Analysis of T-Cell Leukemia/Lymphoma (TCL1) Oncoprotein Interacting Proteins by Immunoprecipitation and Tandem Mass Spectrometry.

TCL1 is a proto-oncogene whose deregulation has been implicated in the pathogenesis of T- and B-cell lymphoproliferative disorders. TCL1 expression is predominantly observed in developing B lymphocytes, whereas its overexpression in T cells is associated with mature T-cell lymphoproliferation in transgenic mice. Although recent studies indicate that dysregulated expression of TCL1 is important in mature B-cell transformation, very little is currently known about the function or interactions of TCL1, specifically in the B-cell context. In this study, we hypothesized that identification of proteins that interact with TCL1 may facilitate our understanding of the functional properties of TCL1. Proteomic analysis provides an opportunity to carry out functional studies of protein-protein interactions and characterization of functional interactomes. Using a functional proteomic approach, we determined the identity of proteins that interact with TCL1 by co-immunoprecipitation with anti-TCL1 antibody followed by liquid chromatography (LC), electrospray ionization (ESI) and tandem mass spectrometry (MS/MS). Immunoprecipitates of the TCL1 expressing SUDHL-16 B-cell lymphoma derived cell line were compared to that of hyperimmune rabbit immunoglobulin and a cell line that does not express TCL1 (SUDHL-1) by 1-dimensional sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Silver-stained protein bands from both immunocomplexes were excised and analyzed by ESI-LC-MS/MS. Proteins which were unique to the TCL1 immunocomplex included transcription factors (Jun B), phosphatases (protein phosphatase 2), ubiquitin-associated proteins (ubiquitin activating enzyme), cell adhesion proteins (ADP ribosylation factor 3) and proteins associated with apoptosis regulation (peroxidoxin 1 and scaffold attachment factor). Analysis of subcellular fractions demonstrated that TCL1 and complexes were localized to both the nuclear and cytoplasmic compartments. Importantly, known TCL1 interactors such as histone 3 were uniquely identified in the TCL1 complex. Proteins identified by MS were confirmed by western blotting and reciprocal immunoprecipitation. This study reveals novel TCL1 interactors and indicates that the protein may exert diverse cellular effects impacting apoptosis, cell survival, cytoskeletal organization and cell adhesion. Our interactome analysis provides unique insights into the cellular function of TCL1, a protein whose deregulation is increasingly implicated in the pathogenesis of a variety of hematopoietic neoplasms.