Cav1.2 Transcript Regulation in Heart and Smooth Muscle

描述（由申请人提供）：人类心脏l型钙通道的一个新的第一外显子已经被发现，使具有不同5'端的转录本数量达到三个，每个转录本可能由其自己的启动子调节。其中两个转录本具有关键意义，因为它们分别占心脏和平滑肌转录本的大多数。本研究假设，这两种主要转录本在心脏、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。已知肾上腺素能药物在心脏中上调然后下调这一通道的转录，但在平滑肌中缺乏相应的信息。该基金将测试三个特定的假设：1)在非洲爪蟾卵母细胞和人类细胞中异种表达不同转录本会产生具有不同振幅、动力学、开放概率、对蛋白激酶C的敏感性和稳态失活特性的Ca电流；2)两种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)并且有心脏特异性转录因子结合到心脏通道启动子中的应答元件，而大多数平滑肌表达是由其他转录因子结合到其他主要通道启动子中的应答元件驱动的。结果将确定不同的n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中受到不同的调节，而不是在心脏和内脏平滑肌中。它们可能为药物干预涉及l型钙通道表达改变的疾病（如高血压）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.