Expression pattern of REIC/Dkk-3 in mouse squamous epithelia

Basal Cells in the Epidermis and Epidermal Differentiation

A definite identification of epidermal stem cells is not known and the mechanism of epidermal differentiation is not fully understood. Toward both of these quests, considerable information is available from the research on lineage tracing and clonal growth analysis in the basal layer of the epidermis, on the hair follicle and the interfollicular epidermal stem cells, and on Wnt signaling along with its role in the developmental patterning and cell differentiation. In this paper, literature on the aforementioned research has been collated and analyzed. In addition, models of the basal layer cellular composition and the epidermal differentiation have been presented. Graphical Abstract.

Tumor necrosis factor-α downregulates the REIC/Dkk-3 tumor suppressor gene in normal human skin keratinocytes

Our previous studies revealed that REIC/Dkk-3 was expressed various tissues, including skin keratinocytes. The aim of the present study was to identify the factors that regulate the expression of the dickkopf Wnt signaling pathway inhibitor 3 (REIC/Dkk‑3) tumor suppressor gene in normal human skin keratinocytes (NHKs). Several growth factors and cytokines that have previously been reported to be involved in the growth and differentiation of keratinocytes were screened as potential regulators. Western blot analysis was performed using protein from NHKs cultured with/without various factors including the epidermal growth factor, tumor necrosis factor‑α, transforming growth factor‑β, interleukin (IL)‑1F9, IL‑6, IL‑8 and Ca2+. The results indicated that only TNF‑α downregulated REIC/Dkk‑3 expression in NHKs. Subsequently, TNF‑α was confirmed to reduce the expression levels of REIC/Dkk‑3 in mouse skin tissue and hair culture models. TNF‑α‑mediated downregulation of REIC/Dkk‑3 expression in NHKs was abrogated by the addition of a TNF‑α‑specific antibody. In conclusion, the results indicate that TNF‑α downregulates REIC/Dkk‑3 expression in normal skin keratinocytes.