Szaszák Márta, Chen Hung-Dar, Chen Hao-Chia, Baukal Albert, Hunyady László, Catt Kevin J
Endocrinology and Reproduction Research Branch, Program in Developmental Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510, USA.
J Endocrinol. 2008 Nov;199(2):165-76. doi: 10.1677/JOE-08-0190. Epub 2008 Aug 21.
Little is known about the protein-protein interactions that regulate the trafficking of the angiotensin II type I receptor (AGTR1) through the biosynthetic pathway. The membrane-proximal region of the cytoplasmic tail of the AGTR1 has been identified by site-directed mutagenesis studies as an essential site for normal AGTR1 folding and surface expression. Based on yeast two-hybrid screening of a human kidney cDNA library with the AGTR1 carboxyl-terminal tail as a bait, we identified the invariant chain (CD74) as a novel interacting protein. This association was confirmed by co-immunoprecipitation and co-localization studies. The binding site for CD74 on the AGTR1 carboxyl-terminal tail was localized to a site previously identified as important for the exit of the AGTR1 from the endoplasmic reticulum (ER), and conserved in many G protein-coupled receptors. Transient co-expression of CD74 with the AGTR1 in CHO-K1 cells consistently reduced the AGTR1 density at the cell surface. Furthermore, the interaction of CD74 with the carboxyl-terminal tail of the AGTR1 caused its retention in the ER and promoted its proteasomal degradation. These observations indicate that CD74 and the AGTR1 become associated in the early biosynthetic pathway, and that CD74 is a negative regulator of AGTR1 expression.
关于调节血管紧张素II 1型受体（AGTR1）通过生物合成途径进行转运的蛋白质-蛋白质相互作用，目前所知甚少。通过定点诱变研究已确定，AGTR1胞质尾的膜近端区域是正常AGTR1折叠和表面表达的必需位点。基于以AGTR1羧基末端尾为诱饵对人肾cDNA文库进行的酵母双杂交筛选，我们鉴定出恒定链（CD74）是一种新型相互作用蛋白。这种关联通过共免疫沉淀和共定位研究得到证实。AGTR1羧基末端尾上CD74的结合位点定位于先前确定对AGTR1从内质网（ER）输出很重要的一个位点，并且在许多G蛋白偶联受体中保守。在CHO-K1细胞中，CD74与AGTR1瞬时共表达始终会降低细胞表面的AGTR1密度。此外，CD74与AGTR1羧基末端尾的相互作用导致其滞留在内质网中，并促进其蛋白酶体降解。这些观察结果表明，CD74和AGTR1在生物合成早期途径中发生关联，并且CD74是AGTR1表达的负调节因子。
