Signaling by Neurotrophic Factors: Activation of Phosphoinositide 3-Kinase by Nerve Growth Factor

Abstract Phosphoinositide 3-kinase (PI 3-kinase) is thought to play an important role in mitogenic signal transduction initiated by both receptor tyrosine kinases and nonreceptor tyrosine kinases. We have shown recently that this enzyme is also potently activated by nerve growth factor (NGF) in PC12 cells, a model cell line in which application of NGF induces differentiation to a neuronal phenotype. This finding implicates PI 3-kinase as a component of the signal transduction pathways required for neuronal development and survival under the control of NGF. Whether PI 3-kinase is activated by other neurotrophic factors is not yet clear, but it is possible that this enzyme plays a pivotal role in the development and maintenance of the mammalian nervous system. In this paper we detail methods that can be used to monitor the regulation of PI 3-kinase and the amounts of its lipid products in stimulated cells. The general utility, advantages, and pitfalls of these experimental approaches are discussed.