title: Multicompartmental distribution of the tuberous sclerosis gene products, hamartin and tuberin.
abstract: Mutations of the TSC1 and TSC2 genes give rise to the clinical disorder of tuberous sclerosis characterized by the development of hamartomas predominantly affecting the central nervous system, kidney, skin, lung, and heart. The function of the gene products, hamartin and tuberin, is not well understood but we have previously suggested a role in vesicular transport. To define the subcellular compartment(s) involved with these two proteins, biochemical characterization of hamartin and tuberin was performed in primary tissues and cell lines. Fractionation of cell lysates identified both proteins in the cytosolic, microsomal, and cytoskeletal compartments. In each of these fractions, hamartin and tuberin formed a stable complex in coimmunoprecipitation analyses. Further, they colocalized extensively in discrete, vesicular structures in the cytoplasm. Within the microsomal compartment, hamartin and tuberin behaved as peripheral membrane proteins that associate with the cytosolic leaflet of membranous domains. Immunoisolation of tuberin-bound vesicles using magnetic beads showed an enrichment of rap1, rab5, and caveolin-1, all of which have been found in specialized lipid microdomains, caveolae. Our data suggest that hamartin and tuberin are multicompartmental proteins that partially reside in caveolin-1-enriched structures and potentially affect their signaling.
authors.affiliation: Department of Surgery, University of Washington, 1959 NE Pacific St., Box 356410, Seattle, WA 98195, USA.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Jones
authors.forename: Baldwin C
authors.initials: BC
authors.lastname: Mak
authors.forename: Atis
authors.initials: A
authors.lastname: Muehlenbachs
authors.forename: Raymond S
authors.initials: RS
authors.lastname: Yeung
mesh_terms: D000818:Animals; D001923:Brain Chemistry; D051242:Caveolin 1; D022461:Caveolins / Q000032:analysis; D002451:Cell Compartmentation / Q000502:physiology*; D002460:Cell Line; D003599:Cytoskeleton / Q000737:chemistry; D003600:Cytosol / Q000737:chemistry; D006801:Humans; D007668:Kidney / Q000737:chemistry / Q000166:cytology; D008099:Liver / Q000737:chemistry; D046911:Macromolecular Substances; D008297:Male; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D008861:Microsomes / Q000737:chemistry / Q000378:metabolism; D009928:Organ Specificity; D021381:Protein Transport / Q000502:physiology; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D012097:Repressor Proteins / Q000737:chemistry / Q000378:metabolism*; D013154:Spleen / Q000737:chemistry; D013347:Subcellular Fractions / Q000737:chemistry / Q000378:metabolism; D013737:Testis / Q000737:chemistry; D014402:Tuberous Sclerosis; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D020696:rab5 GTP-Binding Proteins / Q000032:analysis; D020827:rap1 GTP-Binding Proteins / Q000032:analysis
chemical_list: C495540:CAV1 protein, human; C495537:Cav1 protein, rat; D051242:Caveolin 1; D022461:Caveolins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D011506:Proteins; D012097:Repressor Proteins; C000624650:TSC1 protein, human; C000624653:TSC2 protein, human; C000624652:Tsc1 protein, rat; C000624655:Tsc2 protein, rat; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D020696:rab5 GTP-Binding Proteins; D020827:rap1 GTP-Binding Proteins