MARCH2 regulates autophagy by promoting CFTR ubiquitination and degradation, and PIK3CA-AKT-MTOR signaling

MARCH2 (membrane-associated RING-CH protein 2), an E3 ubiquitin ligase, is mainly associated with the vesicle trafficking. In the present study, for the first time, we demonstrated that MARCH2 negatively regulates autophagy. Our data indicated that overexpression of MARCH2 impaired autophagy, as evidenced by attenuated levels of LC3B-II and impaired degradation of endogenous and exogenous autophagic substrates. By contrast, loss of <i>MARCH2</i> expression had the opposite effects. In vivo experiments demonstrate that <i>MARCH2</i> knockout mediated autophagy results in an inhibition of tumorigenicity. Further investigation revealed that the induction of autophagy by <i>MARCH2</i> deficiency was mediated through the PIK3CA-AKT-MTOR signaling pathway. Additionally, we found that MARCH2 interacts with CFTR (cystic fibrosis transmembrane conductance regulator), promotes the ubiquitination and degradation of CFTR, and inhibits CFTR-mediated autophagy in tumor cells. The functional PDZ domain of MARCH2 is required for the association with CFTR. Thus, our study identified a novel negative regulator of autophagy and suggested that the physical and functional connection between the MARCH2 and CFTR in different conditions will be elucidated in the further experiments.

MARCH2（膜相关RING-CH蛋白2，membrane-associated RING-CH protein 2）是一种E3泛素连接酶（E3 ubiquitin ligase），主要参与囊泡运输过程。本研究首次证实，MARCH2可负调控自噬（autophagy）。研究数据显示，MARCH2过表达会损伤自噬功能，具体表现为LC3B-II水平降低，以及内源性与外源性自噬底物的降解受阻。与之相反，MARCH2表达缺失则会产生完全相反的生物学效应。体内实验结果表明，MARCH2敲除所介导的自噬激活可抑制肿瘤致瘤性。进一步机制研究显示，MARCH2缺失所诱导的自噬是通过PIK3CA-AKT-MTOR信号通路实现的。此外，本研究发现MARCH2可与CFTR（囊性纤维化跨膜传导调节因子，cystic fibrosis transmembrane conductance regulator）相互结合，促进CFTR的泛素化与降解，并抑制肿瘤细胞中CFTR介导的自噬。MARCH2的功能性PDZ结构域是其与CFTR发生相互作用的必要条件。综上，本研究鉴定出一种新型自噬负调控因子，并提示MARCH2与CFTR在不同条件下的物理与功能关联有待后续实验进一步解析阐明。