PV-IgG induces DSG1-dependent Ca2+ flux via IP3R and CRAC in vitro
IP3R is required to redistribute Ca2+ from the ER to the cytosol but not sufficient to increase intracellular Ca2+ concentrations. To achieve this, STIM1 andORAI1 form the so-called CRAC (Ca2+-release-activated-channel), in whichSTIM1 serves as a Ca2+ concentration sensor at the ER membrane . Upon low Ca2+, STIM1 contactsORAI1 at the plasma membrane to replenish the ERs Ca2+ store . We found IP3R and ORAI1 to be equally distributed in all epidermal layers, whereas STIM1immunostaining was more prominent in the granular layer (FigureĀ 1a). Similar to previous studies , PV-IgG containing autoantibodies againstDSG 1 and DSG 3 (Table 1) but not IgG from healthy volunteers led to an increase in intracellular Ca2+ in NHEK cells (Figure 1b/S1a). In agreement with a previous report , the Ca2+ flux was anti-DSG 1-dependent, as no influx was observed for the anti-DSG 3-mAb AK23 (Figure 1b/S1a). Inhibition of CRAC with BTP-2, IP3R with Xestospongin C (Xest),PLC with U-73122 or PI4K with GSK-F1 abolished the Ca2+ flux (Figure 1b/S1a). Co-immunoprecipitation demonstrated that PI4K interacts with DSG 1 but not withDSG 3, DSG1 s downstream target PLC as well asp38MAPK (Figure 1c+d/S1b), which is known to be strongly involved in PV pathogenesis , are part of both complexes. So far, only the interaction of p38MAPK with DSG 3 was shown . Phosphorylated PKC , reported to be responsible for the cytoskeleton reorganization and DSG 3 depletion , was found in both complexes (Figure 1c+d). PV-IgG but not AK23 induced phosphorylation of PLC (Figure 1e+f). Taken together, these results demonstrate that a DSG 1-specific complex exists which, induced by PV-IgG, can initiate a Ca2+ flux dependent pathway.