Natural helix 9 mutants of PPARγ differently affect its transcriptional activity

Mol Metab. 2019 Feb:20:115-127. doi: 10.1016/j.molmet.2018.12.005. Epub 2018 Dec 16.

Abstract

Objective: The nuclear receptor PPARγ is the master regulator of adipocyte differentiation, distribution, and function. In addition, PPARγ induces terminal differentiation of several epithelial cell lineages, including colon epithelia. Loss-of-function mutations in PPARG result in familial partial lipodystrophy subtype 3 (FPDL3), a rare condition characterized by aberrant adipose tissue distribution and severe metabolic complications, including diabetes. Mutations in PPARG have also been reported in sporadic colorectal cancers, but the significance of these mutations is unclear. Studying these natural PPARG mutations provides valuable insights into structure-function relationships in the PPARγ protein. We functionally characterized a novel FPLD3-associated PPARγ L451P mutation in helix 9 of the ligand binding domain (LBD). Interestingly, substitution of the adjacent amino acid K450 was previously reported in a human colon carcinoma cell line.

Methods: We performed a detailed side-by-side functional comparison of these two PPARγ mutants.

Results: PPARγ L451P shows multiple intermolecular defects, including impaired cofactor binding and reduced RXRα heterodimerisation and subsequent DNA binding, but not in DBD-LBD interdomain communication. The K450Q mutant displays none of these functional defects. Other colon cancer-associated PPARγ mutants displayed diverse phenotypes, ranging from complete loss of activity to wildtype activity.

Conclusions: Amino acid changes in helix 9 can differently affect LBD integrity and function. In addition, FPLD3-associated PPARγ mutations consistently cause intra- and/or intermolecular defects; colon cancer-associated PPARγ mutations on the other hand may play a role in colon cancer onset and progression, but this is not due to their effects on the most well-studied functional characteristics of PPARγ.

Keywords: Adipose tissue; FPLD3; Lipodystrophy; Nuclear receptor; PPARG.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Binding Sites
  • Cell Line, Tumor
  • Colorectal Neoplasms / genetics
  • Colorectal Neoplasms / pathology
  • Female
  • HEK293 Cells
  • Humans
  • Lipodystrophy, Familial Partial / genetics*
  • Lipodystrophy, Familial Partial / pathology
  • Mutation, Missense*
  • PPAR gamma / chemistry
  • PPAR gamma / genetics*
  • PPAR gamma / metabolism
  • Phenotype
  • Protein Multimerization

Substances

  • PPAR gamma
  • PPARG protein, human