LDB1 Enforces Stability on Direct and Indirect Oncoprotein Partners in Leukemia

Mol Cell Biol. 2020 May 28;40(12):e00652-19. doi: 10.1128/MCB.00652-19. Print 2020 May 28.

Abstract

The LMO2/LDB1 macromolecular complex is critical in hematopoietic stem and progenitor cell specification and in the development of acute leukemia. This complex is comprised of core subunits of LMO2 and LDB1 as well as single-stranded DNA-binding protein (SSBP) cofactors and DNA-binding basic helix-loop-helix (bHLH) and GATA transcription factors. We analyzed the steady-state abundance and kinetic stability of LMO2 and its partners via Halo protein tagging in conjunction with variant proteins deficient in binding their respective direct protein partners. We discovered a hierarchy of protein stabilities (with half-lives in descending order) as follows: LDB1 > SSBP > LMO2 > TAL1. Importantly, LDB1 is a remarkably stable protein that confers enhanced stability upon direct and indirect partners, thereby nucleating the formation of the multisubunit protein complex. The data imply that free subunits are more rapidly degraded than those incorporated within the LMO2/LDB1 complex. Our studies provided significant insights into LMO2/LDB1 macromolecular protein complex assembly and stability, which has implications for understanding its role in blood cell formation and for therapeutically targeting this complex in human leukemias.

Keywords: LIM domain Only 2; LIM domain protein 1; hematopoietic stem cell; leukemia; multisubunit complex; protein degradation; protein turnover; pulse-chase.

Publication types

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

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism
  • Cell Line, Tumor
  • DNA-Binding Proteins / metabolism*
  • HEK293 Cells
  • Humans
  • LIM Domain Proteins / metabolism*
  • Leukemia / metabolism*
  • Mitochondrial Proteins / metabolism
  • Oncogene Proteins / metabolism*
  • Proteasome Endopeptidase Complex / metabolism
  • Protein Binding
  • Protein Stability
  • Proteolysis
  • Proto-Oncogene Proteins / metabolism
  • T-Cell Acute Lymphocytic Leukemia Protein 1 / metabolism
  • Transcription Factors / metabolism*
  • Ubiquitin / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • DNA-Binding Proteins
  • LDB1 protein, human
  • LIM Domain Proteins
  • LMO2 protein, human
  • Mitochondrial Proteins
  • Oncogene Proteins
  • Proto-Oncogene Proteins
  • SSBP1 protein, human
  • T-Cell Acute Lymphocytic Leukemia Protein 1
  • Transcription Factors
  • Ubiquitin
  • TAL1 protein, human
  • Proteasome Endopeptidase Complex