Huang Yuan, Wright Casey D, Kobayashi Satoru, Healy Chastity L, Elgethun Megan, Cypher Andrew, Liang Qiangrong, O'Connell Timothy D
Cardiovascular Research Center, Sanford Research/Univ. of South Dakota, Dept. of Internal Medicine, Univ. of South Dakota, 1100 E. 21st St., Ste. 700, Sioux Falls, SD 57105, USA.
Am J Physiol Heart Circ Physiol. 2008 Aug;295(2):H699-707. doi: 10.1152/ajpheart.01204.2007. Epub 2008 Jun 13.
Recently, we defined an alpha1A-adrenergic receptor-ERK (alpha1A-AR-ERK) survival signaling pathway in adult cardiac myocytes. Previous studies in neonatal cardiac myocytes indicated that the cardiac-specific transcription factor GATA4 is a downstream mediator of alpha1-ERK signaling and that phosphorylation of GATA4 by ERK increases DNA binding and transcriptional activity. Therefore, we examined GATA4 as a potential downstream effector of alpha1A-ERK survival signaling in adult cardiac myocytes. We measured norepinephrine (NE)-induced cell death in cultured cardiac myocytes lacking alpha1-ARs (cultured from alpha1A/B-AR double-knockout mice, alpha1ABKO mice) that are susceptible to cell death induced by several proapoptotic stimuli, including NE. Our results show that overexpression of GATA4 is sufficient to protect alpha1ABKO cardiac myocytes from NE-induced cell death. However, we found that the alpha1A-subtype did not induce phosphorylation or increase the activity of GATA4 in adult mouse cardiac myocytes in culture or in vivo. Furthermore, we examined the effect of siRNA-mediated knockdown of GATA4 on alpha1A-survival signaling. In alpha1B-knockout cardiac myocytes, which express only the alpha1A-subtype and are protected from NE-induced cell death, GATA4 knockdown did not reverse alpha1A-survival signaling in response to NE. In summary, we found that GATA4 acted as a survival factor by preventing cell death in alpha1ABKO cardiac myocytes, but GATA4 was not activated by alpha1-AR stimulation and was not required for alpha1A-survival signaling in adult cardiac myocytes. This also identifies an important mechanistic difference in alpha1-signaling between adult and neonatal cardiac myocytes.
最近，我们在成年心肌细胞中定义了一条α1A - 肾上腺素能受体 - 细胞外信号调节激酶（α1A - AR - ERK）存活信号通路。先前在新生心肌细胞中的研究表明，心脏特异性转录因子GATA4是α1 - ERK信号的下游介质，并且ERK对GATA4的磷酸化增加了DNA结合和转录活性。因此，我们研究了GATA4作为成年心肌细胞中α1A - ERK存活信号潜在下游效应器的作用。我们在缺乏α1 - ARs的培养心肌细胞（从α1A/B - AR双敲除小鼠，即α1ABKO小鼠培养而来）中测量了去甲肾上腺素（NE）诱导的细胞死亡，这些细胞对包括NE在内的几种促凋亡刺激诱导的细胞死亡敏感。我们的结果表明，GATA4的过表达足以保护α1ABKO心肌细胞免受NE诱导的细胞死亡。然而，我们发现α1A亚型在培养的成年小鼠心肌细胞或体内并未诱导GATA4的磷酸化或增加其活性。此外，我们研究了小干扰RNA（siRNA）介导的GATA4敲低对α1A存活信号的影响。在仅表达α1A亚型且免受NE诱导的细胞死亡的α1B敲除心肌细胞中，GATA4敲低并未逆转对NE的α1A存活信号。总之，我们发现GATA4通过防止α1ABKO心肌细胞死亡而作为一种存活因子，但GATA4未被α1 - AR刺激激活，并且在成年心肌细胞的α1A存活信号中不是必需的。这也确定了成年和新生心肌细胞在α1信号传导方面的一个重要机制差异。
