A protein phosphatase network controls the temporal and spatial dynamics of differentiation commitment in human epidermis

Abstract

Epidermal homeostasis depends on a balance between stem cell renewal and terminal differentiation1,2. While progress has been made in characterising the stem and differentiated cell compartments3, the transition between the two cell states, termed commitment4, is poorly understood. Here we characterise commitment by integrating transcriptomic and proteomic data from disaggregated primary human keratinocytes held in suspension for up to 12h. We have previously shown that commitment begins at approximately 4h and differentiation is initiated by 8h5. We find that cell detachment induces a network of protein phosphatases. The pro-commitment phosphatases - including DUSP6, PPTC7, PTPN1, PTPN13 and PPP3CA - promote terminal differentiation by negatively regulating ERK MAPK and positively regulating key API transcription factors. Their activity is antagonised by concomitant upregulation of the anti-commitment phosphatase DUSP10. The phosphatases form a dynamic network of transient positive and negative interactions, with DUSP6 predominating at commitment. Boolean network modelling identifies a mandatory switch between two stable states (stem cell and differentiated cell) via an unstable (committed) state. In addition phosphatase expression is spatially regulated relative to the location of stem cells, both in vivo and in response to topographical cues in vitro. We conclude that an auto-regulatory phosphatase network maintains epidermal homeostasis by controlling the onset and duration of commitment.