Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults. According to the National Cancer Institute, approximately 16,060 patients will be diagnosed with CLL and approximately 4,580 patients will die of CLL in the US in 2012. At the Moffitt Cancer Center in Tampa, Florida, we see about 200 new CLL patients each year. Although CLL initially responds to chemotherapy, the relapsed CLL occurs at a high rate and acquires chemoresistance. Therefore, CLL is still incurable. We propose to identify the critical mechanisms that CLL cells rely on for their survival and target one such mechanism to block or decelerate aggressive progression of CLL. Robust B cell receptor (BCR) signal transduction was suggested to be responsible for the rapid proliferation of CLL cells, leading to aggressive progression of disease. Although protein antigen has been suggested to trigger the growth and proliferation of CLL cells, this concept that antigen can drive malignant progression of CLL has not been recapitulated in an animal model. Therefore, we have created a novel antigen-specific CLL mouse model, in which we use a desired antigen to activate the BCR and drive malignant progression of CLL. When a B cell is stimulated by its cognate antigen, activation of the endoplasmic reticulum (ER) stress response occurs to support B cell growth and proliferation. We hypothesize that engagement of the BCR by protein antigen can activate the ER stress response in CLL cells to promote malignant progression of CLL in vivo. We have shown that the inositol-requiring enzyme-1 (IRE-1)/X-box- binding protein-1 (XBP-1) pathway of the ER stress response is critical for the survival of CLL cells. Blocking the expression of XBP-1 by a novel small-molecule chemical inhibitor induces apoptosis in CLL cells in culture. To better understand the role of the IRE-1/XBP-1 pathway in the progression of CLL, we have genetically deleted the XBP-1 gene from our novel antigen-specific CLL mouse model. Using this innovative mouse model together with our novel small-molecule inhibitors, we will investigate the mechanisms by which blocking the IRE-1/XBP-1 pathway can decelerate antigen-induced aggressive progression of CLL in vivo. In cells with genetic deletion or chemical knockdown of XBP-1, we observed that IRE-1 is expressed at an elevated level and acquires a unique phosphorylation pattern. IRE-1 has been known for its roles in promoting cell survival and inducing apoptosis, but it is still unclear how IRE-1 accomplishes these two seemingly opposing tasks. We hypothesize that differential phosphorylation patterns may allow IRE-1 to associate with different interacting partners to carry out its functions in promoting survival or inducing apoptosis in CLL. Our goals in this proposal are summarized by two aims: 1) Target the IRE-1/XBP-1 pathway in antigen-induced aggressive progression of CLL in vivo;2) Identify and investigate proteins that interact with IRE-1 to further understand how targeting the IRE-1/XBP-1 pathway can lead to stalled progression of CLL. Our goal is to establish the ER stress response as a useful target for the treatment of CLL.

Public Health Relevance

In this project, we will study how exposure to protein antigen can activate the B cell receptor (BCR) and evoke the endoplasmic reticulum (ER) stress response to promote malignant progression of chronic lymphocytic leukemia (CLL) in mice. We have produced the first antigen-specific CLL mouse model to allow for activation of the BCR to study the contribution of the antigen-induced ER stress response in CLL. Since we have demonstrated that targeting the ER stress response using small-molecule chemical inhibitors can induce CLL cell death in culture, we will further study how blocking the ER stress response pathway can decelerate malignant progression of CLL in vivo. To achieve our goal, we will use both a genetic approach and chemical inhibitors to block the ER stress response pathway in mice. We believe that the knowledge of targeting the ER stress response gained from this research will help us design new therapeutic strategies to benefit patients with CLL.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Basic Mechanisms of Cancer Therapeutics Study Section (BMCT)
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Howcroft, Thomas K
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H. Lee Moffitt Cancer Center & Research Institute
United States
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Tang, Chih-Hang Anthony; Chang, Shiun; Paton, Adrienne W et al. (2018) Phosphorylation of IRE1 at S729 regulates RIDD in B cells and antibody production after immunization. J Cell Biol 217:1739-1755
Betts, Brian C; Locke, Frederick L; Sagatys, Elizabeth M et al. (2018) Inhibition of Human Dendritic Cell ER Stress Response Reduces T Cell Alloreactivity Yet Spares Donor Anti-tumor Immunity. Front Immunol 9:2887
Bagashev, Asen; Sotillo, Elena; Tang, Chih-Hang Anthony et al. (2018) CD19 alterations emerging after CD19-directed immunotherapy cause retention of the misfolded protein in the endoplasmic reticulum. Mol Cell Biol :
Tang, Chih-Hang; Chang, Shiun; Hashimoto, Ayumi et al. (2018) Secretory IgM Exacerbates Tumor Progression by Inducing Accumulations of MDSCs in Mice. Cancer Immunol Res 6:696-710
Schutt, Steven D; Wu, Yongxia; Tang, Chih-Hang Anthony et al. (2018) Inhibition of the IRE-1?/XBP-1 pathway prevents chronic GVHD and preserves the GVL effect in mice. Blood Adv 2:414-427
Xie, Hong; Tang, Chih-Hang Anthony; Song, Jun H et al. (2018) IRE1? RNase-dependent lipid homeostasis promotes survival in Myc-transformed cancers. J Clin Invest 128:1300-1316
De Leo, Alessandra; Chen, Horng-Shen; Hu, Chih-Chi Andrew et al. (2017) Deregulation of KSHV latency conformation by ER-stress and caspase-dependent RAD21-cleavage. PLoS Pathog 13:e1006596
Tavernier, Simon J; Osorio, Fabiola; Vandersarren, Lana et al. (2017) Regulated IRE1-dependent mRNA decay sets the threshold for dendritic cell survival. Nat Cell Biol 19:698-710
Tang, Chih-Hang Anthony; Zundell, Joseph A; Ranatunga, Sujeewa et al. (2016) Agonist-Mediated Activation of STING Induces Apoptosis in Malignant B Cells. Cancer Res 76:2137-52
Zhao, Chenguang; Brown, Rebecca S H; Tang, Chih-Hang Anthony et al. (2016) Site-specific Proteolysis Mobilizes TorsinA from the Membrane of the Endoplasmic Reticulum (ER) in Response to ER Stress and B Cell Stimulation. J Biol Chem 291:9469-81

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