Hines W A, Thorburn A
Department of Human Genetics, Program in Human Molecular Biology and Genetics, Eccles Institute of Human Genetics, Bldg. 533, Rm. 4220, University of Utah, Salt Lake City, UT 84112, USA.
J Mol Cell Cardiol. 1998 Mar;30(3):485-94. doi: 10.1006/jmcc.1997.0613.
The hypertrophic response is characterized by increased myofibril/sarcomere organization, induction of the cardiac specific atrial natriuretic factor (ANF) and myosin light chain-2 (MLC-2v) genes, and an increase in total cell volume. The alpha1-adrenergic agonist phenylephrine induces both the morphological and biochemical markers of hypertrophy in cultured neonatal rat ventricular cardiomyocytes. Previous studies have suggested a functional requirement for the heterotrimeric G-protein, Galphaq, for a subset of the hypertrophic phenotypes. The small GTPases Ras and Rho have also been implicated in phenylephrine-induced hypertrophy. To further delineate the role of Galphaq in hypertrophy, a constitutively active mutant of Galphaq was transiently transfected in primary rat ventricular cardiomyocytes. This molecule was sufficient to induce ANF-, AP1-, and MLC-2-driven gene expression. Co-transfection of Galphaq and dominant negative Ras or dominant negative Raf resulted in dose-dependent inhibition of ANF-driven expression. Both dominant negative Rho, and the Rho inhibitor C3-transferase, also attenuated Galphaq- and Ras-induced ANF-driven gene expression. Cells transfected with active Galphaq did not show a detectable increase in activation of the mitogen activated protein kinases ERK or SAPK. However, activity of the MAP-kinases appears to be important for Galphaq-induced gene expression since the MAP-kinase phosphatase Clone 100 and catalytically inactive SAPK strongly inhibited Galphaq-induced ANF expression. Thus, our studies indicate Galphaq-induced hypertrophic gene expression requires the small G-proteins Ras and Rho. The data also indicates that Galphaq mediated gene expression is dependent on functional MAP-kinases and that multiple signaling pathways contribute to Galphaq-mediated cardiac cell hypertrophy.
肥大反应的特征是肌原纤维/肌节组织增加、心脏特异性心房利钠因子（ANF）和肌球蛋白轻链-2（MLC-2v）基因的诱导以及总细胞体积的增加。α1-肾上腺素能激动剂去氧肾上腺素可诱导培养的新生大鼠心室心肌细胞肥大的形态学和生化标志物。先前的研究表明，异源三聚体G蛋白Gαq对于一部分肥大表型具有功能需求。小GTP酶Ras和Rho也与去氧肾上腺素诱导的肥大有关。为了进一步阐明Gαq在肥大中的作用，将Gαq的组成型活性突变体瞬时转染到原代大鼠心室心肌细胞中。该分子足以诱导ANF、AP1和MLC-2驱动的基因表达。Gαq与显性负性Ras或显性负性Raf的共转染导致ANF驱动表达的剂量依赖性抑制。显性负性Rho和Rho抑制剂C3转移酶也减弱了Gαq和Ras诱导的ANF驱动的基因表达。用活性Gαq转染的细胞未显示出有丝分裂原活化蛋白激酶ERK或SAPK的激活有可检测到的增加。然而，MAP激酶的活性似乎对Gαq诱导的基因表达很重要，因为MAP激酶磷酸酶克隆100和催化无活性的SAPK强烈抑制Gαq诱导的ANF表达。因此，我们的研究表明，Gαq诱导的肥大基因表达需要小G蛋白Ras和Rho。数据还表明，Gαq介导的基因表达依赖于功能性MAP激酶，并且多种信号通路参与了Gαq介导的心脏细胞肥大。
