Project description:mTOR is an important anti-cancer target that integrates diverse signals to control protein synthesis and cell growth. Numerous studies by using mTOR inhibitors and/or gene deletion of mTOR negative regulators have implicated mTOR targeting in suppressing gene expression and cell proliferation. However, we found that gene targeting of mTOR in mouse hematopoietic stem cells (HSCs) results in a loss of quiescence and increased proliferation. Adaptive to mTOR loss, mTOR-/- HSCs increase chromatin access and activate global gene expression, in contrast to short-term inhibition by mTOR inhibitors. Such genomic changes are due to a compensatory activation of a MAPK/Mnk/eIF4E signaling pathway that enhances the translation of RNA pol-II and consequent c-myc expression. This adaptive mechanism can also be adopted by leukemia stem cells undergone long-term mTOR inhibitor treatment to confer resistant to mTOR targeting. Our studies provide new insights and a foregone strategy for overcoming drug resistance in mTOR targeted therapy.
Project description:The mechanistic target of rapamycin (mTOR) is a central regulator of cell growth and an attractive anti-cancer target that integrates diverse signals to control cell proliferation. Previous studies using mTOR inhibitors have shown that mTOR targeting suppresses gene expression and cell proliferation. To date, however, mTOR targeted therapies in cancer have seen very limited efficacy, and one key issue is related to the development of evasive resistance. In this manuscript, through the use of a gene targeting mouse model, we have found that inducible deletion of mTOR in hematopoietic stem cells (HSCs) results in a loss of quiescence and increased proliferation. Adaptive to the mTOR loss, mTOR-/- HSCs increase chromatin accessibility and activate global gene expression, contrary to the effects of short-term inhibition by mTOR inhibitors. Mechanistically, such genomic changes are due to a rewiring and adaptive activation of the ERK/MNK/eIF4E signaling pathway that enhances the protein translation of RNA polymerase II (RNAP II), which in turn leads to increased c-Myc gene expression, allowing the HSCs to thrive despite loss of a functional mTOR pathway. This adaptive mechanism can also be utilized by leukemia cells undergoing long-term mTOR inhibitor treatment to confer resistance to mTOR drug targeting. The resistance can then be counteracted by MNK, CDK9, or c-Myc inhibition. These results provide new insights into the physiological role of mTOR in mammalian stem cell regulation and implicate a novel mechanism of evasive resistance in the context of mTOR targeting.
Project description:Glioblastoma (GBM) is an aggressive primary brain malignancy with poor prognosis due to rapid progression, extensive invasiveness, and intrinsic resistance to standard therapies. Aberrant activation of receptor tyrosine kinases (RTKs), particularly MET, drives tumor proliferation, invasion, and therapy resistance. Here, we show that MET inhibition with crizotinib induces senescence and mitochondrial dysfunction in glioma-initiating cells (GICs), in part via downregulation of the mitochondrial protein BNIP3. However, BNIP3 downregulation activates mTOR signaling, enabling adaptive resistance. Targeting mTOR with everolimus in combination with crizotinib synergistically enhances anti-tumor effects, inducing apoptosis, senescence, and necroptosis, and significantly reducing cell viability and sphere-forming capacity. In orthotopic GBM xenograft models, this combination, particularly in a sequential regimen, markedly prolongs survival without overt toxicity. Our findings identify a BNIP3–mTOR signaling axis as a critical mediator of resistance to MET inhibition and provide a mechanistic rationale for combined MET and mTOR targeting as a promising therapeutic strategy in GBM.
Project description:Hematopoietic stem cells (HSCs) sustain lifelong hematopoiesis by balancing quiescence, self-renewal, and differentiation. However, immunophenotypic definitions of HSCs often fail to capture their functional state, particularly under conditions of stress, aging, or disease, where phenotypic HSCs may accumulate despite profound defects in long-term reconstitution. Here, we identify the chromatin remodeling ATPase Smarca4 (BRG1) as a critical regulator of functional HSC integrity. Conditional deletion of Smarca4 in the adult hematopoietic system leads to rapid hematopoietic failure, characterized by an expansion of phenotypically defined HSCs with impaired durable self-renewal capacity. Mechanistically, Smarca4 cooperates with the lineage-associated transcription factor RUNX1 to maintain chromatin accessibility and enhancer activity at the Pparg locus. Loss of Smarca4 selectively disrupts enhancer-associated H3K27ac, rewires metabolic gene programs, and compromises cellular energy homeostasis in HSCs. Restoration of Pparg expression partially rescues metabolic features and early progenitor composition but fails to restore normal differentiation output. Together, our findings establish Smarca4 as an essential epigenetic coordinator that integrates chromatin architecture with metabolic programming to sustain functional hematopoietic stem cell identity.
Project description:Somatic mutations of ASXL1 are frequently detected in age-related clonal hematopoiesis (CH). However, how ASXL1 mutations drive CH remains elusive. Using knockin (KI) mice expressing a C-terminally truncated form of ASXL1-mutant (ASXL1-MT), we examined the influence of ASXL1-MT on physiological aging in hematopoietic stem cells (HSCs). HSCs expressing ASXL1-MT display competitive disadvantage after transplantation. Nevertheless, in genetic mosaic mouse model, they acquire clonal advantage during aging, recapitulating CH in humans. Mechanistically, ASXL1-MT cooperates with BAP1 to deubiquitinate and activate AKT. Overactive Akt/mTOR signaling induced by ASXL1-MT results in aberrant proliferation and dysfunction of HSCs associated with age-related accumulation of DNA damage. Treatment with an mTOR inhibitor rapamycin ameliorates aberrant expansion of the HSC compartment as well as dysregulated hematopoiesis in aged ASXL1-MT KI mice. Our findings suggest that ASXL1-MT provokes dysfunction of HSCs, whereas it confers clonal advantage on HSCs over time, leading to the development of CH.
Project description:This SuperSeries is composed of the following subset Series: GSE34537: Mesp1 induces a subset of hematopoietic-associated transcription factors in ES cell-derived Flk1+Tie2+ endothelium GSE34541: Identification of gene targets of Meis2 GSE34543: Identification of gene targets of Meis1 Refer to individual Series