WASHINGTON UNIVERSITY SCHOOL OF MEDICINE DEPARTMENT OF MEDICINE

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Our lab's research is focused on aspects of how blood forms clots in normal and pathological disease states. Specifically, we are currently working on the characterization of a protein, ADAMTS13, which regulates the activity of von Willebrand Factor (VWF) by cleaving a peptide bond within VWF to generate smaller fragments. This activity is important since the largest forms of VWF are most active in anchoring platelets to exposed collagen at sites of vascular injury and therefore, promoting hemostasis. If ADAMTS13 activity is absent, small blood clots develop, especially in the brain and kidneys, in a disease called thrombotic thrombocytopenic purpura. Conversely, increased cleavage of VWF leads to a form of the bleeding disorder, von Willebrand Disease.

There are three different areas of active research on ADAMTS13 in our lab at this time. First, we are characterizing the importance of fucosylation in the biosynthesis of ADAMTS13. ADAMTS13 contains fucose residues directly linked to serine or threonine within the thrombospondin type 1 repeat (TSR). Absence of the fucosylation sites impairs secretion of ADAMTS13 from the cell. We are currently studying how secretion is affected by fucosylation. Specifically, we are characterizing the O-fucosyl transferase that transfers the fucose to ADAMTS13 in the endoplasmic reticulum (ER). The O-fucosyl transferase is a soluble ER protein but lacks a KDEL C-terminal sequence. We are studying the mechanism by which the O-fucosyl transferase remains in the ER and the interaction of the O-fucosyl transferase with ADAMTS13.

Another area of research is the structure-function relationship of ADAMTS13 and VWF. We have expressed a construct of about 130 amino acids that contains two domains of the 1427 amino acid full-length ADAMTS13. We have found that this construct (ST2) will co-immunoprecipitate with VWF and will enhance the cleavage of VWF by ADAMTS13 by about ten-fold. We are currently determining the amino acids of VWF with which ST2 interacts and also the amino acids in ST2 that interact with VWF. Future studies will determine the mechanism by which the addition of ST2 to a cleavage reaction enhances digestion of VWF. This work will help us to understand how mutations in ADAMTS13 or VWF lead to disease states.

We are also interested in the interaction of ADAMTS13 with platelets and endothelial cells. VWF is synthesized and secreted from endothelial cells while ADAMTS13 is mainly synthesized in the liver. It is unclear if VWF is cleaved by ADAMTS13 in free plasma or at the endothelial cell surface. We have found that ADAMTS13 associates with the endothelial cell surface. Experiments are underway to identify the mechanism through which ADAMTS13 interacts with the endothelial cell. We will also determine if association with the endothelial cell promotes cleavage of VWF. This work will help us to better understand the pathophysiology of thrombotic disorders and may lead to better ways to control bleeding and thrombosis.

Future directions will include the study of other thrombotic disorders such as malignancy-associated thrombosis and thrombotic thrombocytopenic purpura-like disorders that occur with bone marrow transplantation, HIV, and cancer.

ST2, a small non-catalytic fragment of ADAMTS13, enhances cleavage of VWF by full-length ADAMTS13

Increasing amounts of ST2 were included in VWF cleavage assays with ADAMTS13. Cleaved VWF was detected by SDS-PAGE and immunoblotting. Cleavage results in the generation of C- and N-terminal fragments of VWF. Addition of ST2 enhanced the cleavage of VWF by about ten-fold.

Education

1986	BA, Biology, Washington University, St. Louis, MO
1994	PhD, Molecular Cell Biology and Biochemistry, Washington University, St. Louis, MO
1998	MD, St. Louis University, St. Louis, MO

Post-graduate Training

1998-2000	Intern and Junior Assistant Resident in Medicine, Barnes-Jewish Hospital, St. Louis, MO
2000-2005	Fellow in Hematology-Oncology, Washington University School of Medicine, St. Louis, MO

Academic Positions & Employment

1987-1990	Research Technician, Veterans Administration Medical Center, St. Louis, MO
2005-present	Assistant Professor, Departments of Medicine and Cell Biology & Physiology, Washington University, St. Louis, MO

Professional Societies

American Society of Hematology

Board Certification

2000	American Board of Internal Medicine

Honors & Awards

1986	Loretta Backer Scholarship
1992-1994	Lucille P. Markey Research Fellow
1995	Alpha Omega Alpha Student Research Forum Prize
1998-2004	Physician-Scientist Training Program Fellow

• Updated: March 27, 2008
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