Neurofibromatosis type 1 (NF1) is a highly variable and unpredictable disease, the severity of which appears to be determined by as yet unknown modifier genes. The NF1 gene encodes neurofibromin, whose only agreed upon function is to serve as a negative regulator of Ras. Beyond benign and malignant tumors, NF1 patients also suffer from several less well understood non-tumor symptoms, including an overall growth deficiency and learning problems. A Drosophila NF1 model displays phenotypes resembling these non-tumor symptoms. Strikingly, most Drosophila NF1 phenotypes are not readily modified by attenuating Ras signaling, but are restored by increasing signaling through the cAMP-dependent protein kinase A (PKA) pathway. This has made determining how NF1 affects cAMP signaling a central issue in NF1 research. Our results indicate that the overall growth defect of Drosophila NF1 mutants reflects a non-cell-autonomous requirement for RasGAP activity in specific larval neurons. We initially suggested that this primary Ras signaling defect in turn causes a secondary hormonal defect, which is mitigated by increasing cAMP. New evidence now suggests an alternative dual-function hypothesis, which states that NF1 is not just required in neuroendocrine cells to regulate Ras and the production of one or more hormones, but also in hormone responding cells to efficiently couple hormone receptors to adenylyl cyclase. We propose a combination of genetic and biochemical approaches to test the merits of this hypothesis, which may explain why we and others have reached contradictory conclusions about NF1 functions essential for phenotypic rescue. Our new results have implicated the neuroendocrine Ret tyrosine kinase, and an adenylyl cyclase-coupled neuropeptide receptor and its ligand as genetic suppressors of the NF1 size defect. We propose four interconnected sets of genetic and biochemical experiments to follow up on these results, and to achieve our overall goal of providing a molecular description of mechanisms underlying NF1 defects.

Public Health Relevance

Neurofibromatosis type 1 (NF1) is among the most common genetic diseases of man. Its estimated incidence of 1 in 3,000 suggests there may be 100,000 NF1 patients in the US alone. In this project we will use a combination of biochemical, molecular biological, and genetic approaches in the genetic model organism, Drosophila melanogaster, to identify mechanisms responsible for NF1 defects A better understanding of these mechanisms is a required step on the road to rational therapy for NF1.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM084220-02
Application #
7686701
Study Section
Cellular Signaling and Regulatory Systems Study Section (CSRS)
Program Officer
Krasnewich, Donna M
Project Start
2008-09-15
Project End
2012-08-31
Budget Start
2009-09-01
Budget End
2010-08-31
Support Year
2
Fiscal Year
2009
Total Cost
$353,833
Indirect Cost
Name
Massachusetts General Hospital
Department
Type
DUNS #
073130411
City
Boston
State
MA
Country
United States
Zip Code
02199
Walker, James A; Gouzi, Jean Y; Long, Jennifer B et al. (2013) Genetic and functional studies implicate synaptic overgrowth and ring gland cAMP/PKA signaling defects in the Drosophila melanogaster neurofibromatosis-1 growth deficiency. PLoS Genet 9:e1003958
Gouzi, Jean Y; Moressis, Anastasios; Walker, James A et al. (2011) The receptor tyrosine kinase Alk controls neurofibromin functions in Drosophila growth and learning. PLoS Genet 7:e1002281
Huson, Susan M; Acosta, Maria T; Belzberg, Allan J et al. (2011) Back to the future: proceedings from the 2010 NF Conference. Am J Med Genet A 155A:307-21