β-Catenin promotes the differentiation of epidermal Langerhans dendritic cells.

The epithelial signaling protein and transcriptional regulator β-catenin has recently been implicated in hematopoietic dendritic cell (DC) differentiation as well as in DC-mediated tolerance. We here observed that epidermal Langerhans cells (LCs) but not interstitial/dermal DCs express detectable β-catenin. LCs are unique among the DC family members in that LC networks critically depend on epithelial adhesion molecules as well as on the cytokine transforming growth factor-β1 (TGF-β1). However, despite the important functions of LCs in the immune system, the molecular mechanisms governing LC differentiation and maintenance remain poorly defined. We found that TGF-β1 induces β-catenin in progenitor cells undergoing LC differentiation and that β-catenin promotes LC differentiation. Vitamin D, another epidermal signal, enhanced TGF-β1-mediated β-catenin induction and promoted the expression of multiple epithelial genes by LCs. Moreover, full-length vitamin D receptor (VDR) promoted, whereas a truncated VDR diminished, the positive effects of ectopic β-catenin on LC differentiation. Therefore, we here identified β-catenin as a positive regulator of LC differentiation in response to TGF-β1 and identified a functional interaction between β-catenin and VDR in these cells.