bims-tubesc 2022-10-23 papers

Issue of 2022–10–23
seven papers selected by

Invest New Drugs. 2022 Oct 20.

A phase II study of sapanisertib (TAK-228) a mTORC1/2 inhibitor in rapalog-resistant advanced pancreatic neuroendocrine tumors (PNET): ECOG-ACRIN EA2161.

Lakshmi Rajdev, Ju-Whei Lee, Steven K Libutti, Al B Benson, George A Fisher, Pamela L Kunz, Andrew E Hendifar, Paul Catalano, Peter J O'Dwyer.

This was a two-stage phase II trial of a mTORC1/2 inhibitor (mTORC: mammalian target of rapamycin complex) Sapanisertib (TAK228) in patients with rapalog-resistant pancreatic neuroendocrine tumors (PNETs) (NCT02893930). Approved rapalogs such as everolimus inhibit mTORC1 and have limited clinical activity, possibly due to compensatory feedback loops. Sapanisertib addresses the potential for incomplete inhibition of the mTOR pathway through targeting of both mTORC1 and mTORC2, and thus to reverse resistance to earlier rapamycin analogues. In stage 1, patients received sapanisertib 3 mg by mouth once daily on a continuous dosing schedule in 28-day cycle. This trial adopted a two-stage design with the primary objective of evaluating objective tumor response. The first stage would recruit 13 patients in order to accrue 12 eligible and treated patients. If among the 12 eligible patients at least 1 patient had an objective response to therapy, the study would move to the second stage of accrual where 25 eligible and treated patients would be enrolled. This study activated on February 1, 2017, the required pre-determined number of patients (n = 13) had entered by November 5, 2018 for the first stage response evaluation. The accrual of this trial was formally terminated on December 27, 2019 as no response had been observed after the first stage accrual. Treatment-related grade 3 adverse events were reported in eight (61%) patients with hyperglycemia being the most frequent, in three patients (23%). Other toxicities noted in the trial included fatigue, rash diarrhea, nausea, and vomiting. The median PFS was 5.19 months (95% CI [3.84, 9.30]) and the median OS was 20.44 months (95% CI [5.65, 22.54]). Due to the lack of responses in Stage 1 of the study, the study did not proceed to stage 2. Thus the potential to reverse resistance was not evident.

Keywords: PNET; Sapanisertib; mTORC1/2 inhibitor

DOI: https://doi.org/10.1007/s10637-022-01311-w

J Clin Invest. 2022 Oct 17. pii: e146272. [Epub ahead of print]132(20):

SZT2 maintains hematopoietic stem cell homeostasis via nutrient-mediated mTORC1 regulation.

Na Yin, Gang Jin, Yuying Ma, Hanfei Zhao, Guangyue Zhang, Ming O Li, Min Peng.

The mTORC1 pathway coordinates nutrient and growth factor signals to maintain organismal homeostasis. Whether nutrient signaling to mTORC1 regulates stem cell function remains unknown. Here, we show that SZT2 - a protein required for mTORC1 downregulation upon nutrient deprivation - is critical for hematopoietic stem cell (HSC) homeostasis. Ablation of SZT2 in HSCs decreased the reserve and impaired the repopulating capacity of HSCs. Furthermore, ablation of both SZT2 and TSC1 - 2 repressors of mTORC1 on the nutrient and growth factor arms, respectively - led to rapid HSC depletion, pancytopenia, and premature death of the mice. Mechanistically, loss of either SZT2 or TSC1 in HSCs led to only mild elevation of mTORC1 activity and reactive oxygen species (ROS) production. Loss of both SZT2 and TSC1, on the other hand, simultaneously produced a dramatic synergistic effect, with an approximately 10-fold increase of mTORC1 activity and approximately 100-fold increase of ROS production, which rapidly depleted HSCs. These data demonstrate a critical role of nutrient mTORC1 signaling in HSC homeostasis and uncover a strong synergistic effect between nutrient- and growth factor-mediated mTORC1 regulation in stem cells.

Keywords: Amino acid metabolism; Bone marrow transplantation; Hematology; Hematopoietic stem cells; Metabolism

DOI: https://doi.org/10.1172/JCI146272

Biochem J. 2022 Oct 18. pii: BCJ20220271. [Epub ahead of print]

Methylglyoxal induces multiple serine phosphorylation in insulin receptor substrate 1 via the TAK1-p38-mTORC1 signaling axis in adipocytes.

Su-Ping Ng, Wataru Nomura, Haruya Takahashi, Kazuo Inoue, Teruo Kawada, Tsuyoshi Goto, Yoshiharu Inoue.

Certain metabolic intermediates produced during metabolism are known to regulate a wide range of cellular processes. Methylglyoxal (MG), a natural metabolite derived from glycolysis, has been shown to negatively influences systemic metabolism by inducing glucose intolerance, insulin resistance, and diabetic complications. MG plays a functional role as a signaling molecule that initiates signal transduction. However, the specific relationship between MG-induced activation of signal transduction and its negative effects on metabolism remains unclear. Here, we found that MG activated mammalian target of rapamycin complex 1 (mTORC1) signaling via p38 mitogen-activated protein kinase in adipocytes, and that the transforming growth factor-b-activated kinase 1 (TAK1) is needed to activate p38-mTORC1 signaling following treatment with MG. We also found that MG increased the phosphorylation levels of serine residues in insulin receptor substrate (IRS)-1, which is involved in its negative regulation, thereby attenuating insulin-stimulated tyrosine phosphorylation in IRS-1. The negative effect of MG on insulin-stimulated IRS-1 tyrosine phosphorylation was exerted due to the MG-induced activation of the TAK1-p38-mTORC1 signaling axis. The involvement of the TAK1-p38-mTORC1 signaling axis in the induction of IRS-1 multiple serine phosphorylation was not unique to MG, as the proinflammatory cytokine, tumor necrosis factor-α, also activated the same signaling axis. Therefore, our findings suggest that MG-induced activation of the TAK1-p38-mTORC1 signaling axis caused multiple serine phosphorylation on IRS-1, potentially contributing to insulin resistance.

Keywords: TAK1; adipocytes; insulin signalling; mTOR; methylglyoxal; signalling

DOI: https://doi.org/10.1042/BCJ20220271

Mol Metab. 2022 Oct 14. pii: S2212-8778(22)00184-3. [Epub ahead of print] 101615

Resistance exercise enhances long-term mTORC1 sensitivity to leucine.

Gommaar D'Hulst, Evi Masschelein, Katrien De Bock.

OBJECTIVE: Exercise enhances the sensitivity of mammalian target of rapamycin complex 1 (mTORC1) to amino acids, in particular leucine. How long this enhanced sensitivity lasts, and which mechanisms control enhanced leucine-mediated mTORC1 activation following exercise is currently unknown.
METHODS: C57BL/6J mice were exercised for one night in a resistance-braked running wheel after a 12-day acclimatization period. Mice were gavaged with a submaximal dose of L-leucine or saline acutely or 48 hours after exercise cessation, following 3 h food withdrawal. Muscles were excised 30 min after leucine administration. To study the contribution of mTORC1, we repeated those experiments but blocked mTORC1 activation using rapamycin immediately before the overnight running bout and one hour before the first dose of leucine. mTORC1 signaling, muscle protein synthesis and amino acid sensing machinery were assessed using immunoblot and qPCR. Leucine uptake was measured using L-[14C(U)]-leucine tracer labeling.
RESULTS: When compared to sedentary conditions, leucine supplementation more potently activated mTORC1 and protein synthesis in acutely exercised muscle. This effect was observed in m. soleus but not in m. tibialis anterior nor m. plantaris. The synergistic effect in m. soleus was long-lasting as key downstream markers of mTORC1 as well as protein synthesis remained higher when leucine was administered 48 h after exercise. We found that exercise enhanced the expression of amino acid transporters and promoted uptake of leucine into the muscle, leading to higher free intramuscular leucine levels. This coincided with increased expression of activating transcription factor 4 (ATF4), a main transcriptional regulator of amino acid uptake and metabolism, and downstream activation of amino acid genes as well as leucyl-tRNA synthetase (LARS), a putative leucine sensor. Finally, blocking mTORC1 using rapamycin did not reduce expression and activation of ATF4, suggesting that the latter does not act downstream of mTORC1. Rather, we found a robust increase in eukaryotic initiation factor 2α (eIF2α) phosphorylation, suggesting that the integrated stress response pathway, rather than exercise-induced mTORC1 activation, drives long-term ATF4 expression in skeletal muscle after exercise.
CONCLUSIONS: The enhanced sensitivity of mTORC1 to leucine is maintained at least 48 h after exercise. This shows that the anabolic window of opportunity for protein ingestion is not restricted to the first hours immediately following exercise. Increased mTORC1 sensitivity to leucine coincided with enhanced leucine influx into muscle and higher expression of genes involved in leucine sensing and amino acid metabolism. Also, exercise induced an increase in ATF4 protein expression. Altogether, these data suggest that muscular contractions switch on a coordinated program to enhance amino acid uptake as well as intramuscular sensing of key amino acids involved in mTORC1 activation and the stimulation of muscle protein synthesis.

Keywords: ATF4; exercise; leucine; mTOR; sensitivity

DOI: https://doi.org/10.1016/j.molmet.2022.101615

Endocrinology. 2022 Oct 18. pii: bqac170. [Epub ahead of print]

Angiotensin II regulates mitochondrial mTOR pathway activity dependent on acyl CoA synthetase 4 in adrenocortical cells.

Katia E Helfenberger, Giuliana F Argentino, Yanina Benzo, Lucía Herrera, Paola Finocchietto, Cecilia Poderoso.

Two well-known protein complexes in mammalian cells, mTOR type 1 and type 2 (mTORC1/2) are involved in several cellular processes such as protein synthesis, cell proliferation and commonly dysregulated in cancer. An acyl-CoA synthetase type 4 (ACSL4) is one of the most recently mTORC1/2 regulators described, in breast cancer cells. The expression of ACSL4 is hormone-regulated in adrenocortical cells and required for steroid biosynthesis. mTORC1/2 have been reported to be crucial in the proliferation of human adrenocortical tumor cells H295R and interestingly reported at several subcellular locations, which has brought cell biology to the vanguard of the mTOR signaling field. In the present work, we study the regulation of mTORC1/2 activation by angiotensin II (Ang II) -the trophic hormone for adrenocortical cells-, the subcellular localization of mTORC1/2 signaling proteins and the role of ACSL4 in the regulation of this pathway, in H295R cells. Ang II promotes activation by phosphorylation of mTORC1/2 pathway proteins in a time-dependent manner. Mitochondrial pools of ribosomal protein S6, Akt in threonine 308 and serine 473 and Rictor are phosphorylated and activated. Glycogen synthase kinase type 3 (GSK3) is phosphorylated and inactivated in mitochondria, favoring mTORC1 activation. Epidermal growth factor, a classic mTORC1/2 activator, promoted unique activation kinetics of mTORC1/2 pathway, except for Akt phosphorylation. Here, we demonstrate that ACSL4 is necessary for mTORC1/2 effectors phosphorylation and H295R proliferation, triggered by Ang II. Ang II promotes activation of mitochondrial mTORC1/2 signaling proteins, through ACSL4, with a direct impact on adrenocortical cellular proliferation.

Keywords: acyl-CoA synthetase type 4; adrenocortical human cells; angiotensin II; compartmentalization; mTORC proteins; mitochondria

DOI: https://doi.org/10.1210/endocr/bqac170

J Physiol. 2022 Oct 18.

Inducible deletion of Raptor and mTOR from adult skeletal muscle impairs muscle contractility and relaxation.

Martina Baraldo, Sabrina Zorzato, Achille Homère Tchampda Dondjang, Alessia Geremia, Leonardo Nogara, Ana Georgia Dumitras, Marta Canato, Lorenzo Marcucci, Hendrik Nolte, Bert Blaauw.

KEY POINTS: Skeletal muscle wasting and weakness have been associated with different pathological conditions, including sarcopenia and muscular dystrophy, and is accompanied by altered mTOR signaling Mammalian Target of Rapamycin (mTOR) plays a crucial role in the maintenance of muscle mass and functionality We found that the loss of both mTOR and Raptor results in contractile abnormalities, with severe muscle weakness and delayed relaxation following tetanic stimulation These results are associated with alterations in the expression of genes involved in sarcomere organization and calcium handling, and with an impairment in calcium reuptake after contraction Taken together, these results reveal a mechanistic insight into the role of mTOR in muscle contractility ABSTRACT: Skeletal muscle weakness has been associated with different pathological conditions, including sarcopenia and muscular dystrophy, and is accompanied by altered mTOR signaling. Here we wanted to better elucidate the functional role of mTOR on muscle contractility. Most loss of function studies for mTOR signaling have used the drug rapamycin to inhibit some of the signaling downstream of mTOR. However, as rapamycin does not completely inhibit all mTOR signaling, we generated a double k.o. for mTOR and for the scaffold protein of mTORC1, Raptor, in skeletal muscle. We found that dk.o. mice results in a more severe phenotype compared to Raptor or mTOR deletion alone. Indeed, they display muscle weakness, increased fiber denervation, and a slower muscle relaxation following tetanic stimulation. This is accompanied by a shift towards slow-twitch fibers and changes in the expression levels of calcium-related genes, like Serca1 and Casq1. Indeed, dk.o. mice show a decrease in calcium decay kinetics after tetanus in vivo, suggestive of a reduced calcium reuptake. In addition, RNA sequencing analysis revealed that many downregulated genes are linked to sarcomere organization, like Tcap and Fhod3. These results suggest a key role for mTOR signaling in maintaining a proper fiber relaxation in skeletal muscle. Abstract figure legend This article is protected by copyright. All rights reserved.

Keywords: Raptor; calcium; mTOR; muscle force; relaxation; skeletal muscle

DOI: https://doi.org/10.1113/JP283686