Expression of the HSPB2 and αB-crystallin genes located in a head-to-head manner

之前我们发现了α-晶体蛋白/小热休克蛋白（HSP）家族的一个新成员，并将其命名为HSPB2 （Genomics, 1997）。HSPB2基因与HSP家族的另一成员αB-crystallin基因头对头排列，基因间序列为956 bp，可能存在共同表达的增强子元件。在这项研究中，我们检测了新发现的HSPB2基因的时空表达模式，并与α b -晶体蛋白基因进行了比较。此外，我们还研究了这两个基因在培养细胞和转基因小鼠中的表达调控机制。(1) Northern blotting和原位杂交显示HSPB2基因在心脏和肌肉中表达，而在晶状体中不表达。虽然HSPB2 mRNA的表达水平远低于αB-crystallin，但两者在肌肉组织（准备阶段）的表达发育特征相似。(2)对这两个基因在C2C12细胞和转基因小鼠中的功能启动子分析显示，存在于基因间区（准备中）的肌肉特异性增强子元件的竞争。(3) α b -晶体蛋白（αB-Crystallin），而非HSPB2，在细胞外高钾浓度下在胶质细胞中积累。通过缺失和突变构建的功能启动子分析表明，热休克元件（HSE）在KCl对U-251MG α b -晶体蛋白基因的转录激活中是必不可少的。凝胶迁移位移和抗体超位移实验显示，KCl诱导热休克因子2 （HSF2）的hse结合活性，表明HSF2参与了KCl依赖性胶质细胞α b -晶体蛋白mRNA的增加（提交）。

Previously we identified a new member of the α-crystallin/small heat shock protein (HSP) family and named it HSPB2 (Genomics, 1997). The HSPB2 gene and the αB-crystallin gene, another member of the small HSP family, are arranged in a head-to-head manner with an intergenic sequence of 956 bp, raising a possibility of shared enhancer elements for their expression. In this study we examined spatial and temporal expression patterns of the newly identified HSPB2 gene and compared with that of the αB-crystallin gene. Furthermore, we investigated the regulatory mechanisms of expression of the two genes in cultured cells and transgenic mice. (1) Northern blotting and in situ hybridization revealed that the HSPB2 gene is expressed in heart and muscles but not in eye lens. Although the level of HSPB2 mRNA was much lower than that of αB-crystallin, the developmental profiles of their expression were similar in muscles (in preparation). (2) Functional promoter analysis of the two genes in C2C12 cells and transgenic mice revealed a competition of muscle specific enhancer elements, which arc present in the intergenic region (in preparation). (3) αB-Crystallin, but not HSPB2, accumulates in glial cells in response to high extracellular potassium concentrations. Functional promoter analysis using deletion and mutation constructs revealed that the heat shock element (HSE) is essential for transcriptional activation of the αB-crystallin gene by KCl in U-251MG.Gel mobility shift and antibody supershift assays showed that KCl induces the HSE-binding activity of heat shock factor 2 (HSF2), suggesting that HSF2 is involved in KCl-depedent increases in αB-crystallin mRNA in glial cells (submitted).