Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California, USA.
PLoS One. 2013 Jun 20;8(6):e65967. doi: 10.1371/journal.pone.0065967. Print 2013.
Protein phosphatase 2A (PP2A), the major serine/threonine phosphatase in eukaryotic cells, is a heterotrimeric protein composed of structural, catalytic, and targeting subunits. PP2A assembly is governed by a variety of mechanisms, one of which is carboxyl-terminal methylation of the catalytic subunit by the leucine carboxyl methyltransferase LCMT1. PP2A is nearly stoichiometrically methylated in the cytosol, and although some PP2A targeting subunits bind independently of methylation, this modification is required for the binding of others. To examine the role of this methylation reaction in mammalian tissues, we generated a mouse harboring a gene-trap cassette within intron 1 of Lcmt1. Due to splicing around the insertion, Lcmt1 transcript and LCMT1 protein levels were reduced but not eliminated. LCMT1 activity and methylation of PP2A were reduced in a coordinate fashion, suggesting that LCMT1 is the only PP2A methyltransferase. These mice exhibited an insulin-resistance phenotype, indicating a role for this methyltransferase in signaling in insulin-sensitive tissues. Tissues from these animals will be vital for the in vivo identification of methylation-sensitive substrates of PP2A and how they respond to differing physiological conditions.
蛋白磷酸酶 2A（PP2A）是真核细胞中主要的丝氨酸/苏氨酸磷酸酶，是由结构亚基、催化亚基和靶向亚基组成的异三聚体蛋白。PP2A 的组装受多种机制调控，其中之一是亮氨酸羧基甲基转移酶 LCMT1 对催化亚基的羧基末端甲基化。PP2A 在细胞质中几乎是等摩尔甲基化的，尽管一些 PP2A 靶向亚基可以独立于甲基化结合，但这种修饰对于其他亚基的结合是必需的。为了研究这种甲基化反应在哺乳动物组织中的作用，我们构建了一个在 Lcmt1 内含子 1 中携带基因捕获盒的小鼠。由于插入导致的剪接，Lcmt1 转录本和 LCMT1 蛋白水平降低，但没有完全消除。LCMT1 活性和 PP2A 的甲基化以协调的方式降低，表明 LCMT1 是唯一的 PP2A 甲基转移酶。这些小鼠表现出胰岛素抵抗表型，表明这种甲基转移酶在胰岛素敏感组织中的信号转导中发挥作用。这些动物的组织对于体内鉴定 PP2A 的甲基化敏感底物以及它们如何响应不同的生理条件至关重要。
