Coordinate transcriptional and translational repression of p53 by TGF-β1 impairs the stress response

Reduced S-nitrosylation of TGFβ1 elevates its binding affinity towards the receptor and promotes fibrogenic signaling in the breast

Transforming Growth Factor β (TGFβ) is a pleiotropic cytokine closely linked to tumors. TGFβ is often elevated in precancerous breast lesions in association with epithelial-to-mesenchymal transition (EMT), indicating its contribution to precancerous progression. We previously reported that basal nitric oxide (NO) levels declined along with breast cancer progression. We then pharmacologically inhibited NO production in healthy mammary glands of wild-type mice and found that this induced precancerous progression accompanied by desmoplasia and upregulation of TGFβ activity. In the present study, we tested our hypothesis that NO directly S-nitrosylates (forms an NO-adduct at a cysteine residue) TGFβ to inhibit the activity, whereas the reduction of NO denitrosylates TGFβ and de-represses the activity. We introduced mutations to three C-terminal cysteines of TGFβ1 which were predicted to be S-nitrosylated. We found that these mutations indeed impaired S-nitrosylation of TGFβ1 and shifted the binding affinity towards the receptor from the latent complex. Furthermore, in silico structural analyses predicted that these S-nitrosylation-defective mutations strengthen the dimerization of mature protein, whereas S-nitrosylation-mimetic mutations weaken the dimerization. Such differences in dimerization dynamics of TGFβ1 by denitrosylation/S-nitrosylation likely account for the shift of the binding affinities towards the receptor vs. latent complex. Our findings, for the first time, unravel a novel mode of TGFβ regulation based on S-nitrosylation or denitrosylation of the protein.

p53 mutation and deletion contribute to tumor immune evasion

TP53 (or p53) is widely accepted to be a tumor suppressor. Upon various cellular stresses, p53 mediates cell cycle arrest and apoptosis to maintain genomic stability. p53 is also discovered to suppress tumor growth through regulating metabolism and ferroptosis. However, p53 is always lost or mutated in human and the loss or mutation of p53 is related to a high risk of tumors. Although the link between p53 and cancer has been well established, how the different p53 status of tumor cells help themselves evade immune response remains largely elusive. Understanding the molecular mechanisms of different status of p53 and tumor immune evasion can help optimize the currently used therapies. In this context, we discussed the how the antigen presentation and tumor antigen expression mode altered and described how the tumor cells shape a suppressive tumor immune microenvironment to facilitate its proliferation and metastasis.

Study on Psychological Stress Response and Intervention Countermeasures of Exposed Population under Sudden Public Health Crisis

Background

After the occurrence of public health emergencies, people will have a series of physiological reactions, which will develop into psychological stress disorder in serious cases. Based on this, the purpose of this study is to analyze the psychological stress response and intervention countermeasures of exposed people under sudden public health crisis.

Objective

To explore the psychological stress response and intervention countermeasures of exposed population under sudden public health crisis.

Methods

A total of 400 people under the sudden public health crisis that bring about serious damage to public health, mass diseases of unknown causes, major food and occupational poisoning, and other events that seriously affect public health from December 2020 to December 2021 were selected as the subjects of the study. It was randomly and equally divided into two groups to take different intervention measures, the control group was given routine public health crisis intervention measures, and the research group was given comprehensive intervention. The metabolism, social function defects, health symptoms, psychological status, quality of life, sleep quality, and stress reaction were compared between the two groups.

Results

The rate of good metabolism in the research group was significantly higher than that in the control group (P < 0.05). After intervention, the scores of Social Disability Screening Schedule (SDSS) and Symptom Checklist 90 (SCL-90) decreased in both groups, and the scores of SDSS and SCL-90 in the research group were lower than those in the control group. After intervention, the scores of self-rating depression scale and self-rating anxiety scale in the two groups decreased, and the scores of self-rating depression scale and self-rating anxiety scale in the research group were lower than those in the control group (P < 0.05). The sleep quality of the research group was better than that of the control group (P < 0.05). The stress response indexes such as cortisol, blood glucose, and C-reactive protein in the two groups were decreased after intervention. The stress response indexes such as cortisol, blood glucose, and C-reactive protein in the research group were lower than those in the control group (P < 0.05).

Conclusion

Giving that comprehensive intervention measures to people exposed to sudden public health crisis can effectively relax their stress response, reinvigorate their quality of life and sleep, reduce depression and anxiety, and improve their metabolism, therefore, in the case of the outbreak of public health crisis in the future, it is worth applying for reference and popularizing.

Silencing of lncRNA MIR497HG via CRISPR/Cas13d Induces Bladder Cancer Progression Through Promoting the Crosstalk Between Hippo/Yap and TGF-β/Smad Signaling

A subset of long non-coding RNAs (lncRNAs), categorized as miRNA-host gene lncRNAs (lnc-miRHGs), is processed to produce miRNAs and involved in cancer progression. This work aimed to investigate the influences and the molecular mechanisms of lnc-miRHGs MIR497HG in bladder cancer (BCa). The miR-497 and miR-195 were derived from MIR497HG. We identified that lnc-miRHG MIR497HG and two harbored miRNAs, miR-497 and miR-195, were downregulated in BCa by analyzing The Cancer Genome Atlas and our dataset. Silencing of MIR497HG by CRISPR/Cas13d in BCa cell line 5637 promoted cell growth, migration, and invasion in vitro. Conversely, overexpression of MIR497HG suppressed cell progression in BCa cell line T24. MiR-497/miR-195 mimics rescued significantly the oncogenic roles of knockdown of MIR497HG by CRISPR/Cas13d in BCa. Mechanistically, miR-497 and miR-195 co-ordinately suppressed multiple key components in Hippo/Yap and transforming growth factor β signaling and particularly attenuated the interaction between Yap and Smad3. In addition, E2F4 was proven to be critical for silencing MIR497HG transcription in BCa cells. In short, we propose for the first time to reveal the function and mechanisms of MIR497HG in BCa. Blocking the pathological process may be a potential strategy for the treatment of BCa.

Specific miRNA and Gene Deregulation Characterize the Increased Angiogenic Remodeling of Thoracic Aneurysmatic Aortopathy in Marfan Syndrome

Marfan syndrome (MFS) is a connective tissue disease caused by mutations in the FBN1 gene, leading to alterations in the extracellular matrix microfibril assembly and the early formation of thoracic aorta aneurysms (TAAs). Non-genetic TAAs share many clinico-pathological aspects with MFS and deregulation of some microRNAs (miRNAs) has been demonstrated to be involved in the progression of TAA. In this study, 40 patients undergoing elective ascending aorta surgery were enrolled to compare TAA histomorphological features, miRNA profile and related target genes in order to find specific alterations that may explain the earlier and more severe clinical outcomes in MFS patients. Histomorphological, ultrastructural and in vitro studies were performed in order to compare aortic wall features of MFS and non-MFS TAA. MFS displayed greater glycosaminoglycan accumulation and loss/fragmentation of elastic fibers compared to non-MFS TAA. Immunohistochemistry revealed increased CD133⁺ angiogenic remodeling, greater MMP-2 expression, inflammation and smooth muscle cell (SMC) turnover in MFS TAA. Cultured SMCs from MFS confirmed higher turnover and α-smooth muscle actin expression compared with non-MFS TAA. Moreover, twenty-five miRNAs, including miR-26a, miR-29, miR-143 and miR-145, were found to be downregulated and only miR-632 was upregulated in MFS TAA in vivo. Bioinformatics analysis revealed that some deregulated miRNAs in MFS TAA are implicated in cell proliferation, extracellular matrix structure/function and TGFβ signaling. Finally, gene analysis showed 28 upregulated and seven downregulated genes in MFS TAA, some of them belonging to the CDH1/APC and CCNA2/TP53 signaling pathways. Specific miRNA and gene deregulation characterized the aortopathy of MFS and this was associated with increased angiogenic remodeling, likely favoring the early and more severe clinical outcomes, compared to non-MFS TAA. Our findings provide new insights concerning the pathogenetic mechanisms of MFS TAA; further investigation is needed to confirm if these newly identified specific deregulated miRNAs may represent potential therapeutic targets to counteract the rapid progression of MFS aortopathy.

5-Fluorouracil resistance mechanisms in colorectal cancer: From classical pathways to promising processes

Colorectal cancer (CRC) is a public health problem. It is the third most common cancer in the world, with nearly 1.8 million new cases diagnosed in 2018. The only curative treatment is surgery, especially for early tumor stages. When there is locoregional or distant invasion, chemotherapy can be introduced, in particular 5-fluorouracil (5-FU). However, the disease can become tolerant to these pharmaceutical treatments: resistance emerges, leading to early tumor recurrence. Different mechanisms can explain this 5-FU resistance. Some are disease-specific, whereas others, such as drug efflux, are evolutionarily conserved. These mechanisms are numerous and complex and can occur simultaneously in cells exposed to 5-FU. In this review, we construct a global outline of different mechanisms from disruption of 5-FU-metabolic enzymes and classic cellular processes (apoptosis, autophagy, glucose metabolism, oxidative stress, respiration, and cell cycle perturbation) to drug transporters and epithelial-mesenchymal transition induction. Particular interest is directed to tumor microenvironment function as well as epigenetic alterations and miRNA dysregulation, which are the more promising processes that will be the subject of much research in the future.

Effects of different levels of TGF-β expression and tumor cell necrosis rates in osteosarcoma on the chemotherapy resistance of osteosarcoma

Purpose

The clinical significance of transforming growth factor β (TGF-β) and tumor cell necrosis rate (TCNR) in the expression of osteosarcoma and its effects of chemotherapy resistance on osteosarcoma were explored.

Patients and methods

94 cases of neoadjuvant chemotherapy osteosarcoma patients at the Third Affiliated Hospital of Kunming Medical University between January 2014 and January 2019 were collected. Samples tested for TGF-β were collected before chemotherapy, the tumor cell necrosis rate of pathological samples before and after chemotherapy was determined. Others analyzed covariates included 12 prognostic factors that may be associated with chemotherapy resistance in previous studies: age, BMI, initial diagnosis time (The time from symptom onset to first medical attention), KPS score, initial tumor size, lymphocytes/leukocytes rate (LWR), neutrophils/lymphocytes rate (NLR), albumin, aspartate transaminase (AST), low density lipoprotein (LDL), blood urea nitrogen (BUN), alkaline phosphatase (ALP), the endpoints included progression-free survival (PFS) and overall survival (OS), response evaluation criteria in solid tumours by RECIST guideline (version 1.1).

Result

1. A total of 94 cases were examined for expression of TGF-β in pathological specimens, 45 cases were TGF-β high expression (47.9%) and 49 cases were TGF-β low expression (52.1%); 2. The BMI, LDL, ALP, NLR in TGF-β high expression group was significantly increased compared to TGF-β low expression group; the Initial diagnosis time, KPS in TGF-β high expression group was significantly decreased compared to TGF-β low expression group, all P < 0.05; 3. Effect of chemotherapy was positively with positive cell rate (P < 0.01 r = 0.337) and TGF-β total score (P < 0.0001 r = 0.635), while effect of chemotherapy was no correlation with degree of dyeing score (P > 0.05); there was significant difference in change from baseline after chemotherapy between TGF-β high expression group and TGF-β low expression group (P = 0.045); 4. Median OS 61.4 months in the TGF-β high expression group, median OS 68.1 months in the TGF-β low expression group, one-year survival rate, there was statistically significant difference in two groups (P = 0.045); median PFS 44.8 months in the TGF-β high expression group, median PFS 56.2 months in the TGF-β low expression group, There was no statistically significant difference in two groups (P > 0.05); 5. A total of 92 cases were examined for TCNR after chemotherapy, 62 were TCNR ≤ 90% (67.4%), 30 were TCNR > 90% (32.6%); 6. the Initial diagnosis time, KPS, in TCNR > 90% group was significantly increased compared to TCNR ≤ 90% group; the initial tumor size, BUN, ALP in TCNR > 90% group was significantly decreased compared to TCNR ≤ 90% group, all P < 0.05; 7. TCNR was negatively correlated with the change from baseline after chemotherapy (P < 0.001 r = −0.411); there was no statistically significant difference between TCNR > 90% group and TCNR ≤ 90% group in change from baseline after chemotherapy (P > 0.05); 8. Median OS 67.8 months in the TCNR > 90% group, median OS 61.7 months in the TCNR ≤ 90% group, there was statistically significant difference between two groups (P = 0.040); median PFS 57.4 months in the TCNR > 90% group, median PFS 40.5 months in the TCNR ≤ 90% group, there was statistically significant difference between two groups (P = 0.036); 9. TGF-β total score was negatively correlated with TCNR (P < 0.001 r = −0.571).

Conclusion

The results of this study suggested that the higher expression of TGF-β, the lower expression of TCNR, which more likely to induce chemotherapy resistance among patients with osteosarcoma and lead to poor prognosis.

Identification of transcription factors MYC and C/EBPβ mediated regulatory networks in heart failure based on gene expression omnibus datasets

Background

Heart failure is one of leading cause of death worldwide. However, the transcriptional profiling of heart failure is unclear. Moreover, the signaling pathways and transcription factors involving the heart failure development also are largely unknown. Using published Gene Expression Omnibus (GEO) datasets, in the present study, we aim to comprehensively analyze the differentially expressed genes in failing heart tissues, and identified the critical signaling pathways and transcription factors involving heart failure development.

Methods

The transcriptional profiling of heart failure was identified from previously published gene expression datasets deposited in GSE5406, GSE16499 and GSE68316. The enriched signaling pathways and transcription factors were analyzed using Database for Annotation, Visualization and Integrated Discovery (DAVID) website and gene set enrichment analysis (GSEA) assay. The transcriptional networks were created by Cytoscape.

Results

Compared with the normal heart tissues, 90 genes were particularly differentially expressed in failing heart tissues, and those genes were associated with multiple metabolism signaling pathways and insulin signaling pathway. Metabolism and insulin signaling pathway were both inactivated in failing heart tissues. Transcription factors MYC and C/EBPβ were both negatively associated with the expression profiling of failing heart tissues in GSEA assay. Moreover, compared with normal heart tissues, MYC and C/EBPβ were down regulated in failing heart tissues. Furthermore, MYC and C/EBPβ mediated downstream target genes were also decreased in failing heart tissues. MYC and C/EBPβ were positively correlated with each other. At last, we constructed MYC and C/EBPβ mediated regulatory networks in failing heart tissues, and identified the MYC and C/EBPβ target genes which had been reported involving the heart failure developmental progress.

Conclusions

Our results suggested that metabolism pathways and insulin signaling pathway, transcription factors MYC and C/EBPβ played critical roles in heart failure developmental progress.

TGF-β1 increases sialidase 3 expression in human lung epithelial cells by decreasing its degradation and upregulating its translation

Purpose: We previously found extensive desialylation of glycoconjugates and upregulation of the sialidase enzyme NEU3 in fibrotic lesions in human and mouse lungs. However, studies using microarray analysis of whole lung tissue mRNA and single cell RNA-seq found no significant difference in levels of NEU3 mRNA between IPF patients and controls. This study aimed to elucidate how NEU3 was upregulated in fibrotic lungs.Materials and methods: Transforming growth factor-β1 (TGF-β1), a key driver of fibrosis, was added to A549 human alveolar basal epithelial adenocarcinoma cells and human small airway epithelial cells (HSAEpC). NEU3 expression in A549 cells and HSAEpC was detected by immunofluorescence staining. NEU3 translation and degradation were assessed by polysome profiling (polysomes efficiently translate mRNAs; monosomes poorly translate mRNAs) and cycloheximide chase after treating cells with or without TGF-β1 for 48 h.Results: TGF-β1 increased NEU3 expression and secretion in A549 cells and HSAEpC but did not change total (nuclear + cytosolic) NEU3 mRNA levels. TGF-β1 decreased the degradation rate of NEU3 in A549 cells. TGF-β1 decreased NEU3 mRNA levels in monosomes and increased NEU3 mRNA level in polysomes.Conclusion: TGF-β1 upregulates levels of NEU3 in epithelial cells by both decreasing NEU3 degradation and by increasing the translation of NEU3 mRNA, explaining the apparent paradox of high levels of NEU3 protein in pulmonary fibrosis without a concomitant increase in the expression of NEU3 mRNA.

TGF-β Sustains Tumor Progression through Biochemical and Mechanical Signal Transduction

Transforming growth factor β (TGF-β) signaling transduces immunosuppressive biochemical and mechanical signals in the tumor microenvironment. In addition to canonical SMAD transcription factor signaling, TGF-β can promote tumor growth and survival by inhibiting proinflammatory signaling and extracellular matrix (ECM) remodeling. In this article, we review how TGF-β activated kinase 1 (TAK1) activation lies at the intersection of proinflammatory signaling by immune receptors and anti-inflammatory signaling by TGF-β receptors. Additionally, we discuss the role of TGF-β in the mechanobiology of cancer. Understanding how TGF-β dampens proinflammatory responses and induces pro-survival mechanical signals throughout cancer development is critical for designing therapeutics that inhibit tumor progression while bolstering the immune response.

Role of miR-34a in TGF-β1- and Drug-Induced Epithelial-Mesenchymal Transition in Alveolar Type II Epithelial Cells

Epithelial-mesenchymal transition (EMT) of alveolar type II epithelial cells may play an important role in the pulmonary fibrosis induced by drugs such as bleomycin (BLM) and methotrexate (MTX). In this study, we examined the role of microRNAs (miRNAs) in drug-induced EMT using RLE/Abca3, a cell line having alveolar type II cell-like phenotype. Based on the screening using miRNA microarray analysis, it was found that the expression of some miRNAs, such as miR-34a, was increased by transforming growth factor (TGF)-β1 and BLM. An increase in miR-34a expression due to TGF-β1, BLM, and MTX was also observed in real-time PCR analysis. Therefore, miR-34a was focused upon in further studies. The expression of nectin-1 mRNA and protein, a possible target of miR-34a, was decreased by the treatment with TGF-β1, BLM, and MTX. In addition, when RLE/Abca3 cells were transfected with miR-34a mimic, the expression of nectin-1 mRNA and Abca3 mRNA, another target of miR34a, decreased significantly. Furthermore, the mRNA expression of cytokeratin 19, an epithelial marker, decreased, whereas that of α-smooth muscle actin, a mesenchymal marker, increased in the cells transfected with miR-34a mimic. These results suggest that miR-34a is involved in drug-induced EMT in alveolar epithelial cells, and possibly in lung fibrosis.

Identification of a DNA Damage-Induced Alternative Splicing Pathway That Regulates p53 and Cellular Senescence Markers

Cellular responses to DNA damage are critical determinants of cancer development and aging-associated pathogenesis. Here, we identify and characterize a DNA-damage response (DDR) pathway that regulates alternative splicing of numerous gene products, including the human tumor suppressor TP53, and controls DNA damage-induced cellular senescence. In brief, ionizing radiation (IR) inhibits the activity of SMG1, a phosphoinositide-3-kinase-like kinase family member, reducing the binding of SMG1 to a specific region near exon 9 of p53 precursor mRNA and promoting the binding of ribosomal protein L26 (RPL26) to p53 pre-mRNA. RPL26, in turn, is required for the recruitment of the serine/arginine-rich splicing factor SRSF7 to p53 pre-mRNA and generation of alternatively spliced p53β RNA. Disruption of this pathway via selective knockout of p53β by CRISPR/Cas9 or downregulation of pathway constituents significantly reduces IR-induced senescence markers, and cells lacking p53β expression fail to transcriptionally repress negative regulators of cellular senescence and aging.Significance: We identified a new component of the DDR pathway that regulates alternative splicing of messenger RNAs, including human TP53 mRNA. Modulation of this regulatory pathway affects DNA-damage induction of cellular senescence markers. Cancer Discov; 7(7); 766-81. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 653.

Liquiritigenin attenuates cardiac injury induced by high fructose-feeding through fibrosis and inflammation suppression

Diabetes combined with cardiomyopathy is considered as an essential complication, showing diastolic persistently and causing cardiac injury, which is linked to fibrosis progression and inflammation response. Fibrosis and inflammation response are two markers for cardiomyopathy. Liquiritigenin is a flavanone, isolated from Radix glycyrrhiza, which exhibits various biological properties, including anti-cancer and anti-inflammatory activities. Here, in our study, the protective effects and anti-inflammatory activity of liquiritigenin were explored in mice and cardiac muscle cells treated by fructose to reveal the possible mechanism by which liquiritigenin attenuates cardiac injury. The mice were separated into five groups. The diabetic model of mouse was established with 30% high fructose feeding. Liquiritigenin dramatically reduced the lipid accumulation induced by high fructose diet. Compared to mice only treated with high fructose, mice in the presence of liquiritigenin after fructose feeding developed less cardiac fibrosis with lower levels of alpha smooth muscle-actin (α-SMA), Collagen type I, Collagen type II, TGF-β1 and Procol1a1. Additionally, liquiritigenin markedly down-regulated inflammatory cytokines secretion and phosphorylated NF-κB via inhibiting IKKα/IκBα signaling pathway. Our results indicate that liquiritigenin has a protective role in high fructose feeding-triggered cardiac injury through fibrosis and inflammation response suppression by inactivating NF-κB signaling pathway. Thus, liquiritigenin may be a potential candidate for diabetes-associated cardiac injury.

Dlx-2 and glutaminase upregulate epithelial-mesenchymal transition and glycolytic switch

Most cancer cells depend on enhanced glucose and glutamine (Gln) metabolism for growth and survival. Oncogenic metabolism provides biosynthetic precursors for nucleotides, lipids, and amino acids; however, its specific roles in tumor progression are largely unknown. We previously showed that distal-less homeobox-2 (Dlx-2), a homeodomain transcription factor involved in embryonic and tumor development, induces glycolytic switch and epithelial-mesenchymal transition (EMT) by inducing Snail expression. Here we show that Dlx-2 also induces the expression of the crucial Gln metabolism enzyme glutaminase (GLS1), which converts Gln to glutamate. TGF-β and Wnt induced GLS1 expression in a Dlx-2-dependent manner. GLS1 shRNA (shGLS1) suppressed in vivo tumor metastasis and growth. Inhibition of Gln metabolism by shGLS1, Gln deprivation, and Gln metabolism inhibitors (DON, 968 and BPTES) prevented Dlx-2-, TGF-β-, Wnt-, and Snail-induced EMT and glycolytic switch. Finally, shDlx-2 and Gln metabolism inhibition decreased Snail mRNA levels through p53-dependent upregulation of Snail-targeting microRNAs. These results demonstrate that the Dlx-2/GLS1/Gln metabolism axis is an important regulator of TGF-β/Wnt-induced, Snail-dependent EMT, metastasis, and glycolytic switch.

TGF-β induces p53/Smads complex formation in the PAI-1 promoter to activate transcription

Transforming growth factor β (TGF-β) signaling facilitates tumor development during the advanced stages of tumorigenesis, but induces cell-cycle arrest for tumor suppression during the early stages. However, the mechanism of functional switching of TGF-β is still unknown, and it is unclear whether inhibition of TGF-β signaling results amelioration or exacerbation of cancers. Here we show that the tumor suppressor p53 cooperates with Smad proteins, which are TGF-β signal transducers, to selectively activate plasminogen activator inhibitor type-1 (PAI-1) transcription. p53 forms a complex with Smad2/3 in the PAI-1 promoter to recruit histone acetyltransferase CREB-binding protein (CBP) and enhance histone H3 acetylation, resulting in transcriptional activation of the PAI-1 gene. Importantly, p53 is required for TGF-β-induced cytostasis and PAI-1 is involved in the cytostatic activity of TGF-β in several cell lines. Our results suggest that p53 enhances TGF-β-induced cytostatic effects by activating PAI-1 transcription, and the functional switching of TGF-β is partially caused by p53 mutation or p53 inactivation during cancer progression. It is expected that these findings will contribute to optimization of TGF-β-targeting therapies for cancer.

The aryl hydrocarbon receptor agonist benzo(a)pyrene reactivates LINE-1 in HepG2 cells through canonical TGF-β1 signaling: implications in hepatocellular carcinogenesis

Long interspersed nuclear element-1 (L1) is a genetic element that mobilizes throughout the mammalian genome via retrotransposition and damages host DNA via mutational insertions, chromosomal rearrangements, and reprogramming of gene expression. The cellular mechanisms responsible for aberrant L1 expression during cancer pathogenesis are unclear. Previously, we have shown that L1 reactivation in several human cell lines is dependent upon the activation of aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor member of the PAS superfamily of proteins. We also showed that ectopic expression of L1 reprograms the HepG2 genome leading to epithelial-to-mesenchymal transition (EMT). Here we present evidence that reactivation of L1 and modulation of EMT in HepG2 cells by the AhR ligand benzo(a)pyrene (BaP) is effected through the canonical TGF-β1 signaling pathway. BaP increased TGF-β1 mRNA, SMAD2 phosphorylation and decreased expression of E-Cadherin. The functional relevance of these interactions and the involvement of TGFBR1/ALK5 and SMAD2/3 were confirmed by siRNA interference. Furthermore, expression of L1-encoded ORF1p was positively correlated with the activation of TGF-β1 signaling in human hepatocarcinoma samples at various stages of malignant progression. These results indicate that ligand-mediated AhR activation regulates L1 via canonical TGF-β1 signaling and raise important questions about the molecular etiology of human hepatocarcinomas.

Epithelial-mesenchymal transition and drug resistance in breast cancer (Review)

Breast cancer is the leading cause of cancer death in women worldwide. Insensitivity of tumor cells to drug therapies is an essential reason arousing such high mortality. Epithelial-mesenchymal transition (EMT) is defined by the loss of epithelial characteristics and the acquisition of a mesenchymal phenotype. It is well known that EMT plays an important role in breast cancer progression. Recently, mounting evidence has demonstrated involvement of EMT in antagonizing chemotherapy in breast cancer. Here, we discuss the biological significance and clinical implications of these findings, with an emphasis on novel approaches that effectively target EMT to increase the efficacy of anticancer therapies.

Ribosomal proteins: functions beyond the ribosome

Although ribosomal proteins are known for playing an essential role in ribosome assembly and protein translation, their ribosome-independent functions have also been greatly appreciated. Over the past decade, more than a dozen of ribosomal proteins have been found to activate the tumor suppressor p53 pathway in response to ribosomal stress. In addition, these ribosomal proteins are involved in various physiological and pathological processes. This review is composed to overview the current understanding of how ribosomal stress provokes the accumulation of ribosome-free ribosomal proteins, as well as the ribosome-independent functions of ribosomal proteins in tumorigenesis, immune signaling, and development. We also propose the potential of applying these pieces of knowledge to the development of ribosomal stress-based cancer therapeutics.

TSPAN12 is a critical factor for cancer-fibroblast cell contact-mediated cancer invasion

Communication between cancer cells and their microenvironment controls cancer progression. Although the tumor suppressor p53 functions in a cell-autonomous manner, it has also recently been shown to function in a non-cell-autonomous fashion. Although functional defects have been reported in p53 in stromal cells surrounding cancer, including mutations in the p53 gene and decreased p53 expression, the role of p53 in stromal cells during cancer progression remains unclear. We herein show that the expression of α-smooth muscle actin (α-SMA), a marker of cancer-associated fibroblasts (CAFs), was increased by the ablation of p53 in lung fibroblasts. CAFs enhanced the invasion and proliferation of lung cancer cells when cocultured with p53-depleted fibroblasts and required contact between cancer and stromal cells. A comprehensive analysis using a DNA chip revealed that tetraspanin 12 (TSPAN12), which belongs to the tetraspanin protein family, was derepressed by p53 knockdown. TSPAN12 knockdown in p53-depleted fibroblasts inhibited cancer cell proliferation and invasion elicited by coculturing with p53-depleted fibroblasts in vitro, and inhibited tumor growth in vivo. It also decreased CXC chemokine ligand 6 (CXCL6) secretion through the β-catenin signaling pathway, suggesting that cancer cell contact with TSPAN12 in fibroblasts transduced β-catenin signaling into fibroblasts, leading to the secretion of CXCL6 to efficiently promote invasion. These results suggest that stroma-derived p53 plays a pivotal role in epithelial cancer progression and that TSPAN12 and CXCL6 are potential targets for lung cancer therapy.

Single-cell analyses of transcriptional heterogeneity during drug tolerance transition in cancer cells by RNA sequencing

The acute cellular response to stress generates a subpopulation of reversibly stress-tolerant cells under conditions that are lethal to the majority of the population. Stress tolerance is attributed to heterogeneity of gene expression within the population to ensure survival of a minority. We performed whole transcriptome sequencing analyses of metastatic human breast cancer cells subjected to the chemotherapeutic agent paclitaxel at the single-cell and population levels. Here we show that specific transcriptional programs are enacted within untreated, stressed, and drug-tolerant cell groups while generating high heterogeneity between single cells within and between groups. We further demonstrate that drug-tolerant cells contain specific RNA variants residing in genes involved in microtubule organization and stabilization, as well as cell adhesion and cell surface signaling. In addition, the gene expression profile of drug-tolerant cells is similar to that of untreated cells within a few doublings. Thus, single-cell analyses reveal the dynamics of the stress response in terms of cell-specific RNA variants driving heterogeneity, the survival of a minority population through generation of specific RNA variants, and the efficient reconversion of stress-tolerant cells back to normalcy.

An unconventional role of BMP-Smad1 signaling in DNA damage response: a mechanism for tumor suppression

The genome is under constant attack by self-produced reactive oxygen species and genotoxic reagents in the environment. Cells have evolved a DNA damage response (DDR) system to sense DNA damage, to halt cell cycle progression and repair the lesions, or to induce apoptosis if encountering irreparable damage. The best studied DDR pathways are the PIKK-p53 and PIKK-Chk1/2. Mutations in these genes encoding DDR molecules usually lead to genome instability and tumorigenesis. It is worth noting that there exist unconventional pathways that facilitate the canonical pathways or take over in the absence of the canonical pathways in DDR. This review will summarize on several unconventional pathways that participate in DDR with an emphasis on the BMP-Smad1 pathway, a known regulator of mouse development and bone remodeling.

TGFβ signaling regulates the timing of CNS myelination by modulating oligodendrocyte progenitor cell cycle exit through SMAD3/4/FoxO1/Sp1

Research on myelination has focused on identifying molecules capable of inducing oligodendrocyte (OL) differentiation in an effort to develop strategies that promote functional myelin regeneration in demyelinating disorders. Here, we show that transforming growth factor β (TGFβ) signaling is crucial for allowing oligodendrocyte progenitor (OP) cell cycle withdrawal, and therefore, for oligodendrogenesis and postnatal CNS myelination. Enhanced oligodendrogenesis and subcortical white matter (SCWM) myelination was detected after TGFβ gain of function, while TGFβ receptor II (TGFβ-RII) deletion in OPs prevents their development into mature myelinating OLs, leading to SCWM hypomyelination in mice. TGFβ signaling modulates OP cell cycle withdrawal and differentiation through the transcriptional modulation of c-myc and p21 gene expression, mediated by the interaction of SMAD3/4 with Sp1 and FoxO1 transcription factors. Our study is the first to demonstrate an autonomous and crucial role of TGFβ signaling in OL development and CNS myelination, and may provide new avenues in the treatment of demyelinating diseases.

p53 and ribosome biogenesis stress: the essentials

Cell proliferation and cell growth are two tightly linked processes, as the proliferation program cannot be executed without proper accumulation of cell mass, otherwise endangering the fate of the two daughter cells. It is therefore not surprising that ribosome biogenesis, a key element in cell growth, is regulated by many cell cycle regulators. This regulation is exerted transcriptionally and post-transcriptionally, in conjunction with numerous intrinsic and extrinsic signals. Those signals eventually converge at the nucleolus, the cellular compartment that is not only responsible for executing the ribosome biogenesis program, but also serves as a regulatory hub, responsible for integrating and transmitting multiple stress signals to the omnipotent cell fate gatekeeper, p53. In this review we discuss when, how and why p53 is activated upon ribosomal biogenesis stress, and how perturbation of this critical regulatory interplay may impact human disease.

Translational reprogramming in cellular stress response

Cell survival in changing environments requires appropriate regulation of gene expression, including translational control. Multiple stress signaling pathways converge on several key translation factors, such as eIF4F and eIF2, and rapidly modulate messenger RNA (mRNA) translation at both the initiation and the elongation stages. Repression of global protein synthesis is often accompanied with selective translation of mRNAs encoding proteins that are vital for cell survival and stress recovery. The past decade has seen significant progress in our understanding of translational reprogramming in part due to the development of technologies that allow the dissection of the interplay between mRNA elements and corresponding binding proteins. Recent genome-wide studies using ribosome profiling have revealed unprecedented proteome complexity and flexibility through alternative translation, raising intriguing questions about stress-induced translational reprogramming. Many surprises emerged from these studies, including wide-spread alternative translation initiation, ribosome pausing during elongation, and reversible modification of mRNAs. Elucidation of the regulatory mechanisms underlying translational reprogramming will ultimately lead to the development of novel therapeutic strategies for human diseases.

The p53 response in single cells is linearly correlated to the number of DNA breaks without a distinct threshold

BACKGROUND

The tumor suppressor protein p53 is activated by cellular stress. DNA double strand breaks (DSBs) induce the activation of the kinase ATM, which stabilizes p53 and activates its transcriptional activity. Single cell analysis revealed that DSBs induced by gamma irradiation trigger p53 accumulation in a series of pulses that vary in number from cell to cell. Higher levels of irradiation increase the number of p53 pulses suggesting that they arise from periodic examination of the damage by ATM. If damage persists, additional pulses of p53 are triggered. The threshold of damage required for activating a p53 pulse is unclear. Previous studies that averaged the response across cell populations suggested that one or two DNA breaks are sufficient for activating ATM and p53. However, it is possible that by averaging over a population of cells important features of the dependency between DNA breaks and p53 dynamics are missed.

RESULTS

Using fluorescent reporters we developed a system for following in individual cells the number of DSBs, the kinetics of repair and the p53 response. We found a large variation in the initial number of DSBs and the rate of repair between individual cells. Cells with higher number of DSBs had higher probability of showing a p53 pulse. However, there was no distinct threshold number of breaks for inducing a p53 pulse. We present evidence that the decision to activate p53 given a specific number of breaks is not entirely stochastic, but instead is influenced by both cell-intrinsic factors and previous exposure to DNA damage. We also show that the natural variations in the initial amount of p53, rate of DSB repair and cell cycle phase do not affect the probability of activating p53 in response to DNA damage.

CONCLUSIONS

The use of fluorescent reporters to quantify DNA damage and p53 levels in live cells provided a quantitative analysis of the complex interrelationships between both processes. Our study shows that p53 activation differs even between cells that have a similar number of DNA breaks. Understanding the origin and consequences of such variability in normal and cancerous cells is crucial for developing efficient and selective therapeutic interventions.

TGF-β: an emerging player in drug resistance

The transforming growth factor β (TGF-β) pathway acts as a double-edged sword in tumorigenesis. By constraining epithelial cell growth, TGF-β is a potent tumor suppressor. However, TGF-β also acts as a key player in the induction of epithelial-to-mesenchymal transition (EMT), thereby enhancing invasiveness and metastasis. Furthermore, TGF-β signaling has recently been correlated with resistance against both targeted and conventional anticancer agents. Here, we present data demonstrating a role for TGF-β in chemotherapy resistance in colorectal cancer (CRC). We discuss these results in the context of recent findings indicating TGF-β signaling as an emerging player in cancer drug resistance.