mTORC1 is essential for leukemia propagation but not stem cell self-renewal
01 Jun 2012-Journal of Clinical Investigation (American Society for Clinical Investigation)-Vol. 122, Iss: 6, pp 2114-2129
TL;DR: Transplantation of Raptor-deficient undifferentiated AML cells in a limiting dilution revealed that mTORC1 is essential for leukemia initiation, and it was demonstrated that the reactivation of m TORC1 in those cells restored their leukemia-initiating capacity.
Abstract: Although dysregulation of mTOR complex 1 (mTORC1) promotes leukemogenesis, how mTORC1 affects established leukemia is unclear. We investigated the role of mTORC1 in mouse hematopoiesis using a mouse model of conditional deletion of Raptor, an essential component of mTORC1. Raptor deficiency impaired granulocyte and B cell development but did not alter survival or proliferation of hematopoietic progenitor cells. In a mouse model of acute myeloid leukemia (AML), Raptor deficiency significantly suppressed leukemia progression by causing apoptosis of differentiated, but not undifferentiated, leukemia cells. mTORC1 did not control cell cycle or cell growth in undifferentiated AML cells in vivo. Transplantation of Raptor-deficient undifferentiated AML cells in a limiting dilution revealed that mTORC1 is essential for leukemia initiation. Strikingly, a subset of AML cells with undifferentiated phenotypes survived long-term in the absence of mTORC1 activity. We further demonstrated that the reactivation of mTORC1 in those cells restored their leukemia-initiating capacity. Thus, AML cells lacking mTORC1 activity can self-renew as AML stem cells. Our findings provide mechanistic insight into how residual tumor cells circumvent anticancer therapies and drive tumor recurrence.
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TL;DR: Research data show that more resistant stem cells than common cancer cells exist in cancer patients, and to identify unrecognized differences between cancer stem cells and cancer cells might be able to develop effective classification, diagnose and treat for cancer.
Abstract: Stem cells are defined as cells able to both extensively self-renew and differentiate into progenitors. Research data show that more resistant stem cells than common cancer cells exist in cancer patients.To identify unrecognized differences between cancer stem cells and cancer cells might be able to develope effective classification,diagnose and treat ment for cancer.
2,194 citations
TL;DR: It is shown that phosphorylation of the autophagy-adaptor protein p62 markedly increases p62's binding affinity for Keap1, an adaptor of the Cul3-ubiquitin E3 ligase complex responsible for degrading Nrf2, and that inhibitors of the interaction between phosphorylated p62 and Keap 1 have potential as therapeutic agents against human HCC.
824 citations
Cites background from "mTORC1 is essential for leukemia pr..."
...Phosphorylation of p62 and induction of Nqo1 both decreased upon As(III) exposure in MEFs lacking Raptor (Hoshii et al., 2012), a component of the mTORC1 complex (Figures S2B and S2C)....
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Dissertation•
01 Jan 2010
262 citations
TL;DR: A comprehensive review of the current understanding of the mechanisms and regulation of autophagy in embryonic stem cells, several tissue stem cells (particularly hematopoietic stem cells), as well as a number of cancer stem cells is provided.
Abstract: Autophagy is a highly conserved cellular process by which cytoplasmic components are sequestered in autophagosomes and delivered to lysosomes for degradation. As a major intracellular degradation and recycling pathway, autophagy is crucial for maintaining cellular homeostasis as well as remodeling during normal development, and dysfunctions in autophagy have been associated with a variety of pathologies including cancer, inflammatory bowel disease and neurodegenerative disease. Stem cells are unique in their ability to self-renew and differentiate into various cells in the body, which are important in development, tissue renewal and a range of disease processes. Therefore, it is predicted that autophagy would be crucial for the quality control mechanisms and maintenance of cellular homeostasis in various stem cells given their relatively long life in the organisms. In contrast to the extensive body of knowledge available for somatic cells, the role of autophagy in the maintenance and function of stem cells is only beginning to be revealed as a result of recent studies. Here we provide a comprehensive review of the current understanding of the mechanisms and regulation of autophagy in embryonic stem cells, several tissue stem cells (particularly hematopoietic stem cells), as well as a number of cancer stem cells. We discuss how recent studies of different knockout mice models have defined the roles of various autophagy genes and related pathways in the regulation of the maintenance, expansion and differentiation of various stem cells. We also highlight the many unanswered questions that will help to drive further research at the intersection of autophagy and stem cell biology in the near future.
255 citations
Cites background from "mTORC1 is essential for leukemia pr..."
...Conversely, the deletion of the MTORC1 component RAPTOR, therefore theoretically causing an increase in autophagy, results in a decrease of this myeloid population.(91) However, it remains to be shown definitively that loss or gain of autophagy contributes to this phenotype, as MTOR inhibition signals for many other important cellular functions such as inhibition of protein translation, mitochondrial biogenesis, cell growth, motility and proliferation....
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TL;DR: It is shown that glutamine removal inhibits mTORC1 and induces apoptosis in AML cells, and that l-ases upregulate glutamine synthase expression in leukemic cells and that a GS knockdown enhances l-ase-induced apoptotic response in someAML cells.
238 citations
Cites background from "mTORC1 is essential for leukemia pr..."
...Recently, it was shown in a raptor deficiency mouse model thatmTORC1 inactivation induces apoptosis in differentiated leukemic cells and maintains immature leukemic cells with leukemia initiation potential in a dormant state, underlying the critical role of mTORC1 in leukemia.(4) In vitro, in primary AML cells, mTORC1 inhibition with rapamycin has cytostatic effects but does not induce apoptosis,(2-5) mainly because it does not inhibit 4E-BP1 phosphorylation on ser65....
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References
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Journal Article•
TL;DR: Research data show that more resistant stem cells than common cancer cells exist in cancer patients, and to identify unrecognized differences between cancer stem cells and cancer cells might be able to develop effective classification, diagnose and treat for cancer.
Abstract: Stem cells are defined as cells able to both extensively self-renew and differentiate into progenitors. Research data show that more resistant stem cells than common cancer cells exist in cancer patients.To identify unrecognized differences between cancer stem cells and cancer cells might be able to develope effective classification,diagnose and treat ment for cancer.
2,194 citations
"mTORC1 is essential for leukemia pr..." refers background in this paper
...Deficiency in Pten, a negative regulator of PI3K/AKT signaling, also impairs the quiescence of HSCs, leading to their depletion....
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...Thus, it is unclear how mTORC1 contributes to the control of growth, proliferation, survival, and differentiation under physiological conditions. mTORC1 dysregulation promotes leukemogenesis and depletes HSCs (10–14)....
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...both HSCs and leukemia stem cells (CSCs in leukemia), leading to the idea that leukemia stem cells may originate from HSCs (16)....
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...A recent study using a large number of primary human AML patient samples indicated that human AML stem cells are immunophenotypically similar to progenitors, including lymphoid-primed multipotential progenitors and granulocytemacrophage progenitors (GMPs), rather than to HSCs (22)....
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...Previous studies have suggested that common mechanisms regulate stem cell properties (stemness) in both HSCs and leukemia stem cells (CSCs in leukemia), leading to the idea that leukemia stem cells may originate from HSCs (16)....
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TL;DR: A novel mammalian autophagy factor, Atg13, is reported, which forms a stable approximately 3-MDa protein complex with ULK1 and FIP200, and suggests that mTORC1 suppressesAutophagy through direct regulation of the approximately 3,MDa ULK 1-Atg13-FIP200 complex.
Abstract: Autophagy is an intracellular degradation system, by which cytoplasmic contents are degraded in lysosomes. Autophagy is dynamically induced by nutrient depletion to provide necessary amino acids within cells, thus helping them adapt to starvation. Although it has been suggested that mTOR is a major negative regulator of autophagy, how it controls autophagy has not yet been determined. Here, we report a novel mammalian autophagy factor, Atg13, which forms a stable approximately 3-MDa protein complex with ULK1 and FIP200. Atg13 localizes on the autophagic isolation membrane and is essential for autophagosome formation. In contrast to yeast counterparts, formation of the ULK1-Atg13-FIP200 complex is not altered by nutrient conditions. Importantly, mTORC1 is incorporated into the ULK1-Atg13-FIP200 complex through ULK1 in a nutrient-dependent manner and mTOR phosphorylates ULK1 and Atg13. ULK1 is dephosphorylated by rapamycin treatment or starvation. These data suggest that mTORC1 suppresses autophagy through direct regulation of the approximately 3-MDa ULK1-Atg13-FIP200 complex.
1,754 citations
TL;DR: It is shown that restoring endogenous p53 expression leads to regression of autochthonous lymphomas and sarcomas in mice without affecting normal tissues, and support efforts to treat human cancers by way of pharmacological reactivation of p53.
Abstract: The p53 tumour suppressor is either mutated or inactivated by other alterations in most human cancers. Two papers in this issue show that even brief reactivation of the endogenous p53 genes in established tumours can cause cancer regression in some animal models. In some tumours, p53 reactivation causes cellular senescence associated with an innate immune response that contributes to tumour clearance. These experiments used gene manipulation to alter p53 levels, but they lend further support to the idea that p53-boosting drugs could be a useful form of cancer treatment. One of two papers showing that reactivation of the endogenous p53 tumour suppressor genes in established tumours causes cancer regression. In some tumours, p53 reactivation causes cellular senescence associated with an innate immune response that contributes to tumour clearance. Tumorigenesis is a multi-step process that requires activation of oncogenes and inactivation of tumour suppressor genes1. Mouse models of human cancers have recently demonstrated that continuous expression of a dominantly acting oncogene (for example, Hras, Kras and Myc) is often required for tumour maintenance2,3,4,5; this phenotype is referred to as oncogene addiction6. This concept has received clinical validation by the development of active anticancer drugs that specifically inhibit the function of oncoproteins such as BCR-ABL, c-KIT and EGFR7,8,9,10. Identifying additional gene mutations that are required for tumour maintenance may therefore yield clinically useful targets for new cancer therapies. Although loss of p53 function is a common feature of human cancers11, it is not known whether sustained inactivation of this or other tumour suppressor pathways is required for tumour maintenance. To explore this issue, we developed a Cre-loxP-based strategy to temporally control tumour suppressor gene expression in vivo. Here we show that restoring endogenous p53 expression leads to regression of autochthonous lymphomas and sarcomas in mice without affecting normal tissues. The mechanism responsible for tumour regression is dependent on the tumour type, with the main consequence of p53 restoration being apoptosis in lymphomas and suppression of cell growth with features of cellular senescence in sarcomas. These results support efforts to treat human cancers by way of pharmacological reactivation of p53.
1,728 citations
"mTORC1 is essential for leukemia pr..." refers methods in this paper
...Mice with the Raptorfl allele were crossed with Rosa26-CreERT2 mice (52) obtained from Tyler Jacks (Massachusetts Institute of Tech-...
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TL;DR: A powerful promoter of metabolic homeostasis at both the cellular and whole-animal level, autophagy prevents degenerative diseases and does have a downside, however—cancer cells exploit it to survive in nutrient-poor tumors.
Abstract: Autophagy is a process of self-cannibalization Cells capture their own cytoplasm and organelles and consume them in lysosomes The resulting breakdown products are inputs to cellular metabolism, through which they are used to generate energy and to build new proteins and membranes Autophagy preserves the health of cells and tissues by replacing outdated and damaged cellular components with fresh ones In starvation, it provides an internal source of nutrients for energy generation and, thus, survival A powerful promoter of metabolic homeostasis at both the cellular and whole-animal level, autophagy prevents degenerative diseases It does have a downside, however—cancer cells exploit it to survive in nutrient-poor tumors
1,669 citations
"mTORC1 is essential for leukemia pr..." refers background in this paper
...It has been reported that mTORC1 inhibition activates autophagy, a protein degradation system, to generate energy for survival under conditions of stress or starvation (4)....
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...In addition, mTORC1 regulates mitochondrial biogenesis (2, 3) and autophagy (4)....
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TL;DR: Plat-E as mentioned in this paper is a cell line based on the 293T cell line, which uses EF1 alpha promoter and the Kozak consensus sequence upstream of the initiation codon to ensure high and stable expression of viral structural proteins.
Abstract: A potent retrovirus packaging cell line named Platinum-E (Plat-E) was generated based on the 293T cell line. Plat-E is superior to existing packaging cell lines regarding efficiency, stability and safety. The novel packaging constructs utilized in establishment of Plat-E ensure high and stable expression of viral structural proteins. Conventional packaging constructs made use of the promoter of MuLV-LTR for expression of viral structural genes gag-pol and env, while our packaging constructs utilized the EF1alpha promoter, which is 100-fold more potent than the MuLV-LTR in 293T cells in combination with the Kozak's consensus sequence upstream of the initiation codon resulting in high expression of virus structural proteins in Plat-E cells. To maintain the high titers of retroviruses under drug selection pressure, we inserted the IRES (internal ribosome entry site) sequence between the gene encoding gag-pol or env, and the gene encoding a selectable marker in the packaging constructs. Plat-E cells can stably produce retroviruses with an average titer of 1 x 107/ml for at least 4 months. In addition, as we used only the coding sequences of viral structural genes to avoid inclusion of unnecessary retrovirus sequences in the packaging constructs, the probability of generating the replication competent retroviruses (RCR) by recombination can virtually be ruled out.
1,601 citations