Tuberous Sclerosis

1
Tuberous Sclerosis

• TSC2/ Tuberin

Alison Chappell
2
Objectives

• Characteristics of Disease
• TSC 2 gene
• Hypothetical biochemical function of TSC 2/
  Tuberin
• Mutations and their effects

3
Tuberous Sclerosis

• At least two children are born each day with TS.
  Affects 50,000 Americans and 2 million people
  worldwide.
• Affects multiple organs and is characterized by
  hamartomas (benign tumor cells)
• Although, the tumors rarely into malignancy they
  can cause various problems and difficulties.

4
Major Features of TSC

• Major Organs Skin, Heart, Brain, and Kidney
• Skin facial angiofibromas (most distinctive
  feature, displayed in 70 of all TSC patients),
  hypomelanotic macules
• Heart rhabdomypomas and arrhythmias

5
Major Features of TSC

• Brain cortical tubers, subependymal noduals,
  giant cell astrocytomas (15), seizures (60-90),
  mental retardation/ developmental delay
• Kidney angiomyolipomas, cysts

6
Inheritance / Penetrance

• 33 of TSC patients inherit a mutation from
  their parents.
• The other 66 of TSC patients develop disease due
  to sporadic mutations from the parent passed on
  to the child.
• 100 penetrance
• Autosomal Dominate Disorder yet recessive on the
  cellular level

7
TSC 2 gene

• TSC 2 is located at 16p13 and encodes the amino
  acid protein, Tuberin.
• Functional Regions
• C- Terminus the GTP-ase activating protein
  homology (GAP) for Rap 5 and Rap 1
• Coiled- Coil domain- interaction with TSC 1/
  Harmartin

Goncharova et al. 2002
8
Hypothetical Biochemistry of TSC

• TSC is possibly involved cell cycle regulation,
  vesicular trafficking, and transcriptional
  activation by steroid hormone
• Genetic approach- clone of TSC 2
• Tuberin is highly conserved between organisms-
  Drosphila
• Increased growth (increase of mass per unit time)
  and proliferation (an increase in cell number)

Increased size of wing and eye with TSC 2
mutation. Ito.ed al 1999
9
Model of Tuberin- Hamartin complex and mTOR
pathway Tee et.al 2002
10
mTOR pathway

• Insulin major regulator of cellular growth
• Tuberin/ Harmartin complex act as a tumor
  suppressor on mTOR
• mTOR (active) allows for the phosphorylation of
  S6 by S6K and the inactivation of the 4E-BP1 (4E
  binding protein- eukaryotic initiation factor)
• 5TOP mRNA (5 terminal oligopyrimidine tract)-
  encode ribosomal proteins and several other
  components of translational machinery leading to
  increased cell growth

11
McManus, et al. 2002
12
mTOR pathway, continued.

• PI(3)K (phosphoinositide-3-kinase) is recruited
  to the plasma membrane in response to stimulation
  with growth factors as insulin.
• PI(3)K generates a lipid second messenger
  phosphatidylinositol-3,4,5-trisphosphate induces
  PKB (Akt) and S6K activation.

13
Tuberin and Rap 1

• Tuberins GAP activity for rap1 and rap5.
• Rap 1 and Rap 5 are members of the Ras
  superfamily of GTPases serve roles in
  mitogenesis, neuronal differentiation, and early
  endosome fusion.
• Little research since 1997

14
TSC mutations

• Mutation in TSC 1 or TSC 2 result in the same
  clinical abnormalities.
• Mutation in TSC 1 or 2 in Drosophila revealed
  cells spend less time in G1 and inappropriately
  entered the cell cycle when they should have been
  quiescent.
• The result of these mutations were larger cells
  with normal ploidy. (Tapon et al 2002)

15
TSC 2 mutations

• TSC2 mutations include large deletions,
  insertions and rearrangements (gt1kb) and a
  significant number of missense mutations
• Many mutations localized in the GAP region and a
  few in the binding region of Tuberin to Hamartin

16
TSC 2 mutations

• In HEK293 cells, derived from human embryonic
  kidney cells, Soueke studied the effects of TSC 1
  and TSC 2 on cells. (Soucek, et.al 1998)
• The data suggest that tuberin (TSC 2), not
  hamartin (TSC1), is responsible for G1 regulation
  by the hamartin-tuberin complex.
• Increased Intellectual disability with mutations
  in TSC 2 (Jones et.al 1999)

17
Summary

• Tuberous Sclerosis is an autosomal dominate
  disorder characterized by harmatomas (benign
  tumors).
• TSC 2 produces the protein, Tuberin, has a GTP-
  ase (GAP) activating region and a coiled- coil
  domain which facilitates binding to Hamartin
  (TSC1).
• The biochemical function of TSC is unclear yet
  best evidence is TSC involvement in the mTOR/
  insulin pathway.