Greschik H, Wurtz J M, Hublitz P, Köhler F, Moras D, Schüle R
Institut für Experimentelle Krebsforschung, Klinik für Tumorbiologie an der Universität Freiburg, D-79106 Freiburg, Germany.
Mol Cell Biol. 1999 Jan;19(1):690-703. doi: 10.1128/MCB.19.1.690.
The orphan receptor germ cell nuclear factor (GCNF) is a member of the superfamily of nuclear receptors. During development, GCNF exhibits a restricted brain-specific expression pattern, whereas GCNF expression in the adult is germ cell specific. Therefore, the receptor may participate in the regulation of neurogenesis and reproductive functions. No natural GCNF target gene has yet been identified, but recent data demonstrate specific and high-affinity binding of GCNF either to the direct repeat DNA element AGGTCAAGGTCA (DR0) or to extended half-sites, such as TCAAGGTCA. In this study, we show that murine GCNF (mGCNF) can bind as a homodimer to extended half-sites, thus describing a novel property within the nuclear receptor superfamily. Homodimeric binding to extended half-sites requires the presence of a dimerization function within the mGCNF DNA-binding domain (DBD) and a novel dimerization surface encompassing the putative helix 3 and the helix 12 region of the mGCNF ligand-binding domain (LBD). In addition, the mGCNF LBD has the potential to adopt different conformations with distinct dimerization properties. The helix 12 region of the mGCNF LBD not only regulates the switch between these dimerization conformations but also dictates the DNA-binding behavior and transcriptional properties of the different dimerization conformations. In summary, our findings describe unique DNA-binding and dimerization properties of a nuclear receptor and suggest a novel mechanism that allows mGCNF to modulate target gene activity.
孤儿受体生殖细胞核因子（GCNF）是核受体超家族的成员。在发育过程中，GCNF表现出局限于脑的特异性表达模式，而在成体中GCNF的表达则是生殖细胞特异性的。因此，该受体可能参与神经发生和生殖功能的调节。目前尚未鉴定出天然的GCNF靶基因，但最近的数据表明GCNF能与直接重复DNA元件AGGTCAAGGTCA（DR0）或扩展的半位点（如TCAAGGTCA）发生特异性和高亲和力结合。在本研究中，我们发现小鼠GCNF（mGCNF）能以同二聚体形式结合扩展的半位点，从而揭示了核受体超家族中的一种新特性。与扩展半位点的同二聚体结合需要mGCNF DNA结合结构域（DBD）内存在二聚化功能以及一个包含mGCNF配体结合结构域（LBD）假定的螺旋3和螺旋12区域的新二聚化表面。此外，mGCNF LBD有潜力采用具有不同二聚化特性的不同构象。mGCNF LBD的螺旋12区域不仅调节这些二聚化构象之间的转换，还决定了不同二聚化构象的DNA结合行为和转录特性。总之，我们的研究结果描述了一种核受体独特的DNA结合和二聚化特性，并提出了一种允许mGCNF调节靶基因活性的新机制。
