Role of diacylglycerol kinase $\zeta (DGK \zeta)$ in the regulation of cerebellar purkinje cell synapses

Abstract

Long-term synaptic plasticity is controlled by balanced actions of positive and negative regulators at synapses. Protein kinase $C_\alpha$ ($PKC_\alpha$) is a critical mediator that induces long-term depression (LTD) at cerebellar parallel fiber-Purkinje cell synapses. However, the precise regulation of $PKC_\alpha$ for LTD is not well understood. Here, I investigated the role of diacylglycerol kinase $\zeta$ (DGK$\zeta$) - a kinase that physically interacts with $PKC_\alpha$ as well as postsynaptic density protein 95 (PSD-95) family proteins and functionally inhibits $PKC_\alpha$ by metabolizing diacylglycerol (DAG) - in the regulation of cerebellar LTD. In Purkinje cells of DGK$\zeta$-deficient mice, LTD was impaired and $PKC_\alpha$ was less localized in dendrites and synapses. This impaired LTD was rescued by virus-mediated expression of wild-type DGK$\zeta$, but not by a kinase-dead mutant DGK$\zeta$ or a mutant lacking the ability to localize at synapses, indicating that both the kinase activity and synaptic anchoring functions of DGKζ are required for LTD. In addition, experiments using another DGK$\zeta$ mutant as well as immunoprecipitation analysis revealed an inverse regulatory mechanism, in which $PKC_\alpha$ phosphorylates, inactivates, and then is dissociated from DGK$\zeta$, is required for LTD. These results indicate that DGK$\zeta$ is targeted to synapses, through its interaction with PSD-95 family proteins, to facilitate synaptic localization of $PKC_\alpha$, but maintains $PKC_\alpha$ in a minimally activated state by reducing local DAG until its activation and release from DGK$\zeta$ during LTD. Such local and reciprocal regulation of positive and negative regulators may contribute to the fine tuning of synaptic signaling.