Carbonic Anhydrase 8 Expression in Purkinje Cells Is Controlled by PKCγ Activity and Regulates Purkinje Cell Dendritic Growth

Purkinje cell dendritic development is severely compromised after chronic activation of protein kinase C (PKC). In a recent transgenic mouse model of spinocerebellar ataxia 14, the ser361-to-gly (S361G) mutation of the protein kinase C gamma (PKC gamma) gene was expressed in Purkinje cells. Purkinje cells from these mutant mice in organotypic slice cultures have the same stunted dendritic tree as Purkinje cells after pharmacological activation of PKC. Because the transgene is exclusively present in Purkinje cells, cerebellar tissue from these mice is an attractive starting material for searching genes which might be interacting with PKC gamma in Purkinje cells for inducing the stunted dendritic growth. We have performed a microarray analysis and identified several candidate genes with an increased messenger RNA (mRNA) expression in the PKC gamma-S361G transgenic Purkinje cells. Out of these candidates, we have further studied carbonic anhydrase 8 (CA8). We show here that CA8 mRNA and protein expression is strongly induced in PKC gamma-S361G transgenic Purkinje cells. Overexpression of CA8 in Purkinje cells in dissociated cultures strongly inhibited Purkinje cell dendritic development and produced a dendritic phenotype similar to PKC gamma-S361G. There was no evidence for a direct binding of CA8 to either PKC gamma or the type 1 IP3 receptor. Knockdown of CA8 with miRNA did not alter Purkinje cell dendritic development and did not protect Purkinje cells in dissociated cultures from the stunted dendritic growth induced by PKC gamma-S361G or by PKC activation. Our results indicate that CA8 is a novel important regulator of Purkinje cell dendritic development and that its expression is controlled by PKC gamma activity.