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

此前，我们发现了α-晶体蛋白/小分子热休克蛋白家族中的一个新成员，并将其命名为HSPB2(基因组学，1997年)。HSPB2基因和αB-晶体蛋白基因是小分子热休克蛋白家族中的另一个成员，它们以头对头的方式排列，基因间序列长956bp，这为它们的表达提供了共享增强子元件的可能性。在这项研究中，我们检测了新发现的HSPB2基因的空间和时间表达模式，并与αB-晶体蛋白基因的表达模式进行了比较。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表达的调控机制。(1)Northern杂交和原位杂交结果表明，HSPB2基因在心脏和肌肉中表达，而在眼晶状体中不表达。虽然HSPB2mRNA的表达水平远低于αB-晶状体蛋白的表达水平，但它们在肌肉中表达的发育规律相似(准备阶段)。(2)两个基因在C2C12细胞和转基因小鼠中的功能启动子分析表明，肌肉特异的增强子元件存在竞争，存在于基因间隔区(准备)。(3)细胞外钾浓度过高时，αB-晶体蛋白在神经胶质细胞中积聚，而不是HSPB2.利用缺失和突变构建的功能启动子分析表明，在U-251MGKC中，热休克元件是αB-晶体蛋白基因转录激活所必需的。凝胶迁移率和抗体超移动分析表明，KCl2诱导热休克因子2的HSE结合活性，提示HSF2参与了KCl抑制胶质细胞αB-晶体蛋白基因表达的过程(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).