phorbol ester-induced c-fos gene expression in neurons of normotensive and spontaneously hypertensive rat brains

We have previously demonstrated that pressure application of the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) onto some neurons in the anterior hypothalamic area of rats increases neural activity in vivo and that this PKC activation-induced increase of neural activity is enhanced in spontaneously hypertensive rats (SHR), an animal model for genetic hypertension. Activation of PKC increases expression of the c-fos gene, an important transcription factor and proto-oncogene thought to be a marker of neural activity. To evaluate PKC isoforms responsible for neural activation, we examined which isoforms of PKC are involved in the PKC activation-induced c-fos gene expression in neuronal cultures of Wistar rat and spontaneously hypertensive rat (SHR) brains. PMA increased c-fos gene expression in neuronal cultures of Wistar rat brain and the PMA-induced c-fos gene expression was inhibited by the PKC inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7). The PKCα,β,γ activator thymeleatoxin also increased c-fos gene expression, while the PKCδ,ε activator ingenol did not affect it. In addition, the PMA-induced c-fos gene expression was inhibited by PKCβantisense oligonucleotides (AON) but not by PKCα and PKCγAONs. In SHR brain neuronal cultures, the PMA-induced c-fos gene expression was enhanced as compared with that of Wistar Kyoto rats (WKY), while basal c-fos gene expression was almost the same in both neuronal cultures. The enhancement of PMA-induced c-fos gene expression in SHR brain cultures was abolished by PKCβAON. These findings suggest that in rat brain neuronal cultures, PMA increases c-fos gene expression via activation of PKC and that PKCβisoforms are partly involved in the PMA-induced c-fos gene expression. In neuronal cultures of SHR brain, it appears that the PMA-induced c-fos gene expression is also enhanced via PKCβ.