Protein abundance of AKT and ERK pathway components governs cell-type-specific regulation of proliferation

Activation of the AKT and ERK signaling pathway is a major contributor to cell proliferation. However, the integrated regulation of this multistep process, involving signal processing, cell growth and cell-cycle progression, is poorly understood. Here we study three cell types of hematopoietic origin, in which AKT and ERK signaling is triggered by erythropoietin (Epo). We find that the different cell types exhibit distinct proliferative responses, despite sharing the molecular network for pro-proliferative signaling. Iterating quantitative experiments and mathematical modeling, we show that the cell-type-specific regulation of proliferation emerges from two sources: (1) the protein abundance patterns of signaling components that cause differential flow of signals along the AKT and ERK pathways, and (2) the differential impact of the downstream regulators for protein synthesis and for cell-cycle progression on proliferation. Our integrated mathematical model of Epo-driven proliferation explains cell-type-specific effects of targeted AKT and ERK inhibitors and correctly predicts whether their combined application results in synergy. EpoR receptor as well as EpoR and Pten overexpressing BaF3 cells were growth factor deprived for 5 h and resuspended in RPMI supplemented with 1mg/ml BSA. Cells were stimulated with 1U/ml Epo and RNA was extracted at 0, 1, 2, 3, 4, 5, 7 and 18.5 hours after stimulation using the RNeasy Mini Plus Kit (Qiagen, Hilden, Germany).