Identification and characterization of novel splice variants of the human EPM2A gene mutated in Lafora progressive myoclonus epilepsy

The EPM2A gene, defective in the fatal neurodegenerative disorder Lafora disease (LD), is known to encode two distinct proteins by differential splicing; a phosphatase active cytoplasmic isoform and a phosphatase inactive nuclear isoform. We report here the identification of three novel EPM2A splice variants with potential to code for five distinct proteins in alternate reading frames. These novel isoforms, when ectopically expressed in cell lines, show distinct subcellular localization, interact with and serve as substrates of malin ubiquitin ligase-the second protein defective in LD. Two phosphatase active isoforms interact to form a heterodimeric complex that is inactive as a phosphatase in vitro, suggesting an antagonistic function for laforin isoforms if expressed endogenously in significant amounts in human tissues. Thus alternative splicing could possibly be one of the mechanisms by which EPM2A may regulate the cellular functions of the proteins it codes for.