Decoupling the Functional Pleiotropy of Stem Cell Factor by Tuning c-Kit Signaling

Abstract

SUMMARY Most secreted growth factors and cytokines are functionally pleiotropic because their receptors are expressed on diverse cell types. While important for normal mammalian physiology, pleiotropy limits the efficacy of cytokines and growth factors as therapeutics. Stem cell factor (SCF) is a growth factor that acts through the c-Kit receptor tyrosine kinase to elicit hematopoietic progenitor expansion, but can be toxic when administered in vivo because it concurrently activates mast cells. We engineered a mechanism-based SCF partial agonist that impaired c-Kit dimerization, truncating downstream signaling amplitude. This SCF variant elicited biased activation of hematopoietic progenitors over mast cells in vitro and in vivo. Mouse models of SCF-mediated anaphylaxis, radioprotection, and hematopoietic expansion revealed that this SCF partial agonist retained therapeutic efficacy while exhibiting virtually no anaphylactic off-target effects. The approach of biasing cell activation by tuning signaling thresholds and outputs has applications to many dimeric receptor-ligand systems.

Kinetics of cytokine receptor trafficking determine signaling and functional selectivity

“…Two main findings arise from our study: (1) Intracellular traffic dynamics of cytokine-receptor complexes and STATs binding affinities for phospho-Tyr on cytokine receptor intracellular domains (ICD) act synergistically to define signaling potency and identity, and (2) cells exhibit different gene induction thresholds in response to cytokine partial agonism, which allow them to modulate their responses. The current work, together with previous studies describing signaling tuning in other cytokines systems (Ho et al, 2017;Kim et al, 2017;Moraga et al, 2015b,Mitra et al, 2015, outline a general strategy to design cytokine partial agonists and decouple cytokine functional pleiotropy by modulating cytokinereceptor binding kinetics.…”

EGFR Ligands Differentially Stabilize Receptor Dimers to Specify Signaling Kinetics

“…In one example, biased signaling by c-Kit was achieved by engineered stem cell factor variants with altered dimerization (Ho et al, 2017). In another case, erythropoietin (EPO) harboring a pathogenic mutation was found to signal aberrantly because of altered binding kinetics rather than strength (Kim et al, 2017).…”

Mechanisms of erythrocyte development and regeneration: implications for regenerative medicine and beyond

“…Insights into this have recently been provided by a structure-based engineering approach that interfered with SCF dimerization, yielding an SCF F63A mutant that attenuates Kit dimerization, an important step in Kit signaling, and decreases the magnitude of Kit signaling. This dimerization-defective F63A mutant retains the competence to regulate HSPCs while having considerably reduced activity to regulate mast cells (Ho et al, 2017). It has also been shown that mice with a knock-in mutation of the Kit juxtamembrane phosphorylation site (Y567) have normal steadystate erythropoiesis but exhibit defective stress erythropoiesis (Agosti et al, 2009), and that the mutation of Kit juxtamembrane tyrosines affects mast cells and melanocytes, but not erythroid or intestinal Kit phenotypes (Kimura et al, 2004).…”