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Liu FR, Wei XL, Feng WN, Zhao HY, Zhang Y, Wang ZQ, Zhang DS, Wang FH, Yang S, Pan W, Tian X, Men L, Wang H, Liang E, Wang C, Yang D, Zhai Y, Qiu MZ, Xu RH. Inhibitor of apoptosis proteins (IAP) inhibitor APG-1387 monotherapy or in combination with programmed cell death 1 (PD-1) inhibitor toripalimab in patients with advanced solid tumors: results from two phase I trials. ESMO Open 2024; 9:103651. [PMID: 39059062 DOI: 10.1016/j.esmoop.2024.103651] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2024] [Revised: 06/25/2024] [Accepted: 06/25/2024] [Indexed: 07/28/2024] Open
Abstract
BACKGROUND APG-1387 is a novel second mitochondrial-derived activator of caspases mimetic, small-molecule inhibitor targeting inhibitor of apoptosis proteins. We report results from two phase I trials evaluating the tolerability, safety, and antitumor activity of APG-1387 monotherapy and APG-1387 plus toripalimab [a programmed cell death 1 (PD-1) inhibitor] for advanced solid tumors. PATIENTS AND METHODS Participants aged ≥18 years who had histologically confirmed advanced solid tumors with no appropriate standard of care (or refractory to standard care) were eligible. Patients received escalating intravenous doses of APG-1387 alone or combined with fixed-dose toripalimab (240 mg every 3 weeks) in a '3 + 3' design. Primary endpoints were dose-limiting toxicities (DLTs) and maximum tolerated dose (MTD) in the monotherapy trial, and recommended phase II dose (RP2D) in the combination therapy trial. Secondary endpoints included the pharmacokinetic and pharmacodynamic profiles and preliminary efficacy in both trials. RESULTS In the monotherapy trial, 28 subjects were enrolled and received ≥1 treatment cycle. No DLT was reported among the 28 subjects, and the MTD was not reached. One participant (3.6%) had a grade ≥3 treatment-related adverse event (TRAE) of alanine aminotransferase elevation. In efficacy analysis of 23 participants, none achieved an objective response, and the disease control rate was 21.7%. In the combination trial, 22 subjects were enrolled and included in all analyses. There was one DLT of grade 3 lipase elevation. The MTD was not reached. Four grade ≥3 TRAEs occurred in three participants (13.6%), with the most common being lipase elevation (n = 2). The RP2D was 45 mg weekly. The objective response rate was 13.6%, with complete response achieved in one subject, and the disease control rate was 54.5%. CONCLUSIONS APG-1387 45 mg weekly plus toripalimab was well tolerated and is recommended for further study, with preliminary clinical activity observed in study participants with advanced solid tumors.
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Affiliation(s)
- F-R Liu
- Department of Clinical Research, State Key Laboratory of Oncology in South China, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Guangdong Provincial Clinical Research Center for Cancer, Sun Yat-sen University Cancer Center, Guangzhou
| | - X-L Wei
- Department of Medical Oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Sun Yat-sen University, Guangzhou; Research Unit of Precision Diagnosis and Treatment for Gastrointestinal Cancer, Chinese Academy of Medical Sciences, Guangzhou
| | - W-N Feng
- Department of Pulmonary Oncology, The First People's Hospital of Foshan, Foshan
| | - H-Y Zhao
- Department of Clinical Research, State Key Laboratory of Oncology in South China, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Guangdong Provincial Clinical Research Center for Cancer, Sun Yat-sen University Cancer Center, Guangzhou
| | - Y Zhang
- Department of Clinical Research, State Key Laboratory of Oncology in South China, Guangdong Key Laboratory of Nasopharyngeal Carcinoma Diagnosis and Therapy, Guangdong Provincial Clinical Research Center for Cancer, Sun Yat-sen University Cancer Center, Guangzhou
| | - Z-Q Wang
- Department of Medical Oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Sun Yat-sen University, Guangzhou; Research Unit of Precision Diagnosis and Treatment for Gastrointestinal Cancer, Chinese Academy of Medical Sciences, Guangzhou
| | - D-S Zhang
- Department of Medical Oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Sun Yat-sen University, Guangzhou; Research Unit of Precision Diagnosis and Treatment for Gastrointestinal Cancer, Chinese Academy of Medical Sciences, Guangzhou
| | - F-H Wang
- Department of Medical Oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Sun Yat-sen University, Guangzhou; Research Unit of Precision Diagnosis and Treatment for Gastrointestinal Cancer, Chinese Academy of Medical Sciences, Guangzhou
| | - S Yang
- Department of Pulmonary Oncology, The First People's Hospital of Foshan, Foshan
| | - W Pan
- Ascentage Pharma (Suzhou) Co., Ltd., Suzhou, China
| | - X Tian
- Ascentage Pharma (Suzhou) Co., Ltd., Suzhou, China
| | - L Men
- Ascentage Pharma (Suzhou) Co., Ltd., Suzhou, China
| | - H Wang
- Ascentage Pharma (Suzhou) Co., Ltd., Suzhou, China
| | - E Liang
- Ascentage Pharma Group Inc., Rockville, USA
| | - C Wang
- Ascentage Pharma Group Inc., Rockville, USA
| | - D Yang
- Ascentage Pharma (Suzhou) Co., Ltd., Suzhou, China; Department of Experimental Research, State Key Laboratory of Oncology in South China Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, China
| | - Y Zhai
- Ascentage Pharma (Suzhou) Co., Ltd., Suzhou, China; Ascentage Pharma Group Inc., Rockville, USA.
| | - M-Z Qiu
- Department of Medical Oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Sun Yat-sen University, Guangzhou; Research Unit of Precision Diagnosis and Treatment for Gastrointestinal Cancer, Chinese Academy of Medical Sciences, Guangzhou.
| | - R-H Xu
- Department of Medical Oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Sun Yat-sen University, Guangzhou; Research Unit of Precision Diagnosis and Treatment for Gastrointestinal Cancer, Chinese Academy of Medical Sciences, Guangzhou.
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Zhang M, Huang Y, Bai J, Xu W, Shan H, Sheng L, Gao X, Han Y, Wang S, Bai C, Tian B, Ni Y, Dong Q, Ma F, Zhou X. XAF1 promotes osteoclast apoptosis by antagonizing the XIAP-caspase axis. J Orthop Translat 2024; 47:15-28. [PMID: 38957269 PMCID: PMC11217565 DOI: 10.1016/j.jot.2024.05.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/03/2024] [Revised: 04/04/2024] [Accepted: 05/03/2024] [Indexed: 07/04/2024] Open
Abstract
Background Over-activated osteoclast (OC) is a major cause of diseases related to bone loss and bone metabolism. Both bone resorption inhibition and apoptosis induction of osteoclast are crucial in treating these diseases. X-linked inhibitor of apoptosis protein (XIAP)-associated factor 1 (XAF1) is an important interferon-stimulated and apoptotic gene. However, how XAF1 regulates bone formation and remodeling is unknown. Methods We generate global and chimeric Xaf1 knockout mouse models and utilize these models to explore the function and mechanism of XAF1 in regulating bone formation and remodeling in vivo and in vitro. Results We show that XAF1 depletion enhances osteoclast generation in vitro. XAF1 knockout increases osteoclast number and bone resorption, thereby exacerbating bone loss in both OVX and osteolysis models. Activation of XAF1 with BV6 (a potent XIAP inhibitor) suppresses osteoclast formation. Mechanistically, XAF1 deletion decreases osteoclast apoptosis by facilitating the interaction between XIAP and caspase-3/7. Conclusions Our data illustrates an essential role of XAF1 in controlling osteoclastogenesis in both osteoporosis and osteolysis mouse models and highlights its underlying mechanism, indicating a potential role in clinical treatment.The translational potential of this article: The translation potential of this article is that we first indicated that osteoclast apoptosis induced by XAF1 contribute to the progression of osteoporosis and osteolysis, which provides a novel strategy in the prevention of osteoporosis and osteolysis.
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Affiliation(s)
- Mingchao Zhang
- Department of Orthopedics, the Second Affiliated Hospital of Soochow University, Suzhou, 215004, Jiangsu, China
- National Key Laboratory of Immunity and Inflammation, and Key Laboratory of Synthetic Biology Regulatory Elements, Suzhou Institute of Systems Medicine, Chinese Academy of Medical Sciences & Peking Union Medical College, Suzhou, 215123, Jiangsu, China
| | - Yingkang Huang
- National Key Laboratory of Immunity and Inflammation, and Key Laboratory of Synthetic Biology Regulatory Elements, Suzhou Institute of Systems Medicine, Chinese Academy of Medical Sciences & Peking Union Medical College, Suzhou, 215123, Jiangsu, China
| | - Jinyu Bai
- Department of Orthopedics, the Second Affiliated Hospital of Soochow University, Suzhou, 215004, Jiangsu, China
| | - Wushuang Xu
- Department of Orthopedics, the Second Affiliated Hospital of Soochow University, Suzhou, 215004, Jiangsu, China
| | - Huajian Shan
- Department of Orthopedics, the Second Affiliated Hospital of Soochow University, Suzhou, 215004, Jiangsu, China
| | - Lei Sheng
- Department of Orthopedics, the Second Affiliated Hospital of Soochow University, Suzhou, 215004, Jiangsu, China
| | - Xiang Gao
- Department of Orthopedics, the Second Affiliated Hospital of Soochow University, Suzhou, 215004, Jiangsu, China
| | - Yu Han
- National Key Laboratory of Immunity and Inflammation, and Key Laboratory of Synthetic Biology Regulatory Elements, Suzhou Institute of Systems Medicine, Chinese Academy of Medical Sciences & Peking Union Medical College, Suzhou, 215123, Jiangsu, China
| | - Shiyou Wang
- National Key Laboratory of Immunity and Inflammation, and Key Laboratory of Synthetic Biology Regulatory Elements, Suzhou Institute of Systems Medicine, Chinese Academy of Medical Sciences & Peking Union Medical College, Suzhou, 215123, Jiangsu, China
| | - Chaowen Bai
- Department of Orthopedics, the Second Affiliated Hospital of Soochow University, Suzhou, 215004, Jiangsu, China
| | - Bo Tian
- Department of Orthopedics, the Second Affiliated Hospital of Soochow University, Suzhou, 215004, Jiangsu, China
| | - Yichao Ni
- Department of Orthopedics, the Second Affiliated Hospital of Soochow University, Suzhou, 215004, Jiangsu, China
| | - Qirong Dong
- Department of Orthopedics, the Second Affiliated Hospital of Soochow University, Suzhou, 215004, Jiangsu, China
| | - Feng Ma
- National Key Laboratory of Immunity and Inflammation, and Key Laboratory of Synthetic Biology Regulatory Elements, Suzhou Institute of Systems Medicine, Chinese Academy of Medical Sciences & Peking Union Medical College, Suzhou, 215123, Jiangsu, China
| | - Xiaozhong Zhou
- Department of Orthopedics, the Second Affiliated Hospital of Soochow University, Suzhou, 215004, Jiangsu, China
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Chen M, Wang K, Han Y, Yan S, Yuan H, Liu Q, Li L, Li N, Zhu H, Lu D, Wang K, Liu F, Luo D, Zhang Y, Jiang J, Li D, Zhang L, Ji H, Zhou H, Chen Y, Qin J, Gao D. Identification of XAF1 as an endogenous AKT inhibitor. Cell Rep 2023; 42:112690. [PMID: 37384528 DOI: 10.1016/j.celrep.2023.112690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Revised: 04/06/2023] [Accepted: 06/08/2023] [Indexed: 07/01/2023] Open
Abstract
AKT kinase is a key regulator in cell metabolism and survival, and its activation is strictly modulated. Herein, we identify XAF1 (XIAP-associated factor) as a direct interacting protein of AKT1, which strongly binds the N-terminal region of AKT1 to block its K63-linked poly-ubiquitination and subsequent activation. Consistently, Xaf1 knockout causes AKT activation in mouse muscle and fat tissues and reduces body weight gain and insulin resistance induced by high-fat diet. Pathologically, XAF1 expression is low and anti-correlated with the phosphorylated p-T308-AKT signal in prostate cancer samples, and Xaf1 knockout stimulates the p-T308-AKT signal to accelerate spontaneous prostate tumorigenesis in mice with Pten heterozygous loss. And ectopic expression of wild-type XAF1, but not the cancer-derived P277L mutant, inhibits orthotopic tumorigenesis. We further identify Forkhead box O 1 (FOXO1) as a transcriptional regulator of XAF1, thus forming a negative feedback loop between AKT1 and XAF1. These results reveal an important intrinsic regulatory mechanism of AKT signaling.
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Affiliation(s)
- Min Chen
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, CAS Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai 200031, China
| | - Kangjunjie Wang
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, CAS Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai 200031, China; Key Laboratory of Systems Health Science of Zhejiang Province, School of Life Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310024, China
| | - Ying Han
- University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China; CAS Key Laboratory of Tissue Microenvironment and Tumor, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Nutrition and Health, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Shukun Yan
- University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China; State Key Laboratory of Molecular Biology, Shanghai Institute of Biochemistry and Cell Biology, CAS Center for Excellence in Molecular Cell Science, National Center for Protein Science Shanghai, 333 Haike Road, Shanghai 201210, China
| | - Huairui Yuan
- CAS Key Laboratory of Tissue Microenvironment and Tumor, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Nutrition and Health, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Qiuli Liu
- Department of Urology, Institute of Surgery Research, Daping Hospital, Army Medical University, Chongqing 400042, China
| | - Long Li
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, CAS Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai 200031, China
| | - Ni Li
- CAS Key Laboratory of Tissue Microenvironment and Tumor, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Nutrition and Health, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China
| | - Hongwen Zhu
- Department of Analytical Chemistry and CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai 201203, China
| | - Dayun Lu
- University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China; Department of Analytical Chemistry and CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai 201203, China
| | - Kaihua Wang
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, CAS Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai 200031, China; University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China
| | - Fen Liu
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, CAS Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai 200031, China; University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China
| | - Dakui Luo
- Department of Colorectal Surgery, Fudan University Shanghai Cancer Center, Shanghai 200032, China
| | - Yuxue Zhang
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, CAS Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai 200031, China; University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China
| | - Jun Jiang
- Department of Urology, Institute of Surgery Research, Daping Hospital, Army Medical University, Chongqing 400042, China
| | - Dali Li
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Lei Zhang
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, CAS Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai 200031, China; Key Laboratory of Systems Health Science of Zhejiang Province, School of Life Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310024, China; University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China
| | - Hongbin Ji
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, CAS Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai 200031, China; Key Laboratory of Systems Health Science of Zhejiang Province, School of Life Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310024, China; University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China; School of Life Science and Technology, Shanghai Tech University, 100 Haike Road, Shanghai 201210, China
| | - Hu Zhou
- University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China; Department of Analytical Chemistry and CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai 201203, China
| | - Yong Chen
- Key Laboratory of Systems Health Science of Zhejiang Province, School of Life Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310024, China; University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China; State Key Laboratory of Molecular Biology, Shanghai Institute of Biochemistry and Cell Biology, CAS Center for Excellence in Molecular Cell Science, National Center for Protein Science Shanghai, 333 Haike Road, Shanghai 201210, China; School of Life Science and Technology, Shanghai Tech University, 100 Haike Road, Shanghai 201210, China.
| | - Jun Qin
- University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China; CAS Key Laboratory of Tissue Microenvironment and Tumor, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Nutrition and Health, Chinese Academy of Sciences, 320 Yueyang Road, Shanghai 200031, China; Department of Urology, Institute of Surgery Research, Daping Hospital, Army Medical University, Chongqing 400042, China.
| | - Daming Gao
- State Key Laboratory of Cell Biology, Shanghai Institute of Biochemistry and Cell Biology, CAS Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai 200031, China; Key Laboratory of Systems Health Science of Zhejiang Province, School of Life Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310024, China; University of Chinese Academy of Sciences, Number 19A Yuquan Road, Beijing 100049, China.
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Killing by Degradation: Regulation of Apoptosis by the Ubiquitin-Proteasome-System. Cells 2021; 10:cells10123465. [PMID: 34943974 PMCID: PMC8700063 DOI: 10.3390/cells10123465] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Revised: 12/02/2021] [Accepted: 12/03/2021] [Indexed: 12/13/2022] Open
Abstract
Apoptosis is a cell suicide process that is essential for development, tissue homeostasis and human health. Impaired apoptosis is associated with a variety of human diseases, including neurodegenerative disorders, autoimmunity and cancer. As the levels of pro- and anti-apoptotic proteins can determine the life or death of cells, tight regulation of these proteins is critical. The ubiquitin proteasome system (UPS) is essential for maintaining protein turnover, which can either trigger or inhibit apoptosis. In this review, we will describe the E3 ligases that regulate the levels of pro- and anti-apoptotic proteins and assisting proteins that regulate the levels of these E3 ligases. We will provide examples of apoptotic cell death modulations using the UPS, determined by positive and negative feedback loop reactions. Specifically, we will review how the stability of p53, Bcl-2 family members and IAPs (Inhibitor of Apoptosis proteins) are regulated upon initiation of apoptosis. As increased levels of oncogenes and decreased levels of tumor suppressor proteins can promote tumorigenesis, targeting these pathways offers opportunities to develop novel anti-cancer therapies, which act by recruiting the UPS for the effective and selective killing of cancer cells.
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The pro-apoptotic ARTS protein induces neutrophil apoptosis, efferocytosis, and macrophage reprogramming to promote resolution of inflammation. Apoptosis 2021; 25:558-573. [PMID: 32564202 DOI: 10.1007/s10495-020-01615-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
ARTS (Sept4_i2) is a pro-apoptotic protein and a product of the Sept4 gene. ARTS acts upstream of mitochondria to initiate caspase activation. ARTS induces apoptosis by specifically binding XIAP and allowing de-repression of active caspases required for Mitochondrial Outer Membrane Permeabilzation (MOMP). Moreover, ARTS promotes apoptosis by inducing ubiquitin-mediated degradation of both major anti-apoptotic proteins XIAP and Bcl-2. In the resolution phase of inflammation, the infiltrating leukocytes, which execute the acute innate response, undergo apoptosis and are subsequently cleared by phagocytic macrophages (i.e. efferocytosis). In this course, macrophages undergo reprogramming from inflammatory, to anti-inflammatory, and eventually to resolving macrophages that leave the injury sites. Since engulfment of apoptotic leukocytes is a key signaling step in macrophage reprogramming and resolution of inflammation, we hypothesized that a failed apoptosis in leukocytes in vivo would result in an impaired resolution process. To test this hypothesis, we utilized the Sept4/ARTS-/- mice, which exhibit resistance to apoptosis in many cell types. During zymosan A-induced peritonitis, Sept4/ARTS-/- mice exhibited impaired resolution of inflammation, characterized by reduced neutrophil apoptosis, macrophage efferocytosis and expression of pro-resolving mediators. This was associated with increased pro-inflammatory cytokines and reduced anti-inflammatory cytokines, secreted by resolution-phase macrophages. Moreover, ARTS overexpression in leukocytes in vitro promoted an anti-inflammatory behavior. Overall, our results suggest that ARTS is a key master-regulator necessary for neutrophil apoptosis, macrophage efferocytosis and reprogramming to the pro-resolving phenotype during the resolution of inflammation.
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Abbas R, Larisch S. Targeting XIAP for Promoting Cancer Cell Death-The Story of ARTS and SMAC. Cells 2020; 9:E663. [PMID: 32182843 PMCID: PMC7140716 DOI: 10.3390/cells9030663] [Citation(s) in RCA: 59] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2020] [Revised: 03/04/2020] [Accepted: 03/06/2020] [Indexed: 12/18/2022] Open
Abstract
Inhibitors of apoptosis (IAPs) are a family of proteins that regulate cell death and inflammation. XIAP (X-linked IAP) is the only family member that suppresses apoptosis by directly binding to and inhibiting caspases. On the other hand, cIAPs suppress the activation of the extrinsic apoptotic pathway by preventing the formation of pro-apoptotic signaling complexes. IAPs are negatively regulated by IAP-antagonist proteins such as Smac/Diablo and ARTS. ARTS can promote apoptosis by binding and degrading XIAP via the ubiquitin proteasome-system (UPS). Smac can induce the degradation of cIAPs but not XIAP. Many types of cancer overexpress IAPs, thus enabling tumor cells to evade apoptosis. Therefore, IAPs, and in particular XIAP, have become attractive targets for cancer therapy. In this review, we describe the differences in the mechanisms of action between Smac and ARTS, and we summarize efforts to develop cancer therapies based on mimicking Smac and ARTS. Several Smac-mimetic small molecules are currently under evaluation in clinical trials. Initial efforts to develop ARTS-mimetics resulted in a novel class of compounds, which bind and degrade XIAP but not cIAPs. Smac-mimetics can target tumors with high levels of cIAPs, whereas ARTS-mimetics are expected to be effective for cancers with high levels of XIAP.
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Affiliation(s)
| | - Sarit Larisch
- Laboratory of Cell Death and Cancer Research, Biology& Human Biology Departments, Faculty of Natural Sciences, University of Haifa, Haifa 3498838, Israel;
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7
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Jeong SI, Kim JW, Ko KP, Ryu BK, Lee MG, Kim HJ, Chi SG. XAF1 forms a positive feedback loop with IRF-1 to drive apoptotic stress response and suppress tumorigenesis. Cell Death Dis 2018; 9:806. [PMID: 30042418 PMCID: PMC6057933 DOI: 10.1038/s41419-018-0867-4] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Revised: 06/18/2018] [Accepted: 07/11/2018] [Indexed: 12/30/2022]
Abstract
X-linked inhibitor of apoptosis (XIAP)-associated factor 1 (XAF1) is a proapoptotic tumor suppressor that is frequently inactivated in multiple human cancers. However, the molecular basis for the XAF1-mediated growth inhibition remains largely undefined. Here, we report that XAF1 forms a positive feedback loop with interferon regulatory factor-1 (IRF-1) and functions as a transcriptional coactivator of IRF-1 to suppress tumorigenesis. Under various stressful conditions, XAF1 transcription is activated by IRF-1, and elevated XAF1 stabilizes and activates IRF-1. Mechanistically, XAF1 binds to the multifunctional domain 2 of IRF-1 via the zinc finger domain 6, thereby hindering C-terminus of Hsc70-interacting protein (CHIP) interaction with and ubiquitination of IRF-1. Activation of the IRF-1−XAF1 loop greatly increases stress-induced apoptosis and decreases the invasive capability of tumor cells. Oncogenic Ras and growth factors interfere with the IRF-1−XAF1 interplay via Erk-mediated repression of XAF1 transcription. Furthermore, XAF1 enhances IRF-1-mediated transcription of proapoptotic genes via the XAF1-IRF-1 complex formation on these target promoters. Meanwhile, XAF1 inhibits NF-κB-mediated tumor cell malignancy by reinforcing IRF-1 binding to a subset of coregulated promoters. Expression levels of IRF-1 and XAF1 correlate tightly in both cancer cell lines and primary tumors, and XAF1-induced tumor regression is markedly attenuated in IRF-1-depleted tumors. Collectively, this study identifies a novel mechanism of XAF1-mediated tumor suppression, uncovering XAF1 as a feedback coactivator of IRF-1 under stressful conditions.
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Affiliation(s)
- Seong-In Jeong
- Department of Life Sciences, Korea University, Seoul, 02841, Korea
| | - Jung-Wook Kim
- Department of Internal Medicine, Kyung Hee University Hospital, Seoul, 02447, Korea
| | - Kyung-Phil Ko
- Department of Life Sciences, Korea University, Seoul, 02841, Korea
| | - Byung-Kyu Ryu
- Department of Life Sciences, Korea University, Seoul, 02841, Korea
| | - Min-Goo Lee
- Department of Life Sciences, Korea University, Seoul, 02841, Korea
| | - Hyo-Jong Kim
- Department of Internal Medicine, Kyung Hee University Hospital, Seoul, 02447, Korea
| | - Sung-Gil Chi
- Department of Life Sciences, Korea University, Seoul, 02841, Korea.
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Lin B, Xu D, Leaman DW. X-linked inhibitor of apoptosis-associated factor 1 regulates TNF receptor 1 complex stability. FEBS Lett 2016; 590:4381-4392. [PMID: 27768232 DOI: 10.1002/1873-3468.12467] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Revised: 08/17/2016] [Accepted: 08/30/2016] [Indexed: 11/06/2022]
Abstract
X-linked inhibitor of apoptosis (XIAP)-associated factor 1 (XAF1) is a cytokine-regulated, tumor necrosis factor (TNF) receptor-associated factor (TRAF) domain-containing protein that has a poorly defined cellular function. Here, we show that ectopically expressed XAF1 inhibits TNF-ɑ-induced NF-κB activation, whereas shRNA silencing of endogenous XAF1 augments it. Our data suggest that XAF1 may inhibit TNF-ɑ-induced NF-κB activation by disrupting the assembly of the TRADD/TRAF2/RIP1 complex (complex I) downstream of TNF receptor activation. XAF1 interacts with TRAF2 and inhibits TRAF2-dependent NF-κB activation, in part, by blocking TRAF2 polyubiquitination. Our findings also indicate that although XAF1 does not directly inhibit RIP1-dependent NF-κB activation, it binds RIP1 and disrupts RIP1/TRADD association. Our data suggest that XAF1 acts as a feedback regulator of the TNF receptor signaling pathway to suppress NF-κB activation.
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Affiliation(s)
- Boren Lin
- Department of Biological Sciences, The University of Toledo, OH, USA
| | - Da Xu
- Department of Biological Sciences, The University of Toledo, OH, USA
| | - Douglas W Leaman
- Department of Biological Sciences, The University of Toledo, OH, USA
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Hatakeyama K, Yamakawa Y, Fukuda Y, Ohshima K, Wakabayashi-Nakao K, Sakura N, Tanizawa Y, Kinugasa Y, Yamaguchi K, Terashima M, Mochizuki T. A novel splice variant of XIAP-associated factor 1 (XAF1) is expressed in peripheral blood containing gastric cancer-derived circulating tumor cells. Gastric Cancer 2015; 18:751-61. [PMID: 25216542 DOI: 10.1007/s10120-014-0426-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/12/2014] [Accepted: 08/23/2014] [Indexed: 02/07/2023]
Abstract
BACKGROUND XIAP-associated factor 1 (XAF1) is ubiquitously expressed in normal tissues, but its suppression in cancer cells is strongly associated with tumor progression. Although downregulation of XAF1 is observed in tumors, its expression profile in the peripheral blood of cancer patients has not yet been investigated. Here, we identified a novel XAF1 splice variant in cancer cells and then investigated the expression level of this variant in peripheral blood containing gastric cancer-derived circulating tumor cells (CTCs). METHODS To identify splice variants, RT-PCR and DNA sequencing were performed in mRNAs extracted from many cancer cells. We then carried out quantitative RT-PCR to investigate expression in peripheral blood from all 96 gastric cancer patients and 22 healthy volunteers. RESULTS The XAF1 variant harbored a premature termination codon (PTC) and was differentially expressed in highly metastatic cancer cells versus the parental cells, and that nonsense-mediated mRNA decay (NMD) was suppressed in the variant-expressing cells. Furthermore, splice variants of XAF1 were upregulated in peripheral blood containing CTCs. In XAF1 variant-expressing patients, the expression levels of other NMD-targeted genes also increased, suggesting that the NMD pathway was suppressed in CTCs. CONCLUSIONS Our study identified a novel splice variant of XAF1 in cancer cells. This variant was regulated through the NMD pathway and accumulated in NMD-suppressed metastatic cancer cells and peripheral blood containing CTCs. The presence of XAF1 transcripts harboring the PTC in the peripheral blood may be useful as an indicator of NMD inhibition in CTCs.
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Affiliation(s)
- Keiichi Hatakeyama
- Medical Genetics Division, Shizuoka Cancer Center Research Institute, Shizuoka, Japan
| | - Yushi Yamakawa
- Division of Gastric Surgery, Shizuoka Cancer Center Hospital, 1077 Shimonagakubo, Nagaizumi-cho, Sunto-gun, Shizuoka, 411-8777, Japan
- Division of Colon and Rectal Surgery, Shizuoka Cancer Center Hospital, Shizuoka, Japan
| | - Yorikane Fukuda
- Medical Genetics Division, Shizuoka Cancer Center Research Institute, Shizuoka, Japan
- G&G Science, Fukushima, Japan
| | - Keiichi Ohshima
- Medical Genetics Division, Shizuoka Cancer Center Research Institute, Shizuoka, Japan
| | | | - Naoki Sakura
- Medical Genetics Division, Shizuoka Cancer Center Research Institute, Shizuoka, Japan
| | - Yutaka Tanizawa
- Division of Gastric Surgery, Shizuoka Cancer Center Hospital, 1077 Shimonagakubo, Nagaizumi-cho, Sunto-gun, Shizuoka, 411-8777, Japan
| | - Yusuke Kinugasa
- Division of Colon and Rectal Surgery, Shizuoka Cancer Center Hospital, Shizuoka, Japan
| | - Ken Yamaguchi
- Shizuoka Cancer Center Hospital and Research Institute, Shizuoka, Japan
| | - Masanori Terashima
- Division of Gastric Surgery, Shizuoka Cancer Center Hospital, 1077 Shimonagakubo, Nagaizumi-cho, Sunto-gun, Shizuoka, 411-8777, Japan.
| | - Tohru Mochizuki
- Medical Genetics Division, Shizuoka Cancer Center Research Institute, Shizuoka, Japan
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10
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XAF1 directs apoptotic switch of p53 signaling through activation of HIPK2 and ZNF313. Proc Natl Acad Sci U S A 2014; 111:15532-7. [PMID: 25313037 DOI: 10.1073/pnas.1411746111] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
X-linked inhibitor of apoptosis (XIAP)-associated factor 1 (XAF1) is a tumor suppressor that is frequently inactivated in many human cancers. However, the molecular mechanism underlying its growth-inhibitory function remains largely unknown. Here, we report that XAF1 forms a positive feedback loop with p53 and acts as a molecular switch in p53-mediated cell-fate decisions favoring apoptosis over cell-cycle arrest. XAF1 binds directly to the N-terminal proline-rich domain of p53 and thus interferes with E3 ubiquitin ligase MDM2 binding and ubiquitination of p53. XAF1 stimulates homeodomain-interacting protein kinase 2 (HIPK2)-mediated Ser-46 phosphorylation of p53 by blocking E3 ubiquitin ligase Siah2 interaction with and ubiquitination of HIPK2. XAF1 also steps up the termination of p53-mediated cell-cycle arrest by activating zinc finger protein 313 (ZNF313), a p21(WAF1)-targeting ubiquitin E3 ligase. XAF1 interacts with p53, Siah2, and ZNF313 through the zinc finger domains 5, 6, and 7, respectively, and truncated XAF1 isoforms preferentially expressed in cancer cells fail to form a feedback loop with p53. Together, this study uncovers a novel role for XAF1 in p53 stress response, adding a new layer of complexity to the mechanisms by which p53 determines cell-fate decisions.
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11
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Tse MK, Cho CK, Wong WF, Zou B, Hui SK, Wong BCY, Sze KH. Domain organization of XAF1 and the identification and characterization of XIAP(RING) -binding domain of XAF1. Protein Sci 2012; 21:1418-28. [PMID: 22811387 DOI: 10.1002/pro.2126] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2012] [Revised: 07/05/2012] [Accepted: 07/10/2012] [Indexed: 01/12/2023]
Abstract
X-linked inhibitor of apoptosis protein (XIAP)-associated factor 1 (XAF1) has been implicated as a novel tumor suppressor, which was proposed to exert pro-apoptotic effect by antagonizing the anticaspase activity of XIAP. Here, we delineated the domain architecture of XAF1 by applying limited proteolysis and peptide mass fingerprinting analysis. Our results indicated that XAF1 has a distinct domain organization, with a highly compact N-terminal domain (XAF1(NTD) ) followed by a middle domain (XAF1(MD) ), a 42-residue unstructured linker and a C-terminal domain (XAF1(CTD) ). The search of XIAP binding region within XAF1 revealed that a modest affinity XIAP(RING) binding site (dissociation constant, K(d) , ∼18 μM) is located at the C-terminal portion of XAF1. This C-terminal region, embracing XAF1(CTD) and a flexible tail at C-terminus (residue Thr251-Ser301), is functionally identified as XIAP(RING) -binding domain of XAF1 (XAF1(RBD) ) in the present study. We have also mapped the interaction sites for XAF1(RBD) on XIAP(RING) by using NMR spectroscopy. By applying in vitro ubiquitination assay, we observed that XAF1(RBD) /XIAP interaction is essential for the ubiquitination of GST-XAF1(RBD) fusion protein. In addition, the C-terminal XAF1 fragment harboring XAF1(RBD) was found to be substantially ubiquitinated by XIAP(RING) . Base on these observations, we speculate a possible role of XAF1(RBD) in targeting XAF1 for XIAP-mediated ubiquitination.
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Affiliation(s)
- Man Kit Tse
- Department of Microbiology and State Key Laboratory for Emerging Infectious Diseases, University of Hong Kong, Hong Kong SAR, People's Republic of China
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12
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Grzybowska-Izydorczyk O, Cebula B, Robak T, Smolewski P. Expression and prognostic significance of the inhibitor of apoptosis protein (IAP) family and its antagonists in chronic lymphocytic leukaemia. Eur J Cancer 2010; 46:800-10. [PMID: 20045309 DOI: 10.1016/j.ejca.2009.11.023] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2009] [Revised: 09/22/2009] [Accepted: 11/25/2009] [Indexed: 11/19/2022]
Abstract
Impaired apoptosis is still considered to be an important event in the development and progression of chronic lymphocytic leukaemia (CLL). However, mechanisms of this defect have not been fully elucidated. In this study, expression of inhibitor of apoptosis proteins, IAPs (cIAP1, cIAP2, XIAP and survivin), and their antagonists (Smac/DIABLO and HtrA2/Omi) was comprehensively analysed in 100 untreated CLL patients, using flow cytometry and Western blot techniques. Expression of anti-apoptotic cIAP1 and cIAP2 in leukaemic cells was significantly higher than in non-tumour lymphocytes (p=0.000001 and p=0.014, respectively), whereas the IAP-antagonist, Smac/DIABLO, was decreased in CLL (p=0.010). Higher expression of all analysed IAPs (cIAP1, p=0.002; cIAP2, p=0.026; XIAP, p=0.002; survivin, p=0.00006) and lower levels of Smac/DIABLO (p=0.006) were found in patients with progressive disease, compared to those with stable CLL. High baseline expression of cIAP1 and survivin correlated with worse response to treatment. Co-expression of these proteins was associated with shorter overall survival of CLL patients (p=0.005). In conclusion, CLL cells show the apoptosis-resistant profile of IAPs/IAP-antagonist expression. Upregulation of IAPs is associated with a progressive course of the disease. Co-expression of cIAP1 and survivin seems to be an unfavourable prognostic factor in CLL patients. Further studies with longer follow up are warranted to confirm and expand these findings.
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MESH Headings
- Adult
- Aged
- Aged, 80 and over
- Apoptosis
- Apoptosis Regulatory Proteins
- Biomarkers, Tumor/blood
- Disease Progression
- Epidemiologic Methods
- Female
- High-Temperature Requirement A Serine Peptidase 2
- Humans
- Immunophenotyping
- Inhibitor of Apoptosis Proteins/blood
- Intracellular Signaling Peptides and Proteins/blood
- Leukemia, Lymphocytic, Chronic, B-Cell/blood
- Leukemia, Lymphocytic, Chronic, B-Cell/immunology
- Leukemia, Lymphocytic, Chronic, B-Cell/pathology
- Male
- Middle Aged
- Mitochondrial Proteins/blood
- Neoplasm Proteins/blood
- Prognosis
- Serine Endopeptidases/blood
- Tumor Cells, Cultured
- Up-Regulation
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Affiliation(s)
- Olga Grzybowska-Izydorczyk
- Department of Experimental Haematology, Medical University of Lodz, Copernicus Memorial Hospital, Ciolkowskiego 2, 93-510 Lodz, Poland
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13
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Spolarics Z. The X-files of inflammation: cellular mosaicism of X-linked polymorphic genes and the female advantage in the host response to injury and infection. Shock 2007; 27:597-604. [PMID: 17505297 DOI: 10.1097/shk.0b013e31802e40bd] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Females as compared with males display better general health status, longevity, and improved clinical course after injury and infection. It is generally believed that the female advantage is associated with the effects of sex hormones. This review argues that the sex benefit of females during the host response is associated with polymorphism of X-linked genes and cellular mosaicism for X-linked parental alleles. Cells from females carry both parental X chromosomes (maternal, Xm; or paternal, Xp), whereas males carry only one (Xm). Because of dosage compensation and random X inactivation, half of the cells from females express either Xm or Xp. Therefore, females are cellular mosaics for their X-linked polymorphic genes. This cellular mosaicism in females represents a more adaptive and balanced cellular machinery that is advantageous during the innate immune response. Several genes encoding key metabolic and regulatory proteins reside on the X chromosome, including members of the apoptotic cascade, hormone homeostasis, glucose metabolic enzymes, superoxide-producing machinery, and the toll-like receptor/nuclear factor kappaB/c-Jun N-terminal kinase signaling pathway. Polymorphic forms of these X-linked proteins are likely to manifest in phenotypic differences in the mosaic cell populations in females and may contribute to sex-related differences in the host response to injury and infection. The unique inheritance pattern of X-linked polymorphisms and their potential confounding effects in clinical trials are also discussed; furthermore, we present potential biomarkers for studying mosaic cell populations of innate immunity.
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Affiliation(s)
- Zoltán Spolarics
- Department of Surgery, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey 07103, USA.
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14
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Chung SK, Lee MG, Ryu BK, Lee JH, Han J, Byun DS, Chae KS, Lee KY, Jang JY, Kim HJ, Chi SG. Frequent alteration of XAF1 in human colorectal cancers: implication for tumor cell resistance to apoptotic stresses. Gastroenterology 2007; 132:2459-77. [PMID: 17570219 DOI: 10.1053/j.gastro.2007.04.024] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/27/2006] [Accepted: 02/22/2007] [Indexed: 12/22/2022]
Abstract
BACKGROUND & AIMS X-linked inhibitor of apoptosis protein-associated factor 1 (XAF1) is a candidate tumor suppressor located at the chromosome 17p13 region, but the molecular basis underlying its inactivation in human tumors and growth-inhibiting function has not been well defined. We explored the candidacy of XAF1 as a suppressor in colorectal tumorigenesis. METHODS XAF1 expression was characterized by polymerase chain reaction-based cloning, isoform-specific polymerase chain reaction, ribonuclease protection, and immunoblot assays. Allelic loss of the gene was evaluated by loss of heterozygosity (LOH) assay, and promoter CG dinucleotide (CpG) site methylation was determined using bisulfite sequencing. The effect of XAF1 on tumor growth was examined using flow cytometry, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling, colony formation, and viability assays. RESULTS Expression of 5 XAF1 variants including 2 novel transcripts was down-regulated concomitantly in 11 of 20 (55%) cell lines and 26 of 65 (40%) primary tumors. XAF1 reduction was tumor-specific and showed a correlation with advanced stage and high grade of tumor. LOH of the gene was found in 12 of 33 (36%) tumors. Promoter CpG site methylation was observed frequently in both cell lines and tumor tissues including many LOH tumors, suggesting that biallelic inactivation of XAF1 might be common in colorectal cancers. XAF1 expression suppressed tumor cell growth and enhanced cellular response to various apoptotic stimuli, such as 5-fluorouracil, etoposide, H(2)O(2), gamma-irradiation, ultraviolet, and tumor necrosis factor-alpha, whereas knockdown of its expression protected cells from the stresses. CONCLUSIONS Genetic and epigenetic alteration of XAF1 is a common event in colorectal tumorigenesis and contributes to the malignant tumor progression by providing survival advantages for tumor cells under various stress conditions.
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Affiliation(s)
- Sun-Ku Chung
- School of Life Sciences and Biotechnology, Korea University, Seoul, Korea
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15
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Straszewski-Chavez SL, Visintin IP, Karassina N, Los G, Liston P, Halaban R, Fadiel A, Mor G. XAF1 mediates tumor necrosis factor-alpha-induced apoptosis and X-linked inhibitor of apoptosis cleavage by acting through the mitochondrial pathway. J Biol Chem 2007; 282:13059-72. [PMID: 17329253 DOI: 10.1074/jbc.m609038200] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Tumor necrosis factor-alpha (TNF-alpha) and Fas ligand induce apoptosis by interacting with their corresponding membrane-bound death receptors and activating caspases. Since both systems share several components of the intracellular apoptotic cascade and are expressed by first trimester trophoblasts, it is unknown how these cells remain resistant to Fas ligand while sensitive to TNF-alpha. XAF1 (X-linked inhibitor of apoptosis (XIAP)-associated factor 1) is a proapoptotic protein that antagonizes the caspase-inhibitory activity of XIAP. Here, we demonstrated that XAF1 functions as an alternative pathway for TNF-alpha-induced apoptosis by translocating to the mitochondria and promoting XIAP inactivation. In addition, we showed that the overexpression of XAF1 sensitized first trimester trophoblast cells to Fas-mediated apoptosis. Furthermore, we also determined that the differential expression of XAF1 in first and third trimester trophoblast cells was due to changes in XAF1 gene methylation. Our results establish a novel regulatory pathway controlling trophoblast cell survival and provide a molecular mechanism to explain trophoblast sensitivity to TNF-alpha and the increased number of apoptotic trophoblast cells observed near term. Aberrant XAF1 expression and/or localization may have consequences for normal pregnancy outcome.
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Affiliation(s)
- Shawn L Straszewski-Chavez
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA
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