1. Neurofibromatosis 1 Valerie Khodush March 27, 2007
NF1 because there is a gene (NF2) of similar function that effects the central nervous system as we learned last week.

2. NF-1 Overview Incidence – 1:3500 Von Reckinghausen Disease
Tumor pre-disposing disease
Protein: neurofibromin
( kDa)
Tumor suppressor
Neurofibromatosis is also known as Von Reckinghausen Disease and is the most common tumor pre-disposing disease. The incidence rate of NF1 is about 1/3000 and the protein that the gene codes for is neurofibrin.

3. Remember Ras
As we’ve learned, the ligand binds to the receptor kinase and through a series of proteins, Ras is activated. Remember, Ras is inactive when bound to GDP and active when bound to GTP. This is controlled by various GAP (GTPase Activating Protein) and GEF (Guanine Exchange Factor) proteins.
Gilbert Fig. 6.14

4. NF1 is a Ras-Gap
NF1 is considered a tumor suppressor because it acts as a GTPase activating enzyme, accelerating the conversion of active Ras to inactive Ras. If there is a mutation on NF1, Ras is active for longer periods of time, promoting cell proliferation. NF1 is generally highly expressed, especially in the peripheral and central nervous system. Growth factors, on the other hand, degrade NF1 and increase Ras activity. The RAS-GAP domain function of NF1 makes up approximately 10% of the entire protein, and other functions are believed to be associated with cell growth, adenylate cyclase activity, and for cellular responses to neuropeptides. Now much is known about these pathways and they have been only briefly studied in Drosophila.

5. Mouse Knockout Embryonic lethal at E12.5 to E13.5
Cardiovascular problems
Organ development
Mice that acquire a homozygous mutation die between 12.5 and 13.5 days, as a result of cardiac vessel defect. Overall, the entire organ development is delayed and the embryo has an enlarged head and chest.

6. Mouse Knockout Heterozygous mice develop different cancers
Learning and spatial memory
Double mutants (NF1+/- & p53+/-)
Mice that are heterozygous for the NF1 gene are highly prone to cancer, yet not the same neurofibromatosis that is found in humans. Mice are more likely to develops cancers such as leukemia. Heterozygous mutants show many brain astrocytes with either abnormal attachment, spreading, and/or motility properties. NF1 is shown to be critical and non-redundant, meaning there are no other proteins that can replace its activity. Heterozygous mice do show learning and special memory impairments, as often seen in humans as well. This may be due to a function of NF1 that does not influence the RAS pathway. Double mutants, however, as with a mouse heterozygous for the NF1 gene and the p53 gene develop sarcomas that are very similar to human metastatic nerve tumors.

7. Neurofibromin Chromosome 17
The NF1 gene is located on the 17th chromosome and is very similar in function to the Rb gene that we have already studied. As the Rb gene, it is dominant on an individual level and recessive on the cellular level. How do we know it’s a tumor suppressor? From experiments, we know that a melanoma cell line with a neurofibromin deficiency can be injected with NF1 to inhibit growth and induce differentiation. Also, over expression of NF1 causes growth inhibition but no alteration of GTP-RAS levels. The mutation can be inherited either a familial level or through the germ line. Spontaneous mutations occur as much as 50% of the time. Schwann cells are the neoplastic cells of origin yet the protein is expressed in neurons, white blood cells, gonadal tissue and other neural tissues. Loss of heterozygosity occurs by the Knudson 2 hit hypothesis. The protein consists of 60 exons with different isoforms (different forms of the same protein).

8. Neurofibromin Chromosome 17 Similar to Rb function
The NF1 gene is located on the 17th chromosome and is very similar in function to the Rb gene that we have already studied. As the Rb gene, it is dominant on an individual level and recessive on the cellular level. How do we know it’s a tumor suppressor? From experiments, we know that a melanoma cell line with a neurofibromin deficiency can be injected with NF1 to inhibit growth and induce differentiation. Also, over expression of NF1 causes growth inhibition but no alteration of GTP-RAS levels. The mutation can be inherited either a familial level or through the germ line. Spontaneous mutations occur as much as 50% of the time. Schwann cells are the neoplastic cells of origin yet the protein is expressed in neurons, white blood cells, gonadal tissue and other neural tissues. Loss of heterozygosity occurs by the Knudson 2 hit hypothesis. The protein consists of 60 exons with different isoforms (different forms of the same protein).

9. Neurofibromin Chromosome 17 Similar to Rb function
Dominant versus recessive
The NF1 gene is located on the 17th chromosome and is very similar in function to the Rb gene that we have already studied. As the Rb gene, it is dominant on an individual level and recessive on the cellular level. How do we know it’s a tumor suppressor? From experiments, we know that a melanoma cell line with a neurofibromin deficiency can be injected with NF1 to inhibit growth and induce differentiation. Also, over expression of NF1 causes growth inhibition but no alteration of GTP-RAS levels. The mutation can be inherited either a familial level or through the germ line. Spontaneous mutations occur as much as 50% of the time. Schwann cells are the neoplastic cells of origin yet the protein is expressed in neurons, white blood cells, gonadal tissue and other neural tissues. Loss of heterozygosity occurs by the Knudson 2 hit hypothesis. The protein consists of 60 exons with different isoforms (different forms of the same protein).

10. Neurofibromin Chromosome 17 Similar to Rb function
Dominant versus recessive
Familial/de novo inheritance or spontaneous mutations
The NF1 gene is located on the 17th chromosome and is very similar in function to the Rb gene that we have already studied. As the Rb gene, it is dominant on an individual level and recessive on the cellular level. How do we know it’s a tumor suppressor? From experiments, we know that a melanoma cell line with a neurofibromin deficiency can be injected with NF1 to inhibit growth and induce differentiation. Also, over expression of NF1 causes growth inhibition but no alteration of GTP-RAS levels. The mutation can be inherited either a familial level or through the germ line. Spontaneous mutations occur as much as 50% of the time. Schwann cells are the neoplastic cells of origin yet the protein is expressed in neurons, white blood cells, gonadal tissue and other neural tissues. Loss of heterozygosity occurs by the Knudson 2 hit hypothesis. The protein consists of 60 exons with different isoforms (different forms of the same protein).

11. Neurofibromin Chromosome 17 Similar to Rb function
Dominant versus recessive
Familial/de novo inheritance or spontaneous mutations
Schwann cells/ LOH
The NF1 gene is located on the 17th chromosome and is very similar in function to the Rb gene that we have already studied. As the Rb gene, it is dominant on an individual level and recessive on the cellular level. How do we know it’s a tumor suppressor? From experiments, we know that a melanoma cell line with a neurofibromin deficiency can be injected with NF1 to inhibit growth and induce differentiation. Also, over expression of NF1 causes growth inhibition but no alteration of GTP-RAS levels. The mutation can be inherited either a familial level or through the germ line. Spontaneous mutations occur as much as 50% of the time. Schwann cells are the neoplastic cells of origin yet the protein is expressed in neurons, white blood cells, gonadal tissue and other neural tissues. Loss of heterozygosity occurs by the Knudson 2 hit hypothesis. The protein consists of 60 exons with different isoforms (different forms of the same protein).

12. Neurofibromin Chromosome 17 Similar to Rb function
Dominant versus recessive
Familial/de novo inheritance or spontaneous mutations
Schwann cells/ LOH
Isoforms
The NF1 gene is located on the 17th chromosome and is very similar in function to the Rb gene that we have already studied. As the Rb gene, it is dominant on an individual level and recessive on the cellular level. How do we know it’s a tumor suppressor? From experiments, we know that a melanoma cell line with a neurofibromin deficiency can be injected with NF1 to inhibit growth and induce differentiation. Also, over expression of NF1 causes growth inhibition but no alteration of GTP-RAS levels. The mutation can be inherited either a familial level or through the germ line. Spontaneous mutations occur as much as 50% of the time. Schwann cells are the neoplastic cells of origin yet the protein is expressed in neurons, white blood cells, gonadal tissue and other neural tissues. Loss of heterozygosity occurs by the Knudson 2 hit hypothesis. The protein consists of 60 exons with different isoforms (different forms of the same protein).

13. Neurofibromatosis Predisposition to nervous system tumors
Childhood characteristics of NF1 are variable. All of these individuals have a strong predisposition to nervous system tumors. In addition to this, over 50% of children will have learning disabilities and approximately 10% will have skeletal abnormalities such as bowing of legs or scoliosis (pictured, spine curvature). Many children form café-au-lait macules or freckling on their skin and Lisch nodules which are yellow/brown elevations on the iris (these do not affect vision). Optic nerve tumors are also often associated with NF1 mutations.

14. Neurofibromatosis Predisposition to nervous system tumors
Learning disabilities
Childhood characteristics of NF1 are variable. All of these individuals have a strong predisposition to nervous system tumors. In addition to this, over 50% of children will have learning disabilities and approximately 10% will have skeletal abnormalities such as bowing of legs or scoliosis (pictured, spine curvature). Many children form café-au-lait macules or freckling on their skin and Lisch nodules which are yellow/brown elevations on the iris (these do not affect vision). Optic nerve tumors are also often associated with NF1 mutations.

15. Neurofibromatosis Predisposition to nervous system tumors
Learning disabilities
Skeletal abnormalities
Childhood characteristics of NF1 are variable. All of these individuals have a strong predisposition to nervous system tumors. In addition to this, over 50% of children will have learning disabilities and approximately 10% will have skeletal abnormalities such as bowing of legs or scoliosis (pictured, spine curvature). Many children form café-au-lait macules or freckling on their skin and Lisch nodules which are yellow/brown elevations on the iris (these do not affect vision). Optic nerve tumors are also often associated with NF1 mutations.

16. Neurofibromatosis Predisposition to nervous system tumors
Learning disabilities
Skeletal abnormalities
Skin discoloration
Childhood characteristics of NF1 are variable. All of these individuals have a strong predisposition to nervous system tumors. In addition to this, over 50% of children will have learning disabilities and approximately 10% will have skeletal abnormalities such as bowing of legs or scoliosis (pictured, spine curvature). Many children form café-au-lait macules or freckling on their skin and Lisch nodules which are yellow/brown elevations on the iris (these do not affect vision). Optic nerve tumors are also often associated with NF1 mutations.

17. Neurofibromatosis Predisposition to nervous system tumors
Learning disabilities
Skeletal abnormalities
Skin discoloration
Lisch nodules
Childhood characteristics of NF1 are variable. All of these individuals have a strong predisposition to nervous system tumors. In addition to this, over 50% of children will have learning disabilities and approximately 10% will have skeletal abnormalities such as bowing of legs or scoliosis (pictured, spine curvature). Many children form café-au-lait macules or freckling on their skin and Lisch nodules which are yellow/brown elevations on the iris (these do not affect vision). Optic nerve tumors are also often associated with NF1 mutations.

18. Neurofibromatosis Predisposition to nervous system tumors
Learning disabilities
Skeletal abnormalities
Skin discoloration
Lisch nodules
Optic nerve tumors
Childhood characteristics of NF1 are variable. All of these individuals have a strong predisposition to nervous system tumors. In addition to this, over 50% of children will have learning disabilities and approximately 10% will have skeletal abnormalities such as bowing of legs or scoliosis (pictured, spine curvature). Many children form café-au-lait macules or freckling on their skin and Lisch nodules which are yellow/brown elevations on the iris (these do not affect vision). Optic nerve tumors are also often associated with NF1 mutations.

19. NF1 and Cancer Nervous system tumors
NF1 mutations predispose individuals to nervous system tumors. Skin discoloration will generally appear as young as birth or infancy while the tumors generally begin to develop between the age of 10 and 15.
Harrisingh & Lloyd Fig. 1

20. NF1 and Cancer Nervous system tumors
Neurofibroma versus plexiform neurofibrom
The most common tumors associated with NF1 is a benign growth within a peripheral nerve known as neurofibroma. This nerve is comprised of Schwann cells, fibroblasts, and mast cells. Plexiform neurofibroma is a more diffuse type of neurofibroma and can develop into an MPNST, a highly metastatic cancer but only found in 3-5% of individuals.
Harrisingh & Lloyd Fig. 1

21. NF1 and Cancer Nervous system tumors
Neurofibroma versus plexiform neurofibrom
Malignant Peripheral Nerve Sheath Tumor
Plexiform neurofibroma is a more diffuse type of neurofibroma and can develop into an MPNST, a highly metastatic cancer but only found in 3-5% of individuals.
Harrisingh & Lloyd Fig. 1

22. NF1 and Cancer Nervous system tumors
Neurofibroma versus plexiform neurofibrom
Malignant Peripheral Nerve Sheath Tumor
Multiple mutations involved
Many other mutations and LOH have been found in many MPNSTs including the p53 tumor suppressor, INK4 locus, and other cell-cycle growth regulators. The accumulation of all of these mutations may actually promote the transformation of a neurofibroma into a MPNST. Also found through experiments is the DNA amplification and increased expression of epidermal growth factor receptors in MPNSTs. So, again, if NF1 is mutated, Ras is activated for extended periods of time causing excessive cell proliferation. The RAS pathway is also involved in cell dedifferentiation so LOH in NF1 schwann cells leads to dedifferentiation and neurofibromas form from these cells.
Harrisingh & Lloyd Fig. 1

23. Treatments Surgery Back Braces Radiation Chemotherapy
Treatment is generally aimed at controlling symptoms. Bone malformations may be fixed with surgery and scoliosis specifically may require surgery along with a back brace. Tumors that are disfiguring or painful may be removed surgically as well, but there is no guarantee that they will not grow back. For the small percentage of malignant tumors, radiation and chemotherapy may be used.

24. QUESTIONS