Transcript NF1: Tumor Suppressor Gene

NF1: Tumor
Suppressor Gene
Presentation by
Hana Masood
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Overview of Presentation
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Disease – Neurofibromatosis Type I
NF1 Gene
Protein - Neurofibromin
Protein Function – RasGAP
Biological Role – Active in Ras Pathway
NF1 gene and Neurofibromin Role in Cancer
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Neurofibromatosis Type I
Among most common neurogenetic disorders
-It is heritable; all affected members of family have same form of NF
 Affects 1 in 3,500
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Whereas NF2 affects only 1 in 40,000
Diagnosis based on any 2 of the following clinical criteria:
- Greater than or equal to 6 café-au-lait spots
- Freckles underarm or groin
- Greater than or equal to 2 neurofibromas, or 1 plexiform
neurofibroma
- Iris Lisch nodules identified by ophthalmologist
- Tumor of optic nerve called optic pathway glioma (in astrocytes)
- Bone deformities (i.e. around eye, tibia)
- First degree relative (parent, sibling, or child)
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http://www.understandingnf1.org/id/int_id_win.html
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Neurofibromatosis Type I
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Affects peripheral nerves
brain, and spinal cord
More active as get older
In adolescence, also find
learning disabilities in
reading, math, trouble
following directions, and
paying attention
All racial and ethnic
backgrounds
Symptoms vary person to
person
http://www.understandingnf1.org/exp/int_exp
_wcn.html
European Genetics Foundation
http://www.charite.de/ch/medgen/eumedis/embryolog
y04/neurocutan-disorders.html
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NF1 Gene
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NF1 is a tumor
suppressor gene
NF1 is located on
Chromosome 17 long
arm
- NF2 on other hand is located
on Chromosome 22
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NF1 gene encodes the
protein Neurofibromin
http://www.charite.de/ch/medgen/eumedis/embryology04/neurocutan-disorders.html
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NF1 Gene
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Cloned in 1990
Over 300kb of genomic DNA, 50 exons
Very large and complicated, and genetic
changes can be very small and subtle
A missense mutation in GAP-Related Domain
is one way NF1 is inactivated
- usually a mutation that causes a charge
inversion; mostly change from Lysine to
something like Glutamine in protein
Scheffzek et al, The Embo Journal, 1998, Vol. 17 6
cc.oulu.fi/~anatwww/ NF/Neurofibromin/Ras.jpg
NF1 Gene Inactivation
(Loss of Function)
50% of cases inherited from parent, other 50% of
cases start out as a new NF1 mutation in sperm or
egg that makes the child
 All cell types are initially NF+/- until a subpopulation
of Schwann cells undergo LOH and become NF-/ Bi-allelic inactivation in Schwann cells causes the
lack of expression of Neurofibromin protein
- Schwann cells are the initiating cells in neurofibroma
formation
 So, NF1 behaves as a dominant trait phenotypically,
but is still recessive genotypically
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Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e69
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http://www.understandingnf1.org/id/int_id_win.html
Biochemical and Cell Biological
Role of Neurofibromin
Neurofibromin acts as a
RasGAP that acts
mostly in Schwann cells
- What is a RasGAP?
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Lodish et al. Fig. 20-22
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Neurofibromin Molecule
RasGAP
(250-400 AA)
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2818
Has homology to p120GAP
Expressed in all tissues, highest levels in brain,
kidney, and spleen
Associates with cytokeratin bundles in human
keratinocytes and also binds tubulin
Thus, exerts its effects in part by controlling
organization of cytoskeleton during the
formation of cellular contacts
cc.oulu.fi/~anatwww/ NF/Neurofibromin/Ras.jpg
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Neurofibromin GAP-Related
Domain
http://www.nature.com/emboj/journal/v17/n15/full/7591132a.html 10
Scheffzek et al, The Embo Journal, 1998, Vol. 17
Neurofibromin GAP-Related
Domain and Ras Interaction
http://www.nature.com/emboj/journal/v17/n15/full/7591132a.html 11
Scheffzek et al, The Embo Journal, 1998, Vol. 17
Neurofibromin in Ras Pathway
cc.oulu.fi/~anatwww/ NF/Neurofibromin/Ras.jpg
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Neurofibromin involvement in
Schwann cells – Biological Role
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Neurofibromin involved
in Schwann cell
differentiation
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Schwann cells are a
regenerative cell type that
has no known stem-cell
population
Part of peripheral nerves
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http://fig.cox.miami.edu/~cmallery/150/neuro/sf42x10b.jpg
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Schwann Cells
http://www.unis.org/UNIScienceNet/Schwann%20cell.jpg
http://www.bu.edu/histology/i/21301loa.jpg
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Biological Role of
Neurofibromin
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Following nerve damage, myelinating Schwann
cells produce new cells by de-differentiating,
proliferating, and then re-differentiating
Axons in vivo provide signals that regulate
Schwann cell differentiation
Ras causes de-differentiation and leads to
proliferation, and then Neurofibromin RasGAP
causes re-differentiation of Schwann cells
Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e69, 2004
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Biological Role of
Neurofibromin
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NF1 inactivation causes
constitutive Ras activity in
Schwann cells
Ras signalling drives the
de-differentiation of
myelinating Schwann cells
that lead to tumors if
uncontrolled
Thus, the role of
Neurofibromin is to act as a
tumor suppressor and
control Ras activity by
catalyzing its inactivation
when necessary
Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e69-70, 2004
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Biological Role of
Neurofibromin – Studies
NF1 bi-allelic inactivation is embryonically
lethal in mice
 NF1-/- Schwann cells are angiogenic and
invasive in vitro, and have:
- elevated levels of Ras-GTP (active) compared
to wild-type cells
- altered morphology elongated and hyperrefractile, long processes
• NF1+/- Schwann cells have intermediate
phenotype (some Neurofibromin activity)
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Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e69-70, 2004
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Summary of Biological Role of
Neurofibromin
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Ras pathway in Schwann cell acts by driving the
de-differentiation process itself, not by blocking a
differentiation signal
The Raf/ERK signal can act dominantly over
differentiation signals emanating from axons
Neurofibromin indirectly allows re-differentiation
to happen by controlling the level of dedifferentiation
Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e70, 2004
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NF1 Inactivation Role in
Cancer – De-Differentiation
• NF1+/- Schwann cells might
not have sufficiently
increased Ras signalling to
de-differentiate
• But, state may make
Schwann cells more
susceptible to dedifferentiation and facilitate
loss of second allele (LOH)
to shift equilibrium in favor
of the de-differentiated state
Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e70-71
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NF1 Inactivation Role in Cancer –
Nonautonomous Process
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NF1-/- Schwann cells really
induce neurofibroma formation
in the presence of abnormal
heterozygous NF1
environment that drive
proliferation
Haploinsufficient state of
somatic tissue surrounding
NF1 tumors initiates or
progresses tumor formation
When cellular environment has
both functional NF1 alleles, the
onset, growth potential, and
multicullular nature of NF1-/neurofibromas is suppressed
Zhu et al, Science, 2002, Vol. 296, p. 920, 922
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NF1 Inactivation Role in Cancer –
Nonautonomous Process
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“Tumor formation is a
coordinated process in
which incipient tumor cells
recruit collaborating cells
(i.e. mast, fibroblast cells)
from the environment”
Through heterozygous
inactivation mouse study,
believed that heterozygous
mast cells interacting with
nullizygous Schwann cells
creates a cytokine-rich
microenvironment
permissive for tumor growth
Zhu et al, Science, 2002, Vol. 296, p. 921-22
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NF1 Inactivation Role in Cancer –
Nonautonomous Process
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NF1+/- mice have abnormal responses to skin wounding,
with increased collagen deposition and fibroblast
proliferation, also observed in neurofibroma formation
NF+/- neurons, mast cells, and fibroblasts in mice do
not undergo NF1 LOH, promote abnormal cell
environment
NF+/- fibroblasts have defects in proliferation and
perineurial sheath formation, allowing inappropriate
exposure to circulating growth factors and hormone
NF-/- Schwann cells secrete increased levels of stem
cell factor, thought to stimulate mast cell
chemotaxis, which induces collagen deposition, cell
proliferation, and angiogenesis
Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e71, 2004
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NF1 Inactivation Role in
Cancer - Overall
• Nerve damage could trigger
the production of
proliferative signals by
NF1+/- fibroblasts, nerve
cells, and mast cells that
could result in the
unregulated proliferation of
de-differentiated NF1-/Schwann cells that have
lost Neurofibromin activity
• NF1 patients undergo an
altered response to normal
nerve repair signal with
repeated cycles of
attempted repair resulting in
neurofibroma formation
Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e70-1, 2004
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Role of the Inactivation of NF1 in Cancer
(Neurofibromatosis) - Animation
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Inactivation of NF1 in Cancer
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Neurofibromatosis Type I and
Cancer
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Neurofibromas – benign
Plexiform neurofibromas – subtype of benign
tumors, can undergo transformation by
CDKN2A/p16 or INK4A inactivation (causes loss of
p16 cdk inhibitor) into malignant peripheral nerve
sheath tumors (MPNSTs)
Also, MPNSTs aberrantly express EGFR
MPNSTs are highly aggressive cancers
8-13% of NF1 patients develop it
15-20% of NF1 children develop low-grade
astrocytomas
Arun and Gutmann, Current Opinion in Neurology, 2004, Vol. 17, p. 101
http://www.cancerindex.org/geneweb/NF1.htm#malig
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Neurofibromatosis Type I and
Cancer
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“NF1 patients developing
malignant neoplasms can have
any type of NF1 germline
mutation such as a total gene
deletion, a frameshift mutation,
an in-frame deletion, or a
missense mutation. We
conclude that in our series no
specific type of NF1 germline
mutation was found in NF1
individuals with malignancies,
but that large NF1 gene
deletions were more frequently
found in this group than
reported for the general
population of NF1 individuals.”
Genes Chromosomes Cancer, Vol. 26, p.
376-80, 1999
European Genetics Foundation
http://www.charite.de/ch/medgen/eumedis/embryology04/neurocutan-disorders.html
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What did the Elephant Man
have?
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Joseph Merrick did not have NF1
He really had another disease  Proteus Syndrome
(sine had mutation on another gene)
Genetic Science Learning Center at the University of Utah
http://gslc.genetics.utah.edu/units/disorders/nf1/elephantman.cfm
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Treatment for NF1
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Primary option is surgery for both benign and
malignant tumors
Noncomparative phase II evaluation of cis-retinoic
acid (promaturation agent) and interferon-alpha
(anti-inflammatory and antiangiogenic effects)
Phase I studies for farnesyl protein transferase
inhibitors that inhibit Ras activity
Pirfenidone, an antibiotic drug that regulates
cytokine action, in clinical trial
EGFR inhibitors may be effective in MPNSTs
Possibly therapies that neutralize the effects of
haploinsufficiency before the onset of
tumorogenesis
Arun and Gutmann, Current Opinion in Neurology, 2004, Vol. 17, p. 102, 104
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