Control of Late Cornified Envelope Genes Relevant to Psoriasis Risk: Upregulation by 1,25‐Dihydroxyvitamin D3 and Plant‐derived Delphinidin

Abstract

Psoriasis is a chronic inflammatory skin disease featuring abnormal keratinocyte proliferation and differentiation. A genetic risk factor for psoriasis (PSORS4) is a deletion of LCE3B and LCE3C genes encoding structural proteins in differentiated keratinocytes. Because analogs of 1,25-dihydroxyvitamin D3 (1,25D) are used in psoriasis treatment, we hypothesized that 1,25D and other VDR ligands act via the vitamin D receptor (VDR) to upregulate expression of LCE 3A/3D/3E genes, potentially mitigating the absence of LCE3B/LCE3C gene products. This hypothesis was pursued using cultured keratinocytes, quantitative real time PCR (qPCR) to assess LCE gene expression, competition binding assays to assess direct ligand binding to VDR, and reporter gene assays to assess the ability of VDR ligands to activate transcription in a VDR- and VDR response element-dependent fashion. qPCR results in a human keratinocyte line, HaCaT, suggested that 1,25D and selected alternate or candidate VDR ligands might upregulate LCE transcripts. Further experiments in primary human keratinocytes confirmed that 1,25D and 10 µM delphinidin do indeed upregulate all five LCE3 genes (LCE3A–E), especially in calcium-differentiated cultures. Further, competition binding assays revealed that delphinidin does in fact bind VDR, but only weakly (IC50 approximately 1 mM). Finally, 20 µM delphinidin was shown to be capable of upregulating a luciferase reporter gene linked to a vitamin D responsive element found near the LCE3 gene cluster. Taken together, these results are consistent with delphinidin (or a metabolite) stimulating LCE3 transcription in a VDR/VDRE-dependent manner. We propose that upregulation of LCE genes may be part of the therapeutic effect of 1,25D to ameliorate psoriasis by providing sufficient LCE proteins, especially in individuals missing the LCE3B and 3C genes. Results with delphinidin further suggest that this compound or its metabolite(s) might offer an alternative to 1,25D in psoriasis therapy.