A multiplicity of functions have been ascribed to PKC. Recurring themes are that PKC is involved in receptor desensitization, in modulating membrane structure events, in regulating transcription, in mediating immune responses, in regulating cell growth, and in learning and memory. These functions are achieved by PKC-mediated phosphorylation of other proteins. However, the substrate proteins present for phosphorylation vary, since protein expression is different between different kinds of cells. Thus, effects of PKC are cell-type-specific: