title: LMO2 Oncoprotein Stability in T-Cell Leukemia Requires Direct LDB1 Binding.
abstract: LMO2 is a component of multisubunit DNA-binding transcription factor complexes that regulate gene expression in hematopoietic stem and progenitor cell development. Enforced expression of LMO2 causes leukemia by inducing hematopoietic stem cell-like features in T-cell progenitor cells, but the biochemical mechanisms of LMO2 function have not been fully elucidated. In this study, we systematically dissected the LMO2/LDB1-binding interface to investigate the role of this interaction in T-cell leukemia. Alanine scanning mutagenesis of the LIM interaction domain of LDB1 revealed a discrete motif, R(320)LITR, required for LMO2 binding. Most strikingly, coexpression of full-length, wild-type LDB1 increased LMO2 steady-state abundance, whereas coexpression of mutant proteins deficient in LMO2 binding compromised LMO2 stability. These mutant LDB1 proteins also exerted dominant negative effects on growth and transcription in diverse leukemic cell lines. Mass spectrometric analysis of LDB1 binding partners in leukemic lines supports the notion that LMO2/LDB1 function in leukemia occurs in the context of multisubunit complexes, which also protect the LMO2 oncoprotein from degradation. Collectively, these data suggest that the assembly of LMO2 into complexes, via direct LDB1 interaction, is a potential molecular target that could be exploited in LMO2-driven leukemias resistant to existing chemotherapy regimens.
authors.affiliation: Departments of Medicine and Cancer Biology, Division of Hematology and Oncology, Tennessee Valley Healthcare System, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
authors.forename: Justin H
authors.initials: JH
authors.lastname: Layer
authors.affiliation: Department of Pathology and Laboratory Medicine, Tennessee Valley Healthcare System, Nashville, Tennessee, USA.
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Alford
authors.affiliation: Mass Spectrometry Research Center, Vanderbilt University, Nashville, Tennessee, USA.
authors.forename: W Hayes
authors.initials: WH
authors.lastname: McDonald
authors.affiliation: Departments of Medicine and Cancer Biology, Division of Hematology and Oncology, Tennessee Valley Healthcare System, Vanderbilt University Medical Center, Nashville, Tennessee, USA utpal.dave@vanderbilt.edu.
authors.forename: Utpal P
authors.initials: UP
authors.lastname: Davé
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D060588:LIM Domain Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015458:Leukemia, T-Cell / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D054730:Protein Interaction Domains and Motifs; D060066:Protein Interaction Maps; D055550:Protein Stability; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; C486312:LDB1 protein, human; D060588:LIM Domain Proteins; C085117:LMO2 protein, human; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors