Department of Pharmacology, School of Medicine, University of California San Diego, La Jolla, California 92093.
Center for Translational Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.
J Biol Chem. 2018 May 25;293(21):8056-8064. doi: 10.1074/jbc.M117.809913. Epub 2018 Apr 8.
PH domain leucine-rich repeat protein phosphatase (PHLPP) is a serine/threonine phosphatase that has been shown to regulate cell growth and survival through dephosphorylation of several members of the AGC family of kinases. G-protein-coupled receptor kinase 5 (GRK5) is an AGC kinase that regulates phenylephrine (PE)-induced cardiac hypertrophy through its noncanonical function of directly targeting proteins to the nucleus to regulate transcription. Here we investigated the possibility that the PHLPP2 isoform can regulate GRK5-induced cardiomyocyte hypertrophy in neonatal rat ventricular myocytes (NRVMs). We show that removal of PHLPP2 by siRNA induces hypertrophic growth of NRVMs as measured by cell size changes at baseline, potentiated PE-induced cell size changes, and re-expression of fetal genes atrial natriuretic factor and brain natriuretic peptide. Endogenous GRK5 and PHLPP2 were found to interact in NRVMs, and PE-induced nuclear accumulation of GRK5 was enhanced upon down-regulation of PHLPP2. Conversely, overexpression of PHLPP2 blocked PE-induced hypertrophic growth, re-expression of fetal genes, and nuclear accumulation of GRK5, which depended on its phosphatase activity. Finally, using siRNA against GRK5, we found that GRK5 was necessary for the hypertrophic response induced by PHLPP2 knockdown. Our findings demonstrate for the first time a novel regulation of GRK5 by the phosphatase PHLPP2, which modulates hypertrophic growth. Understanding the signaling pathways affected by PHLPP2 has potential for new therapeutic targets in the treatment of cardiac hypertrophy and failure.
PH 结构域亮氨酸丰富重复蛋白磷酸酶（PHLPP）是一种丝氨酸/苏氨酸磷酸酶，已被证明通过去磷酸化 AGC 家族激酶的几个成员来调节细胞生长和存活。G 蛋白偶联受体激酶 5（GRK5）是一种 AGC 激酶，通过其直接将蛋白质靶向核内以调节转录的非典型功能，调节苯肾上腺素（PE）诱导的心肌肥厚。在这里，我们研究了 PHLPP2 同工型是否可以调节原代培养的新生大鼠心室肌细胞（NRVM）中 GRK5 诱导的心肌肥厚。我们发现，siRNA 去除 PHLPP2 可诱导 NRVM 的肥大生长，如基线时细胞大小变化、增强 PE 诱导的细胞大小变化以及胎儿基因心钠肽和脑钠肽的重新表达所测量。内源性 GRK5 和 PHLPP2 被发现在 NRVM 中相互作用，并且在 PHLPP2 下调时，PE 诱导的 GRK5 核积累增强。相反，过表达 PHLPP2 可阻断 PE 诱导的心肌肥厚、胎儿基因的重新表达和 GRK5 的核积累，这依赖于其磷酸酶活性。最后，使用针对 GRK5 的 siRNA，我们发现 GRK5 是 PHLPP2 敲低诱导的肥大反应所必需的。我们的研究结果首次证明了磷酸酶 PHLPP2 对 GRK5 的一种新的调节作用，这种调节作用调节了心肌肥厚。了解 PHLPP2 影响的信号通路可能为治疗心肌肥厚和衰竭提供新的治疗靶点。
