ABSTRACT
The most common translocation in childhood T-cell acute lymphoblastic leukemia (T-ALL) involves the LMO2 locus, resulting in ectopic expression of the LMO2 gene in human thymocytes. The LMO2 gene was also activated in patients with X-linked Severe Combined Immune Deficiency treated with gene therapy because of retroviral insertion in the LMO2 locus. The LMO2 insertions predisposed these children to T-ALL, yet how LMO2 contributes to T cell transformation remains unclear. The LIM (Lin 11, Isl-1, Mec-3) domain containing LMO2 protein regulates erythropoiesis as part of a large transcriptional complex consisting of LMO2, TAL1, E47, GATA1 and LDB1 that recognizes bipartite E-box-GATA1 sites on target genes. Similarly, a TAL1/E47/LMO2/LDB1 complex is observed in human T-ALL and Tal1 and Lmo2 expression in mice results in disease acceleration. To address the mechanism(s) of Tal1/Lmo2 synergy in leukemia, we generated Lmo2 transgenic mice and mated them with mice that express wild-type Tal1 or a DNA-binding mutant of TAL1. Tal1/Lmo2 and MutTAL1/Lmo2 bitransgenic mice exhibit perturbations in thymocyte development due to reduced E47/HEB transcriptional activity and develop leukemia with identical kinetics. These data demonstrate that the DNA-binding activity of Tal1 is not required to cooperate with Lmo2 to cause leukemia in mice and suggest that Lmo2 may cooperate with Tal1 to interfere with E47/HEB function(s).
Subject(s)
Basic Helix-Loop-Helix Transcription Factors/genetics , DNA-Binding Proteins/genetics , Gene Expression Regulation, Neoplastic/genetics , Leukemia, T-Cell/genetics , Metalloproteins/genetics , Proto-Oncogene Proteins/genetics , T-Lymphocytes/pathology , Adaptor Proteins, Signal Transducing , Animals , Basic Helix-Loop-Helix Transcription Factors/metabolism , Blotting, Southern , Cell Differentiation/genetics , Cell Separation , Chromatin Immunoprecipitation , DNA-Binding Proteins/metabolism , Flow Cytometry , Gene Expression , LIM Domain Proteins , Leukemia, T-Cell/metabolism , Leukemia, T-Cell/pathology , Metalloproteins/metabolism , Mice , Mice, Transgenic , Mutation , Proto-Oncogene Proteins/metabolism , Reverse Transcriptase Polymerase Chain Reaction , T-Cell Acute Lymphocytic Leukemia Protein 1 , Transcription Factor 3/genetics , Transcription Factor 3/metabolismABSTRACT
Large-scale genetic analyses of human tumor samples have been used to identify novel oncogenes, tumor suppressors and prognostic factors, but the functions and molecular interactions of many individual genes have not been determined. In this study we examined the cellular effects and molecular mechanism of the arrestin family member, ARRDC3, a gene preferentially lost in a subset of breast cancers. Oncomine data revealed that the expression of ARRDC3 decreases with tumor grade, metastases and recurrences. ARRDC3 overexpression represses cancer cell proliferation, migration, invasion, growth in soft agar and in vivo tumorigenicity, whereas downregulation of ARRCD3 has the opposite effects. Mechanistic studies showed that ARRDC3 functions in a novel regulatory pathway that controls the cell surface adhesion molecule, beta-4 integrin (ITGbeta4), a protein associated with aggressive tumor behavior. Our data indicates ARRDC3 directly binds to a phosphorylated form of ITGbeta4 leading to its internalization, ubiquitination and ultimate degradation. The results identify the ARRCD3-ITGbeta4 pathway as a new therapeutic target in breast cancer and show the importance of connecting genetic arrays with mechanistic studies in the search for new treatments.
