Álvarez Lautaro D, Dansey M Virginia, Grinman Diego Y, Navalesi Daniela, Samaja Gisela A, Del Fueyo M Celeste, Bastiaensen Niek, Houtman René, Estrin Darío A, Veleiro Adriana S, Pecci Adali, Burton Gerardo
Dpto. Química Orgánica and UMYMFOR (CONICET-UBA), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina.
Dpto. Química Biológica and IFIBYNE (UBA-CONICET), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina.
Biochim Biophys Acta. 2015 Dec;1851(12):1577-86. doi: 10.1016/j.bbalip.2015.09.007. Epub 2015 Oct 3.
Liver X receptors (LXRs) are transcription factors activated by cholesterol metabolites containing an oxidized side chain. Due to their ability to regulate lipid metabolism and cholesterol transport, they have become attractive pharmacological targets. LXRs are closely related to DAF-12, a nuclear receptor involved in nematode lifespan and regulated by the binding of C-27 steroidal acids. Based on our recent finding that the lack of the C-25 methyl group does not abolish their DAF-12 activity, we evaluated the effect of removing it from the (25R)-cholestenoic acid, a LXR agonist.
The binding mode and the molecular basis of action of 27-nor-5-cholestenoic acid were evaluated using molecular dynamics simulations. The biological activity was investigated using reporter gene expression assays and determining the expression levels of endogenous target genes. The in vitro MARCoNI assay was used to analyze the interaction with cofactors.
27-Nor-5-cholestenoic acid behaves as an inverse agonist. This correlates with the capacity of the complex to better bind corepressors rather than coactivators. The C-25 methyl moiety would be necessary for the maintenance of a torsioned conformation of the steroid side chain that stabilizes an active LXRβ state.
We found that a 27-nor analog is able to act as a LXR ligand. Interestingly, this minimal structural change on the steroid triggered a drastic change in the LXR response.
Results contribute to improve our understanding on the molecular basis of LXRβ mechanisms of action and provide a new scaffold in the quest for selective LXR modulators.
肝脏X受体（LXRs）是由含有氧化侧链的胆固醇代谢物激活的转录因子。由于它们具有调节脂质代谢和胆固醇转运的能力，已成为有吸引力的药理学靶点。LXRs与DAF-12密切相关，DAF-12是一种参与线虫寿命并受C-27甾体酸结合调节的核受体。基于我们最近的发现，即缺乏C-25甲基并不消除它们的DAF-12活性，我们评估了从LXR激动剂（25R）-胆甾烯酸中去除该甲基的效果。
使用分子动力学模拟评估27-去甲-5-胆甾烯酸的结合模式和作用分子基础。使用报告基因表达分析和测定内源性靶基因的表达水平来研究其生物活性。体外MARCoNI分析用于分析与辅因子的相互作用。
27-去甲-5-胆甾烯酸表现为反向激动剂。这与复合物更好地结合共抑制因子而非共激活因子的能力相关。C-25甲基部分对于维持稳定活性LXRβ状态的类固醇侧链扭转构象是必要的。
我们发现27-去甲类似物能够作为LXR配体起作用。有趣的是，类固醇上这种最小的结构变化引发了LXR反应的剧烈变化。
结果有助于提高我们对LXRβ作用机制分子基础的理解，并为寻找选择性LXR调节剂提供新的支架。
