Regulation of Cardiac Kv Channel Expression

描述(申请人提供)：心力衰竭与心脏的电和机械功能重塑有关。在许多哺乳动物的各种病理状态下，电重构的一个共同特征是瞬时外向电流(ITO)通道表达减少，这会改变心功能，并可能导致导致猝死的心律失常。当前资助期的实验表明，限制人类Ito通道表达的Kv4.3信使RNA(MRNA)在培养的心肌细胞中受到拉伸和血管紧张素II(AII)的破坏，血管紧张素II是一种与高血压和充血性心力衰竭有关的激素。NADPH氧化酶(NOx)产生的超氧化物和ASK1和p38激酶的激活导致AUF1的失稳，导致AUF1的诱导表达，AUF1是一种在人类心力衰竭中上调的蛋白质，可以直接与通道mRNA中的非规范序列结合。我们最近的研究表明，AII通过内体和CaMKII(钙调蛋白依赖蛋白激酶II)诱导p38激酶的双相激活。此外，AUF1启动子被激活，这意味着转录调控。最后，初步实验表明，AUF1基因敲除的小鼠对横动脉缩窄(TAC)的反应受到损害，这表明AUF1对于体内心脏对压力超负荷的反应是重要的。在这里，我们研究下调Kv4.3基因表达的信号，因为(A)该通道是心脏电重构的进化保守靶点，(B)AUF1可能调节病理性心脏中许多基因的表达，(C)Nox、CaMKII和p38激酶参与心力衰竭和心肌细胞凋亡，以及(D)延迟的内毒素诱导的p38激酶信号转导可能是维持心功能而不发生心力衰竭时心律失常的治疗靶点。目的1将确定心肌细胞内内体-超氧化物信号的时间组织。目的2将确定AUF1表达增强和功能增强的机制。目的3将利用基因敲除小鼠在体内阐明AUF1如何影响健康和病理的心脏。这些研究将揭示控制心肌细胞基因表达的新的分子和细胞机制。 公共卫生相关性：心力衰竭是导致死亡的主要原因，它与导致心脏泵血功能不佳的信号和可能导致猝死的心律失常有关。基于对心肌K+通道表达的研究，我们发现内体和超氧化物诱导了信号的延迟阶段，从而导致了一种mRNA不稳定蛋白的表达。阐明这一途径及其对通道和其他心脏靶点的下游影响可能会导致治疗心力衰竭的新疗法。

DESCRIPTION (provided by applicant): Heart failure is associated with remodeling of the electrical and mechanical function of the heart. A common feature of electrical remodeling seen under a wide variety of pathologic states in many mammals is decreased expression of transient outward current (Ito) channels, which alters heart function and may contribute to arrhythmias that cause sudden death. Experiments in the current funding period showed that Kv4.3 messenger RNA (mRNA), which limits Ito channel expression in humans, is destabilized in cultured cardiac myocytes by stretch and Angiotensin II (AII), a hormone implicated in hypertension and congestive heart failure. Destabilization is induced by Nadph oxidase (Nox)-generated superoxide and activation of ASK1 and p38 kinase, resulting in induced expression of AUF1, a protein upregulated in human heart failure that can directly bind to a non-canonical sequence in the channel mRNA. Our recent studies show that AII acts via endosomes and CamKII (calmodulin dependent protein kinase II) to induce biphasic activation of p38 kinase. Furthermore, the AUF1 promoter is activated, implicating transcriptional regulation. Finally, preliminary experiments suggest that AUF1 knockout mice are compromised in their response to transverse aortic constriction (TAC), showing that AUF1 is important for the in vivo cardiac response to pressure overload. Here we study the signaling responsible for downregulating Kv4.3 gene expression, because (a) this channel is an evolutionarily conserved target of cardiac electrical remodeling, (b) AUF1 may regulate expression of many genes in the pathologic heart, (c) Nox, CamKII and p38 kinase have been implicated in heart failure and cardiac myocyte apoptosis, and (d) delayed endosome-induced p38 kinase signaling may be a therapeutic target for maintaining cardiac function without arrhythmia during heart failure. Aim 1 will determine the temporal organization of endosome-superoxide signaling in cardiac myocytes. Aim 2 will determine the mechanisms responsible for enhanced expression and function of AUF1. Aim 3 will use knockout mice to elucidate in vivo how AUF1 affects the healthy and pathologic heart. New molecular and cellular mechanisms for controlling cardiac myocyte gene expression will be revealed by these studies. PUBLIC HEALTH RELEVANCE: Heart failure, a leading cause of death, is associated with signaling that leads to poor cardiac pumping and arrhythmias that can induce sudden death. Based on studies of cardiac K+ channel expression, we have found that endosomes and superoxide induce a delayed phase of signaling which results in expression of an mRNA destabilizing protein. Elucidating this pathway and its downstream effects on channels and other cardiac targets may lead to new therapies for treating heart failure.