Leucine carboxyl methyltransferase 1 (LCMT-1) methylates protein phosphatase 4 (PP4) and protein phosphatase 6 (PP6) and differentially regulates the stable formation of different PP4 holoenzymes
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The protein phosphatase 2A (PP2A) subfamily of phosphatases, PP2A, PP4, and PP6, are multifunctional serine/threonine protein phosphatases involved in many cellular processes. Carboxyl methylation of the PP2A catalytic subunit (PP2Ac) C-terminal leucine is regulated by the opposing activities of leucine carboxyl methyltransferase 1 (LCMT-1) and protein phosphatase methylesterase 1 (PME-1) and regulates PP2A holoenzyme formation. The site of methylation on PP2Ac is conserved in the catalytic subunits of PP4 and PP6, and PP4 is also methylated on that site, but the identities of the methyltransferase enzyme for PP4 are not known. Whether PP6 is methylated is also not known. Here we use antibodies specific for the unmethylated phosphatases to show that PP6 is carboxyl-methylated and that LCMT-1 is the major methyltransferase for PP2A, PP4, and PP6 in mouse embryonic fibroblasts (MEFs). Analysis of PP2A and PP4 complexes by blue native polyacrylamide gel electrophoresis (BN-PAGE) indicates that PP4 holoenzyme complexes, like those of PP2A, are differentially regulated by LCMT-1, with the PP4 regulatory subunit 1 (PP4R1)-containing PP4 complex being the most dramatically affected by the LCMT-1 loss. MEFs derived from LCMT-1 knock-out mouse embryos have reduced levels of PP2A B regulatory subunit and PP4R1 relative to control MEFs, indicating that LCMT-1 is important for maintaining normal levels of these subunits. Finally, LCMT-1 homozygous knock-out MEFs exhibited hyperphosphorylation of HDAC3, a reported target of the methylation-dependent PP4R1-PP4c complex. Collectively, our data suggest that LCMT-1 coordinately regulates the carboxyl methylation of PP2A-related phosphatases and, consequently, their holoenzyme assembly and function.
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Caution is needed when interpreting biogenesis regulator strains because several of these proteins also affect PP4 and PP6, so their knockout or overexpression may not affect only PP2A.
“Some caution in interpreting data for the PP2A biogenesis regulator strains is however warranted, as several of these proteins, besides PP2A, likely also affect the functions of the PP2A-like phosphatases PP4 and PP6 [23][24][25][26], and hence, their knockout or overexpression may not solely affect PP2A.”
From Physiologic functions of PP2A: Lessons from genetically modified mice (2019) · cites this paper as [26]
A rather similar phenotype was observed in Lcmt1 knockout mice lacking detectable LCMT-1, which is predicted to majorly affect PP2A holoenzyme formation with B55 subunits.
“Interestingly, a rather similar phenotype was observed in Lcmt1 KO mice, lacking any detectable expression of the PP2A methyltransferase LCMT-1, which is predicted to majorly affect PP2A holoenzyme formation with B55 subunits [26,[39][40][41].”
From Physiologic functions of PP2A: Lessons from genetically modified mice (2019) · cites this paper as [26]
At E12.5, Lcmt1 gt/gt embryos have a fetal liver hematopoiesis defect affecting all lineages.
“-At E12.5: reduced embryo and liver weight; fetal liver hematopoiesis | defect (all lineages affected); misshapen eyes; indentation of the back | of the head”
From Physiologic functions of PP2A: Lessons from genetically modified mice (2019) · cites this paper as [26]
At E12.5, Lcmt1 gt/gt embryos have an indentation of the back of the head.
“-At E12.5: reduced embryo and liver weight; fetal liver hematopoiesis | defect (all lineages affected); misshapen eyes; indentation of the back | of the head”
From Physiologic functions of PP2A: Lessons from genetically modified mice (2019) · cites this paper as [26]
At E12.5, Lcmt1 gt/gt embryos have reduced embryo and liver weight.
“-At E12.5: reduced embryo and liver weight; fetal liver hematopoiesis | defect (all lineages affected); misshapen eyes; indentation of the back | of the head”
From Physiologic functions of PP2A: Lessons from genetically modified mice (2019) · cites this paper as [26]
In Lcmt1 -/- E14.5 MEFs, methylation of PP2A, PP4 and PP6 is decreased.
“-In -/-E14.5 MEFs: decreased methylation of PP2A, PP4 and PP6; | selective defects in PP2A-B55 and PP4-PPP4R1 complex formation”
From Physiologic functions of PP2A: Lessons from genetically modified mice (2019) · cites this paper as [26]
At E12.5, Lcmt1 gt/gt embryos have misshapen eyes.
“-At E12.5: reduced embryo and liver weight; fetal liver hematopoiesis | defect (all lineages affected); misshapen eyes; indentation of the back | of the head”
From Physiologic functions of PP2A: Lessons from genetically modified mice (2019) · cites this paper as [26]
In Lcmt1 -/- E14.5 MEFs, formation of PP2A-B55 and PP4-PPP4R1 complexes is selectively defective.
“-In -/-E14.5 MEFs: decreased methylation of PP2A, PP4 and PP6; | selective defects in PP2A-B55 and PP4-PPP4R1 complex formation”
From Physiologic functions of PP2A: Lessons from genetically modified mice (2019) · cites this paper as [26]
In mice with a gene-trap insertion in the first intron of Lcmt1 (German Gene Trap consortium clone), embryonic lethality occurs between E14.5 and E16.5, with 5% dying before E12.5.
“-Embryonic lethality between E14.5 and E16.5 (5% die before E12.5) [26,39,41]”
From Physiologic functions of PP2A: Lessons from genetically modified mice (2019) · cites this paper as [26]
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- Authors
- Hwang, J., Lee, J. A., & Pallas, D. C.
- Affiliations
- Emory University (US)
- Corresponding author
- Pallas, David C.
- Venue
- Journal of Biological Chemistry
- Publisher
- Elsevier BV
- Published
- 2016-09
- Volume
- 291
- Issue
- 40
- Pages
- 21008-21019
- ISSN
- 0021-9258 (ISSN-L)
- PMC
- PMC5076511
- OpenAlex
- W2522883401
- Cited by
- 56
- References
- 60
- Citations by year
- 2026: 3 · 2025: 6 · 2024: 4 · 2023: 7 · 2022: 3 · 2021: 8 · 2020: 11 · 2019: 6 · 2018: 6 · 2017: 1 · 2016: 1
- FWCI
- 2.43
- Type
- journal article
- Language
- en
- Open access
- hybrid
- doi.org
- Licence
- Locations
- Journal of Biological Chemistry (publishedVersion, cc-by)
- PubMed Central (publishedVersion)
- PubMed (publishedVersion)
- Funders
- National Cancer Institute (R01 CA57327, 5F31 CA123640)
- Topics
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Protein Tyrosine Phosphatases
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Protein Kinase Regulation and GTPase Signaling
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Cancer-related gene regulation
- Keywords
- protein phosphatase 4, protein phosphatase 6, protein phosphatase 2A, carboxyl methylation, PP2A catalytic subunit, mouse embryonic fibroblasts
- MeSH terms
- Histone Deacetylase 3, Animals, Cells, Cultured, Embryo, Mammalian, Fibroblasts, Histone Deacetylases, Methylation, Phosphoprotein Phosphatases, Phosphorylation, Protein O-Methyltransferase, Mice, Knockout, Holoenzymes, Mice
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