ST18 affects cell-cell adhesion in pemphigus vulgaris in a tumour necrosis factor-α-dependent fashion.

BACKGROUND: Pemphigus vulgaris (PV) is a life-threatening mucocutaneous autoimmune blistering disease. We previously showed that genetic variants within the ST18 gene promoter area confer a sixfold increase in the propensity to develop PV. ST18, a transcription factor, was found to be overexpressed in the epidermis of patients with PV. In addition, it was found to promote autoantibody-mediated abnormal epidermal cell-cell adhesion and secretion of proinflammatory mediators by keratinocytes. OBJECTIVES: To delineate the mechanism through which ST18 contributes to destabilization of cell-cell adhesion. METHODS: We used quantitative reverse-transcriptase polymerase chain reaction, immunofluorescence microscopy, a luciferase reporter system, site-directed mutagenesis, chromatin immunoprecipitation (ChIP) and the dispase dissociation assay. RESULTS: The ChIP and luciferase reporter assays showed that ST18 directly binds and activates the TNF promoter. Accordingly, increased ST18 expression contributes to PV pathogenesis by destabilizing cell-cell adhesion in a tumour necrosis factor (TNF)-α-dependent fashion. In addition, dual immunofluorescence staining showed increased expression of both ST18 and TNF-α in the skin of patients with PV carrying an ST18-associated PV risk variant, which was found to be associated with a more extensive PV phenotype. CONCLUSIONS: Our findings suggest a role for TNF-α in mediating the deleterious effect of increased ST18 expression in PV skin.