Decoding and re-encoding MAPK fate decision signaling
Cells dynamically sense and respond to ever changing external stimuli through sophisticated signaling networks. Accordingly, signaling dynamics rather than steady states have been recently shown to control cell fate decisions. For multiple signaling systems, heterogeneous dynamic signaling states occur within distinct cells, explaining fate variability observed within a cell population. Measuring single cell signaling dynamics is therefore key to understand how cellular responses correlate with specific cell fate decisions. Here, we combine FRET biosensor imaging, microfluidics and mathematical modelling to map different MAPK signalling network circuitries that fine tune ERK activity dynamics to induce different cell fates in response to three distinct growth factors: EGF, NGF and FGF2. We performed these experiments in the classic PC-12 cell system in which transient versus sustained ERK MAP kinase (MAPK) activation dynamics induce proliferation versus differentiation in response to epidermal (EGF) or nerve (NGF) growth factors. In this system, duration of ERK activation thus specifies cell fate decisions. Imaging of single cell ERK activation dynamics reveals that sustained EGF/NGF application leads to a heterogeneous mix of transient and sustained ERK signaling patterns in distinct cells of a population, different than the population average. EGF biases toward transient, while NGF biases toward sustained ERK activation responses. In contrast, pulsed growth factor application, delivered using a microfluidic pattern, can repeatedly and homogeneously trigger ERK activity transients across the cell population. These datasets enable mathematical modeling to reveal salient features inherent to the MAPK network. Ultimately, this predicts pulsed EGF stimulation regimes at specific frequencies that can bypass the typical feedback activation and rewire the system toward cell differentiation. Thus, ERK activity dynamics rather than growth factor identity is regulating cell fate. Multi-pulsed stimulation can therefore be used to manipulate cell fate decisions at will. Further, we report that fibroblast growth factor (FGF2) evokes a distinct and wider mix of dynamic ERK signaling states than EGF/NGF. This translates a FGF2 dose response challenge into more distinct signaling states, permitting higher information content transfer than EGF/NGF. Dynamically perturbing ERK activity dynamics using pulsed GF stimulation indicates that this property emerges through competition of FGF2 binding to heparin-sulfate proteoglycans (HSPGs) and FGF receptors (FGFR) and specific intracellular feedback structures. Our results provide novel insight into how distinct receptor tyrosine kinase systems differentially wire the MAPK signaling network to fine tune cell population-level, fate decisions.
Institute of Cell Biology, University of Bern
Domain 4 - UMR 168 - Physical chemistry