Project description:Mammalian target of rapamycin (mTOR) complex 1 (mTORC1) is a critical regulator of cell growth by integrating multiple signals (nutrients, growth factors, energy and stress) and is frequently deregulated in many types of cancer. We used a robust experimental paradigm involving the combination of two interventions, one genetic and one pharmacologic to identify genes regulated transcriptionally by mTORC1. In Tsc2+/+, but not Tsc2-/- immortalized mouse embryo fibroblasts (MEFs), serum deprivation downregulates mTORC1 activity. In Tsc2-/- cells, abnormal mTORC1 activity can be downregulated by treatment with rapamycin (sirolimus). By contrast, rapamycin has little effect on mTORC1 in Tsc2+/+ cells in which mTORC1 is already inhibited by low serum. Thus, under serum deprived conditions, mTORC1 activity is low in Tsc2+/+ cells (untreated or rapamycin treated), high in Tsc2-/- cells, but lowered by rapamycin; a pattern referred to as a M-bM-^@M-^\low/low/high/lowM-bM-^@M-^] or M-bM-^@M-^\LLHLM-bM-^@M-^]. We found that mTORC1 regulated the expression of, among other lysosomal genes, V-ATPases through the transcription factor EB (TFEB, Tcfeb in the mouse). The knockdown of Tfeb resulted in the 'flattening' of the LLHL pattern and allowed the identification of genes regulated by mTORC1 through Tfeb Mouse embryo fibroblasts (MEFs) wild type or deficient in Tsc2 expressing a Tfeb shRNA or scrambled shRNA vector were treated with 25 nM rapamycin or vehicle (methanol) for 24 h under low serum conditions (0.1% FBS)
Project description:Mammalian target of rapamycin (mTOR) complex 1 (mTORC1) is a critical regulator of cell growth by integrating multiple signals (nutrients, growth factors, energy and stress) and is frequently deregulated in many types of cancer. We used a robust experimental paradigm involving the combination of two interventions, one genetic and one pharmacologic to identify genes regulated transcriptionally by mTORC1. In Tsc2+/+, but not Tsc2-/- immortalized mouse embryo fibroblasts (MEFs), serum deprivation downregulates mTORC1 activity. In Tsc2-/- cells, abnormal mTORC1 activity can be downregulated by treatment with rapamycin (sirolimus). By contrast, rapamycin has little effect on mTORC1 in Tsc2+/+ cells in which mTORC1 is already inhibited by low serum. Thus, under serum deprived conditions, mTORC1 activity is low in Tsc2+/+ cells (untreated or rapamycin treated), high in Tsc2-/- cells, but lowered by rapamycin; a pattern referred to as a “low/low/high/low” or “LLHL”. We found that mTORC1 regulated the expression of, among other lysosomal genes, V-ATPases through the transcription factor EB (TFEB, Tcfeb in the mouse). The knockdown of Tfeb resulted in the 'flattening' of the LLHL pattern and allowed the identification of genes regulated by mTORC1 through Tfeb
Project description:Mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway is activated by nutrition sufficiency signals and extracellular growth signals. mTORC1 acts the hub that integrates these inputs to orchestrate number of cellular responses such as translation, nucleotide synthesis, lipid synthesis, and lysosome biogenesis. However, the scaffold protein which specifically regulates any single downstream signaling molecule has not been identified to date. Here we show the heteropentamer protein complex Ragulator is critically required to regulate nuclear translocation of transcription factor EB (TFEB). We established a unique RAW264.7 clone that lacks Ragulator but maintained total mTORC1 activity. The clone showed a markedly enhanced nuclear translocation of TFEB even in nutrition-sufficient state, despite the full mTORC1 activity. As a cellular phenotype, the number of lysosomes were increased by 10 times in the Ragulator-deficient clone. These findings suggest that mTORC1 essentially requires the scaffold Ragulator to regulate the subcellular location of TFEB. Our finding implicates that mTORC1 has other scaffold proteins that regulate downstream molecules specifically.
Project description:Nutrient sensing and adaptation in the placenta are essential for pregnancy viability and proper fetal growth. Our recent research demonstrates that the placenta adapts to nutrient insufficiency through mTOR inhibition-mediated trophoblast differentiation toward syncytiotrophoblasts (STBs), a highly specialized multinucleated trophoblast subtype directing extensive maternal-fetal interactions. However, the underlying mechanism remains elusive. Here, we unravel the indispensable role of the mTORC1 downstream transcriptional factor TFEB in STB formation both in vitro and in vivo. Endogenous TFEB deficiency significantly impaired STB differentiation in trophoblast cells and placenta organoids. Mechanistically, TFEB conferred direct transcriptional regulation of the fusogen ERVFRD-1 in human trophoblasts and thereby profoundly promoted STB formation, independent of its canonical function as a master regulator of the autophagy-lysosomal pathway. In line with the in vitro findings, systemic or trophoblast-specific deletion of Tfeb compromised STB formation and placental vascular construction, leading to severe embryonic lethality. Moreover, TFEB directs the trophoblast syncytialization response driven by mTORC1 signaling. Importantly, TFEB expression positively correlates with the reinforced trophoblast syncytialization in human fetal growth restriction (FGR) placentas exhibiting suppressed mTORC1 activity. Our findings substantiate that the TFEB-fusogen axis ensures proper STB formation during placenta development and under nutrient stress, shedding light on TFEB as a mechanistic link between nutrient-sensing machinery and trophoblast differentiation.