胰岛素前体——前胰岛素原跨膜转位进入内质网腔，是β细胞合成胰岛素第一个关键环节，其效率对胰岛素合成至关重要，且依赖于由四个亚基组成的信号肽序列受体复合物(SSR)。近期结构研究表明，亚基SSR3位于复合物中心，且是各亚基联系的纽带。申请人前期工作表明，SSR3下调导致其他亚基水平下降，伴随前胰岛素原转位障碍，胞内胰岛素含量减少。本项目拟在前期工作基础上，利用细胞分子生物学技术，对SSR3在胰岛素生物合成中的作用及机制进行探索性研究。明确SSR3缺失对β细胞功能的影响，探究SSR3在前胰岛素原转位、胰岛素原加工折叠、成熟为胰岛素并有效分泌中的意义，阐明SSR3维持β细胞SSR复合物结构功能、调节胰岛素生物合成中关键分子的加工修饰及内质网内环境稳态中的作用。同时利用β细胞条件敲除小鼠完成对SSR3在胰岛功能中的体内研究。该研究有望深化对胰岛素生物合成的理解，为糖尿病发生发展的分子机制提供参考。

In pancreatic beta cells, the translocation of newly-synthesized preproinsulin, the precursor of insulin, across the membrane into the endoplasmic reticulum(ER) cavity is the premise of insulin production. Upon emerging from the translocon, the signal peptide on preproinsulin is cut off by the signal peptidase and become proinsulin. This process requires the facilitation of the signal peptide sequence receptor complex (SSR), which consists of four subunits. SSR3 is at the central position in SSR complex and critical in maintaining the complex structure and function. Our preliminary data demonstrated that SSR3 down-regulation led to the failure of preproinsulin translocation, with lower level of insulin in β cells as well as the decreased expression of other subunits. Currently, the role of SSR3 in insulin biosynthesis and the underlying mechanism remain to be elucidated. Thus, we will use cellular/molecular biology techniques to determine whether SSR3 deficiency (1) affects β cell viability and function, preproinsulin translocaton, proinsulin folding and processing, insulin secretion and degradation; (2) reduces the stability of SSR complex; (3) dysregulates the expression, modification and function of other important proteins in insulin biosynthesis and ER homeostasis. Meanwhile, the vital role of SSR3 in islet in vivo will be studies in pancreatic β cell conditional knockout mice. This study aims to further our understanding of insulin biosynthesis and might shed a light on the molecular mechanism of diabetes mellitus.