Activating transcription factor 3 promotes colon cancer metastasis

ATF family members as therapeutic targets in cancer: From mechanisms to pharmacological interventions

The activating transcription factor (ATF)/ cAMP-response element binding protein (CREB) family represents a large group of basic zone leucine zip (bZIP) transcription factors (TFs) with a variety of physiological functions, such as endoplasmic reticulum (ER) stress, amino acid stress, heat stress, oxidative stress, integrated stress response (ISR) and thus inducing cell survival or apoptosis. Interestingly, ATF family has been increasingly implicated in autophagy and ferroptosis in recent years. Thus, the ATF family is important for homeostasis and its dysregulation may promote disease progression including cancer. Current therapeutic approaches to modulate the ATF family include direct modulators, upstream modulators, post-translational modifications (PTMs) modulators. This review summarizes the structural domain and the PTMs feature of the ATF/CREB family and comprehensively explores the molecular regulatory mechanisms. On this basis, their pathways affecting proliferation, metastasis, and drug resistance in various types of cancer cells are sorted out and discussed. We then systematically summarize the status of the therapeutic applications of existing ATF family modulators and finally look forward to the future prospect of clinical applications in the treatment of tumors by modulating the ATF family.

ATF3 characterizes aggressive drug-tolerant persister cells in HGSOC

High-grade serous ovarian cancer (HGSOC) represents the most common and lethal subtype of ovarian cancer. Despite initial response to platinum-based standard therapy, patients commonly suffer from relapse that likely originates from drug-tolerant persister (DTP) cells. We generated isogenic clones of treatment-naïve and cisplatin-tolerant persister HGSOC cells. In addition, single-cell RNA sequencing of barcoded cells was performed in a xenograft model with HGSOC cell lines after platinum-based therapy. Published single-cell RNA-sequencing data from neo-adjuvant and non-treated HGSOC patients and patient data from TCGA were analyzed. DTP-derived cells exhibited morphological alterations and upregulation of epithelial-mesenchymal transition (EMT) markers. An aggressive subpopulation of DTP-derived cells showed high expression of the stress marker ATF3. Knockdown of ATF3 enhanced the sensitivity of aggressive DTP-derived cells to cisplatin-induced cell death, implying a role for ATF3 stress response in promoting a drug tolerant persister cell state. Furthermore, single cell lineage tracing to detect transcriptional changes in a HGSOC cell line-derived xenograft relapse model showed that cells derived from relapsed solid tumors express increased levels of EMT and multiple endoplasmic reticulum (ER) stress markers, including ATF3. Single cell RNA sequencing of epithelial cells from four HGSOC patients also identified a small cell population resembling DTP cells in all samples. Moreover, analysis of TCGA data from 259 HGSOC patients revealed a significant progression-free survival advantage for patients with low expression of the ATF3-associated partial EMT genes. These findings suggest that increased ATF3 expression together with partial EMT promote the development of aggressive DTP, and thereby relapse in HGSOC patients.

STEAP3 promotes colon cancer cell proliferation and migration via regulating histone acetylation

Colorectal cancer (CRC) is the third most prevalent diagnosed cancer in men and second most prevalent cancer in women. H3K27ac alterations are more commonly than gene mutations in colorectal cancer. Most colorectal cancer genes have significant H3K27ac changes, which leads to an over-expression disorder in gene transcription. Over-expression of STEAP3 is involved in a variety of tumors, participating in the regulation of cancer cell proliferation and migration. The purpose of this work is to investigate the role of STEAP3 in the regulation of histone modification (H3K27ac) expression in colon cancer. Bioinformatic ChIP-seq, ChIP-qPCR and ATAC-seq were used to analyze the histone modification properties and gene accessibility of STEAP3. Western blot and qRT-PCR were used to evaluate relative protein and gene expression, respectively. CRISPR/Cas9 technology was used to knockout STEAP3 on colon cancer cells to analyze the effect of ATF3 on STEAP3. STEAP3 was over-expressed in colon cancer and associated with higher metastases and more invasive and worse stage of colon cancer. ChIP-seq and ChIP-qPCR analyses revealed significant enrichment of H3K27ac in the STEAP3 gene. In addition, knocking down STEAP3 significantly inhibits colon cancer cell proliferation and migration and down-regulates H3K27ac expression. ChIP-seq found that ATF3 is enriched in the STEAP3 gene and CRISPR/Cas9 technology used for the deletion of the ATF3 binding site suppresses the expression of STEAP3. Over-expression of STEAP3 promotes colon cancer cell proliferation and migration. Mechanical studies have indicated that H3K27ac and ATF3 are significantly enriched in the STEAP3 gene and regulate the over-expression of STEAP3.

Emerging roles of activating transcription factor (ATF) family members in tumourigenesis and immunity: Implications in cancer immunotherapy

Activating transcription factors, ATFs, are a group of bZIP transcription factors that act as homodimers or heterodimers with a range of other bZIP factors. In general, ATFs respond to extracellular signals, indicating their important roles in maintaining homeostasis. The ATF family includes ATF1, ATF2, ATF3, ATF4, ATF5, ATF6, and ATF7. Consistent with the diversity of cellular processes reported to be regulated by ATFs, the functions of ATFs are also diverse. ATFs play an important role in cell proliferation, apoptosis, differentiation and inflammation-related pathological processes. The expression and phosphorylation status of ATFs are also related to neurodegenerative diseases and polycystic kidney disease. Various miRNAs target ATFs to regulate cancer proliferation, apoptosis, autophagy, sensitivity and resistance to radiotherapy and chemotherapy. Moreover, ATFs are necessary to maintain cell redox homeostasis. Therefore, deepening our understanding of the regulation and function of ATFs will provide insights into the basic regulatory mechanisms that influence how cells integrate extracellular and intracellular signals into genomic responses through transcription factors. Under pathological conditions, especially in cancer biology and response to treatment, the characterization of ATF dysfunction is important for understanding how to therapeutically utilize ATF2 or other pathways controlled by transcription factors. In this review, we will demonstrate how ATF1, ATF2, ATF3, ATF4, ATF5, ATF6, and ATF7 function in promoting or suppressing cancer development and identify their roles in tumour immunotherapy.

Omega-3 Fatty Acids DHA and EPA Reduce Bortezomib Resistance in Multiple Myeloma Cells by Promoting Glutathione Degradation

Multiple myeloma (MM) is a hematological malignancy that exhibits aberrantly high levels of proteasome activity. While treatment with the proteasome inhibitor bortezomib substantially increases overall survival of MM patients, acquired drug resistance remains the main challenge for MM treatment. Using a combination treatment of docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA) and bortezomib, it was demonstrated previously that pretreatment with DHA/EPA significantly increased bortezomib chemosensitivity in MM cells. In the current study, both transcriptome and metabolome analysis were performed to comprehensively evaluate the underlying mechanism. It was demonstrated that pretreating MM cells with DHA/EPA before bortezomib potently decreased the cellular glutathione (GSH) level and altered the expression of the related metabolites and key enzymes in GSH metabolism, whereas simultaneous treatment only showed minor effects on these factors, thereby suggesting the critical role of GSH degradation in overcoming bortezomib resistance in MM cells. Moreover, RNA-seq results revealed that the nuclear factor erythroid 2-related factor 2 (NRF2)-activating transcription factor 3/4 (ATF3/4)-ChaC glutathione specific gamma-glutamylcyclotransferase 1 (CHAC1) signaling pathway may be implicated as the central player in the GSH degradation. Pathways of necroptosis, ferroptosis, p53, NRF2, ATF4, WNT, MAPK, NF-κB, EGFR, and ERK may be connected to the tumor suppressive effect caused by pretreatment of DHA/EPA prior to bortezomib. Collectively, this work implicates GSH degradation as a potential therapeutic target in MM and provides novel mechanistic insights into its significant role in combating bortezomib resistance.

BRET analysis reveals interaction between the lysophosphatidic acid receptor LPA2 and the lysophosphatidylinositol receptor GPR55 in live cells

Lysophosphatidic acid (LPA) and lysophosphatidylinositol bind to the G protein-coupled receptors (GPCRs) LPA and GPR55, respectively. LPA₂ , a type 2 LPA receptor, and GPR55 are highly expressed in colon cancer and involved in cancer progression. However, crosstalk between the two receptors and potential effects on cellular physiology are not fully understood. Here, using BRET analysis, we found that LPA₂ and GPR55 interact in live cells. In the presence of both receptors, LPA₂ and/or GPR55 activation facilitated co-internalization, and activation of GPR55, uncoupled with Gα_i , induced reduction of intracellular cAMP. Notably, co-activation of receptors synergistically triggered further decline in the cAMP level, promoted cell proliferation, and increased the expression of cancer progression-related genes, suggesting that physical and functional crosstalk between LPA₂ and GRR55 is involved in cancer progression.

Relationships between blood and follicular fluid urea nitrogen concentrations and between blood urea nitrogen and embryo survival in mares

High blood urea nitrogen (BUN) concentration is linked to low fertility in cows and ewes; however, this relationship has not been reported in mares. The study characterized the relationship between BUN and follicular fluid urea nitrogen (FUN) during follicle growth (Experiment 1) and the impact of BUN from embryo donors on the pregnancy outcome of recipient mares (Experiment 2). In experiment one, follicular fluid and blood samples were collected from mares during diestrus with growing follicles and during estrus with pre-ovulatory follicles (n = 16 and 10 mares, respectively). In experiment two, BUN concentrations of embryo donors were related to pregnancy outcome after embryo transfer. In experiment one, there was a strong positive correlation between BUN and FUN (R = 0.83; P < 0.0001), with higher BUN in mares with growing follicles than with preovulatory follicles (P = 0.004) and higher FUN in growing follicles than in preovulatory follicles (P = 0.031). In experiment two, BUN was higher in donor mares that produced unsuccessful embryos compared to donor mares that produced embryos resulting in successful pregnancies at D14 (P < 0.03). Additionally, there was an effect of age (P = 0.01) and interaction between age and lactation (P = 0.009) in donor mares for embryo survival after embryo transfer. Donor mares with unsuccessful embryos were older than donor mares with successful embryos. Therefore, these experiments showed that BUN was related to follicular fluid environment as well as to the survival of Day 7-8 embryos after transfer to recipient mares.

Activating transcription factor 3 inhibits endometrial carcinoma aggressiveness via JunB suppression

The function of activating transcription factor 3 (ATF3) in cancer is context‑dependent and its role in endometrial carcinoma (EC) is yet to be elucidated. In the present study, ATF3 was indicated to be downregulated, while one of the ATF3‑interacting proteins, JunB, was upregulated in ECs according to western blot analysis. After overexpression in ECs, ATF3 inhibited the proliferation and invasion of EC cells and enhanced apoptosis, as well as suppressed the expression of JunB. The properties of EC cells, including the expression of matrix metalloproteinases, tissue inhibitors of metalloproteinases, the cell cycle and apoptosis were all altered by overexpression of ATF3. Furthermore, luciferase activity assay, chromatin precipitation and DNA affinity assay results indicated that ATF3 exerted the aforementioned functions via JunB binding and activator protein‑1 signaling. However, the interaction between ATF3 and JunB did not occur in EC cells under basal conditions, but in ATF3‑overexpressing ECs, which was capable of mitigating EC proliferation, invasion and metastasis. Collectively, the present results suggested that the ATF3/JunB interaction may serve as a potential therapeutic target for ECs.

Regulators of G-protein signaling, RGS2 and RGS4, inhibit protease-activated receptor 4-mediated signaling by forming a complex with the receptor and Gα in live cells

BACKGROUND

Protease-activated receptor 4 (PAR4) is a seven transmembrane G-protein coupled receptor (GPCR) activated by endogenous proteases, such as thrombin. PAR4 is involved in various pathophysiologies including cancer, inflammation, pain, and thrombosis. Although regulators of G-protein signaling (RGS) are known to modulate GPCR/Gα-mediated pathways, their specific effects on PAR4 are not fully understood at present. We previously reported that RGS proteins attenuate PAR1- and PAR2-mediated signaling through interactions with these receptors in conjunction with distinct Gα subunits.

METHODS

We employed a bioluminescence resonance energy transfer technique and confocal microscopy to examine potential interactions among PAR4, RGS, and Gα subunits. The inhibitory effects of RGS proteins on PAR4-mediated downstream signaling and cancer progression were additionally investigated by using several assays including ERK phosphorylation, calcium mobilization, RhoA activity, cancer cell proliferation, and related gene expression.

RESULTS

In live cells, RGS2 interacts with PAR4 in the presence of Gα_q while RGS4 binding to PAR4 occurs in the presence of Gα_q and Gα_12/13. Co-expression of PAR4 and Gα_q induced a shift in the subcellular localization of RGS2 and RGS4 from the cytoplasm to plasma membrane. Combined PAR4 and Gα_12/13 expression additionally promoted translocation of RGS4 from the cytoplasm to the membrane. Both RGS2 and RGS4 abolished PAR4-activated ERK phosphorylation, calcium mobilization and RhoA activity, as well as PAR4-mediated colon cancer cell proliferation and related gene expression.

CONCLUSIONS

RGS2 and RGS4 forms ternary complex with PAR4 in Gα-dependent manner and inhibits its downstream signaling. Our findings support a novel physiological function of RGS2 and RGS4 as inhibitors of PAR4-mediated signaling through selective PAR4/RGS/Gα coupling. Video Abstract.

Master Regulator Activating Transcription Factor 3 (ATF3) in Metabolic Homeostasis and Cancer

Activating transcription factor 3 (ATF3) is a stress-induced transcription factor that plays vital roles in modulating metabolism, immunity, and oncogenesis. ATF3 acts as a hub of the cellular adaptive-response network. Multiple extracellular signals, such as endoplasmic reticulum (ER) stress, cytokines, chemokines, and LPS, are connected to ATF3 induction. The function of ATF3 as a regulator of metabolism and immunity has recently sparked intense attention. In this review, we describe how ATF3 can act as both a transcriptional activator and a repressor. We then focus on the role of ATF3 and ATF3-regulated signals in modulating metabolism, immunity, and oncogenesis. The roles of ATF3 in glucose metabolism and adipose tissue regulation are also explored. Next, we summarize how ATF3 regulates immunity and maintains normal host defense. In addition, we elaborate on the roles of ATF3 as a regulator of prostate, breast, colon, lung, and liver cancers. Further understanding of how ATF3 regulates signaling pathways involved in glucose metabolism, adipocyte metabolism, immuno-responsiveness, and oncogenesis in various cancers, including prostate, breast, colon, lung, and liver cancers, is then provided. Finally, we demonstrate that ATF3 acts as a master regulator of metabolic homeostasis and, therefore, may be an appealing target for the treatment of metabolic dyshomeostasis, immune disorders, and various cancers.

Metastasis Associated Lung Adenocarcinoma Transcript 1: An update on expression pattern and functions in carcinogenesis

The Metastasis Associated Lung Adenocarcinoma Transcript 1 (MALAT1) is among long non-coding RNAs (lncRNAs) which has disapproved the old term of "junk DNA" which was used for majority of human genome which are not transcribed to proteins. An extensive portion of literature points to the fundamental role of this lncRNA in tumorigenesis process of diverse cancers ranging from solid tumors to leukemia. Being firstly identified in lung cancer, it has prognostic and diagnostic values in several cancer types. Consistent with the proposed oncogenic roles for this lncRNA, most of studies have shown up-regulation of MALAT1 in malignant tissues compared with non-malignant/normal tissues of the same source. However, few studies have shown down-regulation of MALAT1 in breast cancer, endometrial cancer, colorectal cancer and glioma. In the current study, we have conducted a comprehensive literature search and provided an up-date on the role of MALAT1 in cancer biology. Our investigation underscores a potential role as a diagnostic/prognostic marker and a putative therapeutic target for MALAT1.

The mTOR-inhibitor Sirolimus decreases the cyclosporine-induced expression of the oncogene ATF3 in human keratinocytes

BACKGROUND

Due to their immunosuppressive therapy, organtransplant recipients (OTRs) exhibit a high incidence for the development of cutaneous squamous cell carcinoma (cSCC). Randomized studies of kidney-transplanted patients indicate a significant lower susceptibility for cSCC among patients receiving the mTOR-inhibitor Sirolimus, compared to patients without mTOR-regimen. The exact mechanism, how mTOR inhibition affects keratinocyte carcinogenesis remains unclear.

OBJECTIVE

Our aim was to investigate the impact of Sirolimus on the expression level of the oncogene ATF3, which is involved in the development and progression of cSCC.

METHODS

We incubated human keratinocytes, cSSC cell lines and 3D skin equivalents with Sirolimus, exposed the cells to calcineurin inhibitors (CNI) and UVA-radiation and measured the expression level of ATF3 by real-time PCR and western blot.

RESULTS

We show that Sirolimus downregulates the expression of ATF3 induced by cyclosporine or cyclosporine plus UV-radiation in keratinocytes. In line with this we demonstrate a decrease in ATF3 expression, by incubating 3D skin equivalents with Sirolimus prior to cyclosporine and UV-light. However, Sirolimus has no significant impact on the ATF3 expression levels of cyclosporine stimulated cSCC cell lines.

CONCLUSION

Taken together, our study demonstrates that Sirolimus downregulates the CNI or UV-induced ATF3 expression in human keratinocytes, which could be a potential molecular mechanism how Sirolimus reduces cSCC in OTRs. The lack of ATF3 suppression by Sirolimus in cSCC cell lines fits to observations from clinical studies which demonstrated a clinical benefit from the switch to a mTOR-regimen in patients with low tumor burden in early stage of disease.

Overexpression of the transcription factor ATF3 with a regulatory molecular signature associates with the pathogenic development of colorectal cancer

The identification of novel biomarkers of cancer is important for improved diagnosis and prognosis. With an abundant amount of resources in the publicly available database, such as the Cancer Genome Atlas (TCGA) database, an integrative strategy is used to systematically characterize the aberrant patterns of colorectal cancer (CRC) based on RNA-Seq, chromatin immunoprecipitation sequencing (ChIP-Seq), tissue microarray (TMA), gene profiling and molecular signatures. The expression of the transcription factor ATF3 was elevated in human CRC specimens in a TMA by immunochemistry analysis compared to the adjacent normal tissues. In addition, ATF3 overexpression associated with a regulatory molecular signature, and its functions are related to the pathogenic development of CRC. Furthermore, putative ATF3 regulatory elements were identified within the promoters of ATF3 target genes and were confirmed by ChIP-Seq. Critically, in higher ATF3 expression cell lines (HCT116 and RKO) with CRISPR/Cas9 mediated ATF3 knock out, we are able to show that ATF3 target genes such as CEACAM1, DUSP14, HDC, HLF and ULBP2, are required for invasion and proliferation, and they are robustly linked with poor prognosis in CRC. Our findings have important implications for CRC tumorigenesis and may be exploited for diagnostic and therapeutic purposes.

The Activating Transcription Factor 3 (Atf3) Homozygous Knockout Mice Exhibit Enhanced Conditioned Fear and Down Regulation of Hippocampal GELSOLIN

The genetic and molecular basis underlying fear memory formation is a key theme in anxiety disorder research. Because activating transcription factor 3 (ATF3) is induced under stress conditions and is highly expressed in the hippocampus, we hypothesize that ATF3 plays a role in fear memory formation. We used fear conditioning and various other paradigms to test Atf3 knockout mice and study the role of ATF3 in processing fear memory. The results demonstrated that the lack of ATF3 specifically enhanced the expression of fear memory, which was indicated by a higher incidence of the freeze response after fear conditioning, whereas the occurrence of spatial memory including Morris Water Maze and radial arm maze remained unchanged. The enhanced freezing behavior and normal spatial memory of the Atf3 knockout mice resembles the fear response and numbing symptoms often exhibited by patients affected with posttraumatic stress disorder. Additionally, we determined that after fear conditioning, dendritic spine density was increased, and expression of Gelsolin, the gene encoding a severing protein for actin polymerization, was down-regulated in the bilateral hippocampi of the Atf3 knockout mice. Taken together, our results suggest that ATF3 may suppress fear memory formation in mice directly or indirectly through mechanisms involving modulation of actin polymerization.

Serum and Adipose Tissue mRNA Levels of ATF3 and FNDC5/Irisin in Colorectal Cancer Patients With or Without Obesity

Objectives: To explore the activating transcription factor 3 (ATF3) and fibronectin type III domain-containing protein 5 (FNDC5)/irisin protein levels in serum and mRNA levels in subcutaneous and visceral white adipose tissue (sWAT and vWAT) in normal-weight (NW) and overweight/obese (OW/OB) patients with colorectal cancer (CRC). Methods: 76 CRC patients and 40 healthy controls were recruited. Serum ATF3 and irisin levels were detected by using ELISA kits, and the mRNA expression levels in sWAT and vWAT were measured by performing RT-qPCR. Results: The serum ATF3 levels were greater by 37.2%, whereas the irisin levels were lower by 23.3% in NW+CRC patients compared with those in healthy controls. CRC was independently associated with both ATF3 and irisin levels. The probability of CRC greater by 22.3-fold in individuals with high ATF3 levels compared with those with low ATF3 levels, whereas the risk of CRC in subjects with high irisin levels was lower by 78.0% compared to the risk in those with low irisin levels after adjustment for age, gender, BMI, and other biochemical parameters. Serum ATF3 and irisin could differentiate CRC patients from controls with receiver operating characteristic (ROC) curve areas of 0.745 (95% CI, 0.655-0.823) and 0.656 (95% CI, 0.561-0.743), respectively. The combination of ATF3 and irisin exhibited improved diagnosis value accuracy with ROC curve areas of 0.796 (95% CI, 0.710-0.866) as well as 72.6% sensitivity and 80.0% specificity. Conclusion: Increased ATF3 and reduced irisin levels were observed in sera from CRC patients. Individuals with high ATF3 and low irisin levels were more likely to have CRC. ATF3 and irisin represent potential diagnostic biomarkers for CRC patients.

Activating transcription factor 3 promotes malignance of lung cancer cells in vitro

BACKGROUND

Lung cancer remains the most common cause of cancer-related death, with high rates of recurrence and poor outcomes. An abnormally high expression of activating transcription factor 3 (ATF3) in various cancers suggests an oncogenic role; however, its function in lung cancer is largely unknown.

METHODS

Sixty-four pairs of lung cancer tissues were collected for ATF3 expression analysis by quantitative real-time PCR, immunoblotting, and immunohistochemistry staining. Correlations between ATF3 expression with clinicopathological features and overall survival were analyzed. ATF3 expression in a panel of lung cancer cell lines together with normal bronchial epithelial Beas-2B cells was also determined. Human H1299 and A549 cells were used for ATF3 knockdown and/or overexpression assays. Alterations in cell proliferation, cell cycle attribution, migration, and invasion were all assessed in vitro.

RESULTS

Increased ATF3 messenger RNA and protein expression were observed in lung cancer tissues/cells compared with normal tissues/cells. High tumorous ATF3 expression was significantly correlated with positive advanced tumor grade, lymph node metastasis, and shorter overall survival. Experimentally, we found that RNA interference mediated knockdown of ATF3 significantly inhibited the cell proliferation, cell cycle progression, migration, and invasion capacities of lung cancer cells in vitro, whereas forced expression of ATF3 did the opposite.

CONCLUSION

Upregulation of ATF3 in lung cancer promotes cell proliferation, migration, and invasion, and may represent a novel therapeutic target for lung cancer.

Cigarette smoke extract profoundly suppresses TNFα-mediated proinflammatory gene expression through upregulation of ATF3 in human coronary artery endothelial cells

Endothelial dysfunction caused by the combined action of disturbed flow, inflammatory mediators and oxidants derived from cigarette smoke is known to promote coronary atherosclerosis and increase the likelihood of myocardial infarctions and strokes. Conversely, laminar flow protects against endothelial dysfunction, at least in the initial phases of atherogenesis. We studied the effects of TNFα and cigarette smoke extract on human coronary artery endothelial cells under oscillatory, normal laminar and elevated laminar shear stress for a period of 72 hours. We found, firstly, that laminar flow fails to overcome the inflammatory effects of TNFα under these conditions but that cigarette smoke induces an anti-oxidant response that appears to reduce endothelial inflammation. Elevated laminar flow, TNFα and cigarette smoke extract synergise to induce expression of the transcriptional regulator activating transcription factor 3 (ATF3), which we show by adenovirus driven overexpression, decreases inflammatory gene expression independently of activation of nuclear factor-κB. Our results illustrate the importance of studying endothelial dysfunction in vitro over prolonged periods. They also identify ATF3 as an important protective factor against endothelial dysfunction. Modulation of ATF3 expression may represent a novel approach to modulate proinflammatory gene expression and open new therapeutic avenues to treat proinflammatory diseases.

MiR-193a-3p and miR-193a-5p suppress the metastasis of human osteosarcoma cells by down-regulating Rab27B and SRR, respectively

MicroRNAs have been identified as key players in the development and progression of osteosarcoma, which is the most common primary malignancy of bone. Sequencing-based miR-omic and quantitative real-time PCR analyses suggested that the expression of miR-193a-3p and miR-193a-5p was decreased by DNA methylation at their promoter region in a highly metastatic osteosarcoma cell line (MG63.2) relative to their expression in the less metastatic MG63 cell line. Further wound-healing and invasion assays demonstrated that both miR-193a-3p and miR-193a-5p suppressed osteosarcoma cell migration and invasion. Moreover, introducing miR-193a-3p and miR-193a-5p mimics into MG63.2 cells or antagomiRs into MG63 cells confirmed their critical roles in osteosarcoma metastasis. Additionally, bioinformatics prediction along with biochemical assay results clearly suggested that the secretory small GTPase Rab27B and serine racemase (SRR) were direct targets of miR-193a-3p and miR-193a-5p, respectively. These two targets are indeed involved in the miR-193a-3p- and miR-193a-5p-induced suppression of osteosarcoma cell migration and invasion. MiR-193a-3p and miR-193a-5p play important roles in osteosarcoma metastasis through down-regulation of the Rab27B and SRR genes and therefore may serve as useful biomarkers for the diagnosis of osteosarcoma and as potential candidates for the treatment of metastatic osteosarcoma.

Inhibition of kinase and endoribonuclease activity of ERN1/IRE1α affects expression of proliferationrelated genes in U87 glioma cells

Inhibition of ERN1/IRE1α (endoplasmic reticulum to nucleus signaling 1/inositol requiring enzyme-1α), the major signaling pathway of endoplasmic reticulum stress, significantly decreases tumor growth. We have studied the expression of transcription factors such as E2F8 (E2F transcription factor 8), EPAS1 (endothelial PAS domain protein 1), TBX3 (T-box 3), ATF3 (activating transcription factor 3), FOXF1 (forkhead box F1), and HOXC6 (homeobox C6) in U87 glioma cells overexpressing dominant-negative ERN1/IRE1α defective in endoribonuclease (dnr-ERN1) as well as defective in both kinase and endonuclease (dn-ERN1) activity of ERN1/IRE1α. We have demonstrated that the expression of all studied genes is decreased at the mRNA level in cells with modified ERN1/IRE1α; TBX3, however, is increased in these cells as compared to control glioma cells. Changes in protein levels of E2F8, HOXC6, ATF3, and TBX3 corresponded to changes in mRNAs levels. We also found that two mutated ERN1/IRE1α have differential effects on the expression of studied transcripts. The presence of kinase and endonuclease deficient ERN1/IRE1α in glioma cells had a less profound effect on the expression of E2F8, HOXC6, and TBX3 genes than the blockade of the endoribonuclease activity of ERN1/IRE1α alone. Kinase and endonuclease deficient ERN1/IRE1α suppresses ATF3 and FOXF1 gene expressions, while inhibition of only endoribonuclease of ERN1/IRE1α leads to the up-regulation of these gene transcripts. The present study demonstrates that fine-tuning of the expression of proliferation related genes is regulated by ERN1/IRE1α an effector of endoplasmic reticulum stress. Inhibition of ERN1/IRE1α, especially its endoribonuclease activity, correlates with deregulation of proliferation related genes and thus slower tumor growth.