Specificity and function of PP2A carboxymethylation

描述（由申请人提供）： PP 2A是一种多功能的Ser/Thr磷酸酶，参与细胞生长和增殖的调节，包括G2/M转换，以及人类癌症的发展。PP 2A在其催化亚基C-末端亮氨酸α-羧基上被LCMT-1甲基化，并被PME-1脱甲基化。这两种蛋白共同调节C亚基的甲基化，通过改变ts全酶形成间接调节PP 2A，从而改变其亚细胞靶向和底物特异性。可逆甲基化是调节PP 2A的最特异的细胞机制，因此可能有希望作为基于机制的治疗靶点。PP 2A C亚基甲基化水平以细胞周期依赖性方式变化，PP 2A的甲基化依赖性形式调节G2/M转换的几个关键蛋白，表明PP 2A甲基化可能调节进入有丝分裂。PP 4和PPG磷酸酶表现出与PP 2A高度的序列同源性，并且PP 4也被可逆地甲基化。虽然PP 6具有与PP 2A和PP 4相同的三个羧基末端氨基酸，但尚未确定PP 6是否也可以可逆地甲基化。此外，催化PP 4的C-末端亮氨酸的甲酯化的甲基转移酶尚未被鉴定。我的相互关联但独立的目的是：（1）确定LCMT-1，LCMT-2和PME-1对PP 2A，PP 4和PP 6的底物特异性;（2）确定PP 2A催化亚基甲基化是否在G2/M转换中起作用。

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.