Centre for Cutaneous Research, The Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, 4 Newark Street, London E1 2AT, UK.
J Cell Sci. 2012 Jun 15;125(Pt 12):2853-61. doi: 10.1242/jcs.084152. Epub 2012 Mar 27.
Desmosomes are intercellular junctions specialised for strong adhesion that are prominent in the epidermis and heart muscle. Defective desmosomal function due to inherited mutations in the constitutive desmosomal gene desmoplakin (DSP) causes skin or heart disorders and in some instances both. Different mutations have different disease-causing molecular mechanisms as evidenced by the varying phenotypes resulting from mutations affecting different domains of the same protein, but the majority of these mechanisms remain to be determined. Here, we studied two mutations in DSP that lead to different dosages of the two major DSP splice variants, DSPI and DSPII, and compared their molecular mechanisms. One of the mutations results in total DSP haploinsufficiency and is associated with autosomal dominant striate palmoplantar keratoderma (PPK). The other leads to complete absence of DSPI and the minor isoform DSPIa but normal levels of DSPII, and is associated with autosomal recessive epidermolytic PPK, woolly hair and severe arrhythmogenic dilated cardiomyopathy. Using siRNA treatments to mimic these two mutations and additionally a DSPII-specific siRNA, we found striking differences between DSP isoforms with respect to keratinocyte adhesion upon cellular stress with DSPII being the key component in intermediate filament (IF) stability and desmosome-mediated adhesion. In addition, reduction in DSP expression reduced the amount of plakophilin 1, desmocollin (DSC) 2 and DSC3 with DSPI having a greater influence than DSPII on the expression levels of DSC3. These results suggest that the two major DSP splice variants are not completely redundant in function and that DSPII dosage is particularly important for desmosomal adhesion in the skin.
桥粒是细胞间连接的一种特殊形式，其作用是提供强大的黏附力，在表皮和心肌中尤为明显。由于桥粒核心蛋白桥粒芯胶蛋白（DSP）的遗传性突变导致桥粒功能缺陷，会引起皮肤或心脏疾病，在某些情况下还会同时引起这两种疾病。不同的突变具有不同的致病分子机制，这可以从影响同一蛋白不同结构域的突变导致不同表型的情况中得到证明，但这些机制的大多数仍有待确定。在这里，我们研究了导致两种主要 DSP 剪接变体 DSPI 和 DSPII 不同剂量的两种 DSP 突变，并比较了它们的分子机制。其中一种突变导致 DSP 完全单倍体不足，与常染色体显性条纹状掌跖角化病（PPK）有关。另一种突变导致 DSPI 完全缺失和次要异构体 DSPIa，但 DSPII 水平正常，与常染色体隐性表皮松解性 PPK、羊毛状毛发和严重心律失常性扩张型心肌病有关。使用 siRNA 处理来模拟这两种突变，以及另外一种 DSPII 特异性 siRNA，我们发现 DSP 异构体在细胞应激下的角质形成细胞黏附方面存在显著差异，DSPII 是中间丝（IF）稳定性和桥粒介导的黏附的关键组成部分。此外，DSP 表达的减少降低了 plakophilin 1、desmocollin 2（DSC）2 和 DSC3 的含量，其中 DSPI 对 DSC3 的表达水平的影响大于 DSPII。这些结果表明，两种主要的 DSP 剪接变体在功能上并非完全冗余，并且 DSPII 剂量对皮肤中的桥粒黏附特别重要。
