1、1,NF1: Tumor Suppressor Gene,Presentation by Hana Masood,2,Overview of Presentation,Disease Neurofibromatosis Type I NF1 Gene Protein - Neurofibromin Protein Function RasGAP Biological Role Active in Ras Pathway NF1 gene and Neurofibromin Role in Cancer,3,Neurofibromatosis Type I,Among most common n

2、eurogenetic disorders -It is heritable; all affected members of family have same form of NF Affects 1 in 3,500 Whereas NF2 affects only 1 in 40,000 Diagnosis based on any 2 of the following clinical criteria: - Greater than or equal to 6 caf-au-lait spots - Freckles underarm or groin - Greater than

3、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),http:/www.understandingnf1.or

4、g/id/int_id_win.html,4,Neurofibromatosis Type I,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 per

5、son,/exp/int_exp_wcn.html,European Genetics Foundation http:/www.charite.de/ch/medgen/eumedis/embryology04/neurocutan-disorders.html,5,NF1 Gene,NF1 is a tumor suppressor gene NF1 is located on Chromosome 17 long arm - NF2 on other hand is located on Chromosome 22 NF1 ge

6、ne encodes the protein Neurofibromin,http:/www.charite.de/ch/medgen/eumedis/embryology04/neurocutan-disorders.html,6,NF1 Gene,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 o

7、ne way NF1 is inactivated - usually a mutation that causes a charge inversion; mostly change from Lysine to something like Glutamine in protein,cc.oulu.fi/anatwww/ NF/Neurofibromin/Ras.jpg,Scheffzek et al, The Embo Journal, 1998, Vol. 17,7,NF1 Gene Inactivation (Loss of Function),50% of cases inheri

8、ted 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 prot

9、ein - Schwann cells are the initiating cells in neurofibroma formation So, NF1 behaves as a dominant trait phenotypically, but is still recessive genotypically,/id/int_id_win.html,Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e69,8,Biochemical and Cell Biological R

10、ole of Neurofibromin,Neurofibromin acts as a RasGAP that acts mostly in Schwann cells - What is a RasGAP?,Lodish et al. Fig. 20-22,9,Neurofibromin Molecule,Has homology to p120GAP Expressed in all tissues, highest levels in brain, kidney, and spleen Associates with cytokeratin bundles in human kerat

11、inocytes 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,RasGAP (250-400 AA),2818,10,Neurofibromin GAP-Related Domain,Scheffzek et al, The Embo Journal, 1998, Vo

12、l. 17,11,Neurofibromin GAP-Related Domain and Ras Interaction,Scheffzek et al, The Embo Journal, 1998, Vol. 17,12,Neurofibromin in Ras Pathway,cc.oulu.fi/anatwww/ NF/Neurofibromin/Ras.jpg,13,Neurofibromin involvement in Schwann cells Biological Role,Neurofibromin involved in Schwann cell differentia

13、tion Schwann cells are a regenerative cell type that has no known stem-cell population Part of peripheral nerves,/cmallery/150/neuro/sf42x10b.jpg,14,Schwann Cells,/UNIScienceNet/Schwann%20cell.jpg,/histology/i/21301loa.jpg,15,Biological Role o

14、f Neurofibromin,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 Neurofibro

15、min RasGAP causes re-differentiation of Schwann cells Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e69, 2004,16,Biological Role of Neurofibromin,NF1 inactivation causes constitutive Ras activity in Schwann cells Ras signalling drives the de-differentiation of myelinating Schwann cells that lea

16、d 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, 2004,17,Biological Role of Neurofibromin Studies,NF1 bi-allelic inactivation i

17、s 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 hyper-refractile, long processes NF1+/- Schwann cells have intermediate phenotype (some Neurofibrom

18、in activity),Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e69-70, 2004,18,Summary of Biological Role of Neurofibromin,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 different

19、iation signals emanating from axons Neurofibromin indirectly allows re-differentiation to happen by controlling the level of de-differentiation,Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e70, 2004,19,NF1 Inactivation Role in Cancer De-Differentiation,NF1+/- Schwann cells might not have suffi

20、ciently increased Ras signalling to de-differentiate But, state may make Schwann cells more susceptible to de-differentiation 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. e70-71,20,NF1 Inact

21、ivation Role in Cancer Nonautonomous Process,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 cellu

22、lar 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, 922,21,NF1 Inactivation Role in Cancer Nonautonomous Process,“Tumor formation is a coordinated process in which inc

23、ipient 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

24、et al, Science, 2002, Vol. 296, p. 921-22,22,NF1 Inactivation Role in Cancer Nonautonomous Process,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

25、 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

26、stimulate mast cell chemotaxis, which induces collagen deposition, cell proliferation, and angiogenesis,Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e71, 2004,23,NF1 Inactivation Role in Cancer - Overall,Nerve damage could trigger the production of proliferative signals by NF1+/- fibroblasts,

27、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 for

28、mation,Harrisingh and Lloyd, Cell Cycle, 2004, Vol. 3, p. e70-1, 2004,24,Role of the Inactivation of NF1 in Cancer (Neurofibromatosis) - Animation,Inactivation of NF1 in Cancer,25,Neurofibromatosis Type I and Cancer,Neurofibromas benign Plexiform neurofibromas subtype of benign tumors, can undergo t

29、ransformation 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

30、,Arun and Gutmann, Current Opinion in Neurology, 2004, Vol. 17, p. 101 /geneweb/NF1.htm#malig,26,Neurofibromatosis Type I and Cancer,“NF1 patients developing malignant neoplasms can have any type of NF1 germline mutation such as a total gene deletion, a frameshift mutation,

31、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 Chromosom