mTORC1 and p53: clash of the gods?

The multifaceted role of mitochondria in autism spectrum disorder

Normal brain functioning relies on high aerobic energy production provided by mitochondria. Failure to supply a sufficient amount of energy, seen in different brain disorders, including autism spectrum disorder (ASD), may have a significant negative impact on brain development and support of different brain functions. Mitochondrial dysfunction, manifested in the abnormal activities of the electron transport chain and impaired energy metabolism, greatly contributes to ASD. The aberrant functioning of this organelle is of such high importance that ASD has been proposed as a mitochondrial disease. It should be noted that aerobic energy production is not the only function of the mitochondria. In particular, these organelles are involved in the regulation of Ca2+ homeostasis, different mechanisms of programmed cell death, autophagy, and reactive oxygen and nitrogen species (ROS and RNS) production. Several syndromes originated from mitochondria-related mutations display ASD phenotype. Abnormalities in Ca2+ handling and ATP production in the brain mitochondria affect synaptic transmission, plasticity, and synaptic development, contributing to ASD. ROS and Ca2+ regulate the activity of the mitochondrial permeability transition pore (mPTP). The prolonged opening of this pore affects the redox state of the mitochondria, impairs oxidative phosphorylation, and activates apoptosis, ultimately leading to cell death. A dysregulation between the enhanced mitochondria-related processes of apoptosis and the inhibited autophagy leads to the accumulation of toxic products in the brains of individuals with ASD. Although many mitochondria-related mechanisms still have to be investigated, and whether they are the cause or consequence of this disorder is still unknown, the accumulating data show that the breakdown of any of the mitochondrial functions may contribute to abnormal brain development leading to ASD. In this review, we discuss the multifaceted role of mitochondria in ASD from the various aspects of neuroscience.

R-loop formation contributes to mTORC1 activation-dependent DNA replication stress induced by p53 deficiency

DNA replication stress is a significant contributor to spontaneous DNA damage and genome instability. While the impact of p53 deficiency on increasing DNA replication stress is known, the specific molecular mechanism underlying this phenomenon remains poorly understood. This study explores how p53 deficiency induces DNA replication stress by activating mTORC1 through R-loop formation, which is facilitated by the upregulation of RNR. Research has shown that p53 deficiency results in increased γH2AX expression and a higher mutation rate in the HPRT gene. Interestingly, these effects can be alleviated by rapamycin, an mTORC1 inhibitor. Additionally, rapamycin reduces the abundance of R-loop structures in p53KO cells, which is linked to mTORC1's regulation of ribonucleotide reductase (RNR) level. These findings suggest that p53 deficiency-induced DNA replication stress relies on mTORC1 activation, with the upregulation of RNR expression and R-loop formation. Overall, this study underscores the importance of R-loops in mTORC1 activation-dependent DNA replication stress triggered by p53 deficiency.

West Nile Virus Subgenomic RNAs Modulate Gene Expression in a Neuronal Cell Line

Subgenomic flaviviral RNAs (sfRNAs) are small non-coding products of the incomplete degradation of viral genomic RNA. They accumulate during flaviviral infection and have been associated with many functional roles inside the host cell. Studies so far have demonstrated that sfRNA plays a crucial role in determining West Nile virus (WNV) pathogenicity. However, its modulatory role on neuronal homeostasis has not been studied in depth. In this study, we investigated the mechanism of sfRNA biosynthesis and its importance for WNV replication in neuronal cells. We found that sfRNA1 is functionally redundant for both replication and translation of WNV. However, the concurrent absence of sfRNA1 and sfRNA2 species is detrimental for the survival of the virus. Differential expression analysis on RNA-seq data from WT and ΔsfRNA replicon cell lines revealed transcriptional changes induced by sfRNA and identified a number of putative targets. Overall, it was shown that sfRNA contributes to the viral evasion by suppressing the interferon-mediated antiviral response. An additional differential expression analysis among replicon and control Neuro2A cells also clarified the transcriptional changes that support WNV replication in neuronal cells. Increased levels of translation and oxidative phosphorylation, post-translational modification processes, and activated DNA repair pathways were observed in replicon cell lines, while developmental processes such as axonal growth were deficient.

L-Glutamine Substantially Improves 5-Fluorouracil-Induced Intestinal Mucositis by Modulating Gut Microbiota and Maintaining the Integrity of the Gut Barrier in Mice

SCOPE

This study investigates the potential of glutamine to mitigate intestinal mucositis and dysbiosis caused by the chemotherapeutic agent 5-fluorouracil (5-FU).

METHODS AND RESULTS

Over twelve days, Institute of Cancer Research (ICR) mice are given low (0.5 mg kg-1) or high (2 mg kg-1) doses of L-Glutamine daily, with 5-FU (50 mg kg-1) administered between days six and nine. Mice receiving only 5-FU exhibited weight loss, diarrhea, abnormal cell growth, and colonic inflammation, correlated with decreased mucin proteins, increased endotoxins, reduced fecal short-chain fatty acids, and altered gut microbiota. Glutamine supplementation counteracted these effects by inhibiting the Toll-like receptor 4/nuclear factor kappa B (TLR4/NF-κB) pathway, modulating nuclear factor erythroid 2-related factor 2/heme oxygenase 1 (Nrf2/HO-1) oxidative stress proteins, and increasing mammalian target of rapamycin (mTOR) levels, thereby enhancing microbial diversity and protecting intestinal mucosa.

CONCLUSIONS

These findings underscore glutamine's potential in preventing 5-FU-induced mucositis by modulating gut microbiota and inflammation pathways.

Effects of the combination of Epimedii Folium and Ligustri Lucidi Fructus on apoptosis and autophagy in SOP rats and osteoblasts via PI3K/AKT/mTOR pathway

BACKGROUND

This study aimed to investigate the effects of the combination of Epimedii Folium (EF) and Ligustri Lucidi Fructus (LLF) on regulating apoptosis and autophagy in senile osteoporosis (SOP) rats.

METHODS

Firstly, we identified the components in the decoction and drug-containing serum of EL (EF&LLF) by Ultra performance liquid chromatography-quadrupole-time of flight-mass spectrometry (UPLC-Q-TOF-MS). Secondly, SOP rats were treated with EF, LLF, EL and caltrate to evaluate the advantages of EL. Finally, H2O2-, chloroquine-, and MHY1485-induced osteoblasts were treated with different doses of EL to reveal the molecular mechanism of EL. We detected bone microstructure, oxidative stress levels, ALP activity and the expressions of Bax, Bcl-2, caspase3, P53, Beclin-1, p-PI3K, PI3K, p-Akt, Akt, p-mTOR, mTOR, and LC3 in vivo and in vitro.

RESULTS

36 compounds in EL decoction and 23 in EL-containing serum were identified, including flavonoids, iridoid terpenoids, phenylethanoid glycosides, polyols and triterpenoids. EL could inhibit apoptosis activity and increase ALP activity. In SOP rats and chloroquine-inhibited osteoblasts, EL could improve bone tissue microstructure and osteoblasts functions by upregulating Bcl-2, Beclin1, and LC3-II/LC3-I, while downregulating p53 in all treatment groups. In H2O2-induced osteoblasts, EL could upregulate the protein and mRNA expressions of Bcl-2 while downregulate LC3-II/LC3-I, p53 and Beclin1. Besides, EL was able to down-regulate PI3K/AKT/mTOR pathway which activated in SOP rats and MHY1485-induced osteoblasts.

CONCLUSIONS

These findings demonstrate that EL with bone protective effects on SOP rats by regulating autophagy and apoptosis via PI3K/Akt/mTOR signaling pathway, which might be an alternative medicine for the treatment of SOP.

Resistance to PRMT5-targeted therapy in mantle cell lymphoma

ABSTRACT

Mantle cell lymphoma (MCL) is an incurable B-cell non-Hodgkin lymphoma, and patients who relapse on targeted therapies have poor prognosis. Protein arginine methyltransferase 5 (PRMT5), an enzyme essential for B-cell transformation, drives multiple oncogenic pathways and is overexpressed in MCL. Despite the antitumor activity of PRMT5 inhibition (PRT-382/PRT-808), drug resistance was observed in a patient-derived xenograft (PDX) MCL model. Decreased survival of mice engrafted with these PRMT5 inhibitor-resistant cells vs treatment-naive cells was observed (P = .005). MCL cell lines showed variable sensitivity to PRMT5 inhibition. Using PRT-382, cell lines were classified as sensitive (n = 4; 50% inhibitory concentration [IC50], 20-140 nM) or primary resistant (n = 4; 340-1650 nM). Prolonged culture of sensitive MCL lines with drug escalation produced PRMT5 inhibitor-resistant cell lines (n = 4; 200-500 nM). This resistant phenotype persisted after prolonged culture in the absence of drug and was observed with PRT-808. In the resistant PDX and cell line models, symmetric dimethylarginine reduction was achieved at the original PRMT5 inhibitor IC50, suggesting activation of alternative resistance pathways. Bulk RNA sequencing of resistant cell lines and PDX relative to sensitive or short-term-treated cells, respectively, highlighted shared upregulation of multiple pathways including mechanistic target of rapamycin kinase [mTOR] signaling (P < 10-5 and z score > 0.3 or < 0.3). Single-cell RNA sequencing analysis demonstrated a strong shift in global gene expression, with upregulation of mTOR signaling in resistant PDX MCL samples. Targeted blockade of mTORC1 with temsirolimus overcame the PRMT5 inhibitor-resistant phenotype, displayed therapeutic synergy in resistant MCL cell lines, and improved survival of a resistant PDX.

Activation of mTOR signaling in adult lung microvascular progenitor cells accelerates lung aging

Reactivation and dysregulation of the mTOR signaling pathway are a hallmark of aging and chronic lung disease; however, the impact on microvascular progenitor cells (MVPCs), capillary angiostasis, and tissue homeostasis is unknown. While the existence of an adult lung vascular progenitor has long been hypothesized, these studies show that Abcg2 enriches for a population of angiogenic tissue-resident MVPCs present in both adult mouse and human lungs using functional, lineage, and transcriptomic analyses. These studies link human and mouse MVPC-specific mTORC1 activation to decreased stemness, angiogenic potential, and disruption of p53 and Wnt pathways, with consequent loss of alveolar-capillary structure and function. Following mTOR activation, these MVPCs adapt a unique transcriptome signature and emerge as a venous subpopulation in the angiodiverse microvascular endothelial subclusters. Thus, our findings support a significant role for mTOR in the maintenance of MVPC function and microvascular niche homeostasis as well as a cell-based mechanism driving loss of tissue structure underlying lung aging and the development of emphysema.

TP53 somatic mutations in Asian breast cancer are associated with subtype-specific effects

BACKGROUND

Recent genomics studies of breast cancer in Asian cohorts have found a higher prevalence of TP53 mutations in Asian breast cancer patients relative to Caucasian patients. However, the effect of TP53 mutations on Asian breast tumours has not been comprehensively studied.

METHODS

Here, we report an analysis of 492 breast cancer samples from the Malaysian Breast Cancer cohort where we examined the impact of TP53 somatic mutations in relation to PAM50 subtypes by comparing whole exome and transcriptome data from tumours with mutant and wild-type TP53.

RESULTS

We found that the magnitude of impact of TP53 somatic mutations appears to vary between different subtypes. TP53 somatic mutations were associated with higher HR deficiency scores as well as greater upregulation of gene expression pathways in luminal A and luminal B tumours compared to the basal-like and Her2-enriched subtypes. The only pathways that were consistently dysregulated when comparing tumours with mutant and wild-type TP53 across different subtypes were the mTORC1 signalling and glycolysis pathways.

CONCLUSION

These results suggest that therapies that target TP53 or other downstream pathways may be more effective against luminal A and B tumours in the Asian population.

Claspin is Required for Growth Recovery from Serum Starvation through Regulating the PI3K-PDK1-mTOR Pathway in Mammalian Cells

Claspin plays multiple important roles in regulation of DNA replication as a mediator for the cellular response to replication stress, an integral replication fork factor that facilitates replication fork progression and a factor that promotes initiation by recruiting Cdc7 kinase. Here, we report a novel role of Claspin in growth recovery from serum starvation, which requires the activation of PI3 kinase (PI3K)-PDK1-Akt-mTOR pathways. In the absence of Claspin, cells do not proceed into S phase and eventually die partially in a ROS- and p53-dependent manner. Claspin directly interacts with PI3K and mTOR, and is required for activation of PI3K-PDK1-mTOR and for that of mTOR downstream factors, p70S6K and 4EBP1, but not for p38 MAPK cascade during the recovery from serum starvation. PDK1 physically interacts with Claspin, notably with CKBD, in a manner dependent on phosphorylation of the latter protein, and is required for interaction of mTOR with Claspin. Thus, Claspin plays a novel role as a key regulator for nutrition-induced proliferation/survival signaling by activating the mTOR pathway. The results also suggest a possibility that Claspin may serve as a common mediator that receives signals from different PI3K-related kinases and transmit them to specific downstream kinases.

The role of the mTOR pathway in diabetic retinopathy

The retina, the part of the eye, translates the light signal into an electric current that can be sent to the brain as visual information. To achieve this, the retina requires fine-tuned vascularization for its energy supply. Diabetic retinopathy (DR) causes alterations in the eye vascularization that reduce the oxygen supply with consequent retinal neurodegeneration. During DR, the mammalian target of rapamycin (mTOR) pathway seems to coordinate retinal neurodegeneration with multiple anabolic and catabolic processes, such as autophagy, oxidative stress, cell death, and the release of pro-inflammatory cytokines, which are closely related to chronic hyperglycemia. This review outlines the normal anatomy of the retina and how hyperglycemia can be involved in the neurodegeneration underlying this disease through over activation or inhibition of the mTOR pathway.

Visual barcodes for clonal-multiplexing of live microscopy-based assays

While multiplexing samples using DNA barcoding revolutionized the pace of biomedical discovery, multiplexing of live imaging-based applications has been limited by the number of fluorescent proteins that can be deconvoluted using common microscopy equipment. To address this limitation, we develop visual barcodes that discriminate the clonal identity of single cells by different fluorescent proteins that are targeted to specific subcellular locations. We demonstrate that deconvolution of these barcodes is highly accurate and robust to many cellular perturbations. We then use visual barcodes to generate ‘Signalome’ cell-lines by mixing 12 clones of different live reporters into a single population, allowing simultaneous monitoring of the activity in 12 branches of signaling, at clonal resolution, over time. Using the ‘Signalome’ we identify two distinct clusters of signaling pathways that balance growth and proliferation, emphasizing the importance of growth homeostasis as a central organizing principle in cancer signaling. The ability to multiplex samples in live imaging applications, both in vitro and in vivo may allow better high-content characterization of complex biological systems.

Multiplex analyses of samples allow understanding complex processes in cancer initiation, progression and therapy response. Here, the authors present a fluorescence imaging-based visual barcode for livecell clonal-multiplexing which allows identifying signalling pathways clusters in response to different chemotherapy compounds.

p53 at the crossroad of DNA replication and ribosome biogenesis stress pathways

Despite several decades of intense research focused on understanding function(s) and disease-associated malfunction of p53, there is no sign of any “mid-life crisis” in this rapidly advancing area of biomedicine. Firmly established as the hub of cellular stress responses and tumor suppressor targeted in most malignancies, p53’s many talents continue to surprise us, providing not only fresh insights into cell and organismal biology, but also new avenues to cancer treatment. Among the most fruitful lines of p53 research in recent years have been the discoveries revealing the multifaceted roles of p53-centered pathways in the fundamental processes of DNA replication and ribosome biogenesis (RiBi), along with cellular responses to replication and RiBi stresses, two intertwined areas of cell (patho)physiology that we discuss in this review. Here, we first provide concise introductory notes on the canonical roles of p53, the key interacting proteins, downstream targets and post-translational modifications involved in p53 regulation. We then highlight the emerging involvement of p53 as a key component of the DNA replication Fork Speed Regulatory Network and the mechanistic links of p53 with cellular checkpoint responses to replication stress (RS), the driving force of cancer-associated genomic instability. Next, the tantalizing, yet still rather foggy functional crosstalk between replication and RiBi (nucleolar) stresses is considered, followed by the more defined involvement of p53-mediated monitoring of the multistep process of RiBi, including the latest updates on the RPL5/RPL11/5 S rRNA-MDM2-p53-mediated Impaired Ribosome Biogenesis Checkpoint (IRBC) pathway and its involvement in tumorigenesis. The diverse defects of RiBi and IRBC that predispose and/or contribute to severe human pathologies including developmental syndromes and cancer are then outlined, along with examples of promising small-molecule-based strategies to therapeutically target the RS- and particularly RiBi- stress-tolerance mechanisms to which cancer cells are addicted due to their aberrant DNA replication, repair, and proteo-synthesis demands.

Protocatechuic acid protects against thioacetamide-induced chronic liver injury and encephalopathy in mice via modulating mTOR, p53 and the IL-6/ IL-17/ IL-23 immunoinflammatory pathway

Protocatechuic acid (PCA), a natural phenolic acid, is known for antioxidant, anti-inflammatory, anti-apoptotic, and anti-fibrotic activities. However, the protective mechanisms of PCA on thioacetamide (TAA)-induced liver/brain injury are not well addressed. Chronic liver injury was induced in mice by intraperitoneal injection of TAA (200 mg/kg, 3 times/week) for 8 weeks. Simultaneously, PCA (100, 150 mg/kg/day, p.o.) was given daily from the 4th week. Protocatechuic acid ameliorated liver and brain damage indicated by the decrease in serum activities of aminotransferases, gamma-glutamyl transferase, alkaline phosphatase, lactate dehydrogenase, levels of bilirubin, and ammonia concomitant with restoration of normal albumin levels. Additionally, PCA treatment ameliorated oxidative stress in liver and brain, confirmed by the decrease in malondialdehyde and nitric oxide levels and the increase in antioxidant activities. Moreover, PCA showed anti-inflammatory actions through downregulation of TNF-α expression in the liver and IL-6/IL-17/IL-23 levels in the brain, which is confirmed by the decrease in CD4⁺ T brain cell numbers. Most importantly, PCA treatment showed a significant decrease in mTOR level and number of LC3 positive cells in both liver and brain tissues. Consequently, PCA could inhibit mTOR-induced apoptosis, as it showed anti-apoptotic actions through downregulation of caspase-3 expression in liver and p53 expression in liver and brain. Furthermore, liver and brain tissues of treated mice showed restoration of normal histology. It can be concluded that, several mechanisms, including: antioxidant, anti-inflammatory, anti-autophagic and anti-apoptotic activities can be implicated in the hepato- and neuroprotective potentials of PCA.

Transcriptional changes in dendritic cells underlying allergen specific induced tolerance in a mouse model

To investigate food allergy-tolerance mechanisms induced through allergen-specific immunotherapy we used RNA-Sequencing to measure gene expression in lymph-node-derived dendritic cells from Pru p 3-anaphylactic mice after immunotherapy with glycodendropeptides at 2 nM and 5 nM, leading to permanent tolerance and short-term desensitization, respectively. Gene expression was also measured in mice receiving no immunotherapy (anaphylaxis); and in which anaphylaxis could never occur (antigen-only). Compared to anaphylaxis, the antigen-only group showed the greatest number of expression-changes (411), followed by tolerant (186) and desensitized (119). Only 29 genes changed in all groups, including Il12b, Cebpb and Ifngr1. The desensitized group showed enrichment for genes related to chronic inflammatory response, secretory granule, and regulation of interleukin-12 production; the tolerant group showed genes related to cytokine receptor activity and glucocorticoid receptor binding, suggesting distinct pathways for similar outcomes. We identified genes and processes potentially involved in the restoration of long-term tolerance via allergen-specific immunotherapy, representing potential prognostic biomarkers.

Pharmacological CDK4/6 inhibition reveals a p53-dependent senescent state with restricted toxicity

Cellular senescence is a state of stable growth arrest and a desired outcome of tumor suppressive interventions. Treatment with many anti‐cancer drugs can cause premature senescence of non‐malignant cells. These therapy‐induced senescent cells can have pro‐tumorigenic and pro‐disease functions via activation of an inflammatory secretory phenotype (SASP). Inhibitors of cyclin‐dependent kinases 4/6 (CDK4/6i) have recently proven to restrain tumor growth by activating a senescence‐like program in cancer cells. However, the physiological consequence of exposing the whole organism to pharmacological CDK4/6i remains poorly characterized. Here, we show that exposure to CDK4/6i induces non‐malignant cells to enter a premature state of senescence dependent on p53. We observe in mice and breast cancer patients that the CDK4/6i‐induced senescent program activates only a partial SASP enriched in p53 targets but lacking pro‐inflammatory and NF‐κB‐driven components. We find that CDK4/6i‐induced senescent cells do not acquire pro‐tumorigenic and detrimental properties but retain the ability to promote paracrine senescence and undergo clearance. Our results demonstrate that SASP composition is exquisitely stress‐dependent and a predictor for the biological functions of different senescence subsets.

Prolonged disturbance of proteostasis induces cellular senescence via temporal mitochondrial dysfunction and subsequent mitochondrial accumulation in human fibroblasts

Proteolytic activity declines with age, resulting in the accumulation of aggregated proteins in aged organisms. To investigate how disturbance in proteostasis causes cellular senescence, we developed a stress-induced premature senescence (SIPS) model, in which normal human fibroblast MRC-5 cells were treated with the proteasome inhibitor MG132 or the vacuolar-type ATPase inhibitor bafilomycin A1 (BAFA1) for 5 days. Time-course studies revealed a significant increase in intracellular reactive oxygen species (ROS) and mitochondrial superoxide during and after drug treatment. Mitochondrial membrane potential initially decreased, suggesting temporal mitochondrial dysfunction during drug treatment, but was restored along with mitochondrial accumulation after drug treatment. AMP-activated protein kinase alpha was notably activated during treatment; thereafter, intracellular ATP levels significantly increased. SIPS induction by MG132 or BAFA1 was partially attenuated by co-treatment with vitamin E or rapamycin, in which the levels of ROS, mitochondrial accumulation, and protein aggregates were suppressed, implying the critical involvement of oxidative stress and mitochondrial function in SIPS progression. Rapamycin co-treatment also augmented the expression of HSP70 and activation of AKT, which could recover proteostasis and promote cell survival, respectively. Our study proposes a possible pathway from the disturbed proteostasis to cellular senescence via excess ROS production as well as functional and quantitative changes in mitochondria.

Bruton tyrosine kinase inhibitors as potential therapeutic agents for COVID-19: A review

Coronavirus disease 2019 (COVID-19) is first detected in December 2019 in Wuhan, China which is a new pandemic caused by SARS-COV-2 that has greatly affected the whole world. Bruton tyrosine kinase (BTK) inhibitors are drugs that are used for the management of cancer, and are being repurposed for COVID-19. BTK regulates macrophage and B cell activation, development, survival, and signaling. Inhibition of BTK has revealed an ameliorative effect on lung injury in patients with severe COVID-19. Thus, this review aimed to summarize evidence regarding the role of Bruton tyrosine kinase inhibitors against COVID-19. To include findings from diverse studies, publications related to BTK inhibitors and Covid-19 were searched from the databases such as SCOPUS, Web of Science, Medline, Google Scholar, PubMed, and Elsevier, using English key terms. Both experimental and clinical studies suggest that targeting excessive host inflammation with a BTK inhibitor is a potential therapeutic strategy in the treatment of patients with severe COVID-19. Currently, BTK inhibitors such as ibrutinib and acalabrutinib have shown a protective effect against pulmonary injury in a small series group of COVID-19 infected patients. Small molecule inhibitors like BTK inhibitors, targeting a wide range of pro-inflammatory singling pathways, may a key role in the management of COVID-19.

Synthetic mRNAs; Their Analogue Caps and Contribution to Disease

The structure of synthetic mRNAs as used in vaccination against cancer and infectious diseases contain specifically designed caps followed by sequences of the 5′ untranslated repeats of β-globin gene. The strategy for successful design of synthetic mRNAs by chemically modifying their caps aims to increase resistance to the enzymatic deccapping complex, offer a higher affinity for binding to the eukaryotic translation initiation factor 4E (elF4E) protein and enforce increased translation of their encoded proteins. However, the cellular homeostasis is finely balanced and obeys to specific laws of thermodynamics conferring balance between complexity and growth rate in evolution. An overwhelming and forced translation even under alarming conditions of the cell during a concurrent viral infection, or when molecular pathways are trying to circumvent precursor events that lead to autoimmunity and cancer, may cause the recipient cells to ignore their differential sensitivities which are essential for keeping normal conditions. The elF4E which is a powerful RNA regulon and a potent oncogene governing cell cycle progression and proliferation at a post-transcriptional level, may then be a great contributor to disease development. The mechanistic target of rapamycin (mTOR) axis manly inhibits the elF4E to proceed with mRNA translation but disturbance in fine balances between mTOR and elF4E action may provide a premature step towards oncogenesis, ignite pre-causal mechanisms of immune deregulation and cause maturation (aging) defects.

Protein mimetic amyloid inhibitor potently abrogates cancer-associated mutant p53 aggregation and restores tumor suppressor function

Missense mutations in p53 are severely deleterious and occur in over 50% of all human cancers. The majority of these mutations are located in the inherently unstable DNA-binding domain (DBD), many of which destabilize the domain further and expose its aggregation-prone hydrophobic core, prompting self-assembly of mutant p53 into inactive cytosolic amyloid-like aggregates. Screening an oligopyridylamide library, previously shown to inhibit amyloid formation associated with Alzheimer's disease and type II diabetes, identified a tripyridylamide, ADH-6, that abrogates self-assembly of the aggregation-nucleating subdomain of mutant p53 DBD. Moreover, ADH-6 targets and dissociates mutant p53 aggregates in human cancer cells, which restores p53's transcriptional activity, leading to cell cycle arrest and apoptosis. Notably, ADH-6 treatment effectively shrinks xenografts harboring mutant p53, while exhibiting no toxicity to healthy tissue, thereby substantially prolonging survival. This study demonstrates the successful application of a bona fide small-molecule amyloid inhibitor as a potent anticancer agent.

mTORC1 promotes mineralization via p53 pathway

The objectives of our study were to investigate the roles of mTORC1 in odontoblast proliferation and mineralization and to determine the mechanism by which mTORC1 regulates odontoblast mineralization. In vitro, MDPC23 cells were treated with rapamycin (10 nmol/L) and transfected with a lentivirus for short hairpin (shRNA)-mediated silencing of the tuberous sclerosis complex (shTSC1) to inhibit and activate mTORC1, respectively. CCK8 assays, flow cytometry, Alizarin red S staining, ALP staining, qRT-PCR, and western blot analysis were performed. TSC1-conditional knockout (DMP1-Cre⁺ ; TSC1^f/f , hereafter CKO) mice and littermate control (DMP1-Cre^- ; TSC1^f/f , hereafter WT) mice were generated. H&E staining, immunofluorescence, and micro-CT analysis were performed. Transcriptome sequencing analysis was used to screen the mechanism of this process. mTORC1 inactivation decreased the cell proliferation. The qRT-PCR and western blot results showed that mineralization-related genes and proteins were downregulated in mTORC1-inactivated cells. Moreover, mTORC1 overactivation promoted cell proliferation and mineralization-related gene and protein expression. In vivo, the micro-CT results showed that DV/TV and dentin thickness were higher in CKO mice than in controls and H&E staining showed the same results. Mineralization-related proteins expression was upregulated. Transcriptome sequencing analysis revealed that p53 pathway-associated genes were differentially expressed in TSC1-deficient cells. By inhibiting p53 alone or both mTORC1 and p53 with rapamycin and a p53 inhibitor, we elucidated that p53 acts downstream of mTORC1 and that mTORC1 thereby promotes odontoblast mineralization. Taken together, our findings demonstrate that the role of mTORC1 in odontoblast proliferation and mineralization, and confirm that mTORC1 upregulates odontoblast mineralization via the p53 pathway.

Genome-wide Screens Implicate Loss of Cullin Ring Ligase 3 in Persistent Proliferation and Genome Instability in TP53-Deficient Cells

TP53 deficiency is the most common alteration in cancer; however, this alone is typically insufficient to drive tumorigenesis. To identify genes promoting tumorigenesis in combination with TP53 deficiency, we perform genome-wide CRISPR-Cas9 knockout screens coupled with proliferation and transformation assays in isogenic cell lines. Loss of several known tumor suppressors enhances cellular proliferation and transformation. Loss of neddylation pathway genes promotes uncontrolled proliferation exclusively in TP53-deficient cells. Combined loss of CUL3 and TP53 activates an oncogenic transcriptional program governed by the nuclear factor κB (NF-κB), AP-1, and transforming growth factor β (TGF-β) pathways. This program maintains persistent cellular proliferation, induces partial epithelial to mesenchymal transition, and increases DNA damage, genomic instability, and chromosomal rearrangements. Our findings reveal CUL3 loss as a key event stimulating persistent proliferation in TP53-deficient cells. These findings may be clinically relevant, since TP53-CUL3-deficient cells are highly sensitive to ataxia telangiectasia mutated (ATM) inhibition, exposing a vulnerability that could be exploited for cancer treatment.

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Mixed-effect models with MEMcrispR applied to CRISPR screen analyses

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Knockout of neddylation genes increases persistent proliferation in TP53^−/− cells

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TP53^−/−,CUL3^−/− cells exhibit persistent proliferation and partial EMT phenotype

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TP53^−/−,CUL3^−/− cells show increased DNA damage and display sensitivity to ATM inhibition

Activated p53 in the anti-apoptotic milieu of tuberous sclerosis gene mutation induced diseases leads to cell death if thioredoxin reductase is inhibited

Tuberous sclerosis, angiomyolipoma and lymphangioleiomyomatosis are a group of diseases characterized by mutation in tuberous sclerosis genes (TSC 1-2). TSC mutation leads to continuous activation of the mTOR pathway that requires adaptation to increased ATP requirement. With limited treatment options, there is an increasing demand to identify novel therapeutic targets and to understand the correlations between mTOR pathway activation and the lack of cell death in the presence of TSC mutation. In the current study, we demonstrate deregulation of p53 controlled and mitochondria associated cell death processes. The study also reveals that treatment of TSC mutant cells with the drug candidate Proxison combined with reduced concentration of rapamycin can increase production of reactive oxygen species (ROS), can modify miRNA expression pattern associated with p53 regulation and can reduce cell viability.

Methylglyoxal induces p53 activation and inhibits mTORC1 in human umbilical vein endothelial cells

Methylglyoxal (MGO), a precursor of advanced glycation end products (AGEs), is regarded as a pivotal mediator of vascular damage in patients with diabetes. We have previously reported that MGO induces transcriptional changes compatible with p53 activation in cultured human endothelial cells. To further substantiate this finding and to explore the underlying mechanisms and possible consequences of p53 activation, we aimed (1) to provide direct evidence for p53 activation in MGO-treated human umbilical vein endothelial cells (HUVECs), (2) to assess putative mechanisms by which this occurs, (3) to analyze down-stream effects on mTOR and autophagy pathways, and (4) to assess the potential benefit of carnosine herein. Exposure of HUVECs to 800 µM of MGO for 5 h induced p53 phosphorylation. This was paralleled by an increase in TUNEL and γ-H2AX positive cells, indicative for DNA damage. Compatible with p53 activation, MGO treatment resulted in cell cycle arrest, inhibition of mTORC1 and induction of autophagy. Carnosine co-treatment did not counteract MGO-driven effects. In conclusion, our results demonstrate that MGO elicits DNA damage and p53 activation in HUVECs, resulting in modulation of downstream pathways, e.g. mTORC1.

Unbiased approach for the identification of molecular mechanisms sensitive to chemical exposures

Targeted methods that dominated toxicological research until recently did not allow for screening of all molecular changes involved in toxic response. Therefore, it is difficult to infer if all major mechanisms of toxicity have already been discovered, or if some of them are still overlooked. We used data on 591,084 unique chemical-gene interactions to identify genes and molecular pathways most sensitive to chemical exposures. The list of identified pathways did not change significantly when analyses were done on different subsets of data with non-overlapping lists of chemical compounds indicative that our dataset is saturated enough to provide unbiased results. One of the most important findings of this study is that almost every known molecular mechanism may be affected by chemical exposures. Predictably, xenobiotic metabolism pathways, and mechanisms of cellular response to stress and damage were among the most sensitive. Additionally, we identified highly sensitive molecular pathways, which are not widely recognized as major targets of toxicants, including lipid metabolism pathways, longevity regulation cascade, and cytokine-mediated signaling. These mechanisms are relevant to significant public health problems, such as aging, cancer, metabolic and autoimmune disease. Thus, public health field will benefit from future focus of toxicological research on identified sensitive mechanisms.

Upregulation of 5'-terminal oligopyrimidine mRNA translation upon loss of the ARF tumor suppressor

Tumor cells require nominal increases in protein synthesis in order to maintain high proliferation rates. As such, tumor cells must acquire enhanced ribosome production. How the numerous mutations in tumor cells ultimately achieve this aberrant production is largely unknown. The gene encoding ARF is the most commonly deleted gene in human cancer. ARF plays a significant role in regulating ribosomal RNA synthesis and processing, ribosome export into the cytoplasm, and global protein synthesis. Utilizing ribosome profiling, we show that ARF is a major suppressor of 5'-terminal oligopyrimidine mRNA translation. Genes with increased translational efficiency following loss of ARF include many ribosomal proteins and translation factors. Knockout of p53 largely phenocopies ARF loss, with increased protein synthesis and expression of 5'-TOP encoded proteins. The 5'-TOP regulators eIF4G1 and LARP1 are upregulated in Arf- and p53-null cells.

Relevance of the Bruton Tyrosine Kinase as a Target for COVID-19 Therapy

The outbreak of the novel coronavirus disease 2019 (COVID-19) has emerged as one of the biggest global health threats worldwide. As of October 2020, more than 44 million confirmed cases and more than 1,160,000 deaths have been reported globally, and the toll is likely to be much higher before the pandemic is over. There are currently little therapeutic options available and new potential targets are intensively investigated. Recently, Bruton tyrosine kinase (BTK) has emerged as an interesting candidate. Elevated levels of BTK activity have been reported in blood monocytes from patients with severe COVID-19, compared with those from healthy volunteers. Importantly, various studies confirmed empirically that administration of BTK inhibitors (acalabrutinib and ibrutinib) decreased the duration of mechanical ventilation and mortality rate for hospitalized patients with severe COVID-19. Herein, we review the current information regarding the role of BTK in severe acute respiratory syndrome coronavirus 2 infections and the suitability of its inhibitors as drugs to treat COVID-19. The use of BTK inhibitors in the management of COVID-19 shows promise in reducing the severity of the immune response to the infection and thus mortality. However, BTK inhibition may be contributing in other ways to inhibit the effects of the virus and this will need to be carefully studied.

Increased mTOR activity and metabolic efficiency in mouse and human cells containing the African-centric tumor-predisposing p53 variant Pro47Ser

The Pro47Ser variant of p53 (S47) exists in African-descent populations and is associated with increased cancer risk in humans and mice. Due to impaired repression of the cystine importer Slc7a11, S47 cells show increased glutathione (GSH) accumulation compared to cells with wild -type p53. We show that mice containing the S47 variant display increased mTOR activity and oxidative metabolism, as well as larger size, improved metabolic efficiency, and signs of superior fitness. Mechanistically, we show that mTOR and its positive regulator Rheb display increased association in S47 cells; this is due to an altered redox state of GAPDH in S47 cells that inhibits its ability to bind and sequester Rheb. Compounds that decrease glutathione normalize GAPDH-Rheb complexes and mTOR activity in S47 cells. This study reveals a novel layer of regulation of mTOR by p53, and raises the possibility that this variant may have been selected for in early Africa.

Systemic overexpression of C-C motif chemokine ligand 2 promotes metabolic dysregulation and premature death in mice with accelerated aging

Injection of tissues with senescent cells induces changes that mimic aging, and this process is delayed in mice engineered to eliminate senescent cells, which secrete proinflammatory cytokines, including C-C motif chemokine ligand 2 (Ccl2). Circulating levels of Ccl2 correlate with age, but the impact of Ccl2 on tissue homeostasis has not been established. We generated an experimental model by crossbreeding mice overexpressing Ccl2 with progeroid mice bearing a mutation in the lamin A (Lmna) gene. Wild-type animals and progeroid mice that do not overexpress Ccl2 were used as controls. Ccl2 overexpression decreased the lifespan of the progeroid mice and induced the dysregulation of glycolysis, the citric acid cycle and one-carbon metabolism in skeletal muscle, driving dynamic changes in energy metabolism and DNA methylation. This impact on cellular bioenergetics was associated with mitochondrial alterations and affected cellular metabolism, autophagy and protein synthesis through AMPK/mTOR pathways. The data revealed the ability of Ccl2 to promote death in mice with accelerated aging, which supports its putative use as a biomarker of an increased senescent cell burden and for the assessment of the efficacy of interventions aimed at extending healthy aging.

Carbon ion combined with tigecycline inhibits lung cancer cell proliferation by inducing mitochondrial dysfunction

AIMS

Mitochondrial dysfunction is receiving considerable attention due to irreplaceable biological function of mitochondria. Ionizing radiation and tigecycline (TIG) alone can cause mitochondrial dysfunction, playing important role in tumor therapy. However, prior studies fail to investigate combined mechanism of carbon ion irradiation (IR) and TIG on tumor proliferation inhibition. The study aimed to explore the combined effects of both on autophagy and apoptosis.

MATERIALS AND METHODS

NSCLC cells A549 and H1299 were treated with carbon ion, TIG, or both. Cell survival rate, autophagy, apoptosis, expression of mitochondrial signaling proteins were determined by clone formation assay, immunofluorescence of LC3B, flow cytometry and western blotting, respectively; ATP content, mitochondrial membrane potential (MMP) and Ca²⁺ level in mitochondria were used to assessed mitochondrial function.

KEY FINDINGS

Results showed IR combined TIG inhibited cells proliferation by increasing apoptosis in both cells and enhancing autophagy in H1299 cells. Additionally, combination treatment induced the most severe mitochondrial dysfunction by sharply reducing ATP, MMP and increasing Ca²⁺ level of mitochondria. Up-regulation and down-regulation of mitochondrial translation proteins (EF-Tu, GFM1 and MRPS12) expression affected apoptosis and autophagy, while the level of p-mTOR was consistent with their expression in both cell types. In A549 cells, p-AMPK level decreased while p-Akt and p-mTOR increased after combination treatment.

SIGNIFICANCE

Overall, our results showed that p-Akt and p-AMPK antagonistically targeted p-mTOR to regulate mitochondrial translation proteins to affect autophagy and apoptosis. Furthermore, this study suggests that combination of carbon ion and TIG is a potential therapeutic option against tumors.

A Dedicated Evolutionarily Conserved Molecular Network Licenses Differentiated Cells to Return to the Cell Cycle

Differentiated cells can re-enter the cell cycle to repair tissue damage via a series of discrete morphological and molecular stages coordinated by the cellular energetics regulator mTORC1. We previously proposed the term "paligenosis" to describe this conserved cellular regeneration program. Here, we detail a molecular network regulating mTORC1 during paligenosis in both mouse pancreatic acinar and gastric chief cells. DDIT4 initially suppresses mTORC1 to induce autodegradation of differentiated cell components and damaged organelles. Later in paligenosis, IFRD1 suppresses p53 accumulation. Ifrd1^-/- cells do not complete paligenosis because persistent p53 prevents mTORC1 reactivation and cell proliferation. Ddit4^-/- cells never suppress mTORC1 and bypass the IFRD1 checkpoint on proliferation. Previous reports and our current data implicate DDIT4/IFRD1 in governing paligenosis in multiple organs and species. Thus, we propose that an evolutionarily conserved, dedicated molecular network has evolved to allow differentiated cells to re-enter the cell cycle (i.e., undergo paligenosis) after tissue injury. VIDEO ABSTRACT.

Opposing p53 and mTOR/AKT promote an in vivo switch from apoptosis to senescence upon telomere shortening in zebrafish

Progressive telomere shortening during lifespan is associated with restriction of cell proliferation, genome instability and aging. Apoptosis and senescence are the two major outcomes upon irreversible cellular damage. Here, we show a transition of these two cell fates during aging of telomerase deficient zebrafish. In young telomerase mutants, proliferative tissues exhibit DNA damage and p53-dependent apoptosis, but no senescence. However, these tissues in older animals display loss of cellularity and senescence becomes predominant. Tissue alterations are accompanied by a pro-proliferative stimulus mediated by AKT signaling. Upon AKT activation, FoxO transcription factors are phosphorylated and translocated out of the nucleus. This results in reduced SOD2 expression causing an increase of ROS and mitochondrial dysfunction. These alterations induce p15/16 growth arrest and senescence. We propose that, upon telomere shortening, early apoptosis leads to cell depletion and insufficient compensatory proliferation. Following tissue damage, the mTOR/AKT is activated causing mitochondrial dysfunction and p15/16-dependent senescence.

The effects simultaneous inhibition of dipeptidyl peptidase-4 and P2X7 purinoceptors in an in vivo Parkinson's disease model

Loss of dopaminergic neurons following Parkinson's disease (PD) diminishes quality of life in patients. The present study was carried out to investigate the protective effects of simultaneous inhibition of dipeptidyl peptidase-4 (DPP-4) and P2X7 purinoceptors in a PD model and explore possible mechanisms. The 6-hydroxydopamine (6-OHDA) was used as a tool to establish PD model in male Wister rats. The expressions of SIRT1, SIRT3, mTOR, PGC-1α, PTEN, P53 and DNA fragmentation were evaluated by ELISA assay. Behavioral impairments were determined using apomorphine-induced rotational and narrow beam tests. Dopamine synthesis and TH-positive neurons were detected by tyrosine hydroxylase (TH) immunohistochemistry. Neuronal density was determined by Nissl staining. OHDA-lesioned rats exhibited behavioral impairments that reversed by BBG, lin and lin + BBG. We found significant reduced levels of SIRT1, SIRT3, PGC-1α and mTOR in both mid brain and striatum from OHDA-lesioned rats that reversed by BBG, lin and lin + BBG. Likewise, significant increased levels of PTEN and P53 were found in both mid brain and striatum from OHDA-lesioned rats that was reversed by BBG, lin and lin + BBG. TH-positive neurons and neuronal density were markedly reduced OHDA-lesioned rats that reversed by BBG, lin and lin + BBG. Collectively, our results showed protective effects of simultaneous inhibition of DPP-4 and P2X7 purinoceptors in a rat model of PD can be linked to targeting SIRT1/SIRT3, PTEN-mTOR pathways. Moreover, our findings demonstrated that simultaneous inhibition of DPP-4 and P2X7 purinoceptors might have stronger effect on mitochondrial biogenesis compared to only one.

Metastatic role of mammalian target of rapamycin signaling activation by chemoradiotherapy in advanced rectal cancer

Postoperative distant metastasis dramatically affects rectal cancer patients who have undergone neoadjuvant chemoradiotherapy (NACRT). Here, we clarified the association between NACRT‐mediated mammalian target of rapamycin (mTOR) signaling pathway activation and rectal cancer metastatic potential. We performed immunohistochemistry for phosphorylated mTOR (p‐mTOR) and phosphorylated S6 (p‐S6) on surgical specimen blocks from 98 rectal cancer patients after NACRT (cohort 1) and 80 colorectal cancer patients without NACRT (cohort 2). In addition, we investigated the association between mTOR pathway activity, affected by irradiation, and the migration ability of colorectal cancer cells in vitro. Based on the results of the clinical study, p‐mTOR was significantly overexpressed in cohort 1 (with NACRT) as compared to levels in cohort 2 (without NACRT) (P < .001). High p‐mTOR and p‐S6 levels correlated with the development of distant metastasis only in cohort 1. Specifically, high p‐S6 expression (HR 4.51, P = .002) and high pathological T‐stage (HR 3.73, P = .020) after NACRT were independent predictors of the development of distant metastasis. In vitro, p‐S6 levels and migration ability increased after irradiation in SW480 cells (TP53 mutation‐type) but decreased in LoVo cells (TP53 wild‐type), suggesting that irradiation modulates mTOR signaling and migration through cell type‐dependent mechanisms. We next assessed the expression level of p53 by immunostaining in cohort 1 and demonstrated that p‐S6 was overexpressed in samples with high p53 expression as compared to levels in samples with low p53 expression (P = .008). In conclusion, p‐S6 levels after NACRT correlate with postoperative distant metastasis in rectal cancer patients, suggesting that chemoradiotherapy might modulate the mTOR signaling pathway, promoting metastasis.

Inhibiting PAD2 enhances the anti-tumor effect of docetaxel in tamoxifen-resistant breast cancer cells

BACKGROUND

Tamoxifen resistance presents a huge clinical challenge for breast cancer patients. An understanding of the mechanisms of tamoxifen resistance can guide development of efficient therapies to prevent drug resistance.

METHODS

We first tested whether peptidylarginine deiminase 2 (PAD2) may be involved in tamoxifen-resistance in breast cancer cells. The effect of depleting or inhibiting PAD2 in tamoxifen-resistant MCF-7 (MCF7/TamR) cells was evaluated both in vitro and in vivo. We then investigated the potential of Cl-amidine, a PAD inhibitor, to be used in combination with tamoxifen or docetaxel, and further explored the mechanism of the synergistic and effective drug regimen of PADs inhibitor and docetaxel on tamoxifen-resistant breast cancer cells.

RESULTS

We report that PAD2 is dramatically upregulated in tamoxifen-resistant breast cancer. Depletion of PAD2 in MCF7/TamR cells facilitated the sensitivity of MCF7/TamR cells to tamoxifen. Moreover, miRNA-125b-5p negatively regulated PAD2 expression in MCF7/TamR cells, therefore overexpression of miR-125b-5p also increased the cell sensitivity to tamoxifen. Furthermore, inhibiting PAD2 with Cl-amidine not only partially restored the sensitivity of MCF7/TamR cells to tamoxifen, but also more efficiently enhanced the efficacy of docetaxel on MCF7/TamR cells with lower doses of Cl-amidine and docetaxel both in vivo and in vivo. We then showed that combination treatment with Cl-amidine and docetaxel enhanced p53 nuclear accumulation, which synergistically induced cell cycle arrest and apoptosis. Meanwhile, p53 activation in the combination treatment also accelerated autophagy processes by synergistically decreasing the activation of Akt/mTOR signaling, thus enhancing the inhibition of proliferation.

CONCLUSION

Our results suggest that PAD2 functions as an important new biomarker for tamoxifen-resistant breast cancers and that inhibiting PAD2 combined with docetaxel may offer a new approach to treatment of tamoxifen-resistant breast cancers.

Rapamycin, proliferation and geroconversion to senescence

Rapamycin inhibits cell proliferation, yet preserves (re)-proliferative potential (RPP). RPP is a potential of quiescent cells that is lost in senescent cells. mTOR drives conversion from quiescence to senescence (geroconversion). By suppressing geroconversion, rapamycin preserves RPP. Geroconversion is characterized by proliferation-like levels of phospho-S6K/S6/4E-BP1 in nonproliferating cells arrested by p16 and/or p21. mTOR-driven geroconversion is associated with cellular hyperfunction, which in turn leads to organismal aging manifested by age-related diseases.

Human cellular mitochondrial remodelling is governed by miR-2909 RNomics

BACKGROUND

There exists a general recognition of the fact that mitochondrial remodelling as a result of aerobic glycolysis ensures human somatic cells to revert to a more primitive-form exhibiting stem-like phenotype. The present study is an attempt to demonstrate that miR-2909 RNomics within human peripheral blood mononuclear cells (PBMCs) has the inherent capacity to re-program these cells to exhibit mitochondrial remodelling paralleled by aerobic glycolysis together with intracellular lipid inclusions. Such re-programmed PBMCs also expressed genes having ability to sustain their de-differentiation state and survival.

MATERIAL AND METHODS

Human PBMCs were programed to ectopically express miR-2909. Expression levels of genes including glucose transporter-1 (Glut-1), hexokinase (HK), hypoxia inducia factor-1 (HIF-1α), c-Myc, p53,mechanistic target of rapamycin complex (mTORC1), polycombcomplex protein (Bmi-1), Notch,Nanog,Tie-2, Oct-4,CD59, p53, CD34, B-cell lymphoma-2 (Bcl2),sterol regulatory element-binding protein2 (SREBP2), peroxisome proliferator-activated receptor gamma (PPARγ) nuclear respiratory factor 1 (NRF1), mitochondrial transcription factor A (Tfam), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) within miR-2909 expression vector transfected human PBMCs as well as PBMCs transfected with control vector containing scrambled sequence after 48h post-transfection using RT-qPCR and cellular ultrastructural features induced by miR-2909 ectopic expression were observed using transmission electron microscopy and morphometric analysis of an electron micrograph.

RESULTS

Ectopic expression of miR-2909 within human PBMCs resulted in their reprogramming into stem-like phenotype indicated by mitochondrial globular shaped coupled with cristae-poor morphology. Nuclear to cytoplasmic ratio (N/C), quantification of ATP levels, GSSG/GSH ratio, mitochondrial cytochrome c oxidase activity, secreted lactate concentrations, activity of antioxidant enzymes, levels of esterified cholesterol and triglycerides and flow-cytometric detection of apoptosis confirmed the compromised nature of mitochondrial function induced by ectopic miR-2909 expression in human PBMCs.

CONCLUSION

Based upon these results we propose that AATF gene-encoded miR-2909 may act as an epigenetic switch for cellular aerobic-glycolysis to ensure de-differentiation.

mTORC1 Prevents Epithelial Damage During Inflammation and Inhibits Colitis-Associated Colorectal Cancer Development

Epithelial cells lining the intestinal mucosa constitute a selective-semipermeable barrier acting as first line of defense in the organism. The number of those cells remains constant during physiological conditions, but disruption of epithelial cell homeostasis has been observed in several pathologies. During colitis, epithelial cell proliferation decreases and cell death augments. The mechanism responsible for these changes remains unknown. Here, we show that the pro-inflammatory cytokine IFNγ contributes to the inhibition of epithelial cell proliferation in intestinal epithelial cells (IECs) by inducing the activation of mTORC1. Activation of mTORC1 in response to IFNγ was detected in IECs present along the crypt axis and in colonic macrophages. mTORC1 inhibition enhances cell proliferation, increases DNA damage in IEC. In macrophages, mTORC1 inhibition strongly reduces the expression of pro-inflammatory markers. As a consequence, mTORC1 inhibition exacerbated disease activity, increased mucosal damage, enhanced ulceration, augmented cell infiltration, decreased survival and stimulated tumor formation in a model of colorectal cancer CRC associated to colitis. Thus, our findings suggest that mTORC1 signaling downstream of IFNγ prevents epithelial DNA damage and cancer development during colitis.

Biological Aspects of mTOR in Leukemia

The mammalian target of rapamycin (mTOR) is a central processor of intra- and extracellular signals, regulating many fundamental cellular processes such as metabolism, growth, proliferation, and survival. Strong evidences have indicated that mTOR dysregulation is deeply implicated in leukemogenesis. This has led to growing interest in the development of modulators of its activity for leukemia treatment. This review intends to provide an outline of the principal biological and molecular functions of mTOR. We summarize the current understanding of how mTOR interacts with microRNAs, with components of cell metabolism, and with controllers of apoptotic machinery. Lastly, from a clinical/translational perspective, we recapitulate the therapeutic results in leukemia, obtained by using mTOR inhibitors as single agents and in combination with other compounds.

Control of metabolism by p53 - Cancer and beyond

p53 is an important tumour suppressor gene, with loss of p53 contributing to the development of most human cancers. However, the activation of p53 in response to stress signals underpins a role for p53 in diverse aspects of health and disease. Activities of p53 that regulate metabolism can play a role in maintaining homeostasis and protecting cells from damage - so preventing disease development. By contrast, either loss or over-activation of p53 can contribute to numerous metabolic pathologies, including aging, obesity and diabetes.

mTORC1 pathway in DNA damage response

Living organisms have evolved various mechanisms to control their metabolism and response to various stresses, allowing them to survive and grow in different environments. In eukaryotes, the highly conserved mechanistic target of rapamycin (mTOR) signaling pathway integrates both intracellular and extracellular signals and serves as a central regulator of cellular metabolism, proliferation and survival. A growing body of evidence indicates that mTOR signaling is closely related to another cellular protection mechanism, the DNA damage response (DDR). Many factors important for the DDR are also involved in the mTOR pathway. In this review, we discuss how these two pathways communicate to ensure an efficient protection of the cell against metabolic and genotoxic stresses. We also describe how anticancer therapies benefit from simultaneous targeting of the DDR and mTOR pathways.

p53 modulates the effect of ribosomal protein S6 kinase1 (S6K1) on cisplatin toxicity in chronic myeloid leukemia cells

Chronic myeloid leukemia (CML) is characterized by the expression of the oncoprotein, BCR-ABL. BCR-ABL inhibitors revolutionized CML chemotherapy while blast crisis (BC) CML patients are less responsive. Since suppression of ribosomal protein S6 kinase1 (S6K1) phosphorylation reverses the resistance to BCR-ABL inhibitor in CML cells and S6K1 inhibitors augment cisplatin toxicity in lung cancer cells, we speculated that combination of S6K1 inhibitor and cisplatin may be beneficial for eliminating BC CML cells. To our surprise, S6K1 inhibition decreased cisplatin-induced DNA damage and cell death only in p53^-/- BC CML cells but not in p53^+/+ BC CML cells. During the progression of CML, p53 expression either decreases or mutates. Moreover, the expression of p53 affects drug response of CML cells. Our results confirmed that S6K1 inhibition reversed cisplatin toxicity is dependent on p53 expression in CML cells. Moreover, p53 attenuated the phosphorylation and localization of S6K1 via attenuating 3-phosphoinositide dependent protein kinase-1 (PDK1) phosphorylation. Furthermore, S6K1 acts via DNA-PKcs to regulate H2AX phosphorylation and PARP cleavage, respectively. Taken together, our results suggest that p53/PDK1/S6K1 is a novel pathway regulating cisplatin toxicity in BC CML cells.

Do p53 stress responses impact organismal aging?

p53 is a transcriptional regulator that responds to cellular stresses to suppress oncogenesis, but some of these responses can have unintended consequences that influence non-cancer-related aging processes. The impact of these consequences is not well understood-partly due to the many complex processes that influence p53 function and partly due to the vast array of processes that p53 affects. p53 has the potential to both accelerate and hinder cellular aging processes, which would likely have antithetical biological outcomes with regard to organismal aging. To accelerate aging, p53 induces apoptosis or cell cycle arrest as a prerequisite to cellular senescence; both can impair the mobilization of stem and progenitor cell populations. To suppress aging, p53 inhibits unregulated proliferation pathways that could lead to cellular senescence and a senescence-associated secretory phenotype (SASP), which creates a pro-inflammatory and degenerative tissue milieu. A review of mouse models supports both possibilities, highlighting the complexity of the p53 influence over organismal aging. A deeper knowledge of how p53 integrates and is integrated with various biological processes will improve our understanding of its influence over the aging process.

A comprehensive approach to the molecular determinants of lifespan using a Boolean model of geroconversion

Altered molecular responses to insulin and growth factors (GF) are responsible for late‐life shortening diseases such as type‐2 diabetes mellitus (T2DM) and cancers. We have built a network of the signaling pathways that control S‐phase entry and a specific type of senescence called geroconversion. We have translated this network into a Boolean model to study possible cell phenotype outcomes under diverse molecular signaling conditions. In the context of insulin resistance, the model was able to reproduce the variations of the senescence level observed in tissues related to T2DM's main morbidity and mortality. Furthermore, by calibrating the pharmacodynamics of mTOR inhibitors, we have been able to reproduce the dose‐dependent effect of rapamycin on liver degeneration and lifespan expansion in wild‐type and HER2–neu mice. Using the model, we have finally performed an in silico prospective screen of the risk–benefit ratio of rapamycin dosage for healthy lifespan expansion strategies. We present here a comprehensive prognostic and predictive systems biology tool for human aging.

Quantitative analysis of male germline stem cell differentiation reveals a role for the p53-mTORC1 pathway in spermatogonial maintenance

p53 protects cells from DNA damage by inducing cell-cycle arrest upon encountering genomic stress. Among other pathways, p53 elicits such an effect by inhibiting mammalian target of rapamycin complex 1 (mTORC1), the master regulator of cell proliferation and growth. Although recent studies have indicated roles for both p53 and mTORC1 in stem cell maintenance, it remains unclear whether the p53-mTORC1 pathway is conserved to mediate this process under normal physiological conditions. Spermatogenesis is a classic stem cell-dependent process in which undifferentiated spermatogonia undergo self-renewal and differentiation to maintain the lifelong production of spermatozoa. To better understand this process, we have developed a novel flow cytometry (FACS)-based approach that isolates spermatogonia at consecutive differentiation stages. By using this as a tool, we show that genetic loss of p53 augments mTORC1 activity during early spermatogonial differentiation. Functionally, loss of p53 drives spermatogonia out of the undifferentiated state and causes a consistent expansion of early differentiating spermatogonia until the stage of preleptotene (premeiotic) spermatocyte. The frequency of early meiotic spermatocytes is, however, dramatically decreased. Thus, these data suggest that p53-mTORC1 pathway plays a critical role in maintaining the homeostasis of early spermatogonial differentiation. Moreover, our FACS approach could be a valuable tool in understanding spermatogonial differentiation.