钙蛋白酶是广泛分布于人体各种细胞内的钙依赖半胱氨酸蛋白酶，参与多种细胞蛋白的蛋白酶解过程。钙蛋白酶抑制蛋白（CAST）与钙蛋白酶共表达于细胞浆中，是其体内特异性抑制剂。申请者发现CAST基因突变可以引起PLACK综合征，一种以皮肤剥脱为主要特征的疾病。CAST缺失导致表皮棘层松解，桥粒斑蛋白表达紊乱。据此，申请者推测钙蛋白酶及其抑制蛋白系统很可能在桥粒结构的稳定性中发挥重要作用。我们拟在前期研究的基础上，通过PLACK患者皮肤组织标本、培养细胞siRNA敲低CAST表达模型，以及免疫共沉淀方法，明确CAST缺陷时，桥粒结构中被钙蛋白酶酶解的组成蛋白。进而我们选取两种钙相关性棘层松解性皮肤病——慢性家族性良性天疱疮及毛囊角化病进行钙蛋白酶及其抑制蛋白系统表达及活性研究。本研究有望确定钙蛋白酶及其抑制蛋白系统在表皮细胞间粘附中的作用，为临床上棘层松解性皮肤病提供全新致病机理及治疗靶点。

Calpains are a group of calcium-dependent, non-lysosomal cysteine proteases which are ubiquitously expressed in mammalian cells and involved in the proteolysis of various proteins. Calpastatin, encoded by the CAST gene, is the only known endogenous inhibitor of calpains and is co-localized with calpains in cytosol. Previously we have found that loss-of-function mutations in CAST caused PLACK syndrome, an autosomal-recessive disorder characterized by skin fragility and peeling. Deficiency in calpastatin leads to defective epidermal adhesion, characterized by acantholysis and aberrant expression of desmoplakin. Based on these results, we assumed that balance of the calpain-CAST system is crucial for the homeostasis of desmosome, an important structure of epidermal cell-cell adhesion. We seek to determine the target desmosomal component which is proteolysed by over-activated calpains using the skin tissues of patients with PLACK syndrome, the siRNA-knockdown HaCaT cells and co-immunoprecipitation. Then we choose to study two relatively common acantholytic disorders, Hailey-Hailey disease and Darier disease, to find out whether imbalance of the calpain-CAST system is involved in the pathogenesis of acantholysis. This study is expected to determine the role of the calpain-CAST system in epidermal adhesion, and shed new light on the pathogenesis of acantholytic disorders.