Overexpression of the anti-apoptotic protein AVEN contributes to increased malignancy in hematopoietic neoplasms.

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.

The Apaf-1-binding protein Aven is cleaved by Cathepsin D to unleash its anti-apoptotic potential.

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.

Human tumor xenografts in athymic (nude) mice: chemotherapy trials in serially transplanted tumors.

In a total of 38 consecutive attempts at transplanting freshly excised malignant human neoplasms in athymic nu/nu mice during the past year, 12 resulted in successful xenografts. To date, all of these have been subsequently transplanted for two or more generations. These successful xenografts include two squamous cell carcinomas of the head and neck, three squamous cell carcinomas and one undifferentiated large cell carcinoma of the lung, three adenocarcinomas of ovarian or endometrial origin, and one carcinoma of each of the following sites: urinary bladder, stomach, and colon. Chemotherapy trials on three different squamous cell carcinomas serially transplanted in nude mice revealed three different degrees of sensitivity to bleomycin. One tumor which was markedly sensitive to bleomycin showed only a slight response to cis-diamminedichloroplatinum (II). These chemotherapy trials will be expanded to wider panel of transplantable human squamous cells cacinomas of different origins with anti-tumor agents used singly or in combination.