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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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
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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TL;DR: Using this pU‐17 trap vector, one can initially carry out random mutagenesis, and then convert it to a gain‐of‐function mutation by replacing the βgeo gene with any gene of interest to be expressed under the control of the trapped promoter through Cre‐mediated recombination.
Abstract: We have developed a new exchangeable gene trap vector, pU-17, carrying the intron-lox71-splicing acceptor (SA)-βgeo-loxP-pA-lox2272-pSP73-lox511. The SA contains three stop codons in-frame with the ATG of βgalactosidase/neomycin-resistance fusion gene (βgeo) that can function in promoter trapping. We found that the trap vector was highly selective for integrations in the introns adjacent to the exon containing the start codon. Furthermore, by using the Cre-mutant lox system, we successfully replaced the βgeo gene with the enhanced green fluorescent protein (EGFP) gene, established mouse lines with the replaced clones, removed the selection marker gene by mating with Flp-deleter mice, and confirmed that the replaced EGFP gene was expressed in the same pattern as the βgeo gene. Thus, using this pU-17 trap vector, we can initially carry out random mutagenesis, and then convert it to a gain-of-function mutation by replacing the βgeo gene with any gene of interest to be expressed under the control of the trapped promoter through Cre-mediated recombination.
63 citations
"mTORC1 is essential for leukemia pr..." refers methods in this paper
...with CAG-Flp mice (51) to remove the neo cassette and generate mice with...
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TL;DR: Down-regulation of 4E-BP1 by an siRNA sensitized EOL-1 cells to AZD6244-mediated apoptosis in parallel with down- regulation of Mcl-1 is found, and blockade of mTORC1 by RAD001 synergistically enhanced the action of AZD 6244 in leukemia cells.
Abstract: We previously showed that the MEK inhibitor AZD6244 induced apoptosis in acute myelogenous leukemia (AML) HL60 cells. However, the mechanisms of AZD6244 to induce apoptosis remain to be fully elucidated. This study found that exposure of HL60 cells to AZD6244 down-regulated the levels of phosphor (p)-4E-binding protein 1 (4E-BP1), a substrate of mammalian target of rapamycin complex 1 (mTORC1), and anti-apoptotic protein Mcl-1. On the other hand, exposure of EOL-1 and MOLM13 cells to AZD6244 failed to induce apoptosis and levels of p-4E-BP1 and Mcl-1 were not down-regulated in these cells. These observations prompted us to hypothesize that down-regulation od 4E-BP1 and Mcl-1 might play an important role in AZD6244-mediated apoptosis. As expected, down-regulation of 4E-BP1 by an siRNA sensitized EOL-1 cells to AZD6244-mediated apoptosis in parallel with down-regulation of Mcl-1. Moreover, we found that blockade of mTORC1 by RAD001 synergistically enhanced the action of AZD6244 in leukemia cells.
29 citations
"mTORC1 is essential for leukemia pr..." refers background in this paper
...Although previous studies reported that inhibition of 4E-BP phosphorylation is associated with the induction of apoptosis in tumors (39, 40), it was assumed that other molecules downstream of mTORC1 cooperatively contribute to AML propagation....
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