(653e) Systems Modeling of Epidermal Growth Factor and Nerve Growth Factor Signaling: New Insights Into Transient Vs. Sustained ERK Activation Controlling Cell Fate Decisions

Transient vs. sustained ERK activation in PC12 cells is a paradigm for how epidermal growth factor (EGF) and nerve growth factor (NGF) elicit distinct proliferation vs. differentiation cell fate decisions. Despite much effort to uncover how transient vs. sustained ERK dynamics arise, detailed mechanisms remain unclear. To understand transient vs. sustained ERK signaling mechanistically, we have constructed an ordinary differential equation model of EGF and NGF signaling to ERK in PC12 cells that is trained, and thereby consistent with quantitative data from a variety of literature sources and our own experimental data. In particular, the basis of the model topology is largely derived from a quantitative proteomics screen for ERK interaction partners where we surveyed differential dynamic changes in ERK interacting proteins in PC12 cells treated with EGF or NGF. The emergent model structure suggests that only cell surface receptors can stimulate the PLCγ/PKC pathway, activation of which inhibits the key ERK cascade inhibitor RKIP and also activates Ras through the GRP family of GEFs. We furthermore uncover a putative novel positive feedback loop from ERK to NF1, the predominant RasGAP in PC12 cells. The main model prediction is that rapid EGF-induced internalization of the EGF receptor and weak PLCγ activation, as opposed to NGF-induced surface retention of the TrkA receptor and strong PLCγ activation, generates the distinct ERK activation kinetics. Validation experiments show that increasing plasma membrane levels of active EGF receptor by stimulating with TGFα sustains the ERK response relative to that of EGF, whereas PLCγ knockdown makes the NGF-induced ERK response transient. We conclude that receptor compartmentalization and the PLCγ pathway play an important role in determining transient vs. sustained ERK signaling.