Regulation of Cardiac Kv Channel Expression

描述（由申请人提供）：心力衰竭与心脏电和机械功能的重塑有关。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态外向电流（Ito）通道的表达减少，这改变了心脏功能，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通过拉伸和血管紧张素II (AII)（一种与高血压和充血性心力衰竭有关的激素）不稳定。不稳定是由Nadph氧化酶（Nox）产生的超氧化物和ASK1和p38激酶的激活诱导的，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，可以直接结合通道mRNA中的非规范序列。我们最近的研究表明，AII通过内体和CamKII（钙调素依赖性蛋白激酶II）诱导p38激酶的双相激活。此外，AUF1启动子被激活，暗示转录调控。最后，初步实验表明AUF1敲除小鼠对横断主动脉收缩（TAC）的反应受到损害，表明AUF1对体内心脏对压力过载的反应很重要。在这里，我们研究了负责下调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激酶与心力衰竭和心肌细胞凋亡有关。(d)延迟内体诱导的p38激酶信号传导可能是维持心力衰竭期间无心律失常的心功能的治疗靶点。目的1将确定心肌细胞内核内体超氧化物信号的时间组织。目的2将确定AUF1表达和功能增强的机制。目的3将使用基因敲除小鼠来阐明AUF1如何在体内影响健康和病理心脏。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。

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.