Down-Regulation of Overexpressed Sp1 Protein in Human Fibrosarcoma Cell Lines Inhibits Tumor Formation

Specificity Proteins (Sp) and Cancer

The specificity protein (Sp) transcription factors (TFs) Sp1, Sp2, Sp3 and Sp4 exhibit structural and functional similarities in cancer cells and extensive studies of Sp1 show that it is a negative prognostic factor for patients with multiple tumor types. In this review, the role of Sp1, Sp3 and Sp4 in the development of cancer and their regulation of pro-oncogenic factors and pathways is reviewed. In addition, interactions with non-coding RNAs and the development of agents that target Sp transcription factors are also discussed. Studies on normal cell transformation into cancer cell lines show that this transformation process is accompanied by increased levels of Sp1 in most cell models, and in the transformation of muscle cells into rhabdomyosarcoma, both Sp1 and Sp3, but not Sp4, are increased. The pro-oncogenic functions of Sp1, Sp3 and Sp4 in cancer cell lines were studied in knockdown studies where silencing of each individual Sp TF decreased cancer growth, invasion and induced apoptosis. Silencing of an individual Sp TF was not compensated for by the other two and it was concluded that Sp1, Sp3 and Sp4 are examples of non-oncogene addicted genes. This conclusion was strengthened by the results of Sp TF interactions with non-coding microRNAs and long non-coding RNAs where Sp1 contributed to pro-oncogenic functions of Sp/non-coding RNAs. There are now many examples of anticancer agents and pharmaceuticals that induce downregulation/degradation of Sp1, Sp3 and Sp4, yet clinical applications of drugs specifically targeting Sp TFs are not being used. The application of agents targeting Sp TFs in combination therapies should be considered for their potential to enhance treatment efficacy and decrease toxic side effects.

MicroRNA-377: A therapeutic and diagnostic tumor marker

Cancer is considered as one of the main causes of human deaths globally. Despite the recent progresses in therapeutic modalities, there is still a high rate of mortality among cancer patients. Late diagnosis in advanced tumor stages is one of the main reasons for treatment failure in cancer patients. Therefore, it is required to suggest the novel strategies for the early tumor detection. MicroRNAs (miRNAs) have critical roles in neoplastic transformation by regulation of cell proliferation, migration, and apoptosis. They are always considered as non-invasive markers due to their high stability in body fluids. Since, all of the miRNAs have tissue-specific functions in different tumors as tumor suppressor or oncogene; it is required to investigate the molecular mechanisms of every miRNA in different tumors to introduce that as a suitable non-invasive diagnostic marker in cancer patients. For the first time in the present review, we discussed the role of miR-377 during tumor progression. It has been reported that miR-377 mainly functions as a tumor suppressor through the regulation of signaling pathways and transcription factors. This review is an important step toward introducing the miR-377 as a novel diagnostic marker as well as a therapeutic target in cancer patients.

Metformin: A Promising Antidiabetic Medication for Cancer Treatment

Metformin is a widely used drug in patients with type 2 diabetes mellitus. Metformin inhibits hepatic gluconeogenesis and increases glucose utilization in peripheral tissues. In recent years, several studies have shown that metformin is a potential therapeutic agent against cancer, alone or combined with other anticancer treatments. Metformin mainly activates the AMPK complex and regulates intracellular energy status, inhibiting the mitochondrial respiratory chain complex I and reducing the production of reactive oxygen species. Other anticancer targets of metformin are specific transcription factors inhibiting cell proliferation, promoting apoptosis and reducing drug resistance. In addition, metformin modulates tumor cells' response to anticancer treatments, favoring the activity of T cells. In diabetic patients, metformin reduces the occurrence of cancer and improves the prognosis and efficacy of anticancer treatments. In this review, we provided a comprehensive perspective of metformin as an anticancer drug.

Sp1-Induced SETDB1 Overexpression Transcriptionally Inhibits HPGD in a β-Catenin-Dependent Manner and Promotes the Proliferation and Metastasis of Gastric Cancer

PURPOSE

Gastric cancer (GC) has high morbidity and mortality, the cure rate of surgical treatment and drug chemotherapy is not ideal. Therefore, development of new treatment strategies is necessary. We aimed to identify the mechanism underlying Sp1 regulation of GC progression.

METHODS AND METHODS

The levels of Sp1, β-catenin, SET domain bifurcated 1 (SETDB1), and 15-hydroxyprostaglandin dehydrogenase (HPGD) were detected by quantitative reverse transcription polymerase chain reaction and western blot analysis. The targets of SETDB1 were predicted by AnimalTFDB, and dual-luciferase reporter assay was used for confirming the combination of Sp1, β-catenin, and SETDB1. HGC27 or AGS cells (1×106 cells/mouse) were injected into mice via the caudal vein for GC model establishment. The level of Ki67 was detected using immunohistochemistry, and hematoxylin and eosin staining was performed for evaluating tumor metastasis in mice with GC.

RESULTS

HPGD was inhibited, while the protein levels of Sp1, β-catenin, and SETDB1 were up-regulated in GC tissues and cell lines. HPGD overexpression or SETDB1 silencing inhibited the proliferation, invasion, and migration of GC cells, and Sp1 regulated the proliferation, invasion, and migration of GC cells in a β-catenin-dependent manner. Furthermore, HPGD served as a target of SETDB1, and it was negatively regulated by SETDB1; additionally, Sp1 and β-catenin bound to the SETDB1 promoter and negatively regulated HPGD expression. We proved that Sp1 regulated GC progression via the SETDB1/HPGD axis.

CONCLUSIONS

Our findings revealed that Sp1 transcriptionally inhibited HPGD via SETDB1 in a β-catenin-dependent manner and promoted the proliferation and metastasis of GC cells.

Regulation of tumor angiogenesis by microRNAs: State of the art

MicroRNAs (miRNAs, miRs) are small (21-25 nucleotides) endogenous and noncoding RNAs involved in many cellular processes such as apoptosis, development, proliferation, and differentiation via binding to the 3'-untranslated region of the target mRNA and inhibiting its translation. Angiogenesis is a hallmark of cancer, which provides oxygen and nutrition for tumor growth while removing deposits and wastes from the tumor microenvironment. There are many angiogenesis stimulators, among which vascular endothelial growth factor (VEGF) is the most well known. VEGF has three tyrosine kinase receptors, which, following VEGF binding, initiate proliferation, invasion, migration, and angiogenesis of endothelial cells in the tumor environment. One of the tumor microenvironment conditions that induce angiogenesis through increasing VEGF and its receptors expression is hypoxia. Several miRNAs have been identified that affect different targets in the tumor angiogenesis pathway. Most of these miRNAs affect VEGF and its tyrosine kinase receptors expression downstream of the hypoxia-inducible Factor 1 (HIF-1). This review focuses on tumor angiogenesis regulation by miRNAs and the mechanism underlying this regulation.

Specificity Protein Transcription Factors and Cancer: Opportunities for Drug Development

Specificity protein (Sp) transcription factors (TFs) such as Sp1 are critical for early development but their expression decreases with age and there is evidence that transformation of normal cells to cancer cells is associated with upregulation of Sp1, Sp3, and Sp4, which are highly expressed in cancer cells and tumors. Sp1 is a negative prognostic factor for pancreatic, colon, glioma, gastric, breast, prostate, and lung cancer patients. Functional studies also demonstrate that Sp TFs regulate genes responsible for cancer cell growth, survival, migration/invasion, inflammation and drug resistance, and Sp1, Sp3 and Sp4 are also nononcogene addiction (NOA) genes and important drug targets. The mechanisms of drug-induced downregulation of Sp TFs and pro-oncogenic Sp-regulated genes are complex and include ROS-dependent epigenetic pathways that initially decrease expression of the oncogene cMyc. Many compounds such as curcumin, aspirin, and metformin that are active in cancer prevention also exhibit chemotherapeutic activity and these compounds downregulate Sp TFs in cancer cell lines and tumors. The effects of these compounds on downregulation of Sp TFs in normal cells and the contribution of this response to their chemopreventive activity have not yet been determined. Cancer Prev Res; 11(7); 371-82. ©2018 AACR.

Downregulation of Transcription Factor Sp1 Suppresses Malignant Properties of A549 Human Lung Cancer Cell Line with Decreased β4-Galactosylation of Highly Branched N-Glycans

Dramatic changes in the glycan structures of cell surface proteins have been observed upon malignant transformation of cells as induced by the altered expression levels of glycosyltransferases. Such changes are closely associated with the malignant properties of cancer cells. Transcription factor Sp1 regulates the gene expression of various molecules including glycosyltransferases. Herein, we investigated whether or not Sp1-downregulation affects to N-glycosylation of glycoproteins and malignant properties of A549 human lung cancer cell line. We established a stable clone whose Sp1-expression level was reduced to 50% of a control clone by RNA interference. Lectin blotting revealed that the β4-galactosylation of highly branched N-glycans decreases mainly in cell adhesion molecule, E-cadherin. The analysis of underlying mechanism for decreased β4-galactosylation of N-glycans showed that the gene expression level of β4-galactosyltransferase (β4GalT) 1 decreases dramatically by downregulation of Sp1 without changes in those of β4GalT2 and N-acetylglucosaminyltransferase V. Mutations in the Sp1-binding sites of the β4GalT1 gene promoter showed that the promoter activity decreases significantly, indicating that the gene expression is regulated by Sp1. These results indicate that the β4-galactosylation of highly branched N-glycans decreases by downregulation of Sp1 through the reduced expression of the β4GalT1 gene. Furthermore, the Sp1-downregulated cells showed the suppression of the anchorage-independent growth in soft agar and migratory activity when compared to the control cells. The present study demonstrates that downregulation of Sp1 suppresses the malignant properties of A549 cells through the decreased β4-galactosylation of highly branched N-glycans.

The TGF-β-induced up-regulation of NKG2DLs requires AKT/GSK-3β-mediated stabilization of SP1

Natural killer (NK) cells play an important role in preventing cancer development. NK group 2 member D (NKG2D) is an activating receptor expressed in the membrane of NK cells. Tumour cells expressing NKG2DL become susceptible to an immune‐dependent rejection mainly mediated by NK cells. The paradoxical roles of transforming growth factor beta (TGF‐β) in regulation of NKG2DL are presented in many studies, but the mechanism is unclear. In this study, we showed that TGF‐β up‐regulated the expression of NKG2DLs in both PC3 and HepG2 cells. The up‐regulation of NKG2DLs was characterized by increasing the expression of UL16‐binding proteins (ULBPs) 1 and 2. TGF‐β treatment also increased the expression of transcription factor SP1. Knockdown of SP1 significantly attenuated TGF‐β‐induced up‐regulation of NKG2DLs in PC3 and HepG2 cells, suggesting that SP1 plays a key role in TGF‐β‐induced up‐regulation of NKG2DLs. TGF‐β treatment rapidly increased SP1 protein expression while not mRNA level. It might be due to that TGF‐β can elevate SP1 stability by activating PI3K/AKT signalling pathway, subsequently inhibiting GSK‐3β activity and decreasing the association between SP1 and GSK‐3β. Knockdown of GSK‐3β further verified our findings. Taken together, these results revealed that AKT/GSK‐3β‐mediated stabilization of SP1 is required for TGF‐β induced up‐regulation of NKG2DLs. Our study provided valuable evidence for exploring the tumour immune modulation function of TGF‐β.

Association of Sp1 and survivin in epithelial ovarian cancer: Sp1 inhibitor and cisplatin, a novel combination for inhibiting epithelial ovarian cancer cell proliferation

The expression of specificity protein 1 (Sp1) and survivin was evaluated in clinical specimens of epithelial ovarian cancer (EOC) patients. When compared to normal tissue, EOC samples showed high expression of Sp1 and survivin using qPCR (Sp1: ∼2-fold; survivin: ∼5-fold) and Western blot (Sp1: >2.6-fold; survivin: >100-fold). The Sp1 inhibitor, and anti-cancer small molecule, tolfenamic acid (TA), was tested to enhance the response of Cisplatin (Cis) in EOC cell lines. Cell viability (CellTiter-Glo), combination index (CalcuSyn software), apoptosis (Annexin-V staining), cell cycle analyses (flow cytometry), and reactive oxygen species (flow cytometry) were determined. Cell migration and invasion was assessed using matrigel coated transwell chambers. Agilent Technologies proteomics analysis identified potential signaling pathways involved. The combination of TA (50 μM) and Cis (5 μM) synergistically increased the growth inhibition in ES2 (∼80 %, p < 0.001) and OVCAR-3 (60 %, p < 0.001) cells. TA or TA + Cis treatment in ES2 cells caused cell cycle arrest in G1 Phase (TA) or S-Phase (TA + Cis) and unregulated reactive oxygen species. Invasion and migration was decreased in ES2 cells. Global proteomic profiling showed modulation of proteins associated with oxidative phosphorylation, apoptosis, electron transport chain, DNA damage, and cell cycle proteins. These results demonstrate an association of Sp1 and survivin in EOC and confirm targeting these candidates with TA potentially sensitizes EOC cells to cisplatin.

Inhibition of SP1 by the mithramycin analog EC-8042 efficiently targets tumor initiating cells in sarcoma

Tumor initiating cells (TICs), responsible for tumor initiation, and cancer stem cells (CSCs), responsible for tumor expansion and propagation, are often resistant to chemotherapeutic agents. To find therapeutic targets against sarcoma initiating and propagating cells we used models of myxoid liposarcoma (MLS) and undifferentiated pleomorphic sarcoma (UPS) developed from human mesenchymal stromal/stem cells (hMSCs), which constitute the most likely cell-of-origin for sarcoma. We found that SP1-mediated transcription was among the most significantly altered signaling. To inhibit SP1 activity, we used EC-8042, a mithramycin (MTM) analog (mithralog) with enhanced anti-tumor activity and highly improved safety. EC-8042 inhibited the growth of TIC cultures, induced cell cycle arrest and apoptosis and upregulated the adipogenic factor CEBPα. SP1 knockdown was able to mimic the anti-proliferative effects induced by EC-8042. Importantly, EC-8042 was not recognized as a substrate by several ABC efflux pumps involved in drug resistance, and, opposite to the chemotherapeutic drug doxorubicin, repressed the expression of many genes responsible for the TIC/CSC phenotype, including SOX2, C-MYC, NOTCH1 and NFκB1. Accordingly, EC-8042, but not doxorubicin, efficiently reduced the survival of CSC-enriched tumorsphere sarcoma cultures. In vivo, EC-8042 induced a profound inhibition of tumor growth associated to a strong reduction of the mitotic index and the induction of adipogenic differentiation and senescence. Finally, EC-8042 reduced the ability of tumor cells to reinitiate tumor growth. These data suggest that EC-8042 could constitute an effective treatment against both TIC and CSC subpopulations in sarcoma.

Synergistic anti-cancer effects of resveratrol and chemotherapeutic agent clofarabine against human malignant mesothelioma MSTO-211H cells

Dietary phytochemicals as adjuvants have been suggested to play important roles in enhancing chemotherapeutic potential owing to multitargeted chemopreventive properties and lack of substantial toxicity. Here, we investigated the efficacy of the combined treatment of various phytochemicals with the anticancer drug clofarabine in malignant mesothelioma MSTO-211H cells and normal mesothelial MeT-5A cells. The combined treatment of resveratrol and clofarabine produced a synergistic antiproliferative effect in MSTO-211H cells, but not in MeT-5A cells. In MSTO-211H cells, the nuclear accumulation of Sp1 and the levels of p-Akt, Sp1, c-Met, cyclin D1, and p21 were effectively decreased by the combined treatment of them. In combination with clofarabine, the ability of resveratrol to reduce the contents of Sp1 and its target gene products was also evident in a time- and dose-dependent experiment. The inhibition of phosphoinositide 3-kinase using Ly294002 augmented a decrease in the p21 level induced by their combination, but it showed no significant effects on expression of Sp1 and cyclin D1. Taken together, the data provide evidence that the synergistic antiproliferative effect of resveratrol and clofarabine is linked to the inhibition of Akt and Sp1 activities, and suggest that this combination may have therapeutic value in treatment of malignant mesothelioma.

Effect of SP3 silencing on cytokeratin expression pattern in HPV-positive cells

In an attempt to understand the molecular factors underlying squamous cell carcinogenesis in HPV-infected oral and cervical tissues, we examined the Sp3-dependent cytokeratin expression in HPV-positive CaSki cells. Two sets of cytokeratins were examined: the simple epithelial CK 7, 8, 18, 19, and 20, which are generally expressed in simple epithelia and CK4, 10, 13, and 17, which are expressed in squamous epithelia. Two additional CK pairs, i.e. CK6/CK16 and CK4/CK13 were analyzed as controls of the proliferation/differentiation cell status, respectively. We report that Sp3 gene silencing specifically hits CK18 and CK19, which are markers of oral and cervical squamous tumors. These data may be of help in immunopathological definition of squamous carcinogenesis.

Sp1-mediated TRAIL induction in chemosensitization

The regulation of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in cancer chemotherapy is not fully understood. Here, we show that the histone deacetylase (HDAC) inhibitors induce TRAIL in human breast cancer cells. Induction of TRAIL by the HDAC inhibitor MS275 can be enhanced by Adriamycin. Using different reporter constructs in conjunction with transcription activity assays and chromatin immunoprecipitation assays, we provide evidence that the transcription factor Sp1 is responsible for TRAIL induction by MS275 alone or in combination with Adriamycin. Further, we show that the combined treatment of breast cancer cells with MS275 and Adriamycin significantly increases apoptotic cell death via the activation of both death receptor and mitochondrial apoptotic pathways. Down-regulation of TRAIL by small interfering RNA silencing decreased MS275-mediated Adriamycin-induced caspase activation and apoptosis, thus conferring Adriamycin resistance. More importantly, breast cancer T47D cells in which Sp1 was knocked down or Sp1-knockout mouse embryonic stem cells were resistant to the combined treatments. Taken together, our results indicate that induction of TRAIL by the combined treatments with MS275 and Adriamycin is mediated by Sp1 and suggest that transcription factor Sp1 is an important target for the development of novel anticancer agents.

The oncogenic microRNA-27a targets genes that regulate specificity protein transcription factors and the G2-M checkpoint in MDA-MB-231 breast cancer cells

There is evidence that specificity proteins (Sp), such as Sp1, Sp3, and Sp4, are overexpressed in tumors and contribute to the proliferative and angiogenic phenotype associated with cancer cells. Sp1, Sp3, and Sp4 are expressed in a panel of estrogen receptor (ER)-positive and ER-negative breast cancer cell lines, and we hypothesized that regulation of their expression may be due to microRNA-27a (miR-27a), which is also expressed in these cell lines and has been reported to regulate the zinc finger ZBTB10 gene, a putative Sp repressor. Transfection of ER-negative MDA-MB-231 breast cancer cells with antisense miR-27a (as-miR-27a) resulted in increased expression of ZBTB10 mRNA and decreased expression of Sp1, Sp3, and Sp4 at the mRNA and protein levels and also decreased activity in cells transfected with constructs containing Sp1 and Sp3 promoter inserts. In addition, these responses were accompanied by decreased expression of Sp-dependent survival and angiogenic genes, including survivin, vascular endothelial growth factor (VEGF), and VEGF receptor 1 (VEGFR1). Moreover, similar results were observed in MDA-MB-231 cells transfected with ZBTB10 expression plasmid. Both as-miR-27a and ZBTB10 overexpression decreased the percentage of MDA-MB-231 cells in S phase of the cell cycle; however, ZBTB10 increased the percentage of cells in G(0)-G(1), whereas as-miR-27a increased the percentage in G(2)-M. This latter response was associated with induction of Myt-1 (another miR-27a target gene), which inhibits G(2)-M through enhanced phosphorylation and inactivation of cdc2. Thus, the oncogenic activity of miR-27a in MDA-MB-231 cells is due, in part, to suppression of ZBTB10 and Myt-1.

Betulinic acid inhibits prostate cancer growth through inhibition of specificity protein transcription factors

Betulinic acid is a pentacyclic triterpene natural product initially identified as a melanoma-specific cytotoxic agent that exhibits low toxicity in animal models. Subsequent studies show that betulinic acid induces apoptosis and antiangiogenic responses in tumors derived from multiple tissues; however, the underlying mechanism of action is unknown. Using LNCaP prostate cancer cells as a model, we now show that betulinic acid decreases expression of vascular endothelial growth (VEGF) and the antiapoptotic protein survivin. The mechanism of these betulinic acid-induced antiangiogenic and proapoptotic responses in both LNCaP cells and in tumors is due to activation of selective proteasome-dependent degradation of the transcription factors specificity protein 1 (Sp1), Sp3, and Sp4, which regulate VEGF and survivin expression. Thus, betulinic acid acts as a novel anticancer agent through targeted degradation of Sp proteins that are highly overexpressed in tumors.