Human C-terminally truncated ERα variants resulting from the use of alternative exons in the ligand-binding domain

Mol Cell Endocrinol. 2016 Apr 15;425:111-22. doi: 10.1016/j.mce.2016.01.026. Epub 2016 Feb 4.

Abstract

The nuclear receptor genes contain alternative internal and terminal exons, with alternative exon incorporation yielding mRNA variants that encode various receptor types, including some with C-terminal truncation that exhibit constitutive activation or dominant-negative transcriptional transactivation. However, C-terminally truncated estrogen receptor α (ERα) variants with alternative sequences have rarely been reported in humans. Therefore, we assessed human ERα genomic organization and alternative splicing profiles, and identified both alternative exons and C-terminally truncated ERα variants. These naturally occurring C-terminally truncated ERα proteins were localized in the nuclei of transfected cells. In addition, ERαi45c and ERαΔ5 variants exhibited constitutive transactivation of an estrogen responsive element-driven promoter in transfected cells. We manufactured expression vectors encoding artificially truncated ERα constructs and evaluated their transactivation abilities to establish mechanisms determining the constitutive activity and dominant-negative properties of truncated variants. Lack of the region encoded in exon 8 eliminated basal and ligand-induced transcriptional transactivation. The C-terminally truncated ERα variants/constructs containing the helices 5 in their ligand-binding domains did not exhibit constitutive transactivation. Furthermore, we demonstrated that truncation from C-termini to helices 5 in the variant ligand-binding domains was required for constitutive activation and found that the remnant regions of the ligand-binding domains and variant-specific sequences influenced transcriptional transactivation efficiency. In conclusion, we elucidated the structural and functional features of novel C-terminally truncated ERα variants and revealed the mechanisms underlying constitutive transactivation by C-terminally truncated nuclear receptor variants.

Keywords: Alternative splicing; Constitutive transactivation; Estrogen; Estrogen receptor α; Helical motifs; Splice variant.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alternative Splicing*
  • Animals
  • Binding Sites
  • COS Cells
  • Chlorocebus aethiops
  • Estrogen Receptor alpha / chemistry*
  • Estrogen Receptor alpha / genetics*
  • Estrogen Receptor alpha / metabolism
  • Exons
  • Genetic Variation
  • HEK293 Cells
  • Hep G2 Cells
  • Humans
  • Ligands
  • Models, Molecular
  • Promoter Regions, Genetic
  • Protein Structure, Secondary
  • Protein Structure, Tertiary

Substances

  • ESR1 protein, human
  • Estrogen Receptor alpha
  • Ligands