Regulating Neurofibromin Through Degradation, Dimerization, and Binding to SPRED1
Abstract
Neurofibromatosis type I (NF1) is a genetic disorder caused by mutations in the NF1 gene, affecting 1 in 3,500 people worldwide. It is the most common inherited disorder caused by a single gene and manifests in patients as mild symptoms such as café au lait macules and Lisch nodules, as well as more severe symptoms such as neurofibromas (tumor-like growths), skeletal abnormalities, malignant neoplasms, and learning disabilities. As technology continues to develop, it is now increasingly common to perform genetic analysis on patients to determine their NF1 mutational status. There are over 1,500 known mutations in NF1 that are all thought to lead to loss of activity of the neurofibromin protein. Since neurofibromin negatively regulates RAS proteins, these become more active in patient cells. Whereas normal behavior of the RAS proteins dictates how cells survive and multiply, overactive RAS causes cells to divide unnecessarily, causing abnormal growths on different parts of the body. Deregulated RAS signaling also causes issues with learning and memory, as well as normal bone development. Current treatment for patients is limited to surgical resection of tumors, but for the other symptoms, no treatment is available. Clinical trials examining the efficacy of a MEK inhibitor (a drug that blocks activity of the signal pathway activated by RAS) show promise for treating plexiform neurofibromas. However, it is not clear yet how this drug might be used to treat other NF1 symptoms. Experience with this drug to treat cancer has shown that it is not well tolerated due to toxicity, i.e., the detrimental effect the drug has on normal cells in the body. Recently, clinical geneticists have started correlating the types of NF1 mutations with the severity of patient symptoms, so-called genotype-phenotype correlation. This highlights parts of the neurofibromin protein that are important for its function. Once such an area has been identified as a hotspot for mutations that cause the most severe phenotypes, we have found through biochemical analysis that mutations in this region cause the protein to be destabilized. We propose to study the mutated protein in more detail to find out why it is degraded and to see whether we can prevent this degradation and rescue the expression of the protein. In doing so, we hope to provide a clinical advantage over pharmacological RAS pathway blockade, since rescue of neurofibromin activity through protein stabilization should, in theory, be less toxic to normal cells, reducing drug side effects for patients. Our studies have also shown that the neurofibromin protein exists in multiple states within the cell, often as an inactive homodimer (two neurofibromin molecules bound to one another). This is a key step in the regulation of neurofibromin activity that we hope to explore in more detail to really understand how the protein functions to turn off RAS. This project will also build upon previous studies characterizing the interaction between neurofibromin and SPRED1, which locates it in the right part of the cell to turn off RAS. SPRED1 also binds and appears to be regulated by c-KIT, a cell surface receptor that responds to external signals. Mutations in c-KIT can lead to clinical features that resemble NF1, suggesting a role for c-KIT in regulating neurofibromin through interaction with SPRED1. We appreciate that a sound understanding of the molecular basis of this disease is critical to developing successful targeted therapies that will improve quality of life for patients.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 10, 2021
- Source ID
- W81XWH2010129
Entities
People
- Frank McCormick
Organizations
- United States Army
- University of California, San Francisco