Protein kinase C (PKC) is a family of serine-threonine kinases comprising nine genes, all of which are expressed in the central nervous system with isozyme-specific patterns of expression.155 PKC isozymes can be classified into three subgroups based on similarities in structure and regulation: the conventional PKCs (cPKC, α, β, and γ), the novel PKCs (nPKC, δ, ε, η, and θ), and the atypical PKCs (aPKC, ζ, and Ι/λ).156 Conventional PKCs are activated by diacylglycerol (DAG) and calcium, novel PKCs are activated by DAG but not calcium, and the atypical PKCs are not activated by DAG or calcium but instead by other lipid second messengers, such as arachidonic and phosphatidic acid.157 The hydrolysis of phosphatidylinositol-4,5-bis-phosphate by phospholipase C (PLC) generates inositol triphosphosphate (IP3) and DAG. IP3 releases intracellular calcium stores to increase intracellular calcium levels, which can synergize with DAG to activate conventional PKCs.
