ABSTRACT
AVEN has been identified as an inhibitor of apoptosis, which binds to the adaptor protein, APAF-1, and thereby prevents apoptosome formation and mitochondrial apoptosis. Recent data have demonstrated high expression levels of AVEN messenger RNA in acute leukemias as well as a positive correlation between AVEN mRNA overexpression and poor prognosis in childhood acute lymphoblastic leukemia. On the basis of these data, we investigated the potential involvement of AVEN in tumorigenesis. First, we confirmed the overexpression of AVEN in T-cell acute lymphoblastic leukemia/lymphoma (T-ALL) patient samples. We then established a transgenic mouse model with T-cell-specific overexpression of AVEN, with which we demonstrated the oncogenic cooperation of AVEN with heterozygous loss of p53. Finally, we used a subcutaneous xenograft mouse model to show that AVEN knockdown in the T-ALL cell lines, MOLT-4 and CCRF-CEM, and in the acute myeloblastic leukemia cell line, Kasumi-1, leads to a halt in tumor growth owing to the increased apoptosis and decreased proliferation of tumor cells. Collectively, our data demonstrate that the anti-apoptotic molecule, AVEN, functions as an oncoprotein in hematopoietic neoplasms.
Subject(s)
Adaptor Proteins, Signal Transducing/genetics , Apoptosis Regulatory Proteins/genetics , Membrane Proteins/genetics , Precursor Cell Lymphoblastic Leukemia-Lymphoma/genetics , Precursor T-Cell Lymphoblastic Leukemia-Lymphoma/genetics , Adaptor Proteins, Signal Transducing/metabolism , Animals , Apoptosis Regulatory Proteins/metabolism , Base Sequence , Cell Line, Tumor , Gene Expression Regulation, Leukemic , Gene Knockdown Techniques , Genes, p53 , Humans , Lymphoma, T-Cell/genetics , Membrane Proteins/metabolism , Mice , Mice, Inbred C57BL , Mice, Transgenic , Molecular Sequence Data , Precursor T-Cell Lymphoblastic Leukemia-Lymphoma/pathology , Thymocytes/physiology , Xenograft Model Antitumor AssaysABSTRACT
The anti-apoptotic molecule Aven was originally identified in a yeast two-hybrid screen for Bcl-x(L)-interacting proteins and has also been found to bind Apaf-1, thereby interfering with Apaf-1 self-association during apoptosome assembly. Aven is expressed in a wide variety of adult tissues and cell lines, and there is increasing evidence that its overexpression correlates with tumorigenesis, particularly in acute leukemias. The mechanism by which the anti-apoptotic activity of Aven is regulated remains poorly understood. Here we shed light on this issue by demonstrating that proteolytic removal of an inhibitory N-terminal Aven domain is necessary to activate the anti-apoptotic potential of the molecule. Furthermore, we identify Cathepsin D (CathD) as the protease responsible for Aven cleavage. On the basis of our results, we propose a model of Aven activation by which its N-terminal inhibitory domain is removed by CathD-mediated proteolysis, thereby unleashing its cytoprotective function.
