Nucleo-cytoplasmic localization domains regulate Krüppel-like factor 6 (KLF6) protein stability and tumor suppressor function

PLoS One. 2010 Sep 9;5(9):e12639. doi: 10.1371/journal.pone.0012639.


Background: The tumor suppressor KLF6 and its oncogenic cytoplasmic splice variant KLF6-SV1 represent a paradigm in cancer biology in that their antagonistic cancer functions are encoded within the same gene. As a consequence of splicing, KLF6-SV1 loses both the C-terminus C2H2 three zinc finger (ZF) domain, which characterizes all KLF proteins, as well as the adjacent 5' basic region (5BR), a putative nuclear localization signal (NLS). It has been hypothesized that this NLS is a functional domain critical to direct the distinct subcellular localization of the tumor suppressor and its splice variant.

Methodology/principal findings: In this study, we demonstrate using EGFP fusion constructs that KLF6/KLF6-SV1 nucleo-cytoplasmic transport is not regulated by the 5' basic region but activated by a novel NLS encoded within the ZF domain, and a nuclear export signal (NES) located in the first 16 amino acids of the shared N-terminus sequence. We demonstrate KLF6 nuclear export to be Crm1-dependent. The dysregulation of nucleo-cytoplasmic transport when disrupting the KLF6 NLS using site-directed mutagenesis showed that its integrity is necessary for appropriate protein stability. Moreover, these mutations impaired transcriptional induction of two KLF6 well-characterized target genes, E-cadherin and p21, as shown by RT-PCR and luciferase promoter assays. The addition of the ZF domain to KLF6-SV1 results in its nuclear localization and a markedly decreased half-life similar to wild type KLF6.

Conclusions/significance: We describe the domains that control KLF6 nucleo-cytoplasmic shuttling and how these domains play a role in KLF6 protein half-life and tumor suppressor function. The results begin to mechanistically explain, at least in part, the opposing functions of KLF6 and KLF6-SV1 in cancer.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Active Transport, Cell Nucleus
  • Amino Acid Sequence
  • Cell Line
  • Cell Nucleus / chemistry
  • Cell Nucleus / genetics
  • Cell Nucleus / metabolism*
  • Half-Life
  • Humans
  • Kruppel-Like Factor 6
  • Kruppel-Like Transcription Factors / chemistry*
  • Kruppel-Like Transcription Factors / genetics
  • Kruppel-Like Transcription Factors / metabolism*
  • Molecular Sequence Data
  • Nuclear Export Signals
  • Nuclear Localization Signals
  • Protein Stability
  • Protein Structure, Tertiary
  • Proto-Oncogene Proteins / chemistry*
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism*


  • KLF6 protein, human
  • Kruppel-Like Factor 6
  • Kruppel-Like Transcription Factors
  • Nuclear Export Signals
  • Nuclear Localization Signals
  • Proto-Oncogene Proteins