Interplay of ELF5, GATA-3 and FLI-1 Regulate Malignant Transformation of Keratinocytes

Cutaneous squamous cell carcinoma (cSCC) arises from epidermal keratinocytes and is the second most common epithelial malignancy. E74-like factor 5 (ELF5) is a member of the epithelium specific ETS subfamily of transcription factors and is essential for epithelial development, homeostasis and prevention of epithelial tumourigenesis. Malignant transformation of keratinocytes involves the disrupts the progenitor differentiation program causing keratinocytes to fail to complete the differentiation process, leading to dysplastic epithelium and precancerous cells in skin. However, the precise mechanisms that causes the failure of keratinocytes to differentiate completely is not well understood. Our study brings new insights into novel role of ELF5 as tumour suppressor in keratinocytes. We found that ELF5 is abundantly expressed in healthy human skin (both basal and suprabasal layers), while its expression is lost in cSCC tissue biopsies. Using CRISPR-Cas9 knockout technology, functional studies along with transcript and protein analysis, loss of ELF5 in immortalised healthy keratinocytes (HaCaT) leads to decreased ability of cells to differentiation and increased migration, invasion and tumourigenicity, in vitro. While overexpression of ELF5 leads to inhibition of cell migration and proliferation in keratinocytes and in skin cancer cell lines (A431 and SCC-9), in vitro. Further analysis using RNA transcriptomics has uncovered that GATA-3 and FLI-1 are key molecular targets of ELF5 in keratinocytes. ELF5 regulation of both GATA-3 and FLI-1 is required to maintain the balance between healthy keratinocytes (proliferation/differentiation) and to prevent precancerous cell formation (tumourigenicity). Our data indicates that ELF5 plays pivotal role in preventing malignant transformation of keratinocytes and potentially suppresses skin tumourigenesis, which could be targeted for future drug treatments for cSCC. Better understanding of the underlying mechanisms by which ELF5 regulates gene expression and consequently cell activity will provide new knowledge that can be translated into long-term benefits for patients with precancerous legions to cSCC.