Department of Pharmacology and Toxicology and IU Simon Cancer Center, Indiana University School of Medicine, Indianapolis, Indiana 46202, United States.
Biochemistry. 2012 May 1;51(17):3634-41. doi: 10.1021/bi300301a. Epub 2012 Apr 19.
ABCG2 is a member of the ATP-binding cassette transporter superfamily, and its overexpression causes multidrug resistance (MDR) in cancer chemotherapy. ABCG2 may also protect cancer stem cells by extruding cytotoxic materials. ABCG2 has previously been shown to exist as a high-order homo-oligomer consisting of possibly 8-12 subunits, and the oligomerization domain was mapped to the C-terminal domain, including TM5, ECL3, and TM6. In this study, we further investigate this domain in detail for the role of each segment in the oligomerization and drug transport function of ABCG2 using domain swapping and site-directed mutagenesis. We found that none of the three segments (TM5, TM6, and ECL3) is essential for the oligomerization activity of ABCG2 and that any one of these three segments in the full-length context is sufficient to support ABCG2 oligomerization. While TM5 plays an important role in the drug transport function of ABCG2, TM6 and ECL3 are replaceable. Thus, each segment in the TM5-ECL3-TM6 domain plays a distinctive role in the oligomerization and function of ABCG2.
ABCG2 是 ABC 转运体超家族的一员，其过度表达会导致癌症化疗中的多药耐药（MDR）。ABCG2 还可能通过排出细胞毒性物质来保护癌症干细胞。先前已经表明，ABCG2 以可能由 8-12 个亚基组成的高阶同型寡聚物的形式存在，寡聚化结构域被映射到 C 端结构域，包括 TM5、ECL3 和 TM6。在这项研究中，我们使用结构域交换和定点突变进一步详细研究了该结构域，以研究每个片段在 ABCG2 寡聚化和药物转运功能中的作用。我们发现，这三个片段（TM5、TM6 和 ECL3）都不是 ABCG2 寡聚化活性所必需的，并且在全长背景下的这三个片段中的任何一个都足以支持 ABCG2 寡聚化。虽然 TM5 在 ABCG2 的药物转运功能中起着重要作用，但 TM6 和 ECL3 是可替换的。因此，TM5-ECL3-TM6 结构域中的每个片段在 ABCG2 的寡聚化和功能中都起着独特的作用。
