EPM2A

This gene encodes a dual-specificity phosphatase that associates with polyribosomes. The encoded protein may be involved in the regulation of glycogen metabolism. Mutations in this gene have been associated with myoclonic epilepsy of Lafora. Alternative splicing results in multiple transcript variants. [provided by RefSeq, Jul 2008]

Full Name

EPM2A, Laforin Glucan Phosphatase

Research Area

Plays an important role in preventing glycogen hyperphosphorylation and the formation of insoluble aggregates, via its activity as glycogen phosphatase, and by promoting the ubiquitination of proteins involved in glycogen metabolism via its interaction with the E3 ubiquitin ligase NHLRC1/malin. Shows strong phosphatase activity towards complex carbohydrates in vitro, avoiding glycogen hyperphosphorylation which is associated with reduced branching and formation of insoluble aggregates (PubMed:16901901, PubMed:23922729, PubMed:26231210, PubMed:25538239, PubMed:25544560).

Dephosphorylates phosphotyrosine and synthetic substrates, such as para-nitrophenylphosphate (pNPP), and has low activity with phosphoserine and phosphothreonine substrates (in vitro) (PubMed:11001928, PubMed:11220751, PubMed:11739371, PubMed:14532330, PubMed:16971387, PubMed:18617530, PubMed:22036712, PubMed:23922729, PubMed:14722920).

Has been shown to dephosphorylate MAPT (By similarity).

Forms a complex with NHLRC1/malin and HSP70, which suppresses the cellular toxicity of misfolded proteins by promoting their degradation through the ubiquitin-proteasome system (UPS). Acts as a scaffold protein to facilitate PPP1R3C/PTG ubiquitination by NHLRC1/malin (PubMed:23922729).

Also promotes proteasome-independent protein degradation through the macroautophagy pathway (PubMed:20453062).

Isoform 2:
does not bind to glycogen (PubMed:18617530).

Lacks phosphatase activity and might function as a dominant-negative regulator for the phosphatase activity of isoform 1 and isoform 7 (PubMed:18617530, PubMed:22036712).

Isoform 7:
has phosphatase activity (in vitro).

Biological Process

Autophagosome assembly Source: Ensembl
Calcium ion transport Source: Ensembl
Carbohydrate phosphorylation Source: Ensembl
Dephosphorylation Source: UniProtKB
Glial cell proliferation Source: Ensembl
Glycogen biosynthetic process Source: Reactome
Glycogen metabolic process Source: UniProtKB
Habituation Source: Ensembl
L-glutamate transmembrane transport Source: Ensembl
Mitochondrion organization Source: Ensembl
Negative regulation of cell cycle Source: Ensembl
Negative regulation of dephosphorylation Source: UniProtKB
Negative regulation of gene expression Source: Ensembl
Negative regulation of peptidyl-serine phosphorylation Source: Ensembl
Negative regulation of phosphatase activity Source: UniProtKB
Peptidyl-tyrosine dephosphorylation Source: UniProtKB
Phosphorylated carbohydrate dephosphorylation Source: UniProtKB
Positive regulation of macroautophagy Source: Ensembl
Proteasome-mediated ubiquitin-dependent protein catabolic process Source: Ensembl
Protein dephosphorylation Source: UniProtKB
Regulation of cell growth Source: Ensembl
Regulation of glycogen (starch) synthase activity Source: Ensembl
Regulation of proteasomal protein catabolic process Source: Ensembl
Regulation of protein import into nucleus Source: Ensembl
Regulation of protein kinase activity Source: Ensembl
Regulation of protein localization to plasma membrane Source: Ensembl
Regulation of protein ubiquitination Source: Ensembl
Regulation of ubiquitin protein ligase activity Source: Ensembl
Wnt signaling pathway Source: Ensembl

Cellular Location

Cytoplasm. Under glycogenolytic conditions localizes to the nucleus.
Isoform 1: Endoplasmic reticulum membrane; Cytoplasm; Cell membrane. Colocalizes with glycogen synthase in punctate structures in the cytoplasm (PubMed:11739371, PubMed:14532330). Primarily associated with polyribosomes at the rough endoplasmic reticulum, and also detected at the plasma membrane (PubMed:11001928, PubMed:11220751, PubMed:11883934, PubMed:18311786).
Isoform 2: Endoplasmic reticulum membrane; Nucleus; Cytoplasm; Cell membrane. Also found in the nucleus.
Isoform 4&5: Nucleus
Isoform 7: Cytoplasm

Involvement in disease

Epilepsy, progressive myoclonic 2 (EPM2):
A form of progressive myoclonic epilepsy, a clinically and genetically heterogeneous group of disorders defined by the combination of action and reflex myoclonus, other types of epileptic seizures, and progressive neurodegeneration and neurocognitive impairment. EPM2 is an autosomal recessive and severe form of adolescent-onset progressive epilepsy. Typically, as seizures increase in frequency, cognitive function declines towards dementia, and affected individuals die usually within 10 years after onset. EPM2 occurs worldwide, but it is particularly common in the mediterranean countries of southern Europe and northern Africa, in southern India and in the Middle East. At the cellular level, it is characterized by accumulation of starch-like polyglucosans called Lafora bodies (LBs) that are most abundant in organs with the highest glucose metabolism: brain, heart, liver and skeletal muscle. Among other conditions involving polyglucosans, EPM2 is unique in that the inclusions are in neuronal dendrites but not axons and the forming polyglucosan fibrils are associated with the endoplasmic reticulum.

PTM

Polyubiquitinated by NHLRC1/malin.
Phosphorylation on Ser-25 by AMPK affects the phosphatase activity of the enzyme and its ability to homodimerize and interact with NHLRC1, PPP1R3C or PRKAA2.