Cell-to-cell variability in JAK2/STAT5 pathway components and cytoplasmic volumes defines survival threshold in erythroid progenitor cells.

Lorenz Adlung,Leonard Schmiester,Marcel Schilling,Christian Tönsing,Lena Postawa,Paul Stapor,Jens Timmer,Ursula Klingmüller,Jan Hasenauer,Luisa E Schwarzmüller,Dantong Wang

doi:10.1016/j.celrep.2021.109507

Abstract

Survival or apoptosis is a binary decision in individual cells. However, at the cell-population level, a graded increase in survival of colony-forming unit-erythroid (CFU-E) cells is observed upon stimulation with erythropoietin (Epo). To identify components of Janus kinase 2/signal transducer and activator of transcription 5 (JAK2/STAT5) signal transduction that contribute to the graded population response, we extended a cell-population-level model calibrated with experimental data to study the behavior in single cells. The single-cell model shows that the high cell-to-cell variability in nuclear phosphorylated STAT5 is caused by variability in the amount of Epo receptor (EpoR):JAK2 complexes and of SHP1, as well as the extent of nuclear import because of the large variance in the cytoplasmic volume of CFU-E cells. 24-118 pSTAT5 molecules in the nucleus for 120min are sufficient to ensure cell survival. Thus, variability in membrane-associated processes is sufficient to convert a switch-like behavior at the single-cell level to a graded population-level response.

Highlights

Signal transduction has been intensively studied in the past decades at the cell population level with immunoblotting and bulk gene-expression analyses
Cell-to-cell variability of phosphorylated STAT5 in primary erythroid progenitor cells The key intracellular integrator of Epo-induced survival-signal transduction in colony forming unit erythroid (CFU-E) cells is the latent transcription factor STAT5, which is activated by tyrosine phosphorylation
The standard deviation (SD) observed for Phosphorylated STAT5 (pSTAT5) was considerably larger than that for total STAT5 and showed an increase in response to rising Epo doses that correlated with the survival responses (Figure 1D)

Summary

Introduction

Signal transduction has been intensively studied in the past decades at the cell population level with immunoblotting and bulk gene-expression analyses. The Janus kinase 2/signal transducer and activator of transcription 5 (JAK2/STAT5) signal transduction pathway serves as a paradigm in mediating the survival of erythroid progenitor cells (Socolovsky et al, 2001). Rapid signal transduction is facilitated by binding of Epo to its cell-surface receptor, the EpoR, inducing gene expression (Swameye et al, 2003) and CFU-E survival (Bachmann et al, 2011). The Epo-EpoR complex activates the receptor-associated Janus kinase, JAK2, which phosphorylates the cytoplasmic tail of the EpoR on multiple tyrosine residues (Klingmu€ller et al, 1996). Phosphorylated STAT5 (pSTAT5) molecules form dimers (Boehm et al, 2014), translocate to the nucleus, and induce the expression of anti-apoptotic genes, e.g., Bcl2l1 for immediate control of cell survival

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Discussion

Conclusion