A novel Sp1-family-related cis-acting element for transcription of type VII collagen gene (COL7A1)

Novel variants impairing Sp1 transcription factor binding in the COL7A1 promoter cause mild cases of recessive dystrophic epidermolysis bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare and most often severe genodermatosis characterized by recurrent blistering and erosions of the skin and mucous membranes after minor trauma, leading to major local and systemic complications. RDEB is caused by loss-of-function mutations in COL7A1 encoding type VII collagen (C7), the main component of anchoring fibrils which form attachment structures stabilizing the cutaneous basement membrane zone. Most of the previously reported COL7A1 mutations are located in the coding or intronic regions. We describe 6 patients with localized or intermediate RDEB for whom one recessive pathogenic variant in the coding region and a second variant in the COL7A1 promoter were identified. These substitutions, three of which are novel, are localized in two Sp1 binding sites of the promoter region. DNA pull-down assay showed a drastic reduction of Sp1 binding consistent with a dramatic decrease in COL7A1 transcript and almost undetectable C7 protein levels. Our results reveal that mutations in the COL7A1 promoter on the background of a null allele can underlie localized or intermediate RDEB. They further emphasize the functional importance of Sp1 motifs in the proximal COL7A1 promoter which should be carefully investigated for regulatory mutations in the case of RDEB with only one pathogenic variant identified in the coding or intronic regions.

Quantitative analysis of the synthesis and secretion of type VII collagen in cultured human dermal fibroblasts with a sensitive sandwich enzyme-linked immunoassay

Type VII collagen is the major component of anchoring fibrils in the epidermal basement membrane. Its expression has been analyzed by immunostaining or Northern blotting, but rarely at the protein level. In this study, we have quantitatively examined the effects of ascorbic acid and various cytokines/growth factors on the protein synthesis and secretion of type VII collagen by human dermal fibroblasts in culture, using a developed, highly sensitive sandwich enzyme-linked immunoassay with two kinds of specific monoclonal antibodies against the non-collagenous domain-1. Ascorbic acid and its derivative induced a twofold increase in type VII collagen synthesis, and markedly increased the secretion of type VII collagen into the medium when compared with the control culture. This effect was not influenced by the presence of transforming growth factor-beta1 (TGF-beta1). The synthesis of type VII collagen was elevated by TGF-beta1, platelet-derived growth factor, tumor necrosis factor-alpha, and interleukin-1beta, but not by TGF-alpha. Thus, our data indicate that the synthesis and secretion of type VII collagen in human dermal fibroblasts are regulated by ascorbate and the enhancement of type VII collagen gene expression by cytokines/growth factors is accompanied with elevated production of type VII collagen at the protein level.