Protein kinase C (PKC) is a family of serine-threonine kinases that regulate a broad spectrum of cellular functions such as cell migration and polarity, proliferation, differentiation, and cell death. The family is composed of several genes that express structurally related phospholipid-dependent kinases with distinct means of regulation and tissue distribution. Based on their structures and sensitivities to Ca2+ and diacylglycerol (DAG), they have been classified into conventional PKCs (α, β, and γ), novel PKCs (δ, ε, η, and θ), and atypical PKCs (ζ and λ/ι). PKCs share a structural backbone, mainly consisting of a regulatory domain at the N-terminus and a catalytic domain at the C-terminus. All family members require phosphatidylserine, a component of the phospholipid bilayer, for their activation. Some PKCs (PKCα, δ, and ζ) are widely expressed in all tissues, but other isoforms are expressed in a tissuespecific manner. PKCγ, for example, is largely confined to brain and neuronal tissue, PKCι is mainly expressed in testis and insulin secreting cells, and PKCθ is mainly expressed in skeletal muscle. PKC epsilon (PKCε) is a calcium-independent and phorbolester/diacylglycerol-sensitive serine/threonine kinase. PKCε is the only PKC isozyme that has been shown to behave as an oncoprotein. Constitutive activation of PKCε in a small cell lung cancer (SCLC) cell line and the overexpression of PKCε in colonic epithelial cells have been reported.