Leucine Carboxyl Methyltransferase-1 Is Necessary for Normal Progression through Mitosis in Mammalian Cells

• Type of Material: Article
• Authors: Jocelyn A. Lee, Emory University; David C Pallas, Emory University
• Language: English
• Date: 2007-10-19
• Publisher: American Society for Biochemistry and Molecular Biology
• Publication Version: Final Published Version
• Copyright Statement: © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.
• Final Published Version (URL): http://www.jbc.org/content/282/42/30974.long
• Title of Journal or Parent Work: Journal of Biological Chemistry
• ISSN: 0021-9258
• Volume: 282
• Issue: 42
• Start Page: 30974
• End Page: 30984
• Grant/Funding Information: This work was supported by NCI, National Institutes of Health Grant CA57327 (toD. C. P.) and Predoctoral Fellowship Award CA 1236402(toJ. A. L.).; The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
• Research Categories: Biology, Cell; Chemistry, Biochemistry

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 Bα 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 Bα regulatory subunit induced a similar amount of apoptosis, suggesting that LCMT-1 induces apoptosis in part by disrupting the formation of PP2ABαAC heterotrimers. Treatment with a pancaspase inhibitor partially rescued cells from apoptosis induced by LCMT-1 or Bα knockdown. LCMT-1 knockdown cells and Bα knockdown cells were more sensitive to the spindle-targeting drug nocodazole, suggesting that LCMT-1 and Bα are important for spindle checkpoint. Treatment of LCMT-1 and Bα 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.