Editor's Note: Dr. Reenstra is Associate Professor of Pediatrics in the Head Laboratory of Epithelial Cell Biology at the Alfred I. DuPont Hospital for Children at the Thomas Jefferson School of Medicine. He currently works with genistein, a substance derived from soy, to understand the biochemical differences between wild-type and DF508CFTR. He continues to study the mechanisms by which genistein increases DF508-CFTR activity. CFRI funded Dr. Reenstra in the early stages of his work with genistein. He currently receives funding from the Cystic Fibrosis Foundation and the Nemours Foundation. Pending receipt of additional funding, Dr. Reenstra plans to test the effects of genistein on the salt content of sweat in CF patients who have the DF508-CFTR mutation.
As a basic scientist, the major scientific question I hope to answer is how CFTR activity is regulated and how the regulation of the normal, or wild-type, CFTR differs from that of mutant forms of the CFTR. Cystic fibrosis is caused by inherited mutations in a gene called the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). The mutations prevent CFTR from operating properly and have been associated with symptoms ranging from mild to very severe pancreatic and lung disease.
To understand the concept of regulation, think about your car. You dont want your car to always be moving. Sometimes you want to stop, and when you are driving, you dont want to always go at the same speed. In a similar way, cells do not want the CFTR to always be active, and they need to control the level of activity. It is known that in the body CFTR is activated by a process called cyclic AMP-dependent activation. The most common CFTR mutant, DF508CFTR, is poorly activated by this process.
Recent studies, funded in part by CFRI, have shown that a soy-derived natural product, genistein, can activate the CFTR. We discovered that genistein can activate the CFTR by a cyclic AMP-independent process. We also showed that genistein can increase cyclic AMP-dependent activation of normal CFTR. When we studiedDF508CFTR, we observed that neither genistein nor cyclic AMP could cause appreciable increases in activity. However, when the cyclic AMP-dependent pathway was activated in the presence of genistein, the activity of DF508CFTR was as great as that of wild-type CFTR. These results suggest that, in the presence of genistein, cells with DF508CFTR might respond to the natural processes that actin people without CF.
To be activated by genistein or cyclic AMP, CFTR must be at the surface of the cell. Normal cell function also requires that enough CFTR molecules be at the cell surface. However, proteins like CFTR are made in the interior of the cell and are then transferred to the cell surface. Some of the 700 known CFTR mutations make no protein and, therefore, cant be activated by cyclic AMP or genistein. Some mutations make proteins that reach the cell surface but cant be activated by cyclic AMP. The activity of these mutations may be increased in the presence of genistein.
The most common mutation,DF508CFTR, makes a protein, but most of it fails to reach the cell surface. In the laboratory, there are ways to increase the amount of DF508CFTR that reaches the cell surface. Some of these approaches are being studied in clinical trials. Because DF508CFTR is poorly activated by cyclic AMP, getting DF508CFTR to the cell surface is not enough. Likewise, with little DF508CFTR at the cell surface, increasing DF508-CFTR activity with genistein may not restore normal cell function. However, therapeutic strategies that combine both approaches may be valuable in the treatment of CF patients with the DF508-CFTR mutation. Because approximately 90% of CF patients have at least one copy of the DF508-CFTR mutation, this approach could be of benefit to many CF patients.
How will our work with genistein proceed? We will continue to refine our understanding of how genistein activates CFTR and determine if related compounds might make better drugs. Our laboratory and others are starting to test the topical application of genistein with non-CF patients and CF patients with mutations that may be activated by genistein. Because dietary genistein has been shown to reduce the risk of some forms of human cancer, oral administration may be feasible. If the current trials are encouraging, clinical trials of orally administrated genistein may be warranted. Ultimately, genistein, or a similar compound, when combined with drugs that increaseDF508-CFTR expression at the cell surface, may prove to be a useful therapy for CF.
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