157 Uncharacterized protein REDI is required for epidermal differentiation and suppression of cancer invasion

Abstract

Cutaneous squamous cell carcinoma (SCC) often demonstrates loss of epidermal differentiation that is regulated by an ever-increasing number of genes. REDI (Regulator of Epidermal Differentiation and Invasion) is a previously uncharacterized protein that we show controls skin differentiation and functions as a tumor suppressor in SCC. We identified REDI in an RNAseq-based screen for uncharacterized open reading frames with opposite patterns of expression in human SCC and keratinocyte differentiation. REDI is necessary and sufficient for epidermal differentiation; CRISPR/Cas9-mediated depletion of REDI in organotypic human epidermal tissue attenuates differentiation, while enforcing REDI expression enhances it. Proximity-dependent biotin identification was performed in organotypic skin tissue to distill REDI’s interactors and highlighted calcyclin binding protein (CACYBP), a protein not previously implicated in epidermal differentiation. Depletion of CACYBP phenocopies REDI loss and reduces differentiation in human skin tissue. Whole transcriptome analysis confirms that REDI and CACYBP co-control a significant subset of genes involved in keratinization, skin differentiation and development. Given REDI downregulation in SCC and its deletion in 21 TCGA cancer types, we evaluated the impact of REDI gain- and loss-of-function in organotypic human skin tissue programmed to transform into invasive epidermal neoplasia. REDI deletion enhances the extent and depth of invasion of Ras-transformed keratinocytes across the basement membrane, while enforced expression of REDI profoundly blocks early tumor progression. In each case, expression of REDI and the proto-oncogene c-RET are negatively correlated. Efforts are underway to confirm whether pharmacologic inhibition of c-RET offsets the impacts of REDI deletion on neoplastic invasion. Drug repurposing to identify a REDI mimic highlights HDAC inhibitors and inhibitors of PI3K/Akt as potential therapeutic candidates.