TSC2 GENE ENCODES FOR TUBERIN By May Doan

Content

Disease: Tuberous SclerosisTSC2 Gene DiscoveredGeneral Roles within the Organism

Molecular Roles within the CellMutations and CancerPossible TreatmentsSummary

Disease: Tuberous Sclerosis

Autosomal dominant Rare, multisystem

disorder Loci assigned at

chromosomes 9 and 16 Characterized by:

Cortical lesions called tubers

Benign tumors called hamartomas arising from the brain, heart, lungs, and kidneys

Intractable epilepsy Mental retardation Autism

What causes tuberous sclerosis?

TSC2 Gene Discovered PFGE: 5 TSC-related

deletions were IDed at Chromosome 16.

Positional Cloning: These deletions were mapped to a 120kb “candidate region” in which four genes were isolated.

One gene, now TSC2, was interrupted in all five deletions.

Northen blot analysis identified either shortened transcript or reduced expression in TSC patients.

This confirmed that TSC2 (5.5 kb) is the chromosome 16 TSC gene.

So what is TSC2?

TSC2 is a Tumor Supressor Gene Follows Knudson’s “two-hit” hypothesis Loss of Heterozygosity through various

mutations: Germline insertions De novo deletions

TSC2 is NOT TSC1 Similarities Differences

What does TSC2 do within the organism?

General Roles within the OrganismAbnormalities Observed in TSC pathology

Implied Role of TSC2

Picture

Cell size Cell growth

Cell number Cell proliferation

Morphology Differentiation

Location Migration

How does TSC-2 function molecularly? What are the mechanisms in which it executes all these roles?

TSC2 is a Kinase and Molecular Switch Regulate many biological

processes=Participates in many signaling pathways mTOR WNT/B-catenin

TSC2tuberin (kinase domain and GAP domain)

mTOR Pathway

TSC2 a Rheb-GTPase that suppresses mTOR signaling

suspends the phosphorylation of p70S6K and 4E-BP1

thereby regulates cell proliferation

TSC2 MutationsCancer

Possible Treatment: Rapamycin

DAY 4: reduction in tumor size

WEEK 2: extensive tumor cell death

Additional Comments

Have not documented a consistent complete pathologic response to long-term rapamycin treatment.

In fact, after two months, there was evidence of active kidney disease.

Only short-term clinical efficacy with minimal toxocity.

Still issues to be worked out optimal dosing schedule duration of responses potential resistance

WNT/B-Catenin Pathway

Observations/Correlations CyclinD gene promoter is responsive to the

effects of WNT/B-catenin stimulation. CyclinD mRNA is elevated in cortical tumors like

hamartomas. inhibition of TSC2 expression by anti-sense oligos

was accompanied by increased cyclin D1 protein Conclusion

May be a link between the TSC2 and the B-catenin signaling pathway as a possible mechanism of cyclin D1 up-regulation in TSC pathology.

WNT/Beta-Catenin Pathway

Hypothesis: The level of B-catenin is correspondingly up-regulated by increased protein stability Aka: if B-catenin is not degraded, it is overly stable, producing more

than normal CyclinD Known

TSC1/TSC2 act downstream of DSH and upstream of B-catenin. Conclusion

This places the function of the tuberin at the level of the B-catenin degradation complex.

Experiment Co-immunoprecipitation analyses showed interaction between TSC2

and GSK3/Akin amount of endogenous GSK3 associated with tuberin in 293 cells

was reduced by Wnt stimulation. Conclusion

TSC2 binds the GSK3/Axin complex and promotes B-catenin degradation. Upon Wnt stimulation, DSH destabilizes the degradation complex and increases the free B-catenin pool.

Summary

Tuberous Sclerosis is an autosomal dominant disease characterized by skin lesions and hamartomas.

TSC2 was discovered in 1993 through positional cloning.

TSC2 regulates many biological processes. TSC2’s protein product, tuberin, is a kinase and

molecular switch that participates in many pathways Pathway related to cell proliferation: mTOR Rapamycin has had positive clinical results to treat

TSC in rats. Pathway related to cell fate determination and

migration: WNT/B-catenin