Cav1.2 Transcript Regulation in Heart and Smooth Muscle

描述(申请人提供)：发现了人类心脏L型钙通道的一个新的第一外显子，使发现的具有不同5‘端的转录本数量增加到三个，每个转录本可能由其自己的启动子调控。其中两个转录本具有重要意义，因为它们分别占心脏和平滑肌转录本的大部分。这项研究假设，这两个主要转录本在心脏以及血管和内脏平滑肌中的差异表达不仅在通道活性、对蛋白激酶C的敏感性和稳态失活方面产生显著差异，而且在三种组织类型中分别调节表达的能力也更强。众所周知，肾上腺素能药物在转录水平上上调和下调心脏中的这一通道，但对于平滑肌来说，缺乏同样的信息。这项授权将检验三个具体的假设：1)不同转录本在非洲爪哇卵母细胞和人类细胞中的异源表达导致钙电流的幅度、动力学、开放概率、对蛋白激酶C的敏感性和稳态失活特性不同；2)两个主要转录本在心脏和平滑肌中受到肾上腺素能药物的不同影响；3)存在心脏特异的转录因子，它与心脏通道的反应元件结合，而大多数平滑肌细胞的表达是由其他转录因子驱动的，这些转录因子与另一个主要通道启动子中的反应元件结合。结果将确定不同的N末端如何影响通道特性，以及不同的转录本如何在血管平滑肌而不是心脏和内脏平滑肌中进行差异调控。他们可能会为药物干预高血压等涉及L钙通道表达变化的疾病提供新的靶点。

DESCRIPTION (provided by applicant): A novel first exon for the human cardiac L-type calcium channel has been discovered, bringing to three the number of transcripts found with different 5' ends, each likely regulated by its own promoter. Two of these transcripts are of critical significance, since they account for the majority of transcripts in heart and smooth muscle, respectively. This grant hypothesizes that differential expression of these two principal transcripts in heart and in vascular and visceral smooth muscle not only generates significant differences in channel activity, sensitivity to protein kinase C, and steady-state inactivation but also greater ability to separately regulate expression in the three tissue types. Adrenergic agents are known to transcriptionally upregulate and then downregulate this channel in heart, but equivalent information is lacking for smooth muscle. This grant will test three specific hypotheses: 1) that heterologous expression of the different transcripts in Xenopus oocytes and human cells results in Ca currents with different amplitude, kinetics, open probability, sensitivity to protein kinase C and steady state inactivation properties; 2) that the two principal transcripts are differentially affected in heart and smooth muscle by adrenergic agents; 3) and that there are heart-specific transcription factors that bind to response elements in the heart promoter for the channel, whereas most smooth muscle expression is driven by other transcription factors that bind to response elements in the other principal channel promoter. The results will determine how the different N-termini affect channel properties and how the different transcripts are differentially regulated in vascular smooth muscle as opposed to heart and visceral smooth muscle. They could suggest new targets for pharmaceutical intervention in disorders involving alterations in expression of L-type Ca channels, such as hypertension.