Specificity and function of PP2A carboxymethylation

描述(由申请人提供)： PP2A是一种多功能的丝氨酸/苏氨酸磷酸酶，参与调节细胞的生长和增殖，包括G2/M期的转变，并参与人类癌症的发展。PP2A的催化亚基C末端亮氨酸α-羧基被LCMT-1甲基化，并被PME-1去甲基化。这两种蛋白共同调节C亚基的甲基化，通过改变TS全酶的形成间接调节PP2A，从而改变其亚细胞靶向性和底物特异性。可逆甲基化S是调节PP2A最特异的细胞机制，因此有望成为基于机制的治疗靶点。PP2A C亚基甲基化水平以细胞周期依赖的方式变化，甲基化依赖形式的PP2A在G2/M转变过程中调节几个关键蛋白，提示PP2A甲基化可能调节进入有丝分裂。PP4和PPG磷酸酶与PP2A显示出高度的序列同源性，PP4也可逆地甲基化。虽然PP6具有与PP2A和PP4相同的三重羧基末端氨基酸，但目前还不能确定PP6是否也可以可逆甲基化。此外，催化PP4‘S C-末端亮氨酸甲酯化的甲基转移酶尚未确定。我这项研究既相互关联又相互独立的目标是：(1)确定LCMT-1、LCMT-2和PME-1对PP2A、PP4和PP6的底物特异性；(2)确定PP2A催化亚单位甲基化是否在G2/M转变中发挥作用。

DESCRIPTION (provided by applicant): PP2A, a multifunctional Ser/Thr phosphatase, has been implicated in the regulation of cell growth and proliferation, including the G2/M transition, and in the development of human cancers. PP2A is methylated on its catalytic subunit C-terminal leucine alpha-carboxy group by LCMT-1 and is demethylated by PME-1. Together, these two proteins regulate the methylation of the C subunit, indirectly regulating PP2A by altering ts holoenzyme formation, and thus its subcellular targeting and substrate specificity. Reversible methylation s the most specific cellular mechanism for regulating PP2A, and thus may have promise as a mechanism- based therapeutic target. The level of PP2A C subunit methylation changes in a cell cycle-dependent manner and a methylation-dependent form of PP2A regulates several key proteins at the G2/M transition, suggesting PP2A methylation may regulate entry into mitosis. PP4 and PPG phosphatases exhibit a high degree of sequence homology to PP2A and PP4 is also reversibly methylated. Although PP6 has the same hree carboxy-terminal amino acids as PP2A and PP4, it has not been determined whether PP6 can also be reversibly methylated. In addition, the methyltransferase that catalyzes the methyl esterification of PP4's C- terminal leucine has not been identified. My interrelated yet independent aims of this fellowship are (1) to determine the substrate specificities of LCMT-1, LCMT-2, and PME-1 towards PP2A, PP4, and PP6 and (2) :to determine if PP2A catalytic subunit methylation plays a role the G2/M transition.