Xiaodong (Robert) Wang, Ph.D.
Telephone: (419) 383-4182
FAX: (419) 383-2871
• B.S.: Nankai University
• M.S.: Baylor University
• Ph.D.: University of Texas Southwestern Medical Center, Dallas, Texas
• Post-doctoral training: The Scripps Research Institute, La Jolla, CA
• Molecular chaperones
• Intracellular trafficking
• Membrane protein biogenesis
• Drug discovery for protein misfolding diseases
Endoplasmic reticulum (ER) is the portal for newly synthesized proteins to enter the secretory pathway. It is estimated that roughly one third of the eukaryotic genome encodes proteins that are associated with the secretory pathway. Nascent cargo proteins are folded in the ER. Quality control mechanisms exist to ensure that cargo proteins have attained appropriate conformation for their physiological functions. Misfolded cargo proteins cannot pass the ER quality control, leading to loss of function. A classic example is cystic fibrosis where misfolding of a plasma membrane chloride channel occurs in over 90% of patients. In addition, problems arising from the ER quality control or the failure thereof are the bases of an increasing number of human diseases including diabetes, cardiovascular diseases and cancer. Molecular chaperones play significant roles in protein folding and quality control. Our long-term objective is to elucidate the organization and regulation of the cellular machineries involved in protein folding and quality control in the context of pathogenesis and treatment of relevant human diseases.
Selected Current Projects
The role of Hsp105 in the rescue of CFTR misfolding
Cystic fibrosis is the one of most common lethal inherited diseases. It is caused by the functional deficiency of a plasma membrane chloride channel known as cystic fibrosis transmembrane conductance regulator (CFTR). A single mutation (ΔF508) found in over 90% of CF patients interferes with the de novo folding of CFTR, leading to defective exocytic trafficking, reduced peripheral stability and subnormal channel gating. Rescuing the defective conformation of ΔF508 CFTR will benefit the majority of CF patients.
Hsp105 is a high molecular weight member of the Hsp70 super family of molecular chaperones. It protects misfolded proteins from aggregation (holdase activity), facilitates the nucleotide exchange of Hsc70 and functionally relates to Hsp90. Given the established roles for both Hsp70 and Hsp90 in CFTR biogenesis and quality control, Hsp105 is likely to play critical roles in the same process. We found that Hsp105 regulates the co-translational folding/quality control of CFTR, promotes the post-translational maturation of CFTR, and enhances the peripheral stability of the misfolded ΔF508 CFTR. The multi-level regulation of CFTR biogenesis by Hsp105 and its special role in handling misfolded proteins make it an attractive molecular target for rescuing protein misfolding in cystic fibrosis or other human diseases involving protein misfolding.
Hsp70-Hsp90 network on the cytoplasmic face of the ER membrane
The cytoplasmic Hsp70 and Hsp90 are known to form a chaperone relay system in mediating the activation of steroid receptors. Their functional relationship in the context of membrane protein biogenesis is unclear. Using the temperature-dependent maturation of ΔF508 CFTR as a model system, we have obtained evidence that a similar but not identical Hsp70-Hsp90 chaperone network operates on the cytoplasmic face of the ER membrane to facilitate the conformational maturation of integral membrane proteins. We are employing a functional genomic approach to understand the organization and regulation of this chaperone system in an attempt to define the chaperone-mediated folding events on the ER membrane. This will provide critical insights into the cytoplasmic folding events during membrane protein biogenesis in the ER.
Small molecule drug discovery for cystic fibrosis
Deletion of F508 in CFTR induces global conformational change, leading to impaired export, stability and function of the mutant chloride channel. We recently found that global conformational reversion is necessary for effective rescue of CFTR misfolding, and that the first nucleotide binding domain of CFTR plays a pivotal role in the process. Using a combination of biochemical and computational approaches we identified novel small molecule compounds that stabilize the conformation of misfolded CFTR in the cell. Continued development and optimization of these compounds might lead to the generation of effective CFTR small molecule correctors that can be used to treat the vast majority of cystic fibrosis patients.
Regulation of membrane protein biogenesis by immunophilins
Immunophilins possess an enzyme activity that facilitates the isomerization of the proline residues in peptides. High molecular weight immunophilins such as FKBP52 and FKBP38 contain tetratricopeptide repeat (TPR) domain to functionally link them to Hsp90. The presence of Ca2+/Calmodulin-binding domain provides additional mechanism of regulation. We seek to understand the functional and regulatory roles of these TPR immunophilins in membrane protein biogenesis by focusing on the specific folding events they mediate and how these immunophilins crosstalk with Hsp90 and perhaps other chaperones. As FKBP38 is known to regulate the biogenesis of multiple plasma membrane ion channels and the stability of Bcl-2, our work will have a major impact on the development of therapeutics for related diseases such as cystic fibrosis, long QT syndrome and cancer.
- Saxena, A., Banasavadi-Siddegowda, Y.K., Fan, Y., Bhattacharya, S., Roy, G., Giovannucci,
D.R., Frizzell, R.A. and Wang, X. (2012) Human heat shock protein 105/110 kDa (Hsp105/110) regulates the biogenesis
and quality control of misfolded cystic fibrosis transmembrane conductance regulator
at multiple levels. J. Biol. Chem. Epub ahead of print, doi: 10.1074/jbc.M111.297580.
- Fan, Y., Banasavadi-Siddegowda, Y.K. and Wang, X. (2012) Improving cell surface functional expression of ΔF508 CFTR: a quest for therapeutic targets. In: Cystic Fibrosis – Renewed Hopes through Research, D Sriramulu, Editor. InTech, Rijeka. ISBN 978-953-51-0287-8. p333-358.
- Banasavadi‐Siddegowda, Y.K., Mai, J., Fan, Y., Bhattacharya, S., Giovannucci, D.R., Sanchez, E.R., Fischer, G. and Wang, X. (2011). FKBP38 peptidylprolyl isomerase promotes the folding of cystic fibrosis transmembrane conductance regulator in the endoplasmic reticulum. J. Biol. Chem. 286(50): 43071-43080.
- Roy, G., Chalfin, E.M., Saxena, A. and Wang, X. (2010) Interplay between ER exit code and domain conformation in CFTR misprocessing and rescue. Mol. Biol. Cell 21, 597-609.
- Wang, X.*, Koulov, A.V., Kellner, W.A., Riordan, J.R. and Balch, W.E.* (2008) Chemical and biological folding contribute to temperature-sensitive ΔF508 CFTR trafficking. Traffic 9, 1878-1893. (* corresponding authors)
- Wang, X., Venable, J., LaPointe, P., Hutt, D.M., Koulov, A.V., Coppinger, J., Gurkan, C., Kellner, W., Matteson, J., Plutner, H., Riordan, J.R., Kelly, J.W., Yates, J.R., III, and Balch, W.E. (2006) Hsp90 co-chaperone Aha1 rescues misfolding of CFTR in cystic fibrosis. Cell 127, 803-815.
- Plutner, H., Gurkan, C., Wang, X., LaPointe, P., and Balch, W.E. (2005) Microsome-based assay for analysis of endoplasmic reticulum to Golgi transport in mammalian cells. In: Cell Biology: A Laboratory Handbook, Celis J.E., Editor. Elsevier, San Diego. Vol.2, p209-214.
- Wang, X., Matteson, J., An, Y., Moyer, B., Yoo, J-S., Bannykh, S., Wilson, I.A., Riordan, J.R., and Balch, W.E. (2004) COPII-dependent export of cystic fibrosis transmembrane conductance regulator from teh ER uses a di-acidic exit code. J. Cell Biol. 167, 65-74.
- Wang, X., McMahon, M.A., Shelton, S.N., Nampaisansik, M., Ballard, J.L., and Goodman, J.M. (2004) Multiple targeting modules on peroxisomal proteins are not redundant: Discrete functions of targeting signals within Pmp47 and Pex8p. Mol. Biol. Cell 15, 1702-1710.
- Wang, X., Unruh, M.J., and Goodman, J.M. (2001) Discrete targeting signals direct Pmp47 to oleate-induced peroxisomes in Saccharomyces cerevisiae. J. Biol. Chem. 276, 10897-10905.