The human ABCC6 ATP-Binding Cassette (ABC-) transporter has been implicated to play a role in multiple human connective tissue diseases, including pseudoxanthoma elasticum (PXE). The loss of ABCC6 function putatively results in the loss of one or more circulatory factors that regulate the mineralization of elastic tissues systemically. Multiple disease-causing mutations in ABCC6 have been identified in PXE patients, yet their molecular impacts on ABCC6 structure and function are unknown. The work presented in this proposal is directed at addressing several key questions that are fundamental to our understanding of the molecular pathologies in ABCC6 and identifying mechanisms for targeted therapeutic development to correct these defects, specifically: (1) How do mutations alter the biosynthesis and function of ABCC6? (2) Are there mechanisms that can be used to correct these defects to restore protein function? Our preliminary data, systematically evaluating a large library of ABCC6 mutations, demonstrates that mutations can be broadly grouped into multiple structural and mechanistic classes. Two categories result in altered protein folding and are differentially distinguished by their effects on local and global protein structures. The third category of mutation is putatively associated with altered protein function. These studies provide a fundamental understanding of ABCC6 structure and function and novel insight into the molecular defects associated with specific disease-causing mutations. Our preliminary data further suggest a mechanism(s) that restores mutant ABCC6 biosynthesis and function. This mechanism of stabilization rescues multiple severe, disease-causing mutants within ABCC6. Characterization of this rescue provides additional insight into the biosynthesis of wildtype ABCC6 and the defects associated with mutant ABCC6. In addition, these studies lay the groundwork for future mechanism-based targeted therapeutic development. Using a combination of cell biological, biochemical and functional assays, these studies are designed to elucidate the molecular defects and means of correction of ABCC6-associated disease mutations. This combination of approaches, including newly developed structural and functional assays, will provide a comprehensive view of the biosynthetic pathway of the ABCC6 ABC-transporter in both normal and mutant states. By extension, these studies will inform research on other human ABC-transporters, including those regulating cholesterol homeostasis and associated with cystic fibrosis, for which active therapeutic development efforts are ongoing. Thus, these studies will inform current and future PXE research efforts and studies of human diseases associated with ABC-transporters.
Altered biosynthesis and function of ABCC6 is associated with the pathophysiology of multiple human connective tissue disorders, including pseudoxanthoma elasticum, peripheral vascular disease, arthereosclerosis and dystrophic cardiac calcification. The studies proposed in this application seek to define the molecular mechanisms associated with altered ABCC6 biosynthesis and function. Understanding these molecular defects, and their role in disease pathophysiology, will provide important information for the development of targeted therapeutics for the associated connective tissue disorders.
| Ran, Yanchao; Zheng, Aiping; Thibodeau, Patrick H (2018) Structural analysis reveals pathomechanisms associated with pseudoxanthoma elasticum-causing mutations in the ABCC6 transporter. J Biol Chem 293:15855-15866 |
