Fig 2: DSG3 down-regulation affects p53-dependent ST18 promoter activity. (a) NHEKs were transfected with a an empty vector (EV) as a control or with a luciferase reporter construct under the regulation of a 282 bp ST18 promoter fragment harbouring either the rs17315309 wild type or risk alleles. Cells were additionally transfected with control (si-control) or TP53-specific siRNAs (si-p53). Twenty four hours post-transfection, cells were treated either with AK23 antibody (AK23 Ab) or negative control antibody (NC Ab). Results represent the mean ± SE of three independent experiments (**p < 0.01 by 2-tailed t test); (b) Immunohistochemistry (left panel) of p53 nuclear stain in skin biopsy samples obtained from PV patients carrying rs17315309 wild type (n = 5) or risk alleles (n = 3) or from healthy controls (n = 5) (scale bar = 100um). p53 nuclear staining was quantified (right panel) by two independent evaluators (*p < 0.05, **p < 0.01 by 2-tailed t test).

Fig 3: ST18 drives a p53-dependent self-amplifying process promoting autoantibody-mediated membranal DSG3 down-regulation in pemphigus vulgaris. Genetically determined ST18 overexpression (1) enhances autoantibodies-induced DSG3 down-regulation in keratinocytes (2, orange arrow) which triggers p38MAPK-dependent (3) p53 activity (4), which in turn up-regulates ST18 promoter activity (5), thus setting the stage for a self-amplifying pathogenetic cycle in PV.

Fig 4: ST18 enhances antibody-mediated DSG3 down-regulation in keratinocytes. (a) NHEKs were transfected with an ST18 expression vector (ST18) or with a control empty vector (EV); 24 h post transfection, cells were exposed to AK23 for 12 h and were then fixed and immunostained for DSG3 (green signal) and DAPI (blue signal); (b) Expression of DSG3 was quantified by ImageJ software. Results represent the mean ± SE of three independent experiments (**p < 0.01 by 2-tailed t test; scale bar = 20um).