# F-box ubiquitin ligases destabilize neurofibromin

> **NIH NIH R01** · INDIANA UNIVERSITY INDIANAPOLIS · 2021 · $344,531

## Abstract

PROJECT SUMMARY / ABSTRACT
Mutations in the NF1 tumor suppressor gene cause neurofibromatosis type 1 (NF1), the most common human
genetic cancer predisposition syndrome. Individuals with NF1 suffer from a wide range of malignant and
nonmalignant clinical manifestations including plexiform neurofibromas (PN), complex precancerous lesions
which affect 25-40% of NF1 patients and cause major lifelong morbidity and mortality. The NF1 gene encodes
neurofibromin, a GTPase-activating protein (GAP) for p21ras (Ras). We previously determined that loss of a
single allele of Nf1 (Nf1+/-) results in Ras hyperactivation in NF1 patient (NF1+/-) and murine (Nf1+/-) myeloid cells,
a concept known as haploinsufficiency. We generated a genetically engineered murine model of
neurofibromatosis and demonstrated that plexiform neurofibroma formation requires the inflammatory
contribution of Nf1+/- bone marrow. Further, we showed that genetic inhibition of kinase pathways downstream
of neurofibromin in the hematopoietic system prevents tumorigenesis. This work has led to the first ever
successful pharmacological treatment of these tumors in both preclinical models and in our phase II clinical trial.
Despite this success, complementary strategies to correct Ras hyperactivation in neurofibromin-deficient tissues
are needed due to the complexity of Ras-mediated signaling pathways and the heterogeneity of patient response
to kinase inhibitors for these complex tumors that are completely resistant to traditional chemotherapy and
radiation treatment.
Neurofibromin is phosphorylated, ubiquitinated, and degraded at the proteasome in response to growth factor
stimulation, but little is known about the mechanistic aspects of this process. Specifically, the ubiquitin ligase
specificity factor(s) (E3) that govern neurofibromin degradation in the tumor-driving hematopoietic cells are not
known. The F-box ubiquitin ligases degrade selected proteins in a phosphorylation-dependent manner, leading
us to hypothesize that the NF1 E3 belongs to the F-box family. In initial unpublished studies pursued in
preparation for this application, we conducted an RNAi screen, which identified strong novel candidate F-box
ubiquitin ligases for NF1. Here, we propose to mechanistically examine these newly identified F-box proteins
modulating neurofibromin degradation ex vivo and in vivo. We also propose to employ an unbiased functional
genomics strategy to identify kinase(s) that promote F-box-dependent degradation of neurofibromin via the
ubiquitin-proteasome pathway. We will employ a multidisciplinary approach to determine whether disruption of
our candidate neurofibromin E3s in vivo can rescue neurofibromin haploinsufficiency and prevent plexiform
neurofibroma initiation and progression. These studies will also provide basic insights into the regulation of a
common but understudied tumor suppressor gene.

## Key facts

- **NIH application ID:** 10249088
- **Project number:** 5R01NS104489-04
- **Recipient organization:** INDIANA UNIVERSITY INDIANAPOLIS
- **Principal Investigator:** David W Clapp
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $344,531
- **Award type:** 5
- **Project period:** 2018-09-01 → 2023-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10249088

## Citation

> US National Institutes of Health, RePORTER application 10249088, F-box ubiquitin ligases destabilize neurofibromin (5R01NS104489-04). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10249088. Licensed CC0.

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