When the Search for Stemness Genes Meets the Skin Substitute Bioengineering Field: KLF4 Transcription Factor under the Light

Abstract

The transcription factor “Kruppel-like factor 4” (KLF4) is a central player in the field of pluripotent stem cell biology. In particular, it was put under the spotlight as one of the four factors of the cocktail originally described for reprogramming into induced pluripotent stem cells (iPSCs). In contrast, its possible functions in native tissue stem cells remain largely unexplored. We recently published that KLF4 is a regulator of “stemness” in human keratinocytes. We show that reducing the level of expression of this transcription factor by RNA interference or pharmacological repression promotes the ex vivo amplification and regenerative capacity of two types of cells of interest for cutaneous cell therapy: native keratinocyte stem and progenitor cells from adult epidermis, which have been used for more than three decades in skin graft bioengineering, and keratinocytes generated by the lineage-oriented differentiation of embryonic stem cells (ESCs), which have potential for the development of skin bio-bandages. At the mechanistic level, KLF4 repression alters the expression of a large set of genes involved in TGF-β1 and WNT signaling pathways. Major regulators of TGF-β bioavailability and different TGF-β receptors were targeted, notably modulating the ALK1/Smad1/5/9 axis. At a functional level, KLF4 repression produced an antagonist effect on TGFβ1-induced keratinocyte differentiation.

Extracellular Vesicles Derived from Acidified Metastatic Melanoma Cells Stimulate Growth, Migration, and Stemness of Normal Keratinocytes

“…As miRNA can regulate the protein transcription, we analyzed whether miRNA transferred within EVs can modulate the synthesis of its targets in normal keratinocytes. Indeed, the treatment of the Het1-A keratinocytes with "acidic" EVs significantly increased the expression of the miR-7 target-Krüppel-like factor 4 (KLF4)-regulating TGF-β and the WNT-signaling and differentiation in keratinocytes [58], both on the gene and protein levels (Figures 1b, S8 and S9c).…”

“…Notably, the KLF-4 upregulation (Figure 1b) is in line with our observation of induction of the stem-like properties in the keratinocytes by "acidic" EVs. Despite the participation of KLF4 in the differentiation of the keratinocyte [58], it can also upregulate the transcription of many genes, indispensable for EMT and cell growth, so it also serves as an oncogene in many cancers [62,63]. Bio-plex analysis revealed that both types of EVs increased the phosphorylation of EGFR, mTOR, and ERK1/2 in the keratinocytes (Figure 5a,d,e).…”