Karbowniczek M, Zitserman D, Khabibullin D et al.The evolutionarily conserved TSC/Rheb pathway activates Notch in tuberous sclerosis complex and Drosophila external sensory organ development. J Clin Invest 120:93-102

Institute for Cancer Research, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA
The Journal of clinical investigation (Impact Factor: 13.22). 01/2010; 120(1):93-102. DOI: 10.1172/JCI40221
Source: PubMed


Mutations in either of the genes encoding the tuberous sclerosis complex (TSC), TSC1 and TSC2, result in a multisystem tumor disorder characterized by lesions with unusual lineage expression patterns. How these unusual cell-fate determination patterns are generated is unclear. We therefore investigated the role of the TSC in the Drosophila external sensory organ (ESO), a classic model of asymmetric cell division. In normal development, the sensory organ precursor cell divides asymmetrically through differential regulation of Notch signaling to produce a pIIa and a pIIb cell. We report here that inactivation of Tsc1 and overexpression of the Ras homolog Rheb each resulted in duplication of the bristle and socket cells, progeny of the pIIa cell, and loss of the neuronal cell, a product of pIIb cell division. Live imaging of ESO development revealed this cell-fate switch occurred at the pIIa-pIIb 2-cell stage. In human angiomyolipomas, benign renal neoplasms often found in tuberous sclerosis patients, we found evidence of Notch receptor cleavage and Notch target gene activation. Further, an angiomyolipoma-derived cell line carrying biallelic TSC2 mutations exhibited TSC2- and Rheb-dependent Notch activation. Finally, inhibition of Notch signaling using a gamma-secretase inhibitor suppressed proliferation of Tsc2-null rat cells in a xenograft model. Together, these data indicate that the TSC and Rheb regulate Notch-dependent cell-fate decision in Drosophila and Notch activity in mammalian cells and that Notch dysregulation may underlie some of the distinctive clinical and pathologic features of TSC.

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Available from: Elizabeth Petri Henske, Oct 04, 2015
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    • "Chronic activation of the TORC1 complex is associated with human pathologies such as the Tuberous Sclerosis Complex, a tumor suppressor gene syndrome characterized by growth of benign tumors in multiple organs along with neurological manifestations resulting from inactivating mutations in either TSC1 or TSC2 genes [6]. During development, inappropriate TORC1 activity can affect the timing and fidelity of cell fate assignments [7], [8], but the mechanisms governing these defects are unclear. Here we show that chronic activation of TORC1 in the Drosophila pupal epidermis results in hyperpigmentation of mechanosensory bristles and adult cuticle due to increased levels of tyrosine hydroxylase. "
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    ABSTRACT: In Drosophila, the pattern of adult pigmentation is initiated during late pupal stages by the production of catecholamines DOPA and dopamine, which are converted to melanin. The pattern and degree of melanin deposition is controlled by the expression of genes such as ebony and yellow as well as by the enzymes involved in catecholamine biosynthesis. In this study, we show that the conserved TSC/TORC1 cell growth pathway controls catecholamine biosynthesis in Drosophila during pigmentation. We find that high levels of Rheb, an activator of the TORC1 complex, promote premature pigmentation in the mechanosensory bristles during pupal stages, and alter pigmentation in the cuticle of the adult fly. Disrupting either melanin synthesis by RNAi knockdown of melanogenic enzymes such as tyrosine hydroxylase (TH), or downregulating TORC1 activity by Raptor knockdown, suppresses the Rheb-dependent pigmentation phenotype in vivo. Increased Rheb activity drives pigmentation by increasing levels of TH in epidermal cells. Our findings indicate that control of pigmentation is linked to the cellular nutrient-sensing pathway by regulating levels of a critical enzyme in melanogenesis, providing further evidence that inappropriate activation of TORC1, a hallmark of the human tuberous sclerosis complex tumor syndrome disorder, can alter metabolic and differentiation pathways in unexpected ways.
    PLoS ONE 11/2012; 7(11):e48720. DOI:10.1371/journal.pone.0048720 · 3.23 Impact Factor
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    • "To determine if heightened expression of Rheb would affect development of the D. melanogaster nervous system and/or cause behavioral shifts, we overexpressed Rheb in a subset of neurons within the brain. We chose to use Rheb overexpression in the fly nervous system since it has previously been shown to upregulate TOR activity and gives similar phenotypes to Tsc1 null clones [6], [20]–[22]; additionally, use of RNAi constructs seen to reduce Tsc1 or Tsc2 in other tissues were unsuccessful in these two neuronal subsets, presumably due to the resistance of the Drosophila nervous system to RNAi [26]. "
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    ABSTRACT: Mutations in either of two tumor suppressor genes, TSC1 or TSC2, cause tuberous sclerosis complex (TSC), a syndrome resulting in benign hamartomatous tumors and neurological disorders. Cellular growth defects and neuronal disorganization associated with TSC are believed to be due to upregulated TOR signaling. We overexpressed Rheb, an upstream regulator of TOR, in two different subsets of D. melanogaster central brain neurons in order to upregulate the Tsc-Rheb-TOR pathway. Overexpression of Rheb in either the mushroom bodies or the insulin producing cells resulted in enlarged axon projections and cell bodies, which continued to increase in size with prolonged Rheb expression as the animals aged. Additionally, Rheb overexpression in the mushroom bodies resulted in deficiencies in 3 hr but not immediate appetitive memory. Thus, Rheb overexpression in the central brain neurons of flies causes not only morphological phenotypes, but behavioral and aging phenotypes that may mirror symptoms of TSC.
    PLoS ONE 09/2012; 7(9):e44888. DOI:10.1371/journal.pone.0044888 · 3.23 Impact Factor
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