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Single-stranded DNA-binding proteins regulate the abundance of LIM domain and LIM domain-binding proteins

Zhixiong Xu1, Xianzhang Meng, Ying Cai

  • 1Department of Medicine, Vanderbilt University, Nashville, Tennessee 37232, USA.

Genes & Development
|April 18, 2007
PubMed

Insights

Single-stranded DNA-binding proteins (SSBPs) like SSBP2 regulate key developmental proteins, Ldb1 and Lmo2, by preventing their degradation. This enhances erythroid gene expression and DNA-binding activity.

Area of Science:

  • Molecular Biology
  • Developmental Biology
  • Genetics

Background:

  • LIM domain-binding protein (Ldb1) is a crucial cofactor for LIM-homeodomain (LIM-HD) and LIM-only (LMO) proteins during development.
  • The precise stoichiometry of Ldb1, LIM-HD, and LMO proteins is critical for their biological functions.
  • Single-stranded DNA-binding proteins (SSBPs) have recently been identified as Ldb1 interactors with roles in development.

Purpose of the Study:

  • To investigate the role of mammalian SSBPs, specifically SSBP2 and SSBP3, in erythroid DNA-binding complexes.
  • To elucidate the mechanism by which SSBP2 influences the activity and stability of Ldb1 and LMO proteins.
  • To determine the impact of SSBP2 on the transcription of erythroid-specific genes.

Main Methods:

  • Formation of an erythroid DNA-binding complex involving Tal1, GATA-1, Lmo2, Ldb1, SSBP2, and SSBP3.
  • Assessing the effect of SSBP2 on Protein 4.2 (P4.2) gene transcription in an Ldb1-dependent manner.
  • Evaluating the impact of SSBP2 on endogenous Ldb1 and Lmo2 protein levels and DNA-binding activity.
  • Investigating the interaction between SSBP2, Ldb1, Lmo2, and the E3 ubiquitin ligase RLIM.
  • Monitoring Ldb1 ubiquitination and proteasomal degradation.

Main Results:

  • SSBP2 and SSBP3 are components of an erythroid DNA-binding complex with Tal1, GATA-1, Lmo2, and Ldb1, recognizing an E-box-GATA motif.
  • SSBP2 enhances Ldb1-dependent transcription of the P4.2 gene and increases expression of P4.2 and beta-globin in erythroid progenitors.
  • SSBP2 inhibits the interaction of Ldb1 and Lmo2 with RLIM, preventing Ldb1 ubiquitination and subsequent proteasomal degradation.
  • SSBP2 increases endogenous Ldb1 and Lmo2 protein levels and E-box-GATA DNA-binding activity.

Conclusions:

  • SSBPs, particularly SSBP2, play a novel role in regulating the stability and abundance of Ldb1 and LMO proteins.
  • SSBP2 protects Ldb1 and Lmo2 from RLIM-mediated degradation, thereby promoting erythroid differentiation.
  • These findings reveal a new biochemical function for SSBPs in controlling the levels of key developmental transcription factors.

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