Browsing by Subject "mTORC1"

Now showing 1 - 4 of 4
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    Combined Inhibition of SREBP and m-TORC1 Signaling Synergistically Inhibits the Proliferation of B Cell Lymphoma
    (2024-06) Zhu, Zhenhan; Luo, Wei; Capitano, Meagan L; Yuan, Xue
    Sterol regulatory element-binding protein (SREBP) signaling plays a crucial role in maintaining sterol homeostasis during B cell activation and the proliferation of germinal center B cells. It is unclear whether this pathway can be targeted to effectively treat B cell lymphoma. We discovered that inhibiting SREBP signaling or its downstream target HMG-CoA reductase (HMGCR) using Fatostatin or Simvastatin effectively restrains the proliferation of B cell lymphoma cells. However, B cell lymphoma cells activate the mTORC1-pS6 pathway in response to statin treatment, suggesting a possible mechanism to counteract statin-induced cell cycle arrest. Combining low dose statin treatment with the mTORC1 inhibitor rapamycin demonstrates a synergistic effect in inhibiting B cell lymphoma proliferation, cell cycle progression and lipid raft generation. These findings emphasize the potential of a combined therapy approach targeting both SREBP and mTORC1 as a novel treatment strategy for B cell lymphoma.
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    The Essential Role of the Non-Essential Amino Acid Asparagine in Lymphoid Malignancies
    (2023-05) Srivastava, Sankalp; Zhang, Ji; Dong, X. Charlie; Mosley, Amber L.; Wek, Ronald C.
    Cancer cells display increased metabolic demands to support their proliferation and biosynthetic needs. It has been extensively shown in cancers, that amino acids have functions beyond the role of mRNA translation. The breadth of functions makes amino acid restriction an effective strategy for cancer therapy; hence an important line of research involves targeting amino acid acquisition and metabolism therapeutically. Currently, asparagine depletion via L-Asparaginase in acute lymphoblastic leukemia (ALL) remains the only clinically approved therapy to date. In the first project, we showed that ALL cells are auxotrophic for asparagine and rely on exogenous sources for this non-essential amino acid. However, sensitivity to L-Asparaginase therapy is mitigated by the expression of the enzyme asparagine synthetase (ASNS), involved in de novo asparagine biosynthesis. We showed that this adaptive response requires two essential steps; demethylation of the ASNS promoter and recruitment of activating transcription factor 4 (ATF4) to the promoter to drive ASNS transcription. Our follow-up study in ALL cells showed that asparagine bioavailability (through de novo biosynthesis or exogenous sources) is essential to maintain the expression of the critical oncogene c-MYC. c-MYC is a potent transcription factor and is dysregulated in over 60% of cancers, including hematopoietic malignancies. We showed that this regulation by asparagine is primarily at the translation level and c-MYC expression is rescued only when exogenous asparagine is available or when cells can undertake de novo biosynthesis. At the biochemical level, asparagine depletion also causes an induction of ATF4 mediated stress response and suppression of global translation mediated by decreased mammalian target of rapamycin complex 1 (mTORC1) activity. However, we found that neither inhibition of the stress response or rescuing global translation rescued c-MYC protein expression. We also extended this observation to c-MYC-driven lymphomas using cell lines and orthotopic in vivo models. We showed that genetic inhibition of ASNS or pharmacological inhibition of asparagine production can significantly limit c-MYC protein and tumor growth when environmental asparagine is limiting. Overall, our work shows an essential role for asparagine in lymphoid cancers and has expanded on the usage of L-Asparaginase to resistant leukemias and lymphomas.
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    Prospects for mTOR Inhibitor Use in Patients with Polycystic Kidney Disease and Hamartomatous Diseases
    (American Society of Nephrology, 2010-07) Torres, Vicente E.; Boletta, Alessandra; Chapman, Arlene; Gattone, Vincent; Pei, York; Qian, Qi; Wallace, Darren P.; Weimbs, Thomas; Wüthrich, Rudolf P.; Anatomy and Cell Biology, School of Medicine
    Mammalian target of rapamycin (mTOR) is the core component of two complexes, mTORC1 and mTORC2. mTORC1 is inhibited by rapamycin and analogues. mTORC2 is impeded only in some cell types by prolonged exposure to these compounds. mTOR activation is linked to tubular cell proliferation in animal models and human autosomal dominant polycystic kidney disease (ADPKD). mTOR inhibitors impede cell proliferation and cyst growth in polycystic kidney disease (PKD) models. After renal transplantation, two small retrospective studies suggested that mTOR was more effective than calcineurin inhibitor-based immunosuppression in limiting kidney and/or liver enlargement. By inhibiting vascular remodeling, angiogenesis, and fibrogenesis, mTOR inhibitors may attenuate nephroangiosclerosis, cyst growth, and interstitial fibrosis. Thus, they may benefit ADPKD at multiple levels. However, mTOR inhibition is not without risks and side effects, mostly dose-dependent. Under certain conditions, mTOR inhibition interferes with adaptive increases in renal proliferation necessary for recovery from injury. They restrict Akt activation, nitric oxide synthesis, and endothelial cell survival (downstream from mTORC2) and potentially increase the risk for glomerular and peritubular capillary loss, vasospasm, and hypertension. They impair podocyte integrity pathways and may predispose to glomerular injury. Administration of mTOR inhibitors is discontinued because of side effects in up to 40% of transplant recipients. Currently, treatment with mTOR inhibitors should not be recommended to treat ADPKD. Results of ongoing studies must be awaited and patients informed accordingly. If effective, lower dosages than those used to prevent rejection would minimize side effects. Combination therapy with other effective drugs could improve tolerability and results.
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    Role of mTORC1-S6K1 signaling pathway in regulation of hematopoietic stem cell and acute myeloid leukemia
    (Elsevier, 2017-06) Ghosh, Joydeep; Kapur, Reuben; Microbiology and Immunology, School of Medicine
    Dysregulation of the mechanistic target of rapamycin complex 1 (mTORC1)-p70 ribosomal protein kinase 1 (S6K1) signaling pathway occurs frequently in acute myeloid leukemia (AML) patients. This pathway also plays a critical role in maintaining normal cellular processes. Given the importance of leukemia stem cells (LSCs) in the development of minimal residual disease, it is critical to use therapeutic interventions that target the LSC population to prevent disease relapse. The mTORC1-S6K1 pathway has been identified as an important regulator of hematopoietic stem cell (HSC) and LSC functions. Both HSC and LSC functions require regulation of key cellular processes including proliferation, metabolism, and autophagy, which are regulated by mTORC1 pathway. Despite the mTORC1-S6K1 pathway being a critical regulator of AML initiation and progression, inhibitors of this pathway alone have yielded mixed results in clinical studies. Recent studies have identified strategies to develop new mTORC1-S6K1 inhibitors such as RapaLink-1, which could circumvent the drug resistance observed in AML cells and in LSCs. Here, we review recent advances made in identifying the role of different components of this pathway in the regulation of HSCs and LSCs and discuss possible therapeutic approaches.