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Effects of carboxyl-terminal methylation on holoenzyme function of the PP2A subfamily.

ABSTRACT: Phosphoprotein Phosphatases (PPPs) are enzymes highly conserved from yeast and human and catalyze the majority of the serine and threonine dephosphorylation in cells. To achieve substrate specificity and selectivity, PPPs form multimeric holoenzymes consisting of catalytic, structural/scaffolding, and regulatory subunits. For the Protein Phosphatase 2A (PP2A)-subfamily of PPPs, holoenzyme assembly is at least in part regulated by an unusual carboxyl-terminal methyl-esterification, commonly referred to as 'methylation'. Carboxyl-terminal methylation is catalyzed by Leucine carboxyl methyltransferase-1 (LCMT1) that utilizes S-adenosyl-methionine (SAM) as the methyl donor and removed by protein phosphatase methylesterase 1 (PME1). For PP2A, methylation dictates regulatory subunit selection and thereby downstream phosphorylation signaling. Intriguingly, there are four families of PP2A regulatory subunits, each exhibiting different levels of methylation sensitivity. Thus, changes in PP2A methylation stoichiometry alters the complement of PP2A holoenzymes in cells and creates distinct modes of kinase opposition. Importantly, selective inactivation of PP2A signaling through the deregulation of methylation is observed in several diseases, most prominently Alzheimer's disease (AD). In this review, we focus on how carboxyl-terminal methylation of the PP2A subfamily (PP2A, PP4, and PP6) regulates holoenzyme function and thereby phosphorylation signaling, with an emphasis on AD.

SUBMITTER: Nasa I

PROVIDER: S-EPMC8380034 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Regulation of PP2A-subfamily holoenzyme function by carboxyl-terminal methylation

Project description:The family of Phosphoprotein Phosphatases (PPPs) is responsible for most cellular serine and threonine dephosphorylation. PPPs achieve substrate specificity and selectivity by forming multimeric holoenzymes with catalytic, scaffolding, and regulatory subunits. Although there are only ten catalytic PPP subunits encoded in the human genome, the formation of holoenzymes creates hundreds of unique enzymes that oppose kinases and carry out specific dephosphorylation reactions. Thus, to achieve the correct cellular phosphorylation state, the assembly of PPP holoenzymes needs to be tightly controlled. Indeed, changes in the cellular repertoire of PPPs are frequently linked to human disease, including cancer and neurodegeneration. The Protein Phosphatase 2A (PP2A) subfamily of PPPs consists of PP2A, PP4, PP6, and holoenzyme formation is at least in part regulated by carboxyl (C)-terminal methyl-esterification (often referred to as methylation) of the catalytic subunits. This reversible modification is catalyzed by a Leucine Carboxyl Methyltransferase-1 (LCMT1) that utilizes S-adenosyl-methionine (SAM) as the methyl donor and removed by Protein Phosphatase Methylesterase 1 (PME1). For PP2A, C-terminal methylation controls regulatory subunit selection. Notably, different types of regulatory subunits display differential methylation sensitivity. For PP4 and PP6, the role of C-terminal methylation is less well defined. Here, we use mass spectrometry-based proteomics, methylation-ablating mutations, and genome editing to comprehensively elucidate the role of C-terminal methylation in PP2A, PP4, and PP6 function in multiple cell lines. Using these approaches, we quantitatively determine the effects of reduced C-terminal methylation on PP2A, PP4, and PP6 holoenzyme assembly in an unbiased, isoform-specific manner.

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Regulation of PP2A, PP4, and PP6 holoenzyme assembly by carboxyl-terminal methylation.

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