Abstract
Individual human epidermal cells differ in their self-renewal ability. To uncover the molecular basis for this heterogeneity, we performed genome-wide pooled RNA interference screens and identified genes conferring a clonal growth advantage on normal and neoplastic (cutaneous squamous cell carcinoma, cSCC) human epidermal cells. The Hippo effector YAP was amongst the top positive growth regulators in both screens. By integrating the Hippo network interactome with our data sets, we identify WW-binding protein 2 (WBP2) as an important co-factor of YAP that enhances YAP/TEAD-mediated gene transcription. YAP and WPB2 are upregulated in actively proliferating cells of mouse and human epidermis and cSCC, and downregulated during terminal differentiation. WBP2 deletion in mouse skin results in reduced proliferation in neonatal and wounded adult epidermis. In reconstituted epidermis YAP/WBP2 activity is controlled by intercellular adhesion rather than canonical Hippo signalling. We propose that defective intercellular adhesion contributes to uncontrolled cSCC growth by preventing inhibition of YAP/WBP2.
Highlights
Individual human epidermal cells differ in their self-renewal ability
Since the bulk growth of a NHK population in culture is driven by the stem cell (SC) fraction[11,12,13], the majority of hits identified in the screen should represent genes that promote clonal expansion of SCs (Fig. 1b) rather than genes that directly regulate the onset of terminal differentiation
We focused on short-hairpin RNAs (shRNAs) that were significantly under-represented at t 1⁄4 14, since they should target genes that positively regulate SC proliferation and survival or negatively regulate the transition from SC to CP cell (Fig. 1b)
Summary
Individual human epidermal cells differ in their self-renewal ability. To uncover the molecular basis for this heterogeneity, we performed genome-wide pooled RNA interference screens and identified genes conferring a clonal growth advantage on normal and neoplastic (cutaneous squamous cell carcinoma, cSCC) human epidermal cells. A subset of highy proliferative epidermal cells has the potential to generate large stratified colonies that subsequently fuse to form multi-layered cell sheets, recapitulating the organization of the epidermis[9,11,12,13] This culture system has been widely used to study human epidermal SCs and their regulation[11,12,13,14,15], and epidermal sheets generated in vitro are used for autologous transplantation in patients suffering from severe burn wounds or hereditary skin blistering diseases[16,17]. We used an unbiased approach to uncover the molecular basis for this heterogeneity by performing genomewide pooled RNA interference (RNAi) screens in normal epidermal cells and neoplastic (cSCC) cells with increased growth potential This led us to identify the Hippo effector YAP and its co-factor WBP2 as drivers of clonal expansion of normal and neoplastic human epidermal SCs via TEAD transcription factors. By examining the functions of YAP and WBP2 and their upstream regulators we provide new evidence for the role of canonical and non-canonical Hippo signalling in normal and neoplastic epidermis
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