Schematic representation of ERK pathway. PrPC on the cellular surface assembles a signaling platform with src family proteins. Upon activation, this molecular complex modulates the activity of ERK cascade. Src proteins activate MAP/ERK Kinase 1/2 (MEK1/2). The active forms of MEK1/2 complex can phosphorylize the Extracellular signal-Regulate Kinase 1/2 (ERK1/2) that either enters the nucleus and starts gene expression, or remains within the cytosol.