Sartorelli V, Hong N A, Bishopric N H, Kedes L
Institute for Genetic Medicine, University of Southern California, School of Medicine, Los Angeles 90033.
Proc Natl Acad Sci U S A. 1992 May 1;89(9):4047-51. doi: 10.1073/pnas.89.9.4047.
The cardiac alpha-actin gene is expressed in both heart and skeletal muscle. In skeletal myogenic cells, the 177-base-pair promoter of the human cardiac alpha-actin (HCA) gene requires three transcription factors for activation: Sp1, serum response factor (SRF), and MyoD. However, MyoD is undetectable in heart. To search for a functional equivalent of MyoD, we analyzed the transcriptional regulation of the HCA promoter in primary cultures of rat cardiac myocytes. The same DNA sequence elements recognized by SRF, Sp1, and MyoD and required for HCA transcription in skeletal muscle cells were also found to be necessary for expression in cardiomyocytes. Overexpression of Id, a negative regulator of basic helix-loop-helix proteins, selectively attenuated expression of the HCA promoter. Cardiomyocyte nuclei contain a protein complex that specifically interacts with the same required sequence (E box) in the HCA promoter that is bound by MyoD in skeletal myogenic cells. Furthermore, these complexes contain a peptide that is a member of the E2A family of basic helix-loop-helix proteins. Cardiomyocyte nuclei appear to be enriched for a protein that can bind to the E-box site as dimers with the E12 protein. These results suggest that a member of the basic helix-loop-helix family, together with SRF and Sp1, activates the HCA promoter in heart. Alternative strategies for myocardial transcription of HCA are discussed.
心脏α-肌动蛋白基因在心脏和骨骼肌中均有表达。在骨骼肌成肌细胞中，人类心脏α-肌动蛋白（HCA）基因的177个碱基对启动子需要三种转录因子激活：Sp1、血清反应因子（SRF）和MyoD。然而，在心脏中未检测到MyoD。为了寻找MyoD的功能等效物，我们分析了大鼠心肌细胞原代培养物中HCA启动子的转录调控。在骨骼肌细胞中被SRF、Sp1和MyoD识别且HCA转录所需的相同DNA序列元件，在心肌细胞表达中也被发现是必需的。碱性螺旋-环-螺旋蛋白的负调节因子Id的过表达选择性地减弱了HCA启动子的表达。心肌细胞核含有一种蛋白复合物，该复合物与HCA启动子中与骨骼肌成肌细胞中MyoD结合的相同所需序列（E盒）特异性相互作用。此外，这些复合物含有一种肽，该肽是碱性螺旋-环-螺旋蛋白E2A家族的成员。心肌细胞核似乎富含一种能与E12蛋白以二聚体形式结合到E盒位点的蛋白。这些结果表明，碱性螺旋-环-螺旋家族的一个成员与SRF和Sp1一起激活心脏中的HCA启动子。文中还讨论了HCA心肌转录的替代策略。
