Sumoylation is important for stability, subcellular localization, and transcriptional activity of SALL4, an essential stem cell transcription factor

J Biol Chem. 2012 Nov 9;287(46):38600-8. doi: 10.1074/jbc.M112.391441. Epub 2012 Sep 25.

Abstract

SALL4 is a transcription factor that plays a key role in the maintenance and self-renewal of embryonic stem cells and hematopoietic stem cells. Given that little is known about regulation of SALL4, we studied biochemical modifications of SALL4B, a major splicing variant of SALL4, and elucidated their biological function. SALL4B was primarily modified by ubiquitination when it was expressed in both Sf9 and HEK293T cells. A significant fraction of SALL4B was further modified by sumoylation when it was expressed in HEK293T cells. Constitutive SUMO-modification of SALL4B was also detected in Tera-1, a cell line of the teratocarcinoma origin. SALL4B sumoylation was independent of ubiquitination and lysine residues 156, 316, 374, and 401 were essential for sumoylation. Chromatin fraction contained more SUMO-deficient SALL4B. Despite a shorter half-life than the wild-type counterpart, SUMO-deficient SALL4B interacted with OCT4 more efficiently than the wild-type SALL4B. RNAi-mediated silencing of SALL4 expression caused significant down-regulation of both OCT4 and SOX2, which was rescued by ectopic expression of SALL4B but not by SUMO-deficient mutant. Significantly, compared with the wild-type SALL4B, SUMO-deficient mutant exhibited compromised trans-activation or trans-repression activities in reporter gene assays. Combined, our studies reveal sumoylation as a novel form of post-translational modification for regulating the stability, subcellular localization, and transcriptional activity of SALL4.

Publication types

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

MeSH terms

  • Animals
  • Cell Line, Tumor
  • Genes, Reporter
  • HEK293 Cells
  • HeLa Cells
  • Humans
  • Jurkat Cells
  • Lysine / chemistry
  • Octamer Transcription Factor-3 / metabolism
  • RNA Interference
  • Stem Cells / cytology*
  • Sumoylation
  • Transcription Factors / metabolism*
  • Transcription, Genetic*
  • Transcriptional Activation

Substances

  • Octamer Transcription Factor-3
  • POU5F1 protein, human
  • SALL4 protein, human
  • Transcription Factors
  • Lysine