Activation of phosphatidylinositol 3-kinase by cellular prion protein and its role in cell survival

The cellular prion protein (PrPC) is thought to be involved in protection against cell death, however the exact cellular mechanisms involved are still controversial. Herein we present data that strongly indicate a functional link between PrPC expression and phosphatidylinositol 3-kinase (PI 3-kinase) activation, a protein kinase that plays a pivotal role in cell survival. Both mouse neuroblastoma N2a cells and immortalized murine hippocampal neuronal cell lines expressing wild-type PrPC had significantly higher PI 3-kinase activity levels than their respective controls. Moreover, PI 3-kinase activity was found to be elevated in brain lysates from wild-type mice, as compared to prion protein-knockout mice. Recruitment of PI 3-kinase by PrPC was shown to contribute to cellular survival toward oxidative stress by using 3-morpholinosydnonimine (SIN-1) and serum deprivation. Moreover, both PI 3-kinase activation and cytoprotection by PrPC appeared to rely on copper binding to the N-terminal octapeptide of PrPC. Thus, we propose a model in which the interaction of copper(II) with the N-terminal domain of PrPC enables transduction of a signal to PI 3-kinase; the latter, in turn, mediates downstream regulation of cell survival.