714 An essential role for CRL complex signaling in epidermal differentiation

Abstract

Maintenance of skin homeostasis requires meticulous regulation of the induction, repression and degradation of key signaling factors governing progenitor cell homeostasis and terminal differentiation programs. Deregulation of these pathways is a hallmark of the skin barrier disruption often manifested in skin disease. Timed and controlled orchestration of these networks involves ubiquitin and ubiquitin-like proteins, as abnormal targeted degradation or post-translational modifications are evidenced in conditions harboring mutations in these pathways including xeroderma pigmentosum, autosomal recessive congenital ichthyosis, skin cancer, and dermatomyositis. By combining a CRISPR genetic screen of genes encoding ubiquitin and ubiquitin-like signaling proteins with single-cell RNA-sequencing of primary, differentiated keratinocytes, we demonstrate a cluster of 26 proteins with a marked impact on epidermal differentiation. Through analysis of individual gene targets, gene signatures and the cell state affected by these perturbations, we identify new functions for regulating differentiation and proliferation. We demonstrate specific receptor-adaptor-substrates tethered in Cullin-RING E3 ubiquitin ligase complexes (CRLs), having a dramatic effect on key differentiation pathways. This adaptor-receptor-substrate specific effect of CRLs determines terminal differentiation, which has implications for progenitor cell differentiation and therapeutic interventions of this pathway.