Navigating the labyrinth of long non-coding RNAs in colorectal cancer:From chemoresistance to autophagy

Long non-coding RNAs(lncRNAs),with transcript lengths exceeding 200 nucleotides and little or no protein-coding capacity,have been found to impact colorectal cancer(CRC)through various biological processes.LncRNA expression can regulate autophagy,which plays dual roles in the initiation and progression of cancers,including CRC.Abnormal expression of lncRNAs is associated with the emergence of chemoresistance.Moreover,it has been confirmed that targeting autophagy through lncRNA regulation could be a viable approach for combating chemoresistance.Two recent studies titled“Human β-defensin-1 affects the mammalian target of rapamycin pathway and autophagy in colon cancer cells through long non-coding RNA TCONS_00014506”and“Upregulated lncRNA PRNT promotes progression and oxaliplatin resistance of colorectal cancer cells by regulating HIPK2 transcription”revealed novel insights into lncRNAs associated with autophagy and oxaliplatin resistance in CRC,respectively.In this editorial,we particularly focus on the regulatory role of lncRNAs in CRC-related autophagy and chemoresistance since the regulation of chemotherapeutic sensitivity by intervening with the lncRNAs involved in the autophagy process has become a promising new approach for cancer treatment.

Regenerating gene 4 promotes chemoresistance of colorectal cancer by affecting lipid droplet synthesis and assembly

BACKGROUND Regenerating gene 4(REG4)has been proved to be carcinogenic in some cancers,but its manifestation and possible carcinogenic mechanisms in colorectal cancer(CRC)have not yet been elucidated.Our previous study found that the drug resistance of CRC cells may be closely linked to their fat metabolism.AIM To explore the role of REG4 in CRC and its association with lipid droplet formation and chemoresistance.METHODS We conducted a meta-analysis and bioinformatics and pathological analyses of REG4 expression in CRC.The effects of REG4 on the phenotypes and related protein expression were also investigated in CRC cells.We detected the impacts of REG4 on the chemoresistance and lipid droplet formation in CRC cells.Finally,we analyzed how REG4 regulated the transcription and proteasomal degradation of lipogenic enzymes in CRC cells.RESULTS Compared to normal mucosa,REG4 mRNA expression was high in CRC(P<0.05)but protein expression was low.An inverse correlation existed between lymph node and distant metastases,tumor-node-metastasis staging or short overall survival and REG4 mRNA overexpression(P<0.05),but vice versa for REG4 protein expression.REG4-related genes included:Chemokine activity;taste receptors;protein-DNA and DNA packing complexes;nucleosomes and chromatin;generation of second messenger molecules;programmed cell death signals;epigenetic regulation and DNA methylation;transcription repression and activation by DNA binding;insulin signaling pathway;sugar metabolism and transfer;and neurotransmitter receptors(P<0.05).REG4 exposure or overexpression promoted proliferation,antiapoptosis,migration,and invasion of DLD-1 cells in an autocrine or paracrine manner by activating the epidermal growth factor receptor-phosphoinositide 3-kinase-Akt-nuclear factor-κB pathway.REG4 was involved in chemoresistance not through de novo lipogenesis,but lipid droplet assembly.REG4 inhibited the transcription of acetyl-CoA carboxylase 1(ACC1)and ATP-citrate lyase(ACLY)by disassociating the complex formation of anti-acetyl(AC)-acetyl-histone 3-AC-histone 4-inhibitor of growth protein-5-si histone deacetylase;-sterol-regulatory element binding protein 1 in their promoters and induced proteasomal degradation of ACC1 or ACLY.CONCLUSION REG4 may be involved in chemoresistance through lipid droplet assembly.REG4 reduces expression of de novo lipid synthesis key enzymes by inhibiting transcription and promoting ubiquitination-mediated proteasomal degradation.

Cancerous inhibitor of protein phosphatase 2A enhances chemoresistance of gastric cancer cells to oxaliplatin

BACKGROUND Cancerous inhibitor of protein phosphatase 2A(CIP2A)is a newly discovered oncogene.It is an active cell proliferation regulatory factor that inhibits tumor apoptosis in gastric cancer(GC)cells.CIP2A is functionally related to chemoresistance in various types of tumors according to recent studies.The underlying mechanism,however,is unknown.Further,the primary treatment regimen for GC is oxaliplatin-based chemotherapy.Nonetheless,it often fails due to chemoresistance of GC cells to oxaliplatin.AIM The goal of this study was to examine CIP2A expression and its association with oxaliplatin resistance in human GC cells.METHODS Immunohistochemistry was used to examine CIP2A expression in GC tissues and adjacent normal tissues.CIP2A expression in GC cell lines was reduced using small interfering RNA.After confirming the silencing efficiency,3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide tetrazolium and flow cytometry assays were used to evaluate cell proliferation and apoptosis caused by oxaliplatin treatment.Further,the key genes and protein changes were verified using realtime quantitative reverse transcription PCR and Western blotting,respectively,before and after intervention.For bioinformatics analysis,we used the R software and Bioconductor project.For statistical analysis,we used GraphPad Prism 6.0 and the Statistical Package for the Social Sciences software version 20.0(IBM,Armonk,United States).RESULTS A high level of CIP2A expression was associated with tumor size,T stage,lymph node metastasis,Tumor Node Metastasis stage,and a poor prognosis.Further,CIP2A expression was higher in GC cells than in normal human gastric epithelial cells.Using small interfering RNA against CIP2A,we discovered that CIP2A knockdown inhibited cell proliferation and significantly increased GC cell sensitivity to oxaliplatin.Moreover,CIP2A knockdown enhanced oxaliplatin-induced apoptosis in GC cells.Hence,high CIP2A levels in GC may be a factor in chemoresistance to oxaliplatin.In human GC cells,CIP2A regulated protein kinase B phosphorylation,and chemical inhibition of the protein kinase B signaling pathway was significantly associated with increased sensitivity to oxaliplatin.Therefore,the protein kinase B signaling pathway was correlated with CIP2Aenhanced chemoresistance of human GC cells to oxaliplatin.CONCLUSION CIP2A expression could be a novel therapeutic strategy for chemoresistance in GC.

Down.regulation of E.cadherin enhances prostate cancer chemoresistance via Notch signaling

Background:The chemoresistance of prostate cancer(PCa)is invariably associated with the aggressiveness and metastasis of this disease.New emerging evidence indicates that the epithelial-to-mesenchymal transition(EMT)may play pivotal roles in the development of chemoresistance and metastasis.As a hallmark of EMT,E-cadherin is suggested to be a key marker in the development of chemoresistance.However,the molecular mechanisms underlying PCa chemoresistance remain unclear.The current study aimed to explore the association between EMT and chemoresistance in PCa as well as whether changing the expression of E-cadherin would affect PCa chemoresistance.Methods:Parental PC3 and DU145 cells and their chemoresistant PC3-Tx R and DU145-Tx R cells were analyzed.PC3-Tx R and DU145-Tx R cells were transfected with E-cadherin-expressing lentivirus to overexpress E-cadherin;PC3 and DU145 cells were transfected with small interfering RNA to silence E-cadherin.Changes of EMT phenotype-related markers and signaling pathways were assessed by Western blotting and quantitative real-time polymerase chain reaction.Tumor cell migration,invasion,and colony formation were then evaluated by wound healing,transwell,and colony formation assays,respectively.The drug sensitivity was evaluated using MTS assay.Results:Chemoresistant PC3-Tx R and DU145-Tx R cells exhibited an invasive and metastatic phenotype that associated with EMT,including the down-regulation of E-cadherin and up-regulation of Vimentin,Snail,and N-cadherin,comparing with that of parental PC3 and DU145 cells.When E-cadherin was overexpressed in PC3-Tx R and DU145-Tx R cells,the expression of Vimentin and Claudin-1 was down-regulated,and tumor cell migration and invasion were inhibited.In particular,the sensitivity to paclitaxel was reactivated in E-cadherin-overexpressing PC3-Tx R and DU145-Tx R cells.When E-cadherin expression was silenced in parental PC3 and DU145 cells,the expression of Vimentin and Snail was up-regulated,and,particularly,the sensitivity to paclitaxel was decreased.Interestingly,Notch-1 expression was up-regulated in PC3-Tx R and DU145-Tx R cells,whereas the E-cadherin expression was down-regulated in these cells comparing with their parental cells.The use ofγ-secretase inhibitor,a Notch signaling pathway inhibitor,significantly increased the sensitivity of chemoresistant cells to paclitaxel.Conclusion:The down-regulation of E-cadherin enhances PCa chemoresistance via Notch signaling,and inhibiting the Notch signaling pathway may reverse PCa chemoresistance.

p38α MAPK pathway:A key factor in colorectal cancer therapy and chemoresistance

Colorectal cancer (CRC) remains one of the most common malignancies in the world. Although surgical resection combined with adjuvant therapy is effective at the early stages of the disease, resistance to conventional therapies is frequently observed in advanced stages, where treatments become ineffective. Resistance to cisplatin, irinotecan and 5-fluorouracil chemotherapy has been shown to involve mitogen-activated protein kinase (MAPK) signaling and recent studies identified p38&#x003b1; MAPK as a mediator of resistance to various agents in CRC patients. Studies published in the last decade showed a dual role for the p38&#x003b1; pathway in mammals. Its role as a negative regulator of proliferation has been reported in both normal (including cardiomyocytes, hepatocytes, fibroblasts, hematopoietic and lung cells) and cancer cells (colon, prostate, breast, lung tumor cells). This function is mediated by the negative regulation of cell cycle progression and the transduction of some apoptotic stimuli. However, despite its anti-proliferative and tumor suppressor activity in some tissues, the p38&#x003b1; pathway may also acquire an oncogenic role involving cancer related-processes such as cell metabolism, invasion, inflammation and angiogenesis. In this review, we summarize current knowledge about the predominant role of the p38&#x003b1; MAPK pathway in CRC development and chemoresistance. In our view, this might help establish the therapeutic potential of the targeted manipulation of this pathway in clinical settings.

MicroRNAs:Promising chemoresistance biomarkers in gastric cancer with diagnostic and therapeutic potential

Gastric cancer(GC) is the fourth most common cancer worldwide and ranks second in global cancer mortality statistics. Perioperative chemotherapy plays an important role in the management and treatment of advanced stage disease. However,response to chemotherapy varies widely,with some patients presenting no or only minor response to treatment. Hence,chemotherapy resistance is a major clinical problem that impacts on outcome. Unfortunately,to date there are no reliable biomarkers available that predict response to chemotherapy before the start of the treatment,or that allow modification of chemotherapy resistance. MicroRNAs(miRNAs) could provide an answer to this problem. miRNAs are involved in the initiation and progression of a variety of cancer types,and there is evidence that miRNAs impact on resistance towards chemotherapeutic drugs as well. This current review aims to provide an overview about the potential clinical applicability of miRNAs as biomarkers for chemoresistance in GC.The authors focus in this context on the potential of miRNAs to predict sensitivity towards different chemotherapeutics,and on the potential of miRNAs to modulate sensitivity and resistance towards chemotherapy in GC.

Sox2 enhances the tumorigenicity and chemoresistance of cancer stem-like cells derived from gastric cancer

Gastric cancer stem-like cells（GCSCs） have been identified to possess the ability of self-renewal and tumor initi-ation.However,the mechanisms involved remain largely unknown.Here,we isolated and characterized the GCSCs by side population（SP） sorting procedure and cultured sphere cells（SC） from human gastric cancer cell lines SGC-7901,BGC-823,MGC-803,HGC-27 and MKN-28.The sorting and culture assay revealed that SP cells proliferated in an asymmetric division manner.In addition,SP cells exhibited a higher potential of spheroid colony formation and greater drug resistance than non-SP cells（NSP）.Moreover,the SC were found with enhanced capabilities of drug resistance in vitro and tumorigenicity in vivo.Sox2 mRNA and protein was highly and significantly overex-pressed in the SP cells and SC.Importantly,downregulation of Sox2 with siRNA obviously reduced spheroid colony formation and doxorubicin efflux,as well as increased apoptosis rate in sphere cells in vitro and suppressed tumori-genicity in vivo.These results suggest that both SP cells and cultured SC enrich with GCSCs and that Sox2 plays a pivotal role in sustaining stem cell properties and might be a potential target for gastric cancer therapy.

MiR-181b suppresses proliferation of and reduces chemoresistance to temozolomide in U87 glioma stem cells

MicroRNAs regulate self renewal and differentiation of cancer stem cells.There,we sought to identify the expression of miR-181b in glioma stem cells and investigate the biological effect of miR-181b on glioma stem cells in this study.MiR-181b expression was measured by real-time PCR in glioma stem cells isolated from U87 cells by FACS sorting.After miR-181b was overexpressed in U87 glioma stem cells by miR-181b lentiviral expression vector and/or treatment of temozolomide,secondary neurosphere assay,soft agar colony assay and MTT assay were performed.Compared with U87 cells,the expression of miR-181b was significantly decreased in U87 glioma stem cells.Overexpression of miR-181b decreased neurosphere formation by U87 glioma stem cells in vitro and suppressed colony formation in soft agar,and the cell growth inhibition rates increased in a time-dependent manner in U87 glioma stem cells infected with miR-181b lentivirus.Furthermore,miR-181b had a synergistic effect on temozolomide-induced inhibition of secondary neurosphere and soft agar colony,and on cell growth inhibition rates.MiR-181b functions as a tumor suppressor that suppresses proliferation and reduces chemoresistance to temozolomide in glioma stem cells.

c-Met signaling in the development of tumorigenesis and chemoresistance: Potential applications in pancreatic cancer

Pancreatic ductal adenocarcinoma is the 4th leading cause of cancer deaths in the United States. The majority of patients are candidates only for palliative chemotherapy, which has proven largely ineffective in halting tumor progression. One proposed mechanism of chemoresistance involves signaling via the mesenchymal-epithelial transition factor protein (MET), a previously established pathway critical to cell proliferation and migration. Here, we review the literature to characterize the role of MET in the development of tumorigenesis, metastasis and chemoresistance, highlighting the potential of MET as a therapeutic target in pancreatic cancer. In this review, we characterize the role of c-Met in the development of tumorigenesis, metastasis and chemoresistance, highlighting the potential of c-Met as a therapeutic target in pancreatic cancer.

N^(6)-methyladenosine modification of CENPK mRNA by ZC3H13 promotes cervical cancer stemness and chemoresistance

Background:Stemness and chemoresistance contribute to cervical cancer recurrence and metastasis.In the current study,we determined the relevant players and role of N^(6)-methyladenine(m^(6)A)RNA methylation in cervical cancer progression.Methods:The roles of m^(6)A RNA methylation and centromere protein K(CENPK)in cervical cancer were analyzed using bioinformatics analysis.Methylated RNA immunoprecipitation was adopted to detect m^(6)A modification of CENPK mRNA.Human cervical cancer clinical samples,cell lines,and xenografts were used for analyzing gene expression and function.Immunofluorescence staining and the tumorsphere formation,clonogenic,MTT,and EdU assays were performed to determine cell stemness,chemoresistance,migration,invasion,and proliferation in HeLa and SiHa cells,respectively.Western blot analysis,co-immunoprecipitation,chromatin immunoprecipitation,and luciferase reporter,cycloheximide chase,and cell fractionation assays were performed to elucidate the underlying mechanism.Results:Bioinformatics analysis of public cancer datasets revealed firm links between m^(6)A modification patterns and cervical cancer prognosis,especially through ZC3H13-mediated m^(6)A modification of CENPK mRNA.CENPK expression was elevated in cervical cancer,associated with cancer recurrence,and independently predicts poor patient prognosis[hazard ratio=1.413,95%confidence interval=1.078−1.853,P=0.012].Silencing of CENPK prolonged the overall survival time of cervical cancer-bearing mice and improved the response of cervical cancer tumors to chemotherapy in vivo(P<0.001).We also showed that CENPK was directly bound to SOX6 and disrupted the interactions of CENPK withβ-catenin,which promotedβ-catenin expression and nuclear translocation,facilitated p53 ubiquitination,and led to activation of Wnt/β-catenin signaling,but suppression of the p53 pathway.This dysregulation ultimately enhanced the tumorigenic pathways required for cell stemness,DNA damage repair pathways necessary for cisplatin/carboplatin resistance,epithelial-mesenchymal transition involved in metastasis,and DNA replication that drove tumor cell proliferation.Conclusions:CENPK was shown to have an oncogenic role in cervical cancer and can thus serve as a prognostic indicator and novel target for cervical cancer treatment.

Leptin signaling and cancer chemoresistance:Perspectives

Obesity is a major health problem and currently is endemic around the world. Obesity is a risk factor for several different types of cancer, significantly promoting cancer incidence, progression, poor prognosis and resistance to anti-cancer therapies. The study of this resistance is critical as development of chemoresistance is a serious drawback for the successful and effective drug-based treatments of cancer. There is increasing evidence that augmented adiposity can impact on chemotherapeutic treatment of cancer and the development of resistance to these treatments, particularly through one of its signature mediators, the adipokine leptin. Leptin is a pro-inflammatory, pro-angiogenic and pro-tumorigenic adipokine that has been implicated in many cancers promoting processes such as angiogenesis, metastasis, tumorigenesis and survival/resistance to apoptosis. Several possible mechanisms that could potentially be developed by cancer cells to elicit drug resistance have been suggested in the literature. Here, we summarize and discuss the current state of the literature on the role of obesity and leptin on chemoresistance, particularly as it relates to breast and pancreatic cancers. We focus on the role of leptin and its significance in possibly driving these proposed chemoresistance mechanisms, and examine its effects on cancer cell survival signals and expansion of the cancer stem cell sub-populations.

Leptin-induced Notch and IL-1 signaling crosstalk in endometrial adenocarcinoma is associated with invasiveness and chemoresistance

BACKGROUND Obesity is a recognized risk factor for endometrial cancer (EmCa) and other cancer types. Leptin levels are significantly increased in obese individuals. Leptin-induced signaling crosstalk [Notch, Interleukin-1 (IL-1) and leptin outcome, NILCO] has been associated with breast cancer progression. This complex signaling crosstalk affects cancer cell proliferation, migration, invasion, angiogenesis, apoptosis and chemoresistance. NILCO expression was previously detected in human EmCa. However, it is unknown whether leptin regulates NILCO and alters EmCa’s response to chemotherapeutics. It is hypothesized that leptin induces NILCO and increases aggressiveness and chemoresistance in EmCa cells. AIM To determine whether leptin induces NILCO molecules in EmCa affecting cell proliferation, aggressiveness and chemoresistance. METHODS Leptin’s effects on the expression of NILCO molecules [mRNAs and proteins for Notch receptors (Notch1-4), ligands (JAG1 and DLL4) and downstream effectors (survivin, Hey2), and leptin (OB-R) and IL-1 (IL-1R tI) receptors] was examined in EmCa cells (type I: Ishikawa, and HEC-1A, and type II: An3Ca and KLE) using Real-time PCR and Western blot analysis, respectively. In addition, the effects of leptin on cell cycle, proliferation and cell invasion were determined using cytometric analysis (Cellometer Vision CBA system), MTT cell proliferation and Matrigel-based invasion assays, respectively. Inhibitors of leptin (nanoparticlebound leptin peptide receptor antagonist-2, IONP-LPrA2), IL-1 (anti-IL-1R tI antibody) and Notch (siRNA interference RNA) were used to investigate NILCO’s effects on cell proliferation and invasion. Leptin’s effects on Paclitaxel cytotoxicity in EmCa cells was determined by the CCK8 and Cellometer-based Annexin V assays. RESULTS For the first time it was shown that leptin is an inducer of Notch in EmCa. Experimental data suggest that leptin induced the expression of NILCO molecules, promoted proliferation and S- phase progression, and reduced Paclitaxel cytotoxicity on EmCa cells. Leptin’s effects were higher in type II EmCa cells. The progression of this more aggressive form of the disease is associated with obesity. Remarkably, the use of the leptin signaling antagonist, IONPLPrA2, re-sensitized EmCa cells to Paclitaxel. CONCLUSION Present data suggest the notion that leptin-induced NILCO could be a link between obesity and EmCa progression and chemoresistance. Most aggressive type II EmCa cells were higher sensitive to leptin, which appears to increase proliferation, cell cycle progression, aggressiveness, and chemoresistance to Paclitaxel. Therefore, leptin and NILCO could be novel therapeutic targets for type II EmCa, which does not have targeted therapy. Overall, IONP-LPrA2 has a potential as a novel adjuvant drug to enhance the effectiveness of type II EmCa chemotherapy.

Glucose deprivation induces chemoresistance in colorectal cancer cells by increasing ATF4 expression

AIM: To investigate the role of activating transcription factor 4(ATF4) in glucose deprivation(GD) induced colorectal cancer(CRC) drug resistance and the mechanism involved.METHODS: Chemosensitivity and apoptosis were measured under the GD condition. Inhibition of ATF4 using short hairpin RNA in CRC cells under the GD condition and in ATF4-overexpressing CRC cells was performed to identify the role of ATF4 in the GD induced chemoresistance. Quantitative real-time RTPCR and Western blot were used to detect the mR NA and protein expression of drug resistance gene 1(MDR1), respectively.RESULTS: GD protected CRC cells from drug-induced apoptosis(oxaliplatin and 5-fluorouracil) and induced the expression of ATF4, a key gene of the unfolded protein response. Depletion of ATF4 in CRC cells under the GD condition can induce apoptosis and drug resensitization. Similarly, inhibition of ATF4 in the ATF4-overexpressing CRC cells reintroduced therapeutic sensitivity and apoptosis. In addition, increased MDR1 expression was observed in GD-treated CRC cells. CONCLUSION: These data indicate that GD promotes chemoresistance in CRC cells through up-regulating ATF4 expression.

Glutathione metabolism is essential for self-renewal and chemoresistance of pancreatic cancer stem cells

BACKGROUND Cellular metabolism regulates stemness in health and disease.A reduced redox state is essential for self-renewal of normal and cancer stem cells(CSCs).However,while stem cells rely on glycolysis,different CSCs,including pancreatic CSCs,favor mitochondrial metabolism as their dominant energy-producing pathway.This suggests that powerful antioxidant networks must be in place to detoxify mitochondrial reactive oxygen species(ROS)and maintain stemness in oxidative CSCs.Since glutathione metabolism is critical for normal stem cell function and CSCs from breast,liver and gastric cancer show increased glutathione content,we hypothesized that pancreatic CSCs also rely on this pathway for ROS detoxification.AIM To investigate the role of glutathione metabolism in pancreatic CSCs.METHODS Primary pancreatic cancer cells of patient-derived xenografts(PDXs)were cultured in adherent or CSC-enriching sphere conditions to determine the role of glutathione metabolism in stemness.Real-time polymerase chain reaction(PCR)was used to validate RNAseq results involving glutathione metabolism genes in adherent vs spheres,as well as the expression of pluripotency-related genes following treatment.Public TCGA and GTEx RNAseq data from pancreatic cancer vs normal tissue samples were analyzed using the webserver GEPIA2.The glutathione-sensitive fluorescent probe monochlorobimane was used to determine glutathione content by fluorimetry or flow cytometry.Pharmacological inhibitors of glutathione synthesis and recycling[buthionine-sulfoximine(BSO)and 6-Aminonicotinamide(6-AN),respectively]were used to investigate the impact of glutathione depletion on CSC-enriched cultures.Staining with propidium iodide(cell cycle),Annexin-V(apoptosis)and CD133(CSC content)were determined by flow cytometry.Self-renewal was assessed by sphere formation assay and response to gemcitabine treatment was used as a readout for chemoresistance.RESULTS Analysis of our previously published RNAseq dataset E-MTAB-3808 revealed upregulation of genes involved in the KEGG(Kyoto Encyclopedia of Genes and Genomes)Pathway Glutathione Metabolism in CSC-enriched cultures compared to their differentiated counterparts.Consistently,in pancreatic cancer patient samples the expression of most of these up-regulated genes positively correlated with a stemness signature defined by NANOG,KLF4,SOX2 and OCT4 expression(P<10-5).Moreover,3 of the upregulated genes(MGST1,GPX8,GCCT)were associated with reduced disease-free survival in patients[Hazard ratio(HR)2.2-2.5;P=0.03-0.0054],suggesting a critical role for this pathway in pancreatic cancer progression.CSC-enriched sphere cultures also showed increased expression of different glutathione metabolism-related genes,as well as enhanced glutathione content in its reduced form(GSH).Glutathione depletion with BSO induced cell cycle arrest and apoptosis in spheres,and diminished the expression of stemness genes.Moreover,treatment with either BSO or the glutathione recycling inhibitor 6-AN inhibited self-renewal and the expression of the CSC marker CD133.GSH content in spheres positively correlated with intrinsic resistance to gemcitabine treatment in different PDXs r=0.96,P=5.8×1011).Additionally,CD133+cells accumulated GSH in response to gemcitabine,which was abrogated by BSO treatment(P<0.05).Combined treatment with BSO and gemcitabine-induced apoptosis in CD133+cells to levels comparable to CD133-cells and significantly diminished self-renewal(P<0.05),suggesting that chemoresistance of CSCs is partially dependent on GSH metabolism.CONCLUSION Our data suggest that pancreatic CSCs depend on glutathione metabolism.Pharmacological targeting of this pathway showed that high GSH content is essential to maintain CSC functionality in terms of self-renewal and chemoresistance.

MicroRNAs contribute to ATP-binding cassette transporter-and autophagy-mediated chemoresistance in hepatocellular carcinoma

Hepatocellular carcinoma(HCC) has an elevated mortality rate, largely because of high recurrence and metastasis. Additionally, the main obstacle during treatment of HCC is that patients usually develop resistance to chemotherapy.Cancer drug resistance involves many different mechanisms, including alterations in drug metabolism and processing, impairment of the apoptotic machine, activation of cell survival signaling, decreased drug sensitivity and autophagy, among others. Nowadays, miRNAs are emerging as master regulators of normal physiology-and tumor-related gene expression. In HCC,aberrant expression of many miRNAs leads to chemoresistance. Herein, we particularly analyzed miRNA impact on HCC resistance to drug therapy. Certain miRNAs target ABC(ATP-binding cassette) transporter genes. As most of these miRNAs are downregulated in HCC, transporter levels increase and intracellular drug accumulation decrease, turning cells less sensitive to death. Others miRNAs target autophagy-related gene expression, inhibiting autophagy and acting as tumor suppressors. Nevertheless, due to its downregulation in HCC, these miRNAs do not inhibit autophagy or tumor growth and, resistance is favored.Concluding, modulation of ABC transporter and/or autophagy-related gene expression or function by miRNAs could be determinant for HCC cell survival under chemotherapeutic drug treatment. Undoubtedly, more insights on the biological processes, signaling pathways and/or molecular mechanisms regulated by miRNAs are needed. Anyway, miRNA-based therapy together with conventional chemotherapeutic drugs has a great future in cancer therapy.

Circular RNAs:new biomarkers of chemoresistance in cancer

Chemotherapeutics are validated conventional treatments for patients with advanced cancer.However,with continual application of chemotherapeutics,chemoresistance,which is often predictive of poor prognosis,has gradually become a concern in recent years.Circular RNAs(circ RNAs),a class of endogenous noncoding RNAs(nc RNAs)with a closed-loop structure,have been reported to be notable targets and markers for the prognosis,diagnosis,and treatment of many diseases,particularly cancer.Although dozens of studies have shown that circ RNAs play major roles in drug-resistance activity in tumors,the mechanisms by which circ RNAs affect chemoresistance have yet to be explored.In this review,we describe the detailed mechanisms of circ RNAs and chemotherapeutics in various cancers and summarize potential therapeutic targets for drug-resistant tumors.

WNT5A modulates cell cycle progression and contributes to the chemoresistance in pancreatic cancer cells

BACKGROUND： Although there are many studies on the mechanism of chemoresistance in cancers, studies on the relations between WNT5 A and chemoresistance in pancreatic cancer are rare. The present study was to examine the role of WNT5 A in the regulation of cell cycle progression and in chemoresistance in pancreatic cancer tissues and cell lines.METHODS： Fresh pancreatic cancer and paracarcinoma tissues were obtained from 32 patients. The expressions of WNT5 A,AKT/p-AKT and Cyclin D1 were detected by immunohistochemistry,and the correlation between WNT5 A expression and clinicopathological characteristics was analyzed. The relationship between WNT5 A expression and gemcitabine resistance was studied in PANC-1 and MIAPaCa2 cell lines. The effect of WNT5 A on the regulation of cell cycle and gemcitabine cytotoxicity were investigated. The associations among the expressions of p-AKT,Cyclin D1 and WNT5 A were also analyzed in cell lines and the effect of WNT5 A on restriction-point（R-point） progression was evaluated.RESULTS： WNT5 A, p-AKT and Cyclin D1 were highly expressed in pancreatic cancer tissues, and the WNT5 A expression was correlated with the TNM stages. In vitroWNT5 A expression was associated with gemcitabine chemoresistance. The percentage of cells was increased in G0/G1 phase and decreased in S phase after knockdown of WNT5 A in PANC-1. WNT5 A promoted Cyclin D1 expression through phosphorylation of AKT which consequently enhanced G1-S transition and gemcitabine resistance. Furthermore, WNT5 A enhanced the cell cycle progression toward R-point through regulation ofretinoblastoma protein（pRb） and pRb-E2 F complex formation.CONCLUSIONS： WNT5 A induced chemoresistance by regulation of G1-S transition in pancreatic cancer cells. WNT5 A might serve as a predictor of gemcitabine response and as a potential target for tumor chemotherapy.

Zinc oxide nanoparticles reduce the chemoresistance of gastric cancer by inhibiting autophagy

BACKGROUND Gastric cancer(GC)is a common malignancy that results in a high rate of cancerrelated mortality.Cisplatin(DDP)-based chemotherapy is the first-line clinical treatment for GC therapy,but chemotherapy resistance remains a severe clinical challenge.Zinc oxide nanoparticle(ZnO-NP)has been identified as a promising anti-cancer agent,but the function of ZnO-NP in GC development is still unclear.AIM To explore the effect of ZnO-NP on chemotherapy resistance during GC progression.METHODS ZnO-NP was synthesized,and the effect and underlying mechanisms of ZnO-NP on the malignant progression and chemotherapy resistance of GC cells were analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)assays,colony formation assays,transwell assays,wound healing assays,flow cytometry,and Western blot analysis in GC cells and DDP-resistant GC cells,and by tumorigenicity analyses in nude mice.RESULTS Our data revealed that ZnO-NP was able to inhibit proliferation,migration,and invasion and induce apoptosis of GC cells.Meanwhile,ZnO-NP significantly reduced the half maximal inhibitory concentration(IC50)of DDP for the inhibition of cell proliferation of DDP-resistant SGC7901/DDP cell lines.Autophagy was increased in DDP-resistant GC cells,as demonstrated by elevated light chain 3-like protein 2(LC3II)/LC3I and Beclin-1 expression and repressed p62 expression in SGC7901/DDP cells compared to SGC7901 cells.Mechanically,ZnO-NP inhibited autophagy in GC cells and treatment with DDP induced autophagy,which was reversed by ZnO-NP.Functionally,ZnO-NP attenuated the tumor growth of DDP-resistant GC cells in vivo.CONCLUSION We conclude that ZnO-NP alleviates the chemoresistance of GC cells by inhibiting autophagy.Our findings present novel insights into the mechanism by which ZnO-NP regulates the chemotherapy resistance of GC.ZnO-NP may serve as a potential therapeutic candidate for GC treatment.The potential role of ZnO-NP in the clinical treatment of GC needs clarification in future investigations.

Hepatitis B core antigen modulates exosomal miR-135a to target vesicle-associated membrane protein 2 promoting chemoresistance in hepatocellular carcinoma

BACKGROUND Hepatocellular carcinoma(HCC)is one of the most common malignant tumors.The association of hepatitis B virus(HBV)infection with HCC is hitherto documented.Exosomal miRNAs contribute to cancer progression and chemoresistance.HBV X protein has been known to modulate miRNAs that facilitate cell proliferation and the process of hepatocarcinogenesis.However,there has been no report on hepatitis B core antigen(HBc)regulating exosomal miRNAs to induce drug resistance of HCC cells.AIM To elucidate the mechanism by which HBc promotes Doxorubicin hydrochloride(Dox)resistance in HCC.METHODS Exosomes were isolated by ultracentrifugation.The morphology and size of exosomes were evaluated by Dynamic Light Scattering(DLS)and transmission electron microscopy(TEM).The miRNAs differentially expressed in HCC were identified using The Cancer Genome Atlas(TCGA)database.The level of miR-135a-5p in patient tissue samples was detected by quantitative polymerase chain reaction.TargetScan and luciferase assay were used to predict and prove the target gene of miR-135a-5p.Finally,we identified the effects of miR-135a-5p on anti-apoptosis and the proliferation of HCC in the presence or absence of Dox using flow cytometry,Cell counting kit 8(CCK-8)assay and western blot.RESULTS We found that HBc increased the expression of exosomal miR-135a-5p.Integrated analysis of bioinformatics and patient samples found that miR-135a-5p was increased in HCC tissues in comparison with paracancerous tissues.Bioinformatic analysis and in vitro validation identified vesicle-associated membrane protein 2(VAMP2)as a novel target gene of miR-135a-5p.Functional assays showed that exosomal miR-135a-5p induced apoptosis protection,cell proliferation,and chemotherapy resistance in HCC.In addition,the rescue experiment demonstrated that VAMP2 reversed apoptosis protection,cell growth,and drug resistance by miR-135a-5p.Finally,HBc promoted HCC anti-apoptosis,proliferation,and drug resistance and prevented Dox-induced apoptosis via the miR-135a-5p/VAMP2 axis.CONCLUSION These data suggested that HBc upregulated the expression of exosomal miR-135a-5p and promoted anti-apoptosis,cell proliferation,and chemical resistance through miR-135a-5p/VAMP2.Thus,our work indicated an essential role of the miR-135a-5p/VAMP2 regulatory axis in chemotherapy resistance of HCC and a potential molecular therapeutic target for HCC.

Lipid droplets as metabolic determinants for stemness and chemoresistance in cancer

Previously regarded as simple fat storage particles,new evidence suggests thatlipid droplets(LDs)are dynamic and functional organelles involved in keycellular processes such as membrane biosynthesis,lipid metabolism,cellsignalling and inflammation.Indeed,an increased LD content is one of the mostapparent features resulting from lipid metabolism reprogramming necessary tosupport the basic functions of cancer cells.LDs have been associated to differentcellular processes involved in cancer progression and aggressiveness,such astumorigenicity,invasion and metastasis,as well as chemoresistance.Interestingly,all of these processes are controlled by a subpopulation of highly aggressivetumoral cells named cancer stem cells(CSCs),suggesting that LDs may befundamental elements for stemness in cancer.Considering the key role of CSCs onchemoresistance and disease relapse,main factors of therapy failure,the design ofnovel therapeutic approaches targeting these cells may be the only chance forlong-term survival in cancer patients.In this sense,their biology and functionalproperties render LDs excellent candidates for target discovery and design ofcombined therapeutic strategies.In this review,we summarise the currentknowledge identifying LDs and CSCs as main contributors to cancer aggressiveness,metastasis and chemoresistance.