Molecular background of tuberous sclerosis complex - part I

Tuberous sclerosis complex (TSC) is a progressive, dominantly inherited disorder affecting multiple organs mainly: skin, central nervous system, kidneys, lungs, heart and eyes. The prevalance of tuberous sclerosis among general population is estimated to be one in 10,000-30,000. The diagnostic criteria for TS are based on the premise that there are probably no truly one pathognomonic clinical sign but two or more major features are required for formal diagnosis. This disease is associated with mutation in two tumour suppressor genes: TSC1 and TSC2. The main function of protein encoded by TSC1 and TSC2 genes is suppressing signal in the mammalian target of rapamycin (mTOR) pathway. TSC1 is located on chromosome 9q34, the gene contains 23 exons and encodes hamartin. TSC2 is located on chromosome 16p13, the gene contains 41 exons and encodes tuberin. The proteins interact directly with one another and pathological mutations affecting either gene result in TS phenotype. TSC2 protein is the only known GTPase activating protein (GAP) for RAS homolog enriched in brain ( RHEB), so that in the absence of functional TSC1/TSC2 complex, RHEB-GTP levels rise. RHEB-GTP levels have a major role in regulating the state of activation of the mTOR complex. Activated mTOR complex has two primary downstream targets: the ribosomal S6 kinases (S6K1 and S6K2) and the eukaryotic initiation factor E4 - binding protein 1 (E4-BP1). The rapamycin is the one of known inhibitors of mTOR and potential drug for TSC.