Deregulation of PERK in the autoimmune disease pemphigus vulgaris occurs via IgG-independent mechanisms
ABSTRACT Serum and IgG isolated from patients with the autoimmune blistering disease pemphigus vulgaris (PV) trigger complex intracellular pathways in keratinocytes, including alterations of the cell cycle and metabolism, which ultimately lead to cell-cell detachment (acantholysis). We have shown previously that one of the earliest pathogenic events in PV is the activation of protein kinases, including the PKR-like endoplasmic reticulum (ER) kinase PERK.
In the present study we investigated in more detail the role of PERK in the pathogenesis of PV.
PERK levels were assessed by Western blotting and in-cell enzyme-linked immunosorbent assay, and PERK expression was silenced by siRNA technology. The effects of PV sera/IgG on keratinocyte cultures were investigated by flow cytometry, MTT and adhesion assays.
We show that PERK is activated in keratinocytes exposed to PV serum, as demonstrated by an increase in phosphorylated PERK levels and phosphorylation of eIF2α. Decreased expression of PERK by siRNA reduced the effects of PV serum on the cell cycle and keratinocyte viability, two key events in PV pathophysiology. As impairment of metabolic activity in PV is partially due to non-IgG serum factors, we then investigated the activation of PERK in keratinocytes incubated with whole PV serum, purified PV IgG and IgG-depleted PV serum. The data demonstrated that PV sera depleted of IgG, but not PV IgG, triggered PERK phosphorylation and this correlated with a marked reduction of metabolic activity in keratinocytes exposed to IgG-free serum. Knockdown of PERK by siRNA abrogated the changes in the cell cycle and apoptosis induced by IgG-depleted PV serum. Finally, the reduction of metabolic activity observed in keratinocytes exposed to IgG-depleted PV serum was almost absent in PERK-deficient cells.
Taken together, the results demonstrate that activation of PERK participates in the reduction of metabolic activity and cell viability seen in PV and that this phenomenon depends on non-IgG factors. PERK activation may represent a novel signalling mechanism linking ER stress and acantholysis in PV.
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ABSTRACT: Introduction: Desmoglein 3 (Dsg3) is one of desmosomal cadherins and functions in epidermal keratinocyte adhesion. IgG anti-Dsg3 autoantibodies are detected in pemphigus vulgaris, an autoimmune bullous disease showing blisters and erosions on the skin and oral mucosa. Other types of pemphigus also show anti-Dsg3 antibodies. Genetic disease of Dsg3 has not been reported. Areas covered: Many in vitro and in vivo studies have indicated pathogenic role of anti-Dsg3 antibodies. Blisters in pemphigus vulgaris are thought to be developed by loss of keratinocyte adhesions by binding of anti-Dsg3 antibodies to Dsg3 through steric hindrance, internalization of Dsg3, changes in molecular integrity or signal transduction. There are pathogenic and nonpathogenic anti-Dsg3 antibodies reactive with different epitopes. Recent studies of pemphigus vulgaris include existence of non-Dsg3 autoantibodies, B cells and T cells reactive with Dsg3, involvement of TNF-α and IL-1 and activation of intracellular signaling. Expert opinion: Although systemic corticosteroids and immunosuppressive agents are mainstays for treatment of pemphigus, intravenous immunoglobulin, plasmapheresis, immunoadsorption, rituximab and TNF-α inhibitors are emerging. Anti-Dsg3 antibody-targeting therapies are reported in mouse model, but they are not yet available clinically. Clarification of pathogenic role of anti-Dsg3 antibodies in pemphigus should provide us with safer and more effective therapies.Expert Opinion on Therapeutic Targets 01/2013; DOI:10.1517/14728222.2013.744823 · 4.90 Impact Factor
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ABSTRACT: Pemphigus vulgaris (PV) is a paradigm of autoimmune disease affecting intercellular adhesion. The mechanisms that lead to cell-cell detachment (acantholysis) have crucial therapeutic implications and are currently undergoing major scrutiny. The first part of this review focuses on the classical view of the pathogenesis of PV, which is dominated by the cell adhesion molecules of the desmosome, namely desmogleins (Dsgs). Cloning of the DSG3 gene, generation DSG3 knock-out mice and isolation of monoclonal anti-Dsg3 IgG have aided to clarify the pathogenic mechanisms of PV, which are in part dependent on the fate of desmosomal molecules. These include perturbation of the desmosomal network at the transcriptional, translational, and interaction level, kinase activation, proteinase-mediated degradation, and hyper-adhesion. By the use of PV models, translational research has in turn helped shed light into the basic structure, function, and dynamics of assembly of desmosomal cadherins. The combined efforts of basic and applied research has resulted in tremendous advance into the understanding of epidermal adhesion and helped debunk old myths on the supposedly unique role of desmogleins in the mechanisms of cell-cell detachment in PV.Cell Communication & Adhesion 02/2013; DOI:10.3109/15419061.2013.763799 · 1.52 Impact Factor
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ABSTRACT: Abstract The cell adhesion molecule plakophilin 3 (Pkp3) plays an essential role in the maintenance of skin integrity and is targeted in certain autoimmune conditions. In one example, we have shown that Pkp3 is instrumental in mediating the discohesive effects of sera from patients with pemphigus vulgaris (PV), a life-threatening autoimmune disease that targets intercellular adhesion in the epidermis. In the present study, we determine the effect of PV autoimmune globulin (PV IgG) on Pkp3 in an in-vitro model of PV. We demonstrate that Pkp3 becomes tyrosine phosphorylated as early as 30 min upon binding of PV IgG to keratinocyte surface and eventually detaches from its binding partner desmoglein 3 (Dsg3). In parallel, Pkp3 is depleted from the membrane (Triton X-soluble) fraction and accumulates in the cytoplasm within 240 min of incubation with PV IgG. Inhibition of Pkp3 phosphorylation by a Src inhibitor attenuates the discohesive effects of PV IgG. Taken together, the data demonstrate that activation of Src-kinase signalling is crucial for PV acantholysis and acts, at least in part, via phosphorylation of the adaptor protein Pkp3.Autoimmunity 12/2013; DOI:10.3109/08916934.2013.866100 · 2.75 Impact Factor