This family includes the hamartin protein which is thought to function as a tumour suppressor. The hamartin protein interacts with the tuberin protein . Tuberous sclerosis complex (TSC) is an autosomal dominant disorder and is characterised by the presence of hamartomas in many organs, such as brain, skin, heart, lung, and kidney. It is caused by mutation in either TSC1 or TSC2 tumour suppressor genes. TSC1 encodes a protein, hamartin, containing two coiled-coil regions, which have been shown to mediate binding to tuberin. The TSC2 gene codes for tuberin .
This entry includes protein melted from fruit flies and its homologues. They contain a single C-terminal PH domain that is required for membrane targeting. Melted interacts with both Tsc1 and FOXO and can recruit them to the cell membrane []. In vertebrates the melted protein homologue, veph, is expressed in the developing central nervous system []. The human homologue VEPH1 (ventricular zone-expressed PH domain-containing protein homologue 1) has been shown to inhibit TGF-beta signaling by impeding the release of activated SMAD2 from TbetaRI [].
Tuberous sclerosis (TSC) is an autosomal dominant disorder caused by a mutation in either the TSC1 or TSC2 tumour suppressor genes. The disease ischaracterised by hamartomas in one or more organs (including brain, skin,heart and kidney) giving rise to a broad phenotypic spectrum (including seizures, mental retardation, renal dysfunction and dermatological abnormalities. TSC2 encodes tuberin, a putative GTPase activatingprotein for rap1 and rab5. The TSC1 gene was recently identified and codesfor hamartin, a novel protein with no significant similarity to tuberin orany other known vertebrate protein []. Hamartin and tuberin have been shown to associate physically in vivo, their interaction being mediated by predicted coiled-coil domains. It is thought that hamartin and tuberin function in the same complex, rather than in separate pathways.Moreover, because oligomerisation of the hamartin C-terminal coiled coildomain is inhibited by the presence of tuberin, it is possible that tuberinacts as a chaperone, preventing hamartin self-aggregation [].Tuberin is a widely expressed 1784-amino-acid protein. Expression of the wild-type gene in TSC2 mutant tumour cells inhibits proliferation andtumorigenicity. This "suppressor"activity is encoded by a functionaldomain in the C terminus that shares similarity with the GTPase activatingprotein Rap1GAP []. It is thought that tuberin functions as a Rab5GAP in vivo to negatively regulate Rab5-GTP activity in endocytosis []. It also acts as a GTPase-activating protein (GAP) for the small GTPase RheB, a direct activator of the protein kinase activity of mTORC1 [, ].
