Stimulation of mTORC1 with L-leucine rescues defects associated with Roberts syndrome

PLoS Genet. 2013;9(10):e1003857. doi: 10.1371/journal.pgen.1003857. Epub 2013 Oct 3.

Abstract

Roberts syndrome (RBS) is a human disease characterized by defects in limb and craniofacial development and growth and mental retardation. RBS is caused by mutations in ESCO2, a gene which encodes an acetyltransferase for the cohesin complex. While the essential role of the cohesin complex in chromosome segregation has been well characterized, it plays additional roles in DNA damage repair, chromosome condensation, and gene expression. The developmental phenotypes of Roberts syndrome and other cohesinopathies suggest that gene expression is impaired during embryogenesis. It was previously reported that ribosomal RNA production and protein translation were impaired in immortalized RBS cells. It was speculated that cohesin binding at the rDNA was important for nucleolar form and function. We have explored the hypothesis that reduced ribosome function contributes to RBS in zebrafish models and human cells. Two key pathways that sense cellular stress are the p53 and mTOR pathways. We report that mTOR signaling is inhibited in human RBS cells based on the reduced phosphorylation of the downstream effectors S6K1, S6 and 4EBP1, and this correlates with p53 activation. Nucleoli, the sites of ribosome production, are highly fragmented in RBS cells. We tested the effect of inhibiting p53 or stimulating mTOR in RBS cells. The rescue provided by mTOR activation was more significant, with activation rescuing both cell division and cell death. To study this cohesinopathy in a whole animal model we used ESCO2-mutant and morphant zebrafish embryos, which have developmental defects mimicking RBS. Consistent with RBS patient cells, the ESCO2 mutant embryos show p53 activation and inhibition of the TOR pathway. Stimulation of the TOR pathway with L-leucine rescued many developmental defects of ESCO2-mutant embryos. Our data support the idea that RBS can be attributed in part to defects in ribosome biogenesis, and stimulation of the TOR pathway has therapeutic potential.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetyltransferases / genetics*
  • Animals
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism
  • Chromosomal Proteins, Non-Histone / genetics*
  • Chromosomal Proteins, Non-Histone / metabolism
  • Chromosome Segregation
  • Cohesins
  • Craniofacial Abnormalities / genetics*
  • Craniofacial Abnormalities / metabolism
  • Ectromelia / genetics*
  • Ectromelia / metabolism
  • Embryonic Development
  • Humans
  • Hypertelorism / genetics*
  • Hypertelorism / metabolism
  • Leucine / genetics*
  • Mechanistic Target of Rapamycin Complex 1
  • Multiprotein Complexes / genetics*
  • Multiprotein Complexes / metabolism
  • RNA, Ribosomal / genetics
  • Signal Transduction
  • TOR Serine-Threonine Kinases / genetics*
  • TOR Serine-Threonine Kinases / metabolism
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / metabolism
  • Zebrafish / embryology

Substances

  • Cell Cycle Proteins
  • Chromosomal Proteins, Non-Histone
  • Multiprotein Complexes
  • RNA, Ribosomal
  • TP53 protein, human
  • Tumor Suppressor Protein p53
  • Acetyltransferases
  • ESCO2 protein, human
  • Mechanistic Target of Rapamycin Complex 1
  • TOR Serine-Threonine Kinases
  • Leucine

Supplementary concepts

  • Roberts Syndrome

Grants and funding

This work was funded by the Stowers Institute for Medical Research. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.