HTLV-1 is the etiological agent of adult T-cell leukemia lymphoma (ATLL). ATLL cells are characterized by constitutive NF?B activation, a key feature of other lymphomas, myeloma, and solid tumors. The Tax oncoprotein is the key viral determinant for NF?B activation. Our previous studies showed that the classical and especially, the alternative NF?B pathways were critical in conferring resistance to apoptosis. The current study will use innovative, physiological lymphoma models to define the role in tumorigenesis of each NF?B pathway and identify the key NF?B target gene responsible for these effects.
Aim 1. Which NF?B pathway is critical for HTLV tumorigenesis in humanized mice? In this study, a new humanized mouse model is used for HTLV-1 infection and lymphoma development. We will use viral variants expressing Tax mutants with defects in activating the alternative NF?B pathway or both NF?B pathways, in order to define their role in disease pathogenesis. A novel high-throughput viral integration assay is used to monitor clonality of infected cells over the course o these experiments.
Aim 2. Which NF?B targets are required for maintenance and progression of Tax transgenic tumors? In this study, a new inducible Tax transgenic mouse model of lymphoma is utilized to assess the role of specific NF?B target genes in tumor progression using microarray analysis.
Aim 3. Which NF?B target genes are critical for HTLV transformation? In this study, shRNAs to NF?B1 (p105) and NF?B2 (p100) are used to assess each individual pathway. HTLV-1 transformed cells expressing one of both of these shRNAs will be subjected to microarray analysis to determine which pathway is responsible for activation of specific target genes. Moreover, their contribution of select NF?B target genes to resistance to apoptosis will be assessed. It is expected that the information these physiologically relevant mouse models will identify key target genes that may be inhibited in therapeutic trials of ATLL or other lymphomas.
The proposed research program uses mouse models of lymphoma (cancer of lymphocytes) caused by human T cell leukemia virus type 1 (HTLV-1). Our hypothesis is that the most important HTLV-1 gene for causing lymphoma is Tax. Moreover, we propose that the lymphoma-causing ability of Tax is linked to its ability to activate the nuclea kappa B (NF?B) pathway. NFkB is a family of DNA binding proteins that induce the expression of a number of genes. Our goal is to identify the specific genes turned on by Tax and NF?B that are most important for the development and progression of lymphoma. Our first aim utilizes a new model whereby human lymphocytes are reconstituted in immunodeficient mice. These humanized mice can be infected with HTLV-1, which replicates and causes lymphoma. We will use specific HTLV-1 variants which have alterations in their Tax sequence that result in defective NF?B activity. This assay allows us to assess the role of Tax activation of NF?B in a model that reproduces important aspects of HTLV-1 infection and lymphoma development. The second aim utilizes a different mouse model in which Tax alone is expressed, but only when mice are fed the antibiotic doxycycline. These mice develop lymphomas, which resolve when doxycycline is taken out of their diet. We will use tumors from these animals at different times after withdrawing doxycycline to determine if specific NF?B bound genes are altered as tumors resolve. These genes are most likely important for tumor progression. The third aim uses HTLV-1 immortalized cell lines derived from Aim 1. In these experiments, we will shut- off specific arms of the NF?B pathway and examine the consequences on tumor cell line growth and survival. The genes binding NFkB that are shut-off in each case will be examined to determine their individual roles in tumor cell line growth and survival in culture and after transplantation nto mice. Results from these model models will be compared to those from lymphomas characterized by high levels of NF?B. Our work will identify new targets for therapy that will be addressed in our clinical lymphoma trials. The strength of our research program has and will be based on 1) use of state-of-the-art genetic and animal techniques, 2) use of physiologically relevant tumor models, and 3) application of our preclinical findings into clinical studies.
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