title: Leucine carboxyl methyltransferase-1 is necessary for normal progression through mitosis in mammalian cells.
abstract: Protein phosphatase 2A (PP2A) is a multifunctional phosphatase that plays important roles in many cellular processes including regulation of cell cycle and apoptosis. Because PP2A is involved in so many diverse processes, it is highly regulated by both non-covalent and covalent mechanisms that are still being defined. In this study we have investigated the importance of leucine carboxyl methyltransferase-1 (LCMT-1) for PP2A methylation and cell function. We show that reduction of LCMT-1 protein levels by small hairpin RNAs causes up to a 70% reduction in PP2A methylation in HeLa cells, indicating that LCMT-1 is the major mammalian PP2A methyltransferase. In addition, LCMT-1 knockdown reduced the formation of PP2A heterotrimers containing the Balpha regulatory subunit and, in a subset of the cells, induced apoptosis, characterized by caspase activation, nuclear condensation/fragmentation, and membrane blebbing. Knockdown of the PP2A Balpha regulatory subunit induced a similar amount of apoptosis, suggesting that LCMT-1 induces apoptosis in part by disrupting the formation of PP2A(BalphaAC) heterotrimers. Treatment with a pan-caspase inhibitor partially rescued cells from apoptosis induced by LCMT-1 or Balpha knockdown. LCMT-1 knockdown cells and Balpha knockdown cells were more sensitive to the spindle-targeting drug nocodazole, suggesting that LCMT-1 and Balpha are important for spindle checkpoint. Treatment of LCMT-1 and Balpha knockdown cells with thymidine dramatically reduced cell death, presumably by blocking progression through mitosis. Consistent with these results, homozygous gene trap knock-out of LCMT-1 in mice resulted in embryonic lethality. Collectively, our results indicate that LCMT-1 is important for normal progression through mitosis and cell survival and is essential for embryonic development in mice.
authors.affiliation: Department of Biochemistry, Winship Cancer Center, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
authors.forename: Jocelyn A
authors.initials: JA
authors.lastname: Lee
authors.forename: David C
authors.initials: DC
authors.lastname: Pallas
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D053938:DNA Fragmentation / Q000187:drug effects; D020964:Embryo Loss / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D006367:HeLa Cells; D006801:Humans; D008745:Methylation / Q000187:drug effects; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008938:Mitosis / Q000187:drug effects / Q000235:genetics; D015739:Nocodazole / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D011497:Protein O-Methyltransferase / Q000235:genetics / Q000378:metabolism; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D008941:Spindle Apparatus / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D013936:Thymidine / Q000494:pharmacology; D050257:Tubulin Modulators / Q000494:pharmacology
chemical_list: D061945:Caspase Inhibitors; D011480:Protease Inhibitors; D021122:Protein Subunits; D050257:Tubulin Modulators; C524761:LCMT1 protein, human; D008780:Methyltransferases; D011497:Protein O-Methyltransferase; D054648:Protein Phosphatase 2; D020169:Caspases; D015739:Nocodazole; D013936:Thymidine