Quantitative Analysis of Receptor Tyrosine Kinase-Effector Coupling at Functionally Relevant Stimulus Levels [Cell Biology]

January 29th, 2015 by Li, S., Bhave, D., Chow, J. M., Riera, T. V., Schlee, S., Rauch, S., Atanasova, M., Cate, R. L., Whitty, A.

A major goal of current signaling research is to develop a quantitative understanding of how receptor activation is coupled to downstream signaling events and to functional cellular responses. Here we measure how activation of the RET receptor tyrosine kinase on mouse neuroblastoma cells by the neurotrophin artemin (ART) is quantitatively coupled to key downstream effectors. We show that the efficiency of RET coupling to ERK and Akt depends strongly on ART concentration, and is highest at the low (~100 pM) ART levels required for neurite outgrowth. Quantitative discrimination between ERK and Akt pathway signaling is similarly highest at this low ART concentration. Stimulation of the cells with 100 pM ART activated RET at the rate of ~10 molecules/cell/min, leading at 5-10 min to a transient peak of ~150 phosphoERK (pERK) molecules and ~50 pAkt molecules per pRET, after which time the levels of these two signaling effectors fell by 25-50% while pRET levels continued to slowly rise. Kinetic experiments showed that signaling effectors in different pathways respond to RET activation with different lag-times, such that the balance of signal flux among the different pathways evolves over time. Our results illustrate that measurements using high, super-physiological growth factor levels can mislead about quantitative features of receptor signaling. We propose a quantitative model describing how receptor-effector coupling efficiency links signal amplification to signal sensitization between receptor and effector, thereby providing insight into design principles underlying how receptors and their associated signaling machinery decode an extracellular signal to trigger a functional cellular outcome.