Wang Xuyang, Chen Jieru, Huang Jiujiu, Hong Mei
College of Life Sciences, South China Agricultural University, Guangzhou 510642, China.
Guangdong Provincial Key Laboratory of Protein Function and Regulation in Agricultural Organisms, Guangzhou 510642, China.
Pharmaceutics. 2023 Sep 4;15(9):2279. doi: 10.3390/pharmaceutics15092279.
Organic anion transporting polypeptide 1B1 (OATP1B1) is specifically expressed at the basolateral membrane of human hepatocytes and plays important roles in the uptake of various endogenous and exogenous compounds including many drugs. The proper functioning of OATP1B1, hence, is essential for the bioavailability of various therapeutic agents and needs to be tightly regulated. Dileucine-based signals are involved in lysosomal targeting, internalization, and trans-Golgi network to endosome transporting of membrane proteins. In the current study, we analyzed the 3 intracellular and 13 transmembrane dileucine motifs (DLMs) within the sequence of OATP1B1. It was found that the simultaneous replacement of I332 and L333 with alanine resulted in a significantly reduced level of the mature form of OATP1B1. The cell surface expression of I332A/L333A could be partially rescued by MG132, as well as agents that prevent clathrin-dependent protein internalization, suggesting that this dileucine motif may be involved in the endocytosis of OATP1B1. On the other hand, I376/L377 and I642/L643, which are localized at transmembrane helices (TM) 8 and 12, respectively, are involved in the interaction of the transporter with its substrates. I642A/L643A exhibited a significantly decreased protein level compared to that of the wild-type, implying that the motif is important for maintaining the stability of OATP1B1 as well.
有机阴离子转运多肽1B1（OATP1B1）特异性表达于人类肝细胞的基底外侧膜，在摄取包括许多药物在内的各种内源性和外源性化合物过程中发挥重要作用。因此，OATP1B1的正常功能对于各种治疗药物的生物利用度至关重要，且需要受到严格调控。基于双亮氨酸的信号参与溶酶体靶向、内化以及膜蛋白从反式高尔基体网络到内体的转运过程。在本研究中，我们分析了OATP1B1序列中的3个细胞内和13个跨膜双亮氨酸基序（DLM）。结果发现，将I332和L333同时替换为丙氨酸会导致OATP1B1成熟形式的水平显著降低。MG132以及阻止网格蛋白依赖性蛋白内化的试剂可部分挽救I332A/L333A的细胞表面表达，这表明该双亮氨酸基序可能参与OATP1B1的内吞作用。另一方面，分别位于跨膜螺旋（TM）8和12的I376/L377和I642/L643参与转运蛋白与其底物的相互作用。与野生型相比，I642A/L643A的蛋白水平显著降低，这意味着该基序对于维持OATP1B1的稳定性也很重要。
