Temporal Regulation of ERK Activity by Light Reveals a Memory Effect in Pc12 Cell Neurite Outgrowth

Abstract

It has been proposed that differential activation kinetics allows cells to use a common set of signaling pathways to induce different cellular outcomes. For example, nerve growth factor (NGF) and epidermal growth factor (EGF) induce different activation kinetics of extracellular signal-regulated kinase (ERK) and result in the distinct outcomes of differentiation and proliferation, respectively. However, direct and quantitative linkage between time kinetics of ERK activation and the cellular response is still lacking due to difficulties in perturbing the kinetics of intracellular signaling pathways. Here, we construct a light-gated protein-protein interaction system that uses light to regulate the activation and inactivation of ERK. We find that light-induced ERK activation alone is sufficient to stimulate significant neurite outgrowth in PC12 cells in the absence of growth factors. Intermittent on/off light control reveals a memory effect in ERK-stimulated neurite outgrowth in PC12 cells. The memory effect shows a 45 min off-time threshold, below which a full-speed neurite outgrowth is maintained despite that ERK is gradually turned off. When the off-time is greater than the threshold, the speed of neurite outgrowth decreases with a half time of 2 h as cells slowly lose their memory of prior ERK activation. Interestingly, the 45-min time threshold and the 2-h half time memory are independent of the prior duration of ERK activation. Overall, light-controlled signaling kinetics enables precise dissection of the temporal dimension of signal transduction in cells.