Role of Bmi-1 in regulation of ionizing irradiation-induced epithelial-mesenchymal transition and migration of breast cancer cells

A radiosensitizer, gallotannin-rich extract from Bouea macrophylla seeds, inhibits radiation-induced epithelial-mesenchymal transition in breast cancer cells

Background

Radioresistance can pose a significant obstacle to the effective treatment of breast cancers. Epithelial–mesenchymal transition (EMT) is a critical step in the acquisition of stem cell traits and radioresistance. Here, we investigated whether Maprang seed extract (MPSE), a gallotannin-rich extract of seed from Bouea macrophylla Griffith, could inhibit the radiation-induced EMT process and enhance the radiosensitivity of breast cancer cells.

Methods

Breast cancer cells were pre-treated with MPSE before irradiation (IR), the radiosensitizing activity of MPSE was assessed using the colony formation assay. Radiation-induced EMT and stemness phenotype were identified using breast cancer stem cells (CSCs) marker (CD24^−/low/CD44⁺) and mammosphere formation assay. Cell motility was determined via the wound healing assay and transwell migration. Radiation-induced cell death was assessed via the apoptosis assay and SA-β-galactosidase staining for cellular senescence. CSCs- and EMT-related genes were confirmed by real-time PCR (qPCR) and Western blotting.

Results

Pre-treated with MPSE before irradiation could reduce the clonogenic activity and enhance radiosensitivity of breast cancer cell lines with sensitization enhancement ratios (SERs) of 2.33 and 1.35 for MCF7 and MDA-MB231cells, respectively. Pretreatment of breast cancer cells followed by IR resulted in an increased level of DNA damage maker (γ-H2A histone family member) and enhanced radiation-induced cell death. Irradiation induced EMT process, which displayed a significant EMT phenotype with a down-regulated epithelial marker E-cadherin and up-regulated mesenchymal marker vimentin in comparison with untreated breast cancer cells. Notably, we observed that pretreatment with MPSE attenuated the radiation-induced EMT process and decrease some stemness-like properties characterized by mammosphere formation and the CSC marker. Furthermore, pretreatment with MPSE attenuated the radiation-induced activation of the pro-survival pathway by decrease the expression of phosphorylation of ERK and AKT and sensitized breast cancer cells to radiation.

Conclusion

MPSE enhanced the radiosensitivity of breast cancer cells by enhancing IR-induced DNA damage and cell death, and attenuating the IR-induced EMT process and stemness phenotype via targeting survival pathways PI3K/AKT and MAPK in irradiated breast cancer cells. Our findings describe a novel strategy for increasing the efficacy of radiotherapy for breast cancer patients using a safer and low-cost natural product, MPSE.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03363-6.

Extended lifespan of bronchial epithelial cells maintains normal cellular phenotype and transcriptome integrity

Genetic studies have identified several epithelial-derived genes associated with airway diseases. However, techniques used to study gene function frequently exceed the proliferative potential of primary human bronchial epithelial cells (HBECs) isolated from patients. Increased expression of the polycomb group protein BMI-1 extends the lifespan of HBECs while maintaining cell context plasticity. Herein we aimed to assess how BMI-1 expression impacted cellular functions and global mRNA expression. HBECs from six donors were transduced with lentivirus containing BMI-1 and cells were characterised, including by RNA sequencing and impedance measurement. BMI-1-expressing HBECs (B-HBECs) have a proliferative advantage and show comparable in vitro properties to low passage primary HBECs, including cell attachment/spreading and barrier formation. The B-HBEC mRNA signature was modestly different to HBECs, with only 293 genes differentially expressed (5% false discovery rate). Genes linked to epithelial mesenchymal transition and cell cycle were enriched in B-HBECs. We investigated the expression of genes implicated in asthma from genetic and expression studies and found that 97.6% of genes remained unaltered. We have shown that increased BMI-1 expression in HBECs delays lung epithelial cell senescence by promoting cell cycle progression and highlighted the flexible utility for B-HBECs as an important platform for studying airway epithelial mechanisms.

A method to extend the lifespan of primary human bronchial epithelial cells that maintain a normal epithelial cell phenotype, thus providing a platform to investigate respiratory disease mechanisms over prolonged periodshttps://bit.ly/353Rklc

Hypoxic exposure activates the B cell-specific Moloney murine leukaemia virus integration site 1/PI3K/Akt axis and promotes EMT in leukaemia stem cells

Acute myeloid leukemia (AML) is a malignant tumor of the immature myeloid hematopoietic cells in the bone marrow. Disease recurrence driven by leukaemia stem cells (LSCs), a sub-population of leukaemia cells presenting self-renewal capacity and differentiation potential, is a major problem in the treatment of AML. Although a hypoxic microenvironment is considered to promote AML malignant behaviours and is considered a potential therapeutic target, the effect of hypoxic stimulation of LSCs is still largely unknown. Therefore, the present study analysed the effects of hypoxia on the malignant behaviours of LSCs. Hypoxia exposure upregulated hypoxia-inducible factor (HIF)-1α, which upregulated the transcription of B cell-specific Moloney murine leukaemia virus integration site 1 (BMI-1). Hypoxia exposure also activated the PI3K/Akt pathway and promoted the epithelial mesenchymal transition (EMT) in LSCs via hypoxia-mediated activation of HIF-1α. BMI-1 served an important role in the hypoxia-induced activation of the PI3K/Akt pathway and the promotion of EMT. Hypoxia exposure promoted chemoresistance against cytarabine arabinoside by inducing HIF-1α, thus activating the transcriptional activity of HIF-1α. Knockdown of BMI-1 disrupted hypoxia-induced chemoresistance in LSCs, indicating that HIF-1α-induced BMI-1 has a role in hypoxia-promoted malignant behaviours. Furthermore, it was demonstrated that induced BMI-1 inhibits the self-renewal capacity in LSCs under hypoxic conditions. The present study provides in vitro evidence demonstrating that hypoxia exposure regulates LSCs by activating HIF-1α/BMI-1 signalling, in turn modulating PI3K/Akt signalling and EMT. These results highlight potentially novel therapeutic targets of LSCs to improve the treatment of AML.

Cancer Stem Cells-Origins and Biomarkers: Perspectives for Targeted Personalized Therapies

The use of biomarkers in diagnosis, therapy and prognosis has gained increasing interest over the last decades. In particular, the analysis of biomarkers in cancer patients within the pre- and post-therapeutic period is required to identify several types of cells, which carry a risk for a disease progression and subsequent post-therapeutic relapse. Cancer stem cells (CSCs) are a subpopulation of tumor cells that can drive tumor initiation and can cause relapses. At the time point of tumor initiation, CSCs originate from either differentiated cells or adult tissue resident stem cells. Due to their importance, several biomarkers that characterize CSCs have been identified and correlated to diagnosis, therapy and prognosis. However, CSCs have been shown to display a high plasticity, which changes their phenotypic and functional appearance. Such changes are induced by chemo- and radiotherapeutics as well as senescent tumor cells, which cause alterations in the tumor microenvironment. Induction of senescence causes tumor shrinkage by modulating an anti-tumorigenic environment in which tumor cells undergo growth arrest and immune cells are attracted. Besides these positive effects after therapy, senescence can also have negative effects displayed post-therapeutically. These unfavorable effects can directly promote cancer stemness by increasing CSC plasticity phenotypes, by activating stemness pathways in non-CSCs, as well as by promoting senescence escape and subsequent activation of stemness pathways. At the end, all these effects can lead to tumor relapse and metastasis. This review provides an overview of the most frequently used CSC markers and their implementation as biomarkers by focussing on deadliest solid (lung, stomach, liver, breast and colorectal cancers) and hematological (acute myeloid leukemia, chronic myeloid leukemia) cancers. Furthermore, it gives examples on how the CSC markers might be influenced by therapeutics, such as chemo- and radiotherapy, and the tumor microenvironment. It points out, that it is crucial to identify and monitor residual CSCs, senescent tumor cells, and the pro-tumorigenic senescence-associated secretory phenotype in a therapy follow-up using specific biomarkers. As a future perspective, a targeted immune-mediated strategy using chimeric antigen receptor based approaches for the removal of remaining chemotherapy-resistant cells as well as CSCs in a personalized therapeutic approach are discussed.

BMI-1 expression increases in oral leukoplakias and correlates with cell proliferation

Oral leukoplakia (OL) is a white lesion of an indeterminate risk not related to any excluded (other) known diseases or disorders that carry no increased risk for cancer. Many biological markers have been used in an attempt to predict malignant transformation; however, no reliable markers have been established so far.

BMI‑1 promotes invasion and metastasis in endometrial adenocarcinoma and is a poor prognostic factor

Endometrial adenocarcinoma is one of the most common types of gynecological malignancies and its incidence and mortality rates are increasing. Due to tumor recurrence and metastasis, the overall five-year survival rate of patients with endometrial adenocarcinoma is shortened. The aim of the present was to investigate the role of the polycomb group protein B-lymphoma Mo-MLV insertion region 1 (BMI-1) in the invasion, metastasis and the epithelial-mesenchymal transition (EMT) of endometrial adenocarcinoma cells, as well its effects on the prognosis of patients with endometrial adenocarcinoma. Immunohistochemistry was used to examine the expression profile of BMI-1 in normal and endometrial adenocarcinoma tissues. Western blotting was used to examine the expression levels of BMI-1 and EMT markers. Kaplan-Meier plots and a Cox proportional hazards model were used to assess the overall survival. MTT cell viability assays were used to detect the proliferation of endometrial cancer cells. Transwell assays were used to examine cell migration and invasion. Small interfering RNA was used to downregulate BMI-1 expression levels, to study its effect on EMT. Immunohistochemical and clinicopathological analyses showed that BMI-1 expression was increased in endometrial adenocarcinoma tissue compared with the normal endometrial tissue (P<0.05). The increased expression levels of BMI-1 were closely associated with stage, myometrial invasion and lymph node metastasis (P<0.05). Kaplan-Meier plots and a Cox proportional hazards model showed that increased BMI-1 expression was associated with a less favorable prognosis [P=0.040, hazards ratio (HR)=1.596] and was associated with late-stage adenocarcinoma (P=0.006, HR=1.670). Myometrial invasion (P=0.006, HR=1.509) and lymph node metastasis (P=0.004, HR=1.703) were determined to predict a less favorable prognosis. Downregulation of BMI-1 reduced migration and invasion in endometrial cancer cells in vivo. It was also found that downregulation of BMI-1 increased the expression levels of the epithelial markers E-cadherin and keratin, and decreased the expression levels of the mesenchymal markers N-cadherin, vimentin and the downstream transcription factor, Slug. In conclusion, BMI-1 expression was correlated with tumor invasion and metastasis, contributing to deep myometrial invasion and lymph node metastasis, and was a poor prognostic factor for endometrial adenocarcinoma.

Involvement of A2B Receptor in DNA Damage Response and Radiosensitizing Effect of A2B Receptor Antagonists on Mouse B16 Melanoma

It is therapeutically important to elucidate the factors involved in the radiation resistance of tumors. We previously showed that ATP is released from mouse melanoma B16 cells in response to γ-irradiation, but the role of adenosine, a metabolite of ATP, is still unclear. Here, we show that the adenosine A2B receptor is involved in DNA damage repair and radioresistance in mouse melanoma B16 cells. The DNA damage response after γ-irradiation was attenuated by pretreatment with A2B receptor antagonists, such as PSB603, while it was enhanced by pretreatment with A2B receptor agonists, such as BAY60-6583. γ-Irradiation decreased the cell survival rate, and pretreatment with PSB603 further reduced the survival rate. On the other hand, pretreatment with BAY60-6583 increased the cell survival rate after irradiation. The DNA damage response and the cell survival rate after γ-irradiation were both decreased in A2B-knockdown cells. In vivo experiments in mice confirmed that tumor growth was suppressed and delayed in the irradiated group pretreated with PSB603, compared with the irradiation-alone group. Our results indicate that adenosine A2B receptor contributes to radioresistance, and could be a new target for the development of agents to increase the efficacy of radiotherapy.

microRNA: The Impact on Cancer Stemness and Therapeutic Resistance

Cancer ranks as the second leading cause of death worldwide, causing a large social and economic burden. However, most anti-cancer treatments face the problems of tumor recurrence and metastasis. Therefore, finding an effective cure for cancer needs to be solved urgently. Recently, the discovery of cancer stem cells (CSCs) provides a new orientation for cancer research and therapy. CSCs share main characteristics with stem cells and are able to generate an entire tumor. Besides, CSCs usually escape from current anti-cancer therapies, which is partly responsible for tumor recurrence and poor prognosis. microRNAs (miRNAs) belong to small noncoding RNA and regulate gene post-transcriptional expression. The dysregulation of miRNAs leads to plenty of diseases, including cancer. The aberrant miRNA expression in CSCs enhances stemness maintenance. In this review, we summarize the role of miRNAs on CSCs in the eight most common cancers, hoping to bridge the research of miRNAs and CSCs with clinical applications. We found that miRNAs can act as tumor promoter or suppressor. The dysregulation of miRNAs enhances cell stemness and contributes to tumor metastasis and therapeutic resistance via the formation of feedback loops and constitutive activation of carcinogenic signaling pathways. More importantly, some miRNAs may be potential targets for diagnosis, prognosis, and cancer treatments.

Increased elasticity of melanoma cells after low-LET proton beam due to actin cytoskeleton rearrangements

Cellular response to non-lethal radiation stress include perturbations in DNA repair, angiogenesis, migration, and adhesion, among others. Low-LET proton beam radiation has been shown to induce somewhat different biological response than photon radiation. For example, we have shown that non-lethal doses of proton beam radiation inhibited migration of cells and that this effect persisted long-term. Here, we have examined cellular elasticity and actin cytoskeleton organization in BLM cutaneous melanoma and Mel270 uveal melanoma cells. Proton beam radiation increased cellular elasticity to a greater extent than X-rays and both types of radiation induced changes in actin cytoskeleton organization. Vimentin level increased in BLM cells after both types of radiation. Our data show that cell elasticity increased substantially after low-LET proton beam and persisted long after radiation. This may have significant consequences for the migratory properties of melanoma cells, as well as for the cell susceptibility to therapy.

ROS Production and Distribution: A New Paradigm to Explain the Differential Effects of X-ray and Carbon Ion Irradiation on Cancer Stem Cell Migration and Invasion

Although conventional radiotherapy promotes the migration/invasion of cancer stem cells (CSCs) under normoxia, carbon ion (C-ion) irradiation actually decreases these processes. Unraveling the mechanisms of this discrepancy, particularly under the hypoxic conditions that pertain in niches where CSCs are preferentially localized, would provide a better understanding of the origins of metastases. Invasion/migration, proteins involved in epithelial-to-mesenchymal transition (EMT), and expression of MMP-2 and HIF-1α were quantified in the CSC subpopulations of two head-and-neck squamous cell carcinoma (HNSCC) cell lines irradiated with X-rays or C-ions. X-rays triggered HNSCC-CSC migration/invasion under normoxia, however this effect was significantly attenuated under hypoxia. C-ions induced fewer of these processes in both oxygenation conditions. The differential response to C-ions was associated with a lack of HIF-1α stabilization, MMP-2 expression, or activation of kinases of the main EMT signaling pathways. Furthermore, we demonstrated a major role of reactive oxygen species (ROS) in the triggering of invasion/migration in response to X-rays. Monte-Carlo simulations demonstrated that HO^● radicals are quantitatively higher after C-ions than after X-rays, however they are very differently distributed within cells. We postulate that the uniform distribution of ROS after X-rays induces the mechanisms leading to invasion/migration, which ROS concentrated in C-ion tracks are unable to trigger.

The SNAIL/miR-128 axis regulated growth, invasion, metastasis, and epithelial-to-mesenchymal transition of gastric cancer

miR-128 is expressed in various tumors, but its expression and function in gastric cancer have not been defined. Thus, the goal of this study was to characterize miR-128 in gastric cancer. We found first that miR-128 is down-regulated in gastric cancer cell lines and tissues, and this dysregulation is correlated with DNA methylation and the transcription factor SNAIL. Using prediction tools, western blotting, and luciferase reporter assays, we found that Bmi-1 was the direct target of miR-128. Additionally, overexpression of miR-128 inhibited gastric cancer cell migration, invasion, and proliferation by targeting Bmi-1 in vitro and in vivo. We also documented, with receiver operating characteristic curves and Kaplan-Meier survival analysis, that miR-128 and Bmi-1 may be useful markers for diagnosing and estimating the prognosis of gastric cancer patients. As the epithelial-to-mesenchymal transition is an important mechanism associated with cancer invasion and metastasis, we inferred that miR-128 could regulate this mechanism in gastric cancer. In fact, we found that miR-128 could reverse epithelial-to-mesenchymal transition induced by Bmi-1 via the PI3K/AKT pathway. Because SNAIL also acts as a mesenchymal marker, our findings identified a novel positive feedback loop in which the transcription factor SNAIL curbs the expression of miR-128, and then down-regulated miR-128 promotes the expression of Bmi-1; finally, overexpression of Bmi-1 drives the epithelial-to-mesenchymal transition process via the PI3K/AKT pathway, and the expression of SNAIL is up-regulated.

Effects of radiation on the metastatic process

Radiotherapy remains one of the corner stones in the treatment of various malignancies and often leads to an improvement in overall survival. Nonetheless, pre-clinical evidence indicates that radiation can entail pro-metastatic effects via multiple pathways. Via direct actions on cancer cells and indirect actions on the tumor microenvironment, radiation has the potential to enhance epithelial-to-mesenchymal transition, invasion, migration, angiogenesis and metastasis. However, the data remains ambiguous and clinical observations that unequivocally prove these findings are lacking. In this review we discuss the pre-clinical and clinical data on the local and systemic effect of irradiation on the metastatic process with an emphasis on the molecular pathways involved.

Radiation therapy-induced metastasis: radiobiology and clinical implications

Radiation therapy is an effective means of achieving local control in a wide range of primary tumours, with the reduction in the size of the tumour(s) thought to mediate the observed reductions in metastatic spread in clinical trials. However, there is evidence to suggest that the complex changes induced by radiation in the tumour environment can also present metastatic risks that may counteract the long-term efficacy of the treatment. More than 25 years ago, several largely theoretical mechanisms by which radiation exposure might increase metastatic risk were postulated. These include the direct release of tumour cells into the circulation, systemic effects of tumour and normal tissue irradiation and radiation-induced changes in tumour cell phenotype. Here, we review the data that has since emerged to either support or refute these putative mechanisms focusing on how the unique radiobiology underlying modern radiotherapy modalities might alter these risks.

Hinokitiol up-regulates miR-494-3p to suppress BMI1 expression and inhibits self-renewal of breast cancer stem/progenitor cells

Hinokitiol (β-thujaplicin) is a tropolone-related compound that has anti-microbe, anti-inflammation, and anti-tumor effects. Cancer stem/progenitor cells (CSCs) are a subpopulation of cancer cells with tumor initiation, chemoresistant, and metastatic properties and have been considered the important therapeutic target in future cancer therapy. Previous studies reported that hinokitiol exhibits an anti-cancer activity against murine tumor cells through the induction of autophagy. The current research revealed that hinokitiol suppressed the self-renewal capabilities of human breast CSCs (BCSCs) and inhibited the expression of BMI1 at protein level without suppressing its mRNA. Treatment of hinokitiol in mammospheres induced the expression of miR-494-3p and inhibition of miR-494-3p expression in BCSCs. This treatment abolished the suppressive effects of hinokitiol in mammosphere formation and BMI1 expression. BMI1 is a target of miR-494-3p by luciferase-based 3′UTR reporter assay. Overexpression of miR-494-3p in BCSCs caused the down-regulation of BMI1 protein, inhibition of mammosphere forming capability, and suppression of their tumorigenicity. Moreover, miR-494-3p expression was significantly and inversely correlated with patient survival in two independent public database sets. Furthermore, treatment of hinokitiol in vivo suppressed the growth of xenograft human breast tumors as well as the expression of BMI1 and ALDH1A1 in xenograft tumors. In conclusion, these data suggest that hinokitiol targets BCSCs through the miR-494-3p-mediated down-modulation of BMI1 expression.

CD90 positive cells exhibit aggressive radioresistance in esophageal squamous cell carcinoma

BACKGROUND

Cancer stem cells (CSCs) are widely abundant and considered to be an important factor in therapy resistance. They are also promising potential targets for conquering tumors. We explored the effects of radiation on stem cell-like tumor cells via the candidate marker CD90 to provide new ideas for the comprehensive treatment of esophageal squamous cell carcinoma (ESCC).

METHODS

We constructed CD90 overexpression ESCC cells by lentiviral transfection and observed differences of toxicity, proliferation, clone number, apoptosis, migration, invasion, and in vivo tumor formation after irradiation.

RESULTS

We found that the population of CD90 positive cells showed CSC-like characteristics, including increased tumorigenicity and migration in ESCC cells. We discovered that these capacities were strengthened to varying degrees in remaining cells after irradiation. Further exploration revealed that the genes of ETS-1 and its downstream target MMPs changed significantly, which are correlated with the epithelial mesenchymal transition (EMT). These effects lead to enhanced tumor growth and resistance to radiation.

CONCLUSIONS

We show that CD90 overexpressing ESCC cells exhibit CSC-like characteristics and radiation resistance. From a clinical perspective, ESCC patients with tumors that have high CD90 expression, which inhibits apoptosis, could exhibit more local invasion as well as distant metastasis, indicating a poorer prognosis. Research on the mechanism of CD90 may provide a new perspective to therapeutic strategies for patients with ESCC.

Induction of metastasis, cancer stem cell phenotype, and oncogenic metabolism in cancer cells by ionizing radiation

Radiation therapy is one of the major tools of cancer treatment, and is widely used for a variety of malignant tumours. Radiotherapy causes DNA damage directly by ionization or indirectly via the generation of reactive oxygen species (ROS), thereby destroying cancer cells. However, ionizing radiation (IR) paradoxically promotes metastasis and invasion of cancer cells by inducing the epithelial-mesenchymal transition (EMT). Metastasis is a major obstacle to successful cancer therapy, and is closely linked to the rates of morbidity and mortality of many cancers. ROS have been shown to play important roles in mediating the biological effects of IR. ROS have been implicated in IR-induced EMT, via activation of several EMT transcription factors—including Snail, HIF-1, ZEB1, and STAT3—that are activated by signalling pathways, including those of TGF-β, Wnt, Hedgehog, Notch, G-CSF, EGFR/PI3K/Akt, and MAPK. Cancer cells that undergo EMT have been shown to acquire stemness and undergo metabolic changes, although these points are debated. IR is known to induce cancer stem cell (CSC) properties, including dedifferentiation and self-renewal, and to promote oncogenic metabolism by activating these EMT-inducing pathways. Much accumulated evidence has shown that metabolic alterations in cancer cells are closely associated with the EMT and CSC phenotypes; specifically, the IR-induced oncogenic metabolism seems to be required for acquisition of the EMT and CSC phenotypes. IR can also elicit various changes in the tumour microenvironment (TME) that may affect invasion and metastasis. EMT, CSC, and oncogenic metabolism are involved in radioresistance; targeting them may improve the efficacy of radiotherapy, preventing tumour recurrence and metastasis. This study focuses on the molecular mechanisms of IR-induced EMT, CSCs, oncogenic metabolism, and alterations in the TME. We discuss how IR-induced EMT/CSC/oncogenic metabolism may promote resistance to radiotherapy; we also review efforts to develop therapeutic approaches to eliminate these IR-induced adverse effects.

Egr-1 regulates irradiation-induced autophagy through Atg4B to promote radioresistance in hepatocellular carcinoma cells

Although hepatocellular carcinoma (HCC) is usually response to radiation therapy, radioresistance is still the major obstacle that limits the efficacy of radiotherapy for HCC patients. Therefore, further investigation of underlying mechanisms in radioresistant HCC cells is warranted. In this study, we determined the effect of early growth response factor (Egr-1) on irradiation-induced autophagy and radioresistance in HCC cell lines SMMC-7721 and HepG2. We showed that autophagy-related gene 4B (Atg4B) is induced by Egr-1 upon ionizing radiation (IR) in HCC cells. Luciferase reporter assays and chromatin immunoprecipitation (ChIP) revealed that Egr-1 binds to the Atg4B promoter to upregulate its expression in HCC cells. Suppression of Egr-1 function by dominant-negative Egr-1 dampens IR-induced autophagy, cell migration, and increases cell sensitivity to radiotherapy. Together, these results suggest that Egr-1 contributes to HCC radioresistance through directly upregulating target gene Atg4B, which may serve as a protective mechanism by preferential activation of the autophagy.

MicroRNA-194 represses glioma cell epithelial‑to‑mesenchymal transition by targeting Bmi1

MicroRNA-194 (miR-194) is frequently dysregulated in many types of cancer. However, the function of miR-194 in glioma remains unknown. In the present study, we aimed to investigate the biological functions of miR-194 in glioma and the potential molecular mechanism of miR-194 involved in glioma progression. We found that miR-194 expression was significantly reduced in glioma specimens and cell lines, as detected by real-time quantitative polymerase chain reaction (RT-qPCR) analysis. The overexpression of miR-194 inhibited while the suppression of miR-194 promoted cell migration, invasion and epithelial mesenchymal transition (EMT) in glioma cells. Bioinformatics analysis showed that the B cell-specific moloney murine leukemia virus insertion site 1 (Bmi1) was a direct target of miR-194, which was validated by dual-luciferase reporter assay, RT-qPCR and western blot analysis. The restoration of Bmi1 expression significantly abrogated the suppressive effect of miR-194 on glioma cell EMT. Taken together, the present study suggests that miR-194 inhibits glioma cell EMT by targeting Bmi1 providing novel insights into understanding the pathogenesis of glioma. The restoration of miR-194 may be a potential therapeutic strategy for glioma treatment.

Invasive oral cancer stem cells display resistance to ionising radiation

There is a significant amount of evidence to suggest that human tumors are driven and maintained by a sub-population of cells, known as cancer stem cells (CSC). In the case of head and neck cancer, such cells have been characterised by high expression levels of CD44 cell surface glycoprotein, while we have previously shown the presence of two diverse oral CSC populations in vitro, with different capacities for cell migration and proliferation. Here, we examined the response of oral CSC populations to ionising radiation (IR), a front-line measure for the treatment of head and neck tumors. We show that oral CSC initially display resistance to IR-induced growth arrest as well as relative apoptotic resistance. We propose that this is a result of preferential activation of the DNA damagerepair pathway in oral CSC with increased activation of ATM and BRCA1, elevated levels of DNA repair proteins RAD52, XLF, and a significantly faster rate of DNA double-strand-breaks clearance 24 hours following IR. By visually identifying CSC sub-populations undergoing EMT, we show that EMT-CSC represent the majority of invasive cells, and are more radio-resistant than any other population in re-constructed 3D tissues. We provide evidence that IR is not sufficient to eliminate CSC in vitro, and that sensitization of CD44^hi/ESA^low cells to IR, followed by secondary EMT blockade, could be critical in order to reduce primary tumor recurrence, but more importantly to be able to eradicate cells capable of invasion and distant metastasis.

Radiation induces the generation of cancer stem cells: A novel mechanism for cancer radioresistance

Radioresistance remains a major obstacle for the radiotherapy treatment of cancer. Previous studies have demonstrated that the radioresistance of cancer is due to the existence of intrinsic cancer stem cells (CSCs), which represent a small, but radioresistant cell subpopulation that exist in heterogeneous tumors. By contrast, non-stem cancer cells are considered to be radiosensitive and thus, easy to kill. However, recent studies have revealed that under conditions of radiation-induced stress, theoretically radiosensitive non-stem cancer cells may undergo dedifferentiation subsequently obtaining the phenotypes and functions of CSCs, including high resistance to radiotherapy, which indicates that radiation may directly result in the generation of novel CSCs from non-stem cancer cells. These findings suggest that in addition to intrinsic CSCs, non-stem cancer cells may also contribute to the relapse and metastasis of cancer following transformation into CSCs. This review aims to investigate the radiation-induced generation of CSCs, its association with epithelial-mesenchymal transition and its significance with regard to the radioresistance of cancer.

Does the mobilization of circulating tumour cells during cancer therapy cause metastasis?

Despite progressive improvements in the management of patients with locoregionally confined, advanced-stage solid tumours, distant metastasis remains a very common - and usually fatal - mode of failure after attempted curative treatment. Surgery and radiotherapy are the primary curative modalities for these patients, often combined with each other and/or with chemotherapy. Distant metastasis occurring after treatment can arise from previously undetected micrometastases or, alternatively, from persistent locoregional disease. Another possibility is that treatment itself might sometimes cause or promote metastasis. Surgical interventions in patients with cancer, including biopsies, are commonly associated with increased concentrations of circulating tumour cells (CTCs). High CTC numbers are associated with an unfavourable prognosis in many cancers. Radiotherapy and systemic antitumour therapies might also mobilize CTCs. We review the preclinical and clinical data concerning cancer treatments, CTC mobilization and other factors that might promote metastasis. Contemporary treatment regimens represent the best available curative options for patients who might otherwise die from locally confined, advanced-stage cancers; however, if such treatments can promote metastasis, this process must be understood and addressed therapeutically to improve patient survival.

Effects of radiation on metastasis and tumor cell migration

It is well known that tumor cells migrate from the primary lesion to distant sites to form metastases and that these lesions limit patient outcome in a majority of cases. However, the extent to which radiation influences this process and to which migration in turn alters radiation response remains controversial. There are preclinical and clinical reports showing that focal radiotherapy can both increase the development of distant metastasis, as well as that it can induce the regression of established metastases through the abscopal effect. More recently, preclinical studies have suggested that radiation can attract migrating tumor cells and may, thereby, facilitate tumor recurrence. In this review, we summarize these phenomena and their potential mechanisms of action, and evaluate their significance for modern radiation therapy strategies.

miRNA-223 inhibits epithelial-mesenchymal transition in gastric carcinoma cells via Sp1

Sp1 plays critical roles in epithelial-mesenchymal transition (EMT) of certain cancer. However, few studies have indicated whether Sp1 is involved in the EMT of gastric cancer, and whether abnormal expression of Sp1 in gastric cancer EMT is regulated in a post-transcriptional manner, and the involvement of miRNAs in this regulation. In this study, we selected 20 cases of gastric cancers, their liver metastases and para-carcinoma tissues to examine the levels of Sp1 protein and mRNA by immunohistochemistry and fluorescent PCR, which showed that Sp1 was increased in gastric cancers and their metastases compared with adjacent tissues, but there was no difference in Sp1 mRNA between these three groups, suggesting changes in Sp1 may be attributed to inactivation of post-transcriptional regulation. We verified by a luciferase reporter system that miRNA-223 binds to 3'-UTR of Sp1 gene and inhibits its translation, in agreement with negative correlation between miRNA-223 and Sp1 protein levels in gastric cancer cells. By employing TGF-β1 to induce MGC-803, BGC-823 and SGC-7901, we successfully built cellular EMT model. Then, we overexpressed miRNA-223 in the model by using a lentiviral system, which diminished EMT indicators and suppressed proliferation and invasion ability, and induced apoptosis. Finally, we verified the specificity of the regulation pathway miRNA-223/Sp1/EMT. These findings suggest that low expression of miRNA-223 in gastric cancer cells is an important cause for EMT. miRNA-223 specifically regulates the EMT process of gastric cancer cells through its target gene Sp1. Overexpression of miRNA-223 in these cells inhibits EMT via the miRNA-223/Sp1/EMT pathway.

Expression of microRNA-452 via adenoviral vector inhibits non-small cell lung cancer cells proliferation and metastasis

The microRNA miR-452 has been shown to function as a tumor suppressor. However, the cellular mechanism and potential application of miR-452-mediated cancer suppression remain great unknown. This study aims to identify how miR-452 acts in regulating non-small cell lung cancer (NSCLC) proliferation and metastasis. Expression of miR-452 via adenoviral (Ad) vector inhibits the proliferation, invasion, and migration of NSCLC cells A549 or H460. Our data also shows that miR-452 down-regulates the expression of Bmi-1 as well as pro-survival or anti-apoptosis regulators Survivin, cIAP-1, and cIAP-2. By such gene interference, miR-452 modulates NSCLC cell epithelial-mesenchymal transition (EMT) and further disrupts their migration and invasion. Moreover, miR-452 blocks the activation of PI3K/AKT pathway, which is also required for EMT process. These data reveal that miR-452 treatment could be a novel target or strategy for NSCLC treatment.