The long-term goal of our laboratory is to understand the pathways and biochemical mechanisms controlling the activation and execution of apoptosis in mammalian cells. Apoptosis is a biochemically and morphologically distinct form of programmed cell death. Initiated by a variety of intercellular and intracellular signals, apoptosis is executed through an intrinsic cellular suicide program that results in early DNA fragmentation accompanied by nuclear and cytoplasmic condensation. Apoptosis is believed to play an essential role in development, tissue homeostasis, defense against viral infection, and clearance of damaged cells in multicellular organisms. Inappropriate activation or suppression of apoptosis are associated with the pathogenesis of some of the most devastating human diseases, such as cancer, neurodegenerative disease, auto-immune disease, AIDS, and ischemic stroke.
We have been focusing our research efforts on the dissection of two of the best characterized biochemical events during apoptosis, namely the activation of Caspase 3 protease and fragmentation of DNA into nucleosomal fragments. We have set up in vitro systems that duplicate these two events and fractionated cytosol from large scale cultured HeLa cells to identify and purify the individual protein factors contributing to Caspase 3 activation and the DNA fragmentation reaction. These studies identified protein components that can reconstitute these apoptotic events.
Purification of three components elucidated the caspase activation cycle. Apaf-1, the factor responsible for Caspase 3 activation, cause caspase activation of its partner, Caspase 9, through the formation of a multimeric protein complex regulated by cytochrome c binding and dATP hydrolysis. This complex has pointed to the role of cytochrome c release as a key regulatory step for apoptotis. Nucleosomal DNA fragmentation occurs during apoptosis upon activation of a 40 kD novel protein DNA Fragmentation Factor (DFF40). This activity is suppressed in normal cells by its inhibitor DFF45 which is removed after caspase cleavage.
Our future research will diverge into two directions: one is to study the biochemical mechanism of Apaf-1 activation and DNA fragmentation using purified recombinant proteins; another is to study the signal transduction pathways that regulate the activity of these factors during apoptosis.
We have set out a variety of techniques involving biochemistry, molecular biology and cell biology in the laboratory. We hope to use the combination of these techniques to uncover the mystery of programmed cell death.
RESEARCH INTERESTS
Why and how cells die
RECENT PUBLICATIONS
Lin Li, Ranny Mathew Thomas, Hidetaka Suzuki, Jef K. De Brabander, Xiaodong Wang, Patrick G. Harran, "A Small Molecule Smac Mimic Potentiates TRAIL- and TNF-Mediated Cell Death" Science, 305(5689):1471-1474, September 2004
Xuejun Jiang, Hyun-Eui Kim, Hongjun Shu, Yingmin Zhao, Haichao Zhang, James Kofron, Jennifer Donnelly, Dave Burns, Shi-chung Ng, Saul Rosenberg, and Xiaodong Wang, "Distinctive roles of PHAP proteins and prothymosin-alpha in a death Regulatory Pathway." Science, 299:214-5, January 2003
Devrim Acehan, Xuejun Jiang, David Gene Morgan, John E. Heuser, Xiaodong Wang and Christopher W. Akey, "Three-dimensional structure of the apoptosome: implications for assembly, procaspase-9 binding, and activation." Mol. Cell., 9:423-432, February 2002
Mohanish Deshmukh, Chunying Du, Xiaodong Wang, and Eugene M. Johnson, Jr., "Exogenous Smac induces competence and permits caspase activation in sympathetic neurons." J. Neurosci, 22:8018-8027, Month
Jonathan P. Carson, Marcelina Behnam, Jennifer N. Sutton, Chunying Du, Xiaodong Wang, Donald F. Hunt, Michael J. Weber, and George Kulik., "Smac Is Required for Cytochrome c-induced Apoptosis in Prostate Cancer LNCaP Cells." Cancer Res., 62:18-23, Select Month or Season 2002
SIGNIFICANT PUBLICATIONS
Chunying Du, Min Fang, Yucheng Li, Lily Li, and Xiaodong Wang, "Smac, a mitochondrial protein that promotes cytochrome c-dependent caspase activation by eliminating IAP inhibition." Cell, 102:33-42, 2000
Lily Y. Li, Xu Luo, and Xiaodong Wang, "Endonuclease G (EndoG) is an apoptotic DNase when released from Mitochondria." Nature, 412:95-99, 2001
Xuejun Jiang, Hyun-Eui Kim, Hongjun Shu, Yingmin Zhao, Haichao Zhang, James Kofron, Jennifer Donnelly, Dave Burns, Shi-chung Ng, Saul Rosenberg, and Xiaodong Wang, "Distinctive roles of PHAP proteins and prothymosin-alpha in a death Regulatory Pathway." Science, 299:223-226, 2002
Xuesong Liu, Caryn Naekyung Kim, Jie Yang, Ronald Jemmerson, and Xiaodong Wang, "Induction of apoptotic program in cell-free extracts: requirement for dATP and cytochrome c." Cell, 86:147-157, 1996
Xu Luo, Imawati Budihardjo, Hua Zou, Clive Slaughter, and Xiaodong Wang, "Bid, a Bcl-2 interacting protein, mediates cytochrome c release from mitochondria in response to activation of cell surface death receptors." Cell, 94:481-490, 1998
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