SummaryGene expression is a multistep process that involves transcription, translation and turnover of mRNAs and proteins. Although it is one of the most fundamental processes of life, the entire cascade has never been quantified on a genome-wide scale. Here, we simultaneously measured mRNA and protein abundance and turnover by parallel metabolic pulse labeling for more than 5,000 genes in mammalian cells. While mRNA and protein levels correlated better than previously thought, corresponding half-lives showed no correlation. Employing a quantitative model we obtain the first genome-scale prediction of synthesis rates of mRNAs and proteins. We find that the cellular abundance of proteins is predominantly controlled at the level of translation. Genes with similar combinations of mRNA and protein stabilities shared functional properties, suggesting that half-lives evolved under energetic and dynamic constraints. Quantitative information about all stages of gene expression obtained in this study provides a rich resource and helps understanding the underlying design principles.

Cytokines are pleiotropic and readily diffusible messenger molecules, raising the question of how their action can be confined to specific target cells. The T cell cytokine interleukin-2 (IL-2) is essential for the homeostasis of regulatory T (Treg) cells that suppress (auto) immunity and stimulates immune responses mediated by conventional T cells. We combined mathematical modeling and experiments to dissect the dynamics of the IL-2 signaling network that links the prototypical IL-2 producers, conventional T helper (Th) cells, and Treg cells. We show how the IL-2-induced upregulation of highaffinity IL-2 receptors (IL-2R) establishes a positive feedback loop of IL-2 signaling. This feedback mediates a digital switch for the proliferation of Th cells and functions as an analog amplifier for the IL-2 uptake capacity of Treg cells. Unlike other positive feedbacks in cell signaling that augment signal propagation, the IL-2/IL-2R loop enhances the capture of the signal molecule and its degradation. Thus Treg and Th cells can compete for IL-2 and restrict its range of action through efficient cellular uptake. Depending on activation status and spatial localization of the cells, IL-2 may be consumed exclusively by Treg or Th cells, or be shared between them. In particular, a Treg cell can deprive a stimulated Th cell of its IL-2, but only when the cells are located in close proximity, within a few tens of micrometers. The present findings explain how IL-2 can play two disctinct roles in immune regulation and point to a hitherto largely unexplored spatiotemporal complexity of cytokine signaling.bi-stability | cell-to-cell communication | cytokine networks | mathematical modeling | reaction-diffusion systems

No abstract