Faculty of Medicine, Institute of Anatomy, Ludwig-Maximilians-Universität München, Munich, Germany.
Division of Cell and Developmental Biology, Institute of Biology, Sächsische Inkubator für Klinische Translation (SIKT), University of Leipzig, Leipzig, Germany.
Front Immunol. 2018 Mar 19;9:528. doi: 10.3389/fimmu.2018.00528. eCollection 2018.
Keratins are crucial for the anchorage of desmosomes. Severe alterations of keratin organization and detachment of filaments from the desmosomal plaque occur in the autoimmune dermatoses pemphigus vulgaris and pemphigus foliaceus (PF), which are mainly caused by autoantibodies against desmoglein (Dsg) 1 and 3. Keratin alterations are a structural hallmark in pemphigus pathogenesis and correlate with loss of intercellular adhesion. However, the significance for autoantibody-induced loss of intercellular adhesion is largely unknown. In wild-type (wt) murine keratinocytes, pemphigus autoantibodies induced keratin filament retraction. Under the same conditions, we used murine keratinocytes lacking all keratin filaments (KtyII k.o.) as a model system to dissect the role of keratins in pemphigus. KtyII k.o. cells show compromised intercellular adhesion without antibody (Ab) treatment, which was not impaired further by pathogenic pemphigus autoantibodies. Nevertheless, direct activation of p38MAPK anisomycin further decreased intercellular adhesion indicating that cell cohesion was not completely abrogated in the absence of keratins. Direct inhibition of Dsg3, but not of Dsg1, interaction pathogenic autoantibodies as revealed by atomic force microscopy was detectable in both cell lines demonstrating that keratins are not required for this phenomenon. However, PF-IgG shifted Dsg1-binding events from cell borders toward the free cell surface in wt cells. This led to a distribution pattern of Dsg1-binding events similar to KtyII k.o. cells under resting conditions. In keratin-deficient keratinocytes, PF-IgG impaired Dsg1-binding strength, which was not different from wt cells under resting conditions. In addition, pathogenic autoantibodies were capable of activating p38MAPK in both KtyII wt and k.o. cells, the latter of which already displayed robust p38MAPK activation under resting conditions. Since inhibition of p38MAPK blocked autoantibody-induced loss of intercellular adhesion in wt cells and restored baseline cell cohesion in keratin-deficient cells, we conclude that p38MAPK signaling is (i) critical for regulation of cell adhesion, (ii) regulated by keratins, and (iii) targets both keratin-dependent and -independent mechanisms.
角蛋白对于桥粒的锚定至关重要。在自身免疫性皮肤病天疱疮和落叶型天疱疮（PF）中，角蛋白组织严重改变并且细丝从桥粒斑上脱离，这主要是由针对桥粒芯糖蛋白 1（Dsg）1 和 3 的自身抗体引起的。角蛋白改变是天疱疮发病机制中的结构标志，与细胞间黏附丧失相关。然而，自身抗体诱导的细胞间黏附丧失的意义在很大程度上尚不清楚。在野生型（wt）鼠角质形成细胞中，天疱疮自身抗体诱导角蛋白丝回缩。在相同条件下，我们使用缺乏所有角蛋白丝的鼠角质形成细胞（KtyII k.o.）作为模型系统来剖析角蛋白在天疱疮中的作用。KtyII k.o.细胞在没有抗体（Ab）处理的情况下显示出细胞间黏附受损，但致病性天疱疮自身抗体进一步损害细胞间黏附的能力没有受损。然而，直接激活 p38MAPK anisomycin 进一步降低细胞间黏附，表明在没有角蛋白的情况下细胞内聚没有完全被消除。原子力显微镜显示，直接抑制 Dsg3 而不是 Dsg1 的相互作用，可检测到致病性自身抗体，这表明该现象不需要角蛋白。然而，PF-IgG 将 Dsg1 结合事件从细胞边缘转移到 wt 细胞的游离细胞表面，导致 Dsg1 结合事件的分布模式类似于静止状态下的 KtyII k.o.细胞。在角蛋白缺陷的角质形成细胞中，PF-IgG 损害了 Dsg1 的结合强度，与静止状态下的 wt 细胞没有差异。此外，致病性自身抗体能够在 KtyII wt 和 k.o.细胞中激活 p38MAPK，后者在静止状态下已经显示出强烈的 p38MAPK 激活。由于抑制 p38MAPK 阻断了 wt 细胞中天疱疮自身抗体诱导的细胞间黏附丧失，并恢复了角蛋白缺陷细胞中的基线细胞内聚，因此我们得出结论，p38MAPK 信号传导：（i）是细胞黏附调节的关键；（ii）受角蛋白调节；（iii）是角蛋白依赖和非依赖机制的靶点。
