Tuberous Sclerosis TSC2/ Tuberin Alison Chappell

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

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.

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

Major Features of TSC Brain: cortical tubers, subependymal noduals, giant cell astrocytomas (15%), seizures (60-90%), mental retardation/ developmental delay Kidney: angiomyolipomas, cysts

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

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

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

Model of Tuberin- Hamartin complex and mTOR pathway Tee et.al 2002

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) 5’TOP mRNA (5’ terminal oligopyrimidine tract)- encode ribosomal proteins and several other components of translational machinery leading to increased cell growth

McManus, et al. 2002

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.

Tuberin and Rap 1 Tuberin’s 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

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)

TSC 2 mutations TSC2 mutations include large deletions, insertions and rearrangements (>1kb) 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

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)

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.