Functional analysis of a novel E3 ubiquitin ligase family.

最近研究表明，在生理条件下，具有抗原提呈细胞功能的树突状细胞(DC)存在MHC II类分子的翻译后调节。在这里，我们报告了3月-I，一个E3泛素连接酶，在B细胞中MHC H的翻译后调节中发挥关键作用。在B细胞中，3月-I的表达尤其高，并且强制表达诱导了MHC II的泛素化。在3月-I缺陷小鼠(3月-I KO)的B细胞中，表面MHC II的半衰期延长，泛素化的MHC II完全消失。此外，3月I基因缺陷的B细胞在其表面高表达外源抗原负载的MHC II，并表现出较强的呈递外源抗原的能力。这些结果表明，MHC II在B细胞中的功能是通过3月1日泛素化来调节的

The presence of post-translational regulation of MHC class II (MHC II) under physiological conditions has been demonstrated recently in dendritic cells (DCs) that potently function as antigen-presenting cells (APCs). Here, we report that MARCH-I, an E3 ubiquitin ligase, plays a pivotal role in the post-translational regulation of MHC H in B cells. MARCH-I expression was particularly high in B cells, and the forced expression of MARCH-I induced the ubiquitination of MHC II. In B cells from MARCH-I-deficient mice (MARCH-I KO), the half-life of surface MHC II was prolonged and the ubiquitinated form of MHC II completely disappeared. In addition, MARCH-I-deficient B cells highly expressed exogenous-antigen-loaded MHC II on their surface and showed high ability to present exogenous antigens. These results suggest that the function of MHC II in B cells is regulated through ubiquitination by MARCH-I