雌激素通过LRP16基因5′侧翼GC富含区上调其转录的分子机制

Mechanism of Transcriptional Activation of LRP16 Gene Expression by 17-Estradiol via 5′-Flanking GC-rich Region

LRP16是一个明确的雌激素(E2)反应性靶基因,已往研究在LRP16基因上游调控区鉴定了一个E2反应性1/2ERE/GC富含的ERα作用位点(-676bp到-214bp;命名为A区).为进一步鉴定雌激素上调LRP16基因表达的最大化反应区域,对LRP16基因上游调控区进行缺失突变,通过相对荧光素酶活性分析观察到LRP16基因的一段5′近端侧翼序列(-213bp到-24bp;命名为B区)具有明显的E2反应性.通过与A区比较,认为B区最大化的呈递了E2对LRP16基因的转激活效应.序列分析表明,B区缺乏经典的ERE元件,而包含多个富含GC序列.针对Sp1的siRNA实验结果提示,Sp1参与了E2对该区域的转激活.针对GC富含区进一步的缺失突变,及荧光素酶活性分析,识别了一段30bp(-213bp到-184bp)的序列在B区呈递E2反应活性中发挥核心作用.超级凝胶电泳实验结果表明,Sp1蛋白与这段30bp的DNA序列在体外存在直接结合作用.染色质免疫共沉淀实验结果证实,ERα、Sp1与B区存在E2依赖性相互作用.本文在LRP16的5′-侧翼区识别了一段最大化呈递E2活性的DNA片段.机制研究表明,在E2存在条件下,ERα通过Sp1与该区域的直接作用上调LRP16基因的表达.

LRP16 gene has been characterized as an estrogen-responsive gene. Previous studies have identified an E2-responsive 1/2ERE/GC-rich site at the 5′-flanking promoter of the LRP16 gene （the - 676 bp to -214 bp region, namely region A）. To map the responsive fragment that maximally confer the estrogen transactivation within the 5′-regulatory region of LRP16, deletion analyses were further performed. The results of cotransfection and the luciferase assays showed that the fragment from - 213 bp to - 24 bp （namely region B） gave rise to the maximal responsiveness of E2. Sequence analysis showed that the classical ERE （estrogen response element） was lacked within this region, but six GC-rich sites existing. The results of cotransfection assays combining with Spl-siRNA indicated that Spl protein was required for the responsiveness of region B to estrogen. A 30 bp fragment within region B（ - 213 bp to - 184 bp） was identified to be essential for the maximal E2-responsiveness by further deletion and mutation analyses. Gel mobility shift assays showed that the Spl protein can directly bind to this region. The results of ChIP confirmed that cooperative c/Spl interactions at region B were necessary for E2-induced transactivation. Taken together, a minimal DNA fragment of LRP16 gene 5′-flanking region was identified, which was essential for the maximal reponsiveness to estrogen. And the interaction of ligand-bound ERα/Spl complex and DNA fragment involved in this regulatory mechanism.