MHY1485 activates mTOR and protects osteoblasts from dexamethasone

Neddylation activated TRIM25 desensitizes triple-negative breast cancer to paclitaxel via TFEB-mediated autophagy

BACKGROUND

Paclitaxel (PTX) treatment resistance is an important factor leading to poor prognosis in triple-negative breast cancer (TNBC), therefore there is an urgent need to identify new target for combination therapy. Neddylation is a post-translational process that introduces a ubiquitin-like protein called neural precursor cell expressed developmentally downregulated protein 8 (NEDD8). Previous studies have found that neddylation is activated in multiple tumors, but its relationship with PTX chemotherapy sensitivity has not been reported.

METHODS

Differences in UBC12 and NEDD8 expression levels between PTX-sensitive and PTX-insensitive TNBC tissues were validated using public databases and immunohistochemistry. The in vitro and in vivo functional experiments were used to observe the effect of neddylation inhibition combined with PTX therapy on tumor progression. Co-IP, western blot and PCR assays were used to investigate the molecular mechanisms. Molecular docking was used to simulate the protein binding of UBC12 and TRIM25. Molecular dynamics simulation was used to observe the changes in TRIM25 protein conformation.

RESULTS

We found that in TNBC that is insensitive to PTX, NEDD8 and NEDD8 conjugating enzyme UBC12 are highly expressed. Treatment with the NEDD8-activating enzyme (NAE) inhibitor mln4924 or knockdown of UBC12 significantly increased the sensitivity of the tumor to PTX, and this increase in sensitivity is related to UBC12-mediated autophagy activation. Mechanistically, UBC12 can transfer NEDD8 to E3 ubiquitin ligase tripartite motif containing 25 (TRIM25) at K117. Molecular dynamics simulations indicate that the neddylation modification of TRIM25 reduces steric hindrance in its RING domain, facilitating the binding of TRIM25 and ubiquitylated substrates. Subsequently, TRIM25 promotes the nuclear translocation of transcription factor EB (TFEB) and transcription of autophagy related genes by increasing K63-polyubiquitination of TFEB, thereby reducing tumor sensitivity to PTX.

CONCLUSIONS

Neddylation is activated in PTX-insensitive TNBC. Specifically, autophagy gene transcriptional activation mediated by the UBC12/TRIM25/TFEB axis reduces TNBC sensitivity to PTX. Neddylation suppression combination with PTX treatment shows a synergistic anti-tumor effect.

A loss of primary cilia by a reduction in mTOR signaling correlates with age-related deteriorations in condylar cartilage

Age-related deterioration of condylar cartilage is an etiological factor in temporomandibular joint-osteoarthritis (TMJ-OA). However, its underlying mechanism remains unknown. Therefore, we examined age-related changes and the relationship between mTOR signaling and primary cilia in condylar cartilage to determine the intrinsic mechanisms of age-related TMJ-OA. Age-related morphological changes were analyzed using micro-computed tomography and safranin O-stained histological samples of the mandibular condyle of C57BL/6J mice (up to 78 weeks old). Immunohistochemistry was used to assess the activity of mTOR signaling, primary cilia frequency, and Golgi size of condylar chondrocytes. Four-week-old mice receiving an 11-week series of intraperitoneal injections of rapamycin, a potent mTOR signaling inhibitor, were used for the histological evaluation of the condylar cartilage. The condylar cartilage demonstrated an age-related reduction in cartilage area, including chondrocyte size, cell density, and cell size distribution. The Golgi size, primary cilia frequency, and mTOR signaling also decreased with age. Rapamycin injections resulted in both diminished cartilage area and cell size, resembling the phenotypes observed in aged mice. Rapamycin-injected mice also exhibited a smaller Golgi size and lower primary cilia frequency in condylar cartilage. We demonstrated that a loss of primary cilia due to a decline in mTOR signaling was correlated with age-related deteriorations in condylar cartilage. Our findings provide new insights into the tissue homeostasis of condylar cartilage, contributing to understanding the etiology of age-related TMJ-OA.

mTOR Regulates Mineralocorticoid Receptor Transcriptional Activity by ULK1-Dependent and -Independent Mechanisms

The mineralocorticoid receptor (MR) is a transcription factor for genes mediating diverse, cell-specific functions, including trophic effects as well as promoting fluid/electrolyte homeostasis. It was reported that in intercalated cells, phosphorylation of the MR at serine 843 (S843) by Unc-51-like kinase (ULK1) inhibits MR activation and that phosphorylation of ULK1 by mechanistic target of rapamycin (mTOR) inactivates ULK1, and thereby prevents MR inactivation. We extended these findings with studies in M1 mouse cortical collecting duct cells stably expressing the rat MR and a reporter gene. Pharmacological inhibition of ULK1 dose-dependently increased ligand-induced MR transactivation, while ULK1 activation had no effect. Pharmacological inhibition of mTOR and CRISPR/gRNA gene knockdown of rapamycin-sensitive adapter protein of mTOR (Raptor) or rapamycin-insensitive companion of mTOR (Rictor) decreased phosphorylated ULK1 and ligand-induced activation of the MR reporter gene, as well as transcription of endogenous MR-target genes. As predicted, ULK1 inhibition had no effect on aldosterone-mediated transcription in M1 cells with the mutated MR-S843A (alanine cannot be phosphorylated). In contrast, mTOR inhibition dose-dependently decreased transcription in the MR-S843A cells, though not as completely as in cells with the wild-type MR-S843. mTOR, Raptor, and Rictor coprecipitated with the MR and addition of aldosterone increased their phosphorylated, active state. These results suggest that mTOR significantly regulates MR activity in at least 2 ways: by suppressing MR inactivation by ULK1, and by a yet ill-defined mechanism that involves direct association with MR. They also provide new insights into the diverse functions of ULK1 and mTOR, 2 key enzymes that monitor the cell's energy status.

mTORC1 Signaling and Negative Lens-Induced Axial Elongation

Purpose

The mechanism underlying axial elongation during myopia progression remains unknown. Epidermal growth factor receptor (EGFR) signaling is associated with axial elongation. We explored whether mammalian target of rapamycin complex 1 (mTORC1) signaling acts as the downstream pathway of EGFR and participates in negative lens-induced axial elongation (NLIAE).

Methods

Three-week-old male pigmented guinea pigs underwent binocular NLIAE. (1) To investigate whether EGFR is the upstream regulator of mTORC1, an EGFR inhibitor (20 µg erlotinib) was intravitreally injected once a week for three weeks. (2) To assess the effect of mTORC1 inhibition on NLIAE, an mTORC1 inhibitor (2 µg, 10 µg, and 20 µg everolimus) was intravitreally injected once a week for three weeks. (3) To explore the long-term effect of mTORC1 overactivation on axial elongation, an mTORC1 agonist (4 µg MHY1485) was intravitreally injected once a week for three months. Biometric measurements included axial length and choroidal thickness were performed.

Results

Compared with the guinea pigs without NLIAE, NLIAE was associated with activation of mTORC1 signaling, which was suppressed by intravitreal erlotinib injection. Intravitreally injected everolimus suppressed NLIAE-induced axial elongation, mTORC1 activation, choroidal thinning, and hypoxia-inducible factor-1α expression in the sclera. Immunofluorescence revealed that the retinal pigment epithelium was the primary location of mTORC1 activation during NLIAE. Combining NLIAE and MHY1485 intravitreal injections significantly promoted axial elongation, choroidal thinning, and peripapillary choroidal atrophy.

Conclusions

The mTORC1 signaling is associated with increased axial elongation, as in NLIAE, raising the possibility of inhibiting mTORC1 as a novel treatment for slowing myopia progression.

Mammalian Target of Rapamycin Inhibition Decreases Angiotensin II-Induced Steroidogenesis in HAC15 Human Adrenocortical Carcinoma Cells

BACKGROUND

Mammalian target of rapamycin (mTOR) inhibitors suppress adrenal cortical carcinoma cell proliferation and cortisol production; the relationship between mTOR and aldosterone production has not been examined.

METHODS

HAC15 cells were incubated with an mTOR activator and several inhibitors including AZD8055 (AZD) in the presence and absence of angiotensin II (AngII). The expression of rapamycin-sensitive adapter protein of mTOR (Raptor) and rapamycin-insensitive companion of mTOR (Rictor), adaptor proteins of mTOR complex 1 and 2, respectively, were studied in the HAC15 cells and deleted by CRISPR/gRNA.

RESULTS

The mTOR inhibitors decreased aldosterone induced by AngII. Inhibition of mTOR by AZD significantly suppressed AngII-induced aldosterone and cortisol formation in a dose-dependent manner, whereas the mTOR activator MHY had no effect. AZD did not alter forskolin-induced aldosterone production showing that it is specific to the AngII signaling pathway. AngII-mediated ERK and mTOR activation were suppressed by AZD, along with a concomitant dose-dependent reduction of AngII-induced steroidogenic enzymes including steroidogenic acute regulatory protein, 3β-hydroxysteroid dehydrogenase-type 2, CYP17A1, and aldosterone synthase protein. Furthermore, mTOR components ribosomal protein S6 kinase (P70S6K) and protein kinase B phosphorylation levels were decreased by AZD. As mTOR exerts its main effects by forming complexes with adaptor proteins Raptor and Rictor, the roles of these individual complexes were studied. We found an increase in the phosphorylation of Raptor and Rictor by AngII and that their CRISPR/gRNA-mediated knockdown significantly attenuated AngII-induced aldosterone and cortisol production.

CONCLUSION

mTOR signaling has a critical role in transducing the AngII signal initiating aldosterone and cortisol synthesis in HAC15 cells and that inhibition of mTOR could be a therapeutic option for conditions associated with excessive renin-angiotensin system-mediated steroid synthesis.

The crucial role of thioredoxin interacting protein in the liver insulin resistance induced by di (2-ethylhexyl) phthalates

The widespread usage of plastic products in human life has led to extensive exposure to plasticizers and resulted in serious health problems for humans, which has become a focus of toxicology research in the world. We aimed to explore the potential mechanism of liver insulin resistance induced by di(2-ethylhexyl) phthalate (DEHP) and working on a novel treatment to alleviate insulin resistance caused by excessive exposure to DEHP. For this purpose, in vivo and in vitro experiments were conducted, and the pivotal factors in the insulin signaling pathway were analyzed. In vivo study showed DEHP could lead to liver injury and insulin resistance. DEHP could break the balance of oxidative stress and cause accumulation of inflammatory factors. Genomics and proteomics experiment results revealed that DEHP could inhibit the mRNA and protein expression of insulin receptor, insulin receptor substrate, PI3K/Akt/mTOR, and glucose transporter 4. Nevertheless, the liver insulin resistance induced by DEHP could be reversed by Verapamil (thioredoxin interacting protein (TXNIP) inhibitor). Thus, we confirmed that DEHP caused insulin resistance by affecting the TXNIP in liver, further damaging the conduction of insulin signaling pathway. Therefore, adding Verapamil to the treatment of patients with insulin resistance due to plasticizers might be more effective.

MHY1485 enhances X-irradiation-induced apoptosis and senescence in tumor cells

The mammalian target of rapamycin (mTOR) is a sensor of nutrient status and plays an important role in cell growth and metabolism. Although inhibition of mTOR signaling promotes tumor cell death and several mTOR inhibitors have been used clinically, recent reports have shown that co-treatment with MHY1485, an mTOR activator, enhances the anti-cancer effects of anti-PD-1 antibody and 5-fluorouracil. However, it remains unclear whether MHY1485 treatment alters the effects of radiation on tumor cells. In this study, the radiosensitizing effects of MHY1485 were investigated using murine CT26 and LLC cell lines. We examined mTOR signaling, tumor cell growth, colony formation, apoptosis, senescence, oxidative stress, p21 accumulation and endoplasmic reticulum (ER) stress levels in cells treated with MHY1485 and radiation, either alone or together. We found that MHY1485 treatment inhibited growth and colony formation in both cell lines under irradiation and no-irradiation conditions, results that were not fully consistent with MHY1485's known role in activating mTOR signaling. Furthermore, we found that combined treatment with MHY1485 and radiation significantly increased apoptosis and senescence in tumor cells in association with oxidative stress, ER stress and p21 stabilization, compared to radiation treatment alone. Our results suggested that MHY1485 enhances the radiosensitivity of tumor cells by a mechanism that may differ from MHY1485's role in mTOR activation.

Alda-1 Attenuates Hyperoxia-Induced Acute Lung Injury in Mice

Acute lung injury (ALI), a milder form of acute respiratory distress syndrome (ARDS), is a leading cause of mortality in older adults with an increasing prevalence. Oxygen therapy, is a common treatment for ALI, involving exposure to a high concentration of oxygen. Unfortunately, hyperoxia induces the formation of reactive oxygen species which can cause an increase in 4-HNE (4-hydroxy 2 nonenal), a toxic byproduct of lipid peroxidation. Mitochondrial aldehyde dehydrogenase 2 (ALDH2) serves as an endogenous shield against oxidative stress-mediated damage by clearing 4-HNE. Alda-1 [(N-(1, 3 benzodioxol-5-ylmethyl)-2, 6- dichloro-benzamide)], a small molecular activator of ALDH2, protects against reactive oxygen species-mediated oxidative stress by promoting ALDH2 activity. As a result, Alda-1 shields against ischemic reperfusion injury, heart failure, stroke, and myocardial infarction. However, the mechanisms of Alda-1 in hyperoxia-induced ALI remains unclear. C57BL/6 mice implanted with Alzet pumps received Alda-1 in a sustained fashion while being exposed to hyperoxia for 48 h. The mice displayed suppressed immune cell infiltration, decreased protein leakage and alveolar permeability compared to controls. Mechanistic analysis shows that mice pretreated with Alda-1 also experience decreased oxidative stress and enhanced levels of p-Akt and mTOR pathway associated proteins. These results show that continuous delivery of Alda-1 protects against hyperoxia-induced lung injury in mice.

Cell Death Triggered by the Autophagy Inhibitory Drug 3-Methyladenine in Growing Conditions Proceeds With DNA Damage

Macroautophagy (hereafter autophagy) is a multistep intracellular catabolic process with pleiotropic implications in cell fate. Attending to its activation, autophagy can be classified into inducible or constitutive. Constitutive, or basal autophagy, unfolds under nutrient-replete conditions to maintain the cellular homeostasis. Autophagy inhibitory drugs are powerful tools to interrogate the role of autophagy and its consequences on cell fate. However, 3-methyladenine and various of these compounds present an intrinsic capacity to trigger cell death, for instance the broadly-employed 3-methyladenine. To elucidate whether the inhibition of basal autophagy is causative of cell demise, we have employed several representative compounds acting at different phases of the autophagic process: initiation (SBI0206965 and MHY1485), nucleation (3-methyladenine, SAR405, Spautin-1 and Cpd18), and completion (Bafilomycin A₁ and Chloroquine). These compounds inhibited the basal autophagy of MEF cultures in growing conditions. Among them, 3-methyladenine, SBI-0206965, Chloroquine, and Bafilomycin A₁ triggered BAX- and/or BAK-dependent cytotoxicity and caspase activation. 3-methyladenine was the only compound to induce a consistent and abrupt decrease in cell viability across a series of ontologically unrelated human cell lines. 3-methyladenine-induced cytotoxicity was not driven by the inhibition of the AKT/mTOR axis. Autophagy-deficient Fip200-/- MEFs displayed an increased sensitivity to activate caspases and to undergo cell death in response to 3-methyladenine. The cytotoxicity induced by 3-methyladenine correlated with a massive DNA damage, as shown by γ-H2A.X. This genotoxicity was observed at 10 mM 3-methyladenine, the usual concentration to inhibit autophagy and was maximized in Fip200-/- MEFs. In sum, our results suggest that, in growing conditions, autophagy acts as a protective mechanism to diminish the intrinsic cytotoxicity of 3-methyladenine. However, when the cellular stress exerted by 3-methyladenine surpasses the protective effect of basal autophagy, caspase activation and DNA damage compromise the cell viability.

FGF23 protects osteoblasts from dexamethasone-induced oxidative injury

Dexamethasone (DEX) can exert a cytotoxic effect on cultured osteoblasts. The current study explored the potential osteoblast cytoprotective effect of fibroblast growth factor 23 (FGF23). In OB-6 human osteoblastic cells and primary murine osteoblasts, FGF23 induced phosphorylation of the receptor FGFR1 and activated the downstream Akt-S6K1 signaling. FGF23-induced FGFR1-Akt-S6K phosphorylation was largely inhibited by FGFR1 shRNA, but augmented with ectopic FGFR1 expression in OB-6 cells. FGF23 attenuated DEX-induced death and apoptosis in OB-6 cells and murine osteoblasts. Its cytoprotective effects were abolished by FGFR1 shRNA, Akt inhibition or Akt1 knockout. Conversely, forced activation of Akt inhibited DEX-induced cytotoxicity in OB-6 cells. Furthermore, FGF23 activated Akt downstream nuclear-factor-E2-related factor 2 (Nrf2) signaling to alleviate DEX-induced oxidative injury. On the contrary, Nrf2 shRNA or knockout almost reversed FGF23-induced osteoblast cytoprotection against DEX. Collectively, FGF23 activates FGFR1-Akt and Nrf2 signaling cascades to protect osteoblasts from DEX-induced oxidative injury and cell death.

Molecular mechanisms and clinical implications of miRNAs in drug resistance of colorectal cancer

Systemic chemotherapy is identified as a curative approach to prolong the survival time of patients with colorectal cancer (CRC). Although great progress in therapeutic approaches has been achieved during the last decades, drug resistance still extensively persists and serves as a major hurdle to effective anticancer therapy for CRC. The mechanism of multidrug resistance remains unclear. Recently, mounting evidence suggests that a great number of microRNAs (miRNAs) may contribute to drug resistance in CRC. Certain of these miRNAs may thus be used as promising biomarkers for predicting drug response to chemotherapy or serve as potential targets to develop personalized therapy for patients with CRC. This review mainly summarizes recent advances in miRNAs and the molecular mechanisms underlying miRNA-mediated chemoresistance in CRC. We also discuss the potential role of drug resistance-related miRNAs as potential biomarkers (diagnostic and prognostic value) and envisage the future orientation and challenges in translating the findings on miRNA-mediated chemoresistance of CRC into clinical applications.

Target of rapamycin signaling inhibits autophagy in sea cucumber Apostichopus japonicus

Autophagy mediated by mTOR pathway is a particularly important immune defense mechanism in the pathogens infected mammals. However, the role of TOR in echinoderm autophagy is largely unknown. Here, a cDNA encoding TOR protein was cloned and characterized from sea cucumber Apostichopus japonicus (designated as AjTOR) and its biological functions were also investigated. The AjTOR gene encoded a peptide of 2499 amino acids with the representative domains of DUF3385, FAT, FRB, PI3Kc, and FATC, which exhibited highly conservation with vertebrate orthologs. Phylogenetic analysis supported that AjTOR belonged to a new member of TOR family. Moreover, tissues distribution analysis indicated that AjTOR was ubiquitously expressed in all the tested tissues, with the highest transcription in muscle. Vibrio splendidus infection in vivo and LPS challenge in vitro could both significantly down-regulate the mRNA expression of AjTOR. What's more, transmission electron microscopy observations showed that rapamycin treatment resulted in rapid formation of autophagosomes in coelomocytes both at 3 and 6 h, however, injection with mTOR activator of MHY1485 showed an inhibitory effect on autophagosomes formation compared to the control, suggesting blocking the expression of AjTOR could accelerates autophagy signals. Our findings supported that AjTOR served as a negative regulator in sea cucumber authophay.

miR-107 inhibition upregulates CAB39 and activates AMPK-Nrf2 signaling to protect osteoblasts from dexamethasone-induced oxidative injury and cytotoxicity

To human osteoblasts dexamethasone (DEX) treatment induces significant oxidative injury and cytotoxicity. Inhibition of CAB39 (calcium binding protein 39)-targeting microRNA can induce CAB39 upregulation, activating AMP-activated protein kinase (AMPK) signaling and offering osteoblast cytoprotection. Here we identified a novel CAB39-targeting miRNA: the microRNA-107 (miR-107). RNA-Pull down assay results demonstrated that the biotinylated-miR-107 directly binds to CAB39 mRNA in OB-6 human osteoblastic cells. Forced overexpression of miR-107, by infection of pre-miR-107 lentivirus or transfection of wild-type miR-107 mimic, largely inhibited CAB39 expression in OB-6 cells and primary human osteoblasts. Contrarily, miR-107 inhibition, by antagomiR-107, increased its expression, resulting in AMPK cascade activation. AntagomiR-107 largely attenuated DEX-induced cell death and apoptosis in OB-6 cells and human osteoblasts. Importantly, osteoblast cytoprotection by antagomiR-107 was abolished with AMPK in-activation by AMPKα1 dominant negative mutation, silencing or knockout. Further studies demonstrated that antagomiR-107 activated AMPK downstream Nrf2 cascade to inhibit DEX-induced oxidative injury. Conversely, Nrf2 knockout almost abolished antagomiR-107-induced osteoblast cytoprotection against DEX. Collectively, miR-107 inhibition induced CAB39 upregulation and activated AMPK-Nrf2 signaling to protect osteoblasts from DEX-induced oxidative injury and cytotoxicity.

Scutellarin, a modulator of mTOR, attenuates hepatic insulin resistance by regulating hepatocyte lipid metabolism via SREBP-1c suppression

High levels of consumption of saturated lipids have been largely associated with the increasing prevalence of metabolic diseases. In particular, saturated fatty acids such as palmitic acid (PA) have been implicated in the development of insulin resistance (IR). Scutellarin (Scu) is one of the effective traditional Chinese medicines considered beneficial for liver diseases and diabetes. In this study, we investigated the effect of Scu on IR and lipid metabolism disorders in vitro and in high fat diet (HFD)-fed mice. In vitro, we found that Scu decreased insulin-dependent lipid accumulation and the mRNA expression of CD36, Fasn, and ACC in PA-treated HepG2 cells. Additionally, Scu upregulated Akt phosphorylation and improved the insulin signalling pathway. Moreover, Scu downregulated mammalian target of rapamycin (mTOR) phosphorylation and the n-SREBP-1c protein level and also reduced lipid accumulation via the mTOR-dependent pathway, as confirmed by the molecular docking of Scu to mTOR. In HFD-fed C57BL/6 mice, Scu improved oral glucose tolerance, pyruvate tolerance and the IR index and also increased the Akt phosphorylation level. Moreover, Scu reduced hepatocyte steatosis, decreased lipid accumulation and triglyceride levels, inhibited mTOR phosphorylation, and decreased the SREBP-1c level in the liver. Taken together, these findings suggest that Scu ameliorates hepatic IR by regulating hepatocyte lipid metabolism via the mTOR-dependent pathway through SREBP-1c suppression.

PGK1 depletion activates Nrf2 signaling to protect human osteoblasts from dexamethasone

Activation of nuclear-factor-E2-related factor 2 (Nrf2) cascade can alleviate dexamethasone (DEX)-induced oxidative injury and death of human osteoblasts. A recent study has shown that phosphoglycerate kinase 1 (PGK1) inhibition/depletion will lead to Kelch-like ECH-associated protein 1 (Keap1) methylglyoxal modification, thereby activating Nrf2 signaling cascade. Here, in OB-6 osteoblastic cells and primary human osteoblasts, PGK1 silencing, by targeted shRNA, induced Nrf2 signaling cascade activation, causing Nrf2 protein stabilization and nuclear translocation, as well as increased expression of ARE-dependent genes (HO1, NQO1, and GCLC). Functional studies demonstrated that PGK1 shRNA largely attenuated DEX-induced oxidative injury and following death of OB-6 cells and primary osteoblasts. Furthermore, PGK1 knockout, by the CRISPR/Cas9 method, similarly induced Nrf2 signaling activation and protected osteoblasts from DEX. Importantly, PGK1 depletion-induced osteoblast cytoprotection against DEX was almost abolished by Nrf2 shRNA. In addition, Keap1 shRNA mimicked and nullified PGK1 shRNA-induced anti-DEX osteoblast cytoprotection. At last we show that PGK1 expression is downregulated in human necrotic femoral head tissues of DEX-taking patients, correlating with HO1 depletion. Collectively, these results show that PGK1 depletion protects human osteoblasts from DEX via activation of Keap1-Nrf2 signaling cascade.

Activation of G-Protein-Coupled Receptor 30 Protects Neurons against Excitotoxicity through Inhibiting Excessive Autophagy Induced by Glutamate

Autophagy is a protecting intracellular pathway to transmit unnecessary or dysfunctional components to the lysosome for degeneration. Autophagic imbalance is connected with neurodegeneration. Neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, and Huntington's disease are closely related to excitotoxicity and neuronal loss. Activation of G-protein-coupled receptor 30 (GPR30), an estrogen membrane receptor, protects neurons from excitotoxicity-induced cell death. However, whether autophagy is involved in the neuroprotective effect of GPR30 activation is not well-known. In this study, methyl thiazolyl tetrazolium (MTT), Western blot, monodansylcadaverine (MDC) staining, and immunofluorescent staining were employed to detect the role of autophagy in cultured primary cortical neurons after glutamate exposure and G1 treatment. Pretreatment of G1 (GPR30 specific agonist) reduced neuronal loss through inhibiting excessive autophagy induced by glutamate exposure, which was blocked by GPR30 antagonist G15, phosphatidylinositol-3-kinase (PI3K), and the mammalian target of rapamycin (mTOR) inhibitors. These data suggest that GPR30 protects neurons from cell loss primarily by modulating PI3K-AKT-mTOR signaling pathway. In addition, G1 alone did not affect the basal autophagy and cell viability. We conclude that GPR30 activation reduces glutamate-induced excessive autophagy in neurons and protects neurons against excitotoxicity.

Dysregulation of cPWWP2A-miR-579 axis mediates dexamethasone-induced cytotoxicity in human osteoblasts

Dexamethasone (DEX) induces significant cytotoxicity to human osteoblasts. cPWWP2A is recently-indentified novel circular RNA (circRNA), acting as an endogenous sponge of microRNA-579 (miR-579). The present study tested the expression and potential functions of the cPWWP2A-miR-579 axis in DEX-treated osteoblasts. We show that cPWWP2A is downregulated in the necrotic femoral head tissues of DEX-taking human patients as well as in DEX-treated human osteoblasts. In OB-6 osteoblastic cells and primary human osteoblasts ectopic overexpression of cPWWP2A potently inhibited DEX-induced miR-579 accumulation, cell death, apoptosis and programmed necrosis. Silencing miR-579, by targeted siRNAs, also attenuated DEX-induced cytotoxicity in human osteoblasts. Significantly, mimicking DEX-induced actions, cPWWP2A silencing or forced miR-579 overexpression induced significant cytotoxicity in human osteoblasts. Further analyses demonstrated that miR-579's targets, including SIRT1 and PDK1 (phosphoinositide-dependent protein kinase 1), were downregulated in DEX-treated osteoblasts. Their levels were decreased as well in the necrotic femoral head tissues of DEX-taking human patients. Taken together we show that dysregulation of the cPWWP2A-miR-579 axis is involved in DEX-induced cytotoxicity in human osteoblasts.

Silencing FOXO1 attenuates dexamethasone-induced apoptosis in osteoblastic MC3T3-E1 cells

Dexamethasone (DEX), a widely used glucocorticoid with strong anti-inflammatory and immunosuppressive activities, has been reported to induce apoptosis in osteoblasts, but the underlying mechanisms are still not comprehensively investigated. FOXO1 plays an important role in the regulation of cell proliferation and apoptosis. Our study aims to explore the role of FOXO1 in DEX-induced apoptosis of osteoblastic MC3T3-E1 cells through bioinformatics and experiments. We first employed bioinformatics to identify DEX-related genes and revealed their functions by GO enrichment analysis including FOXO1 associated biological processes. Expression level of FOXO1 was validated by GEO data. Then, experiments were performed to verify the hypothesis. CCK8 was used to detect cell viability and apoptosis was detected by flow cytometry. SiRNA was used to silence FOXO1 and western-blot was employed to detect protein expression. Results demonstrated DEX-related genes involved in cell proliferation, apoptosis and angiogenesis and FOXO1 was a regulator of apoptosis. DEX could up-regulate FOXO1 expression, inhibit cell viability, promote apoptosis. SiRNA-FOXO1 could attenuate DEX-induced apoptosis in MC3T3-E1. These findings suggested DEX could affect some vital biological processes of MC3T3-E1 and FOXO1 played an essential role in DEX-induced apoptosis in MC3T3-E1.

NUMB maintains bone mass by promoting degradation of PTEN and GLI1 via ubiquitination in osteoblasts

The adaptor protein NUMB is involved in asymmetric division and cell fate determination and recognized as an antagonist of Notch. Previous studies have proved that Notch activation in osteoblasts contributes to a high bone mass. In this study,  however, an osteopenic phenotype was found in 9-week-old mice using osteoblastic specific Col1a1–2.3-Cre to ablate both Numb and its homologue Numbl . The trabecular bone mass decreased dramatically while the cortical bone mass was unaffected. Here, the Notch signal was not activated, while the tensin homologue deleted on human chromosome 10 (PTEN), which dephosphorylates phosphatidylinositide 3-kinases, was elevated, attenuating protein kinase B (Akt). The ubiquitination assay revealed that NUMB may physiologically promote PTEN ubiquitination in the presence of neural precursor cell-expressed developmentally downregulated protein 4–1. In addition, the deficiency of Numb/Numbl also activated the Hedgehog pathway through GLI1. This process was found to improve the ratio of the receptor activator of nuclear factor-kB ligand to osteoprotegerin, which enhanced the differentiation of osteoclasts and bone resorption . In conclusion, this study provides an insight into  new functons of   NUMB and NUMBL on bone homeostasis.

The related proteins NUMB and NUMBL maintain the survival of bone-generating osteoblast cells. NUMB was previously recognized to antagonize Notch signaling pathway ; In this study, it observes  that genetically altered mice, unable to express the two proteins, suffered from degraded bone quality. This suggests that the two proteins play a more complex, nuanced role in the process of bone mass maintenance. The team’s studies showed that NUMB and NUMBL suppression inhibits a signaling pathway important to skeletal development and protein synthesis in osteoblasts, though raise that further investigations are essential to elucidate the exact mechanistic action of these proteins. The authors of this study suggest that NUMB constitutes a potential target for therapies targeting bone loss and reduced bone strength in patients with osteoporosis.

Porcine Reproductive and Respiratory Syndrome Virus Infection Induces both eIF2α Phosphorylation-Dependent and -Independent Host Translation Shutoff

Porcine reproductive and respiratory syndrome virus (PRRSV) is an Arterivirus that has caused tremendous economic losses in the global swine industry since it was discovered in the late 1980s. Inducing host translation shutoff is a strategy used by many viruses to optimize their replication and spread. Here, we demonstrate that PRRSV infection causes host translation suppression, which is strongly dependent on viral replication. By screening PRRSV-encoded nonstructural proteins (nsps), we found that nsp2 participates in the induction of host translation shutoff and that its transmembrane (TM) domain is required for this process. nsp2-induced translation suppression is independent of protein degradation pathways and the phosphorylation of eukaryotic initiation factor 2α (eIF2α). However, the overexpression of nsp2 or its TM domain significantly attenuated the mammalian target of rapamycin (mTOR) signaling pathway, an alternative pathway for modulating host gene expression. PRRSV infection also attenuated the mTOR signaling pathway, and PRRSV-induced host translation shutoff could be partly reversed when the attenuated mTOR phosphorylation was reactivated by an activator of the mTOR pathway. PRRSV infection still negatively regulated the host translation when the effects of eIF2α phosphorylation were completely reversed. Taken together, our results demonstrate that PRRSV infection induces host translation shutoff and that nsp2 is associated with this process. Both eIF2α phosphorylation and the attenuation of the mTOR signaling pathway contribute to PRRSV-induced host translation arrest.IMPORTANCE Viruses are obligate parasites, and the production of progeny viruses relies strictly on the host translation machinery. Therefore, the efficient modulation of host mRNA translation benefits viral replication, spread, and evolution. In this study, we provide evidence that porcine reproductive and respiratory syndrome virus (PRRSV) infection induces host translation shutoff and that the viral nonstructural protein nsp2 is associated with this process. Many viruses induce host translation shutoff by phosphorylating eukaryotic initiation factor 2α (eIF2α). However, PRRSV nsp2 does not induce eIF2α phosphorylation but attenuates the mTOR signaling pathway, another pathway regulating the host cell translational machinery. We also found that PRRSV-induced host translation shutoff was partly reversed by eliminating the effects of eIF2α phosphorylation or reactivating the mTOR pathway, indicating that PRRSV infection induces both eIF2α phosphorylation-dependent and -independent host translation shutoff.

Inhibition of Mast Cell Function and Proliferation by mTOR Activator MHY1485

Mast cells integrate innate and adaptive immunity and are implicated in pathophysiological conditions, including allergy, asthma, and anaphylaxis. Cross-linking of the high-affinity IgE receptor (FcεRI) initiates diverse signal transduction pathways and induces release of proinflammatory mediators by mast cells. In this study, we demonstrated that hyperactivation of mechanistic target of rapamycin (mTOR) signaling using the mTOR activator MHY1485 suppresses FcεRI-mediated mast cell degranulation and cytokine secretion. MHY1485 treatment increased ribosomal protein S6 kinase (S6K) and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) phosphorylation, which are downstream targets of mTOR complex 1 (mTORC1), but decreased phosphorylation of Akt on mTOR complex 2 (mTORC2) target site serine 473. In addition, this activator decreased β-hexosaminidase, IL-6, and tumor necrosis factor α (TNF-α) release in murine bone marrow-derived mast cells (BMMCs) after FcεRI stimulation. Furthermore, MHY1485-treated BMMCs showed significantly decreased proliferation when cultured with IL-3. These findings suggested hyperactivation of mTORC1 as a therapeutic strategy for mast cell-related diseases.

Assessment of GSK1904529A as a promising anti-osteosarcoma agent

The insulin growth factor-I receptor (IGF1R) signaling is a key mechanism for osteosarcoma (OS) cell proliferation. GSK1904529A is a novel small molecule IGF1R kinase inhibitor. Its activity against OS cells was tested. In both established OS cell lines (Saos-2 and MG-63) and primary human OS cells, treatment with GSK1904529A (at nM concentrations) significantly inhibited cell proliferation. At the molecular level, GSK1904529A almost completely blocked IGF1R activation in OS cells, and inhibited downstream AKT-ERK activation. IGF1R silence by targeted shRNA also inhibited AKT-ERK activation and Saos-2 cell proliferation. Significantly, GSK1904529A was unable to further inhibit proliferation of IGF1R-silenced Saos-2 cells. In vivo, GSK1904529A administration orally inhibited Saos-2 tumor growth in nude mice. Together, these results suggest that targeting IGF1R by GSK1904529A inhibits OS cell growth in vitro and in vivo.

Targeted activation of AMPK by GSK621 ameliorates H2O2-induced damages in osteoblasts

GSK621 is a novel AMP-activated protein kinase (AMPK) activator. This study tested its potential cytoprotective effect in hydrogen peroxide (H₂O₂)-treated osteoblasts. In cultured MC3T3-E1 osteoblastic cells and primary murine osteoblasts, GSK621 significantly attenuated H₂O₂-induced cell death and apoptosis. AMPK activation was required for GSK621-induced osteoblast cytoprotection. Inhibition of AMPK, by AMPKα1 T172A mutation or shRNA silence, almost completely blocked GSK621-induced osteoblast cytoprotection. Reversely, introduction of a constitutively-active AMPKα1 (T172D) alleviated H₂O₂ injuries in MC3T3-E1 cells. Further, GSK621 increased nicotinamide adenine dinucleotide phosphate (NADPH) content in osteoblasts to inhibit H₂O₂-induced reactive oxygen species (ROS) production. Meanwhile, GSK621 activated cytoprotective autophagy in the osteoblasts. On the other hand, pharmacological inhibition of autophagy alleviated GSK621-mediated osteoblast cytoprotection against H₂O₂. These results suggest that targeted activation of AMPK by GSK621 ameliorates H₂O₂-induced osteoblast cell injuries.

microRNA-19a protects osteoblasts from dexamethasone via targeting TSC1

Activation of mTOR complex 1 (mTORC1) could protect human osteoblasts from dexamethasone. Tuberous sclerosis complex 1 (TSC1) is mTORC1 upstream inhibitory protein. We demonstrate here that microRNA-19a (“miR-19a”, -3p) targets the 3' untranslated regions of TSC1 mRNA. Expression of miR-19a downregulated TSC1 in OB-6 osteoblastic cells and primary human osteoblasts. miR-19a activated mTORC1 and protected human osteoblasts from dexamethasone. mTORC1 inhibition, by RAD001 or Raptor shRNA, almost completely abolished miR-19a-induced osteoblast cytoprotection against dexamethasone. Knockdown of TSC1 by targeted shRNA similarly induced mTORC1 activation and protected osteoblasts. Moreover, miR-19a activated mTORC1-dependent NF-E2-related factor 2 (Nrf2) signaling and inhibited dexamethasone-induced reactive oxygen species production in osteoblasts. Together, miR-19a protects human osteoblasts from dexamethasone possibly via targeting TSC1-mTORC1 signaling.

Activation of AMP-activated protein kinase by compound 991 protects osteoblasts from dexamethasone

Dexamethasone (Dex) induces direct cytotoxicity to cultured osteoblasts. The benzimidazole derivative compound 991 ("C991") is a novel and highly-efficient AMP-activated protein kinase (AMPK) activator. Here, in both MC3T3-E1 osteoblastic cells and primary murine osteoblasts, treatment with C991 activated AMPK signaling, and significantly attenuated Dex-induced apoptotic and non-apoptotic cell death. AMPKα1 knockdown (by shRNA), complete knockout (by CRISPR/Cas9 method) or dominant negative mutation (T172A) not only blocked C991-mediated AMPK activation, but also abolished its pro-survival effect against Dex in osteoblasts. Further studies showed that C991 boosted nicotinamide adenine dinucleotide phosphate (NADPH) activity and induced mRNA expression of NF-E2-related factor 2 (Nrf2)-regulated genes (heme oxygenase-1 and NADPH quinone oxidoreductase 1). Additionally, C991 alleviated Dex-induced reactive oxygen species (ROS) production in osteoblasts. Notably, genetic AMPK inhibition reversed the anti-oxidant actions by C991 in Dex-treated osteoblasts. Together, we conclude that C991 activates AMPK signaling to protect osteoblasts from Dex.

Activation of Nrf2 by MIND4-17 protects osteoblasts from hydrogen peroxide-induced oxidative stress

MIND4-17 is a recently developed NF-E2-related factor 2 (Nrf2) activator, which uniquely causes Nrf2 disassociation from Keap1. Here, we showed that pretreatment with MIND4-17 significantly inhibited hydrogen peroxide (H₂O₂)-induced viability reduction of primary osteoblasts and OB-6 osteoblastic cells. Meanwhile, MIND4-17 inhibited both apoptotic and non-apoptotic osteoblast cell death by H₂O₂. MIND4-17 treatment induced Keap1-Nrf2 disassociation, causing Nrf2 stabilization, accumulation and nuclear translocation in osteoblasts, leading to transcription of several Nrf2-dependent genes, including heme oxygenase 1 (HO-1), NAD(P)H quinone oxidoreductase 1 (NQO1), γ-glutamylcysteine synthetase modifier subunit (GCLM) and catalytic subunit (GCLC). Additionally, MIND4-17 largely attenuated H₂O₂-reactive oxygen species (ROS) production, lipid peroxidation and DNA damages. Nrf2 knockdown by targeted short hairpin RNA (shRNA) exacerbated H₂O₂-induced cytotoxicity in OB-6 osteoblastic cells, and nullified MIND4-17-mediated cytoprotection against H₂O₂. Meanwhile, Keap1 shRNA took over MIND4-17′s actions and protected OB-6 cells from H₂O₂. Together, MIND4-17 activates Nrf2 signaling and protects osteoblasts from H₂O₂.

miR-338-3p confers 5-fluorouracil resistance in p53 mutant colon cancer cells by targeting the mammalian target of rapamycin

Evidence demonstrate that p53 mutations and microRNAs (miRs) are important components of 5-FU resistance in colorectal cancer (CRC). miR-338-3p has been reported associated with cancer prognosis. However whether or not it influences chemotherapy sensitivity and the underlying mechanisms have not been elucidated. Here, three types of human colon cancer cell lines, HT29 (mutant p53), HCT116 (wild-type p53), and HCT116 p53^-/- (deficient p53), were treated with 5-FU. We showed that expression of miR-338-3p was correlated with apoptosis and 5-FU resistance in colon cancer cells. Ectopic expression of miR-338-3p conferred resistance to 5-FU in HCT116 cells. Further experiments indicated that miR-338-3p mediated 5-FU resistance through down-regulation of mTOR expression. Moreover, inhibition of miR-338-3p in HT29 and HCT116 p53^-/- cells increased their sensitivity to 5-FU treatment. Furthermore, we detected autophagy changes in our experiment because mTOR was known prominently regulating autophagy and the competition between autophagy and apoptosis in response to 5-FU was a mechanism influencing 5-FU sensitivity. Our results reveal a critical and novel role of miR-338-3p in the correlation of 5-FU resistance with p53 status. Moreover, the miR-338-3p inhibitor has the potential to overcome 5-FU resistance in p53 mutant colon cancer cells.

MicroRNA-200a activates Nrf2 signaling to protect osteoblasts from dexamethasone

Treatment with dexamethasone in human osteoblasts leads to oxidative stress and cell injures. NF-E2-related factor 2 (Nrf2) is a key anti-oxidant signaling. We want to induce Nrf2 activation via microRNA-mediated silencing its suppressor Keap1. Our results show that microRNA-200a ("miR-200a") expression depleted Keap1, causing Nrf2 protein stabilization in OB-6 osteoblastic cells. Reversely, the miR-200a anti-sense led to Keap1 upregulation and Nrf2 degradation. miR-200a expression activated Nrf2 signaling, which inhibited dexamethasone-induced reactive oxygen species production and OB-6 cell death/apoptosis. Keap1 shRNA also activated Nrf2 and protected OB-6 cells from dexamethasone. Importantly, miR-200a was in-effective in Keap1-silenced (by shRNA) OB-6 cells. In the primary human osteoblasts, Keap1 silence by targeted-shRNA or miR-200a protected cells from dexamethasone. Significantly, miR-200a level was decreased in necrotic femoral head tissues, which was correlated with Keap1 mRNA upregulation. Together, miR-200a expression activates Nrf2 signaling and protects human osteoblasts from dexamethasone.

AntagomiR-451 inhibits oxygen glucose deprivation (OGD)-induced HUVEC necrosis via activating AMPK signaling

Oxygen glucose deprivation (OGD) application in cultured human umbilical vein endothelial cells (HUVECs) mimics ischemic injuries. AntagomiR-451, the miroRNA-451 ("miR-451") inhibitor, could activate pro-survival AMP-activated protein kinase (AMPK) signaling. In the current study, we showed that forced-expression of antagomiR-451 depleted miRNA-451 and significantly attenuated OGD-induced necrosis of HUVECs. Activation of AMPK was required for antagomiR-451-mediated pro-survival actions. AMPK inhibition, by AMPKα shRNA or dominant negative mutation, almost completely abolishedantagomiR-451-mediated HUVEC protection again OGD. Reversely, forced-activation of AMPK by exogenous expression of constructively-active AMPKα inhibited OGD-induced HUVEC necrosis. At the molecular level, antagomiR-451 expression in HUVECs inhibited OGD-induced programmed necrosis, the latter was evidenced by mitochondrial p53-cyclophilinD (Cyp-D) association, mitochondrial depolarization as well as reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) breach. Together, we suggest that antagomiR-451 activates AMPK to inhibit OGD-induced programmed necrosis in HUVECs.

PP2A catalytic subunit silence by microRNA-429 activates AMPK and protects osteoblastic cells from dexamethasone

Activation of AMP-activated protein kinase (AMPK) could efficiently protect osteoblasts from dexamethasone (Dex). Here, we aim to induce AMPK activation through miRNA-mediated downregulating its phosphatase, protein phosphatase 2A (PP2A). We discovered that microRNA-429 ("miR-429") targets the catalytic subunit of PP2A (PP2A-c). Significantly, expression of miR-429 downregulated PP2A-c and activated AMPK (p-AMPKα1 Thr172) in human osteoblastic cells (OB-6 and hFOB1.19 lines). Remarkably, miR-429 expression alleviated Dex-induced osteoblastic cell death and apoptosis. On the other hand, miR-429-induced AMPK activation and osteoblast cytoprotection were almost abolished when AMPKα1 was either silenced (by targeted shRNA) or mutated (T172A inactivation). Further studies showed that miR-429 expression in osteoblastic cells increased NADPH (nicotinamide adenine dinucleotide phosphate) content to significantly inhibit Dex-induced oxidative stress. Such effect by miR-429 was again abolished with AMPKα1 silence or mutation. Together, we propose that PP2A-c silence by miR-429 activates AMPK and protects osteoblastic cells from Dex.