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

以前我们鉴定了α-晶状体蛋白/小热休克蛋白（HSP）家族的一个新成员，并将其命名为HSPB 2（Genomics，1997）。HSPB 2基因和小HSP家族的另一个成员α B-晶状体蛋白基因以头对头的方式排列，基因间序列为956 bp，这提高了它们表达的共享增强子元件的可能性。在这项研究中，我们研究了新发现的HSPB 2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)北方杂交和原位杂交结果表明，HSPB 2基因在心脏和肌肉中表达，而在眼透镜中不表达。虽然HSPB 2的mRNA水平远低于α B-晶状体蛋白，但它们在肌肉中的表达的发育模式相似（制备中）。(2)在C2 C12细胞和转基因小鼠中的两个基因的功能启动子分析揭示了肌肉特异性增强子元件的竞争，其存在于基因间区域（制备中）。(3)α B-晶体蛋白，而不是HSPB 2，在神经胶质细胞中积累，以响应高细胞外钾浓度。利用缺失和突变构建体进行的启动子功能分析表明，热休克元件（HSE）是KCl激活U-251 MG中α B-晶状体蛋白基因转录所必需的;凝胶迁移率改变和抗体超迁移实验表明，KCl诱导热休克因子2（HSF 2）的HSE结合活性，提示HSF 2参与了神经胶质细胞中α B-晶状体蛋白mRNA的KCl依赖性增加（已提交）。

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).