p38 MAPK Activation Is Downstream of the Loss of Intercellular Adhesion in Pemphigus Vulgaris

Abstract

Pemphigus vulgaris (PV) is a potentially fatal blistering disease characterized by autoantibodies against the desmosomal adhesion protein desmoglein (Dsg) 3. Whether autoantibody steric hindrance or signaling through pathways such as p38 MAPK is primary in disease pathogenesis is controversial. PV mAbs that cause endocytosis of Dsg3 but do not dissociate keratinocytes because of compensatory adhesion by Dsg1 do not activate p38. The same mAbs plus exfoliative toxin to inactivate Dsg1 but not exfoliative toxin alone activate p38, suggesting that p38 activation is secondary to loss of adhesion. Mice with epidermal p38␣ deficiency blister after passive transfer of PV mAbs; however, acantholytic cells retain cell surface Dsg3 compared with wild-type mice. In cultured keratinocytes, p38 knockdown prevents loss of desmosomal Dsg3 by PV mAbs, and exogenous p38 activation causes internalization of Dsg3, desmocollin 3, and desmoplakin. p38␣ MAPK is therefore not required for the loss of intercellular adhesion in PV, but may function downstream to augment blistering via Dsg3 endocytosis. Treatments aimed at increasing keratinocyte adhesion could be used in conjunction with immunosuppressive agents, potentially leading to safer and more effective combination therapy regimens. Pemphigus vulgaris (PV)2 is a potentially fatal autoimmune blistering disorder caused by autoantibodies to keratinocyte cell adhesion proteins known as desmogleins (1). The pathognomonic histologic finding in PV is suprabasal acantholysis, or the detachment of intact keratinocytes from each other because of loss of intercellular adhesion. A characteristic clinical finding in PV is Nikolsky's sign, in which blisters can be induced in otherwise normal-appearing skin by applying pressure or mechanical shear force, reflecting the loss of intercellular adhesion even in skin without overt blisters (2).PV autoantibodies primarily target desmoglein (Dsg) 3, a transmembrane adhesion molecule of desmosomes (3). Passive transfer experiments using neonatal mice have established the pathogenicity of the anti-Dsg3 autoantibodies in PV (4, 5). The anatomic site of blister formation is thought to be due to the tissue-specific expression patterns of different Dsg isoforms, also known as the desmoglein compensation theory. Dsg3 is expressed by basal keratinocytes of mucosa and skin, whereas Dsg1 is expressed by basal keratinocytes in skin but not mucosa (6, 7). Therefore, patients with Dsg3 autoantibodies demonstrate blistering in the mucosa, where compensatory adhesion by Dsg1 is not present (mucosal-dominant PV). In some patients who progress to develop Dsg1 in addition to Dsg3 autoantibodies, suprabasal blisters appear in both the mucosa and skin (mucocutaneous PV) (8 -10).Epitope mapping studies have shown that pathogenic PV autoantibodies preferentially bind the amino-terminal domain of Dsg3 that is predicted to form the transadhesive interface between cells, based on analogy to ultrastructural models for the classical cadherins (11-13). PV IgG has also been shown...

Hepatocyte Growth Factor Activator Inhibitor Type 1 Maintains the Assembly of Keratin into Desmosomes in Keratinocytes by Regulating Protease-Activated Receptor 2–Dependent p38 Signaling

“…51 Human keratinocytes treated with pemphigus vulgaris IgG showed p38 activation and retraction of KIF from the cell membrane. 5 The retraction of KIF was prevented by a p38 MAPK inhibitor. 6 Similar results were observed in the current study, in which a p38 inhibitor abolished the decreased assembly of KIF to desmosomes induced by HAI-1 loss.…”

“…In our three-dimensional (3D) organotypic skin model, 2.5 Â 10 4 SF-TY cells suspended in 0.1 mL of FBS were mixed with 1 mL of DMEM containing 2.2 mg/mL type I collagen (KOKEN Co, Tokyo, Japan), 10 mmol/L HEPES, and 10 mmol/L NaHCO 3 , which was transferred into a 12-well cellculture insert (pore size, 0.4 mm; Millipore). After incubation in DMEM with 10% FBS overnight, 5 Â 10 5 HaCaT cells were placed on the fibroblast-containing collagen gel and incubated for 24 hours. Then, the gel surface was raised to the air-liquid interface and cultured for 3 weeks to allow HaCaT cells to stratify and differentiate.…”

“…7,8 It is known that p38 MAPK is increased in psoriatic skin, and it is rapidly phosphorylated in response to pemphigus vulgaris IgG. 5 Activated p38 promotes KIF retraction and disruption of desmosome-mediated cell-cell adhesion. 6 Desmosomes consist of two desmosome-specific cadherin family members, desmogleins and desmocollins, as well as a collection of cytoplasmic plaque proteins, including desmoplakin, plakoglobin, and plakophilins.…”

Fructose 1, 6‐diphosphate regulates desmosomal proteins and collagen fibres in human skin equivalents

“…One of the key signalling pathways that regulate the activity of desmosomal proteins is the MAPK pathway (23,24). To investigate these underlying molecular mechanisms, we examined whether the activity of any MAPK is altered by FDP treatment in NHEKs.…”

Pathogenic Relevance of IgG and IgM Antibodies against Desmoglein 3 in Blister Formation in Pemphigus Vulgaris

“…23,24 Polyclonal anti-Dsg3 IgG antibodies in sera from pemphigus patients and pemphigus model mice are now widely accepted to comprise mixtures of both pathogenic and nonpathogenic IgGs, based on the results of studies using monoclonal antibodies from patients and mice. 5,6 A growing number of studies suggest that inhibition of signaling pathways such as MAPK and c-Myc, [25][26][27] as well as endocytic processing of Dsg3, 28,29 can prevent loss of keratinocyte adhesion in PV IgG-treated cells. Overall, these studies suggest that PV IgG may modulate the assembly and disassembly kinetics of desmosomes, and that modifying keratinocyte signaling pathways can blunt keratinocyte sensitivity to PV IgG.…”