Skeletal muscle differentiation induces wide-ranging nucleosome repositioning in muscle gene promoters

In a previous report, we demonstrated that Cbx1, PurB and Sp3 inhibited cardiac muscle differentiation by increasing nucleosome density around cardiac muscle gene promoters. Since cardiac and skeletal muscle express many of the same proteins, we asked if Cbx1, PurB and Sp3 similarly regulated skeletal muscle differentiation. In a C2C12 model of skeletal muscle differentiation, Cbx1 and PurB knockdown increased myotube formation. In contrast, Sp3 knockdown inhibited myotube formation, suggesting that Sp3 played opposing roles in cardiac muscle and skeletal muscle differentiation. Consistent with this finding, Sp3 knockdown also inhibited various muscle-specific genes. The Cbx1, PurB and Sp3 proteins are believed to influence gene-expression in part by altering nucleosome position. Importantly, we developed a statistical approach to determine if changes in nucleosome positioning were significant and applied it to understanding the architecture of muscle-specific genes. Through this novel statistical approach, we found that during myogenic differentiation, skeletal muscle-specific genes undergo a set of unique nucleosome changes which differ significantly from those shown in commonly expressed muscle genes. While Sp3 binding was associated with nucleosome loss, there appeared no correlation with the aforementioned nucleosome changes. In summary, we have identified a novel role for Sp3 in skeletal muscle differentiation and through the application of quantifiable MNase-seq have discovered unique fingerprints of nucleosome changes for various classes of muscle genes during myogenic differentiation.

LINC00115 regulates lung adenocarcinoma progression via sponging miR-154-3p to modulate Sp3 expression

The most commonly diagnosed and most lethal subtype of lung cancer is lung adenocarcinoma (LUAD). Therefore, more detailed understanding of the potential mechanism and identification of potential targets of lung adenocarcinoma is needed. A growing number of reports reveals that long non-coding RNAs (lncRNAs) play crucial roles in cancer progression. In present study, we found that lncRNA LINC00115 was upregulated in LUAD tissues and cells. Functional studies revealed that LINC00115 knockdown inhibits the proliferation, growth, invasion, and migration of LUAD cells. Mechanically, we indicated that miR-154-3p is target microRNA of LINC00115, and the effect of downregulated LINC00115 on LUAD cells was partially reversed by the miR-154-3p antisense oligonucleotide (ASO-miR-154-3p). Further investigation revealed that Specificity protein 3 (Sp3) directly interacted with miR-154-3p, and the Sp3 level was positively correlated with the LINC00115 expression. Rescue experiments further showed that Sp3 overexpression partially restored the effect of downregulated LINC00115 on LUAD cells. Similarly, in vivo experiments confirmed that downregulated LINC00115 inhibited xenograft growth and Sp3 expression. Our results demonstrated that LINC00115 knockdown inhibited LUAD progression via sponging miR-154-3p to modulate Sp3 expression. These data indicate that the LINC00115/miR-154-3p/Sp3 axis can be a potential therapeutic target of LUAD.

Transcriptional activation of CSTB gene expression by transcription factor Sp3

CSTB has been reported to be associated with the pathogenesis of many malignant tumors, especially hepatocellular carcinoma (HCC). However, how the expression of this gene is regulated is largely unknown. We initially cloned and analyzed the promoter region of the CSTB gene by luciferase assay and the Sp3 binding site (CCCCGCCCCGCG) was found in it. The results of electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) experiments verified that the transcription factor, Sp3 could bind to the " CCCCGCCCCGCG ″ site of the CSTB gene promoter. We showed that the overexpression of Sp3 significantly increased the endogenous mRNA and protein expression levels of CSTB, whereas knockdown of Sp3 decreased the mRNA and protein expression levels according to quantitative real-time PCR (qRT‒PCR) and western blotting. In conclusion, CSTB gene expression is closely regulated by transcription factor Sp3, which may be a potential mechanism for the dysregulation of CSTB expression in HCC.

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.

Roseburia intestinalis and Its Metabolite Butyrate Inhibit Colitis and Upregulate TLR5 through the SP3 Signaling Pathway

The pathogenesis of ulcerative colitis (UC) is unclear, but it is generally believed to be closely related to an imbalance in gut microbiota. Roseburia intestinalis (R. intestinalis) might play a key role in suppressing intestinal inflammation, but the mechanism of its anti-inflammatory effect is unknown. In this study, we investigated the role of R. intestinalis and Toll-like receptor 5 (TLR5) in relieving mouse colitis. We found that R. intestinalis significantly upregulated the transcription of TLR5 in intestinal epithelial cells (IECs) and improved colonic inflammation in a colitis mouse model. The flagellin of R. intestinalis activated the release of anti-inflammatory factors (IL-10, TGF-β) and reduced inflammation in IECs. Furthermore, butyrate, the main metabolic product secreted by R. intestinalis, regulated the expression of TLR5 in IECs. Our data show that butyrate increased the binding of the transcription factor Sp3 (specificity protein 3) to the TLR5 promoter regions, upregulating TLR5 transcription. This work provides new insight into the anti-inflammatory effects of R. intestinalis in colitis and a potential target for UC prevention and treatment.

Caspase-Mediated Cleavage of the Transcription Factor Sp3: Possible Relevance to Cancer and the Lytic Cycle of Kaposi's Sarcoma-Associated Herpesvirus

The open reading frame 50 (ORF50) protein of Kaposi's sarcoma-associated herpesvirus (KSHV) is the master regulator essential for initiating the viral lytic cycle. Previously, we have demonstrated that the ORF50 protein can cooperate with Sp3 to synergistically activate a set of viral and cellular gene promoters through highly conserved ORF50-responsive elements that harbor a Sp3-binding motif. Herein, we show that Sp3 undergoes proteolytic cleavage during the viral lytic cycle, and the cleavage of Sp3 is dependent on caspase activation. Since similar cleavage patterns of Sp3 could be detected in both KSHV-positive and KSHV-negative lymphoma cells undergoing apoptosis, the proteolytic cleavage of Sp3 could be a common event during apoptosis. Mutational analysis identifies 12 caspase cleavage sites in Sp3, which are situated at the aspartate (D) positions D17, D19, D180, D273, D275, D293, D304 (or D307), D326, D344, D530, D543, and D565. Importantly, we noticed that three stable Sp3 C-terminal fragments generated through cleavage at D530, D543, or D565 encompass an intact DNA-binding domain. Like the full-length Sp3, the C-terminal fragments of Sp3 could still retain the ability to cooperate with ORF50 protein to activate specific viral and cellular gene promoters synergistically. Collectively, our findings suggest that despite the proteolytic cleavage of Sp3 under apoptotic conditions, the resultant Sp3 fragments may retain biological activities important for the viral lytic cycle or for cellular apoptosis. IMPORTANCE The ORF50 protein of Kaposi's sarcoma-associated herpesvirus (KSHV) is the key viral protein that controls the switch from latency to lytic reactivation. It is a potent transactivator that can activate target gene promoters via interacting with other cellular DNA-binding transcription factors, such as Sp3. In this report, we show that Sp3 is proteolytically cleaved during the viral lytic cycle, and up to 12 caspase cleavage sites are identified in Sp3. Despite the proteolytic cleavage of Sp3, several resulting C-terminal fragments that have intact zinc-finger DNA-binding domains still retain substantial influence in the synergy with ORF50 to activate specific gene promoters. Overall, our studies elucidate the caspase-mediated cleavage of Sp3 and uncover how ORF50 utilizes the cleavage fragments of Sp3 to transactivate specific viral and cellular gene promoters.

Downregulation of SENP1 suppresses LPS-induced macrophage inflammation by elevating Sp3 SUMOylation and disturbing Sp3-NF-κB interaction

Macrophages participate in all stages of sepsis and affect immune homeostasis and inflammatory processes. Small ubiquitin-like modifier (SUMO) protease SENP1 plays an important role in cellular inflammation by regulating proteins in SUMOylation. However, the roles and related mechanisms of SENP1 in macrophage inflammation during sepsis are largely unknown. In the present study, SENP1 expression was significantly promoted in lipopolysaccharide (LPS)-induced RAW 264.7 cells; furthermore, the knock down of SENP1 reduced the expression of inflammatory cytokines interleukin-6 and tumor necrosis factor-α. Momordin Ic (MC), a new type of SENP1 inhibitor, reduces LPS-induced cellular inflammation by depressing SENP1 expression. Moreover, the effect of SENP1 on LPS-induced inflammatory response was dependent on SENP1-Sp3 interaction and the promotion of Sp3 expression via Sp3 deSUMOylation. Furthermore, MC-depressed Sp3 expression disturbed Sp3-nuclear factor (NF)-κB interaction and then alleviated LPS-induced cellular inflammation. These results suggest that SENP1 promotes LPS-induced macrophage inflammation by promoting Sp3 expression via deSUMOylation and Sp3-NF-κB interaction in sepsis.

Sp3 Transcription Factor Cooperates with the Kaposi's Sarcoma-Associated Herpesvirus ORF50 Protein To Synergistically Activate Specific Viral and Cellular Gene Promoters

The Kaposi's sarcoma-associated herpesvirus (KSHV)-encoded open reading frame 50 (ORF50) protein is the key transactivator responsible for the latent-to-lytic switch. Here, we investigated the transcriptional activation of the ORF56 gene (encoding a primase protein) by ORF50 and successfully identified an ORF50-responsive element located in the promoter region between positions -97 and -44 (designated 56p-RE). This 56p-RE element contains a noncanonical RBP-Jκ-binding sequence and a nonconsensus Sp1/Sp3-binding sequence. Electrophoretic mobility shift assays revealed that RBP-Jκ, Sp3, and ORF50 could form stable complexes on the 56p-RE element. Importantly, transient-reporter analysis showed that Sp3, but not RBP-Jκ or Sp1, acts in synergy with ORF50 to activate the 56p-RE-containing reporter construct, and the synergy mainly depends on the Sp1/Sp3-binding region of the 56p-RE element. Sequence similarity searches revealed that the promoters for ORF21 (thymidine kinase), ORF60 (ribonucleotide reductase, small subunit), and cellular interleukin-10 (IL-10) contain a sequence motif similar to the Sp1/Sp3-binding region of the 56p-RE element, and we found that these promoters could also be synergistically activated by ORF50 and Sp3 via the conserved motifs. Noteworthily, the conversion of the Sp1/Sp3-binding sequence of the 56p-RE element into a consensus high-affinity Sp-binding sequence completely lost the synergistic response to ORF50 and Sp3. Moreover, transcriptional synergy could not be detected through other ORF50-responsive elements from the viral PAN, K12, ORF57, and K6 promoters. Collectively, the results of our study demonstrate that ORF50 and Sp3 can act in synergy on the transcription of specific gene promoters, and we find a novel conserved cis-acting motif in these promoters essential for transcriptional synergy.IMPORTANCE Despite the critical role of ORF50 in the KSHV latent-to-lytic switch, the molecular mechanism by which ORF50 activates its downstream target genes, especially those that encode the viral DNA replication enzymes, is not yet fully understood. Here, we find that ORF50 can cooperate with Sp3 to synergistically activate promoters of the viral ORF56 (primase), ORF21 (thymidine kinase), and ORF60 (ribonucleotide reductase) genes via similar Sp1/Sp3-binding motifs. Additionally, the same synergistic effect can be seen on the promoter of the cellular IL-10 gene. Overall, our data reveal an important role for Sp3 in ORF50-mediated transactivation, and we propose a new subclass of ORF50-responsive elements in viral and cellular promoters.

Nrf2-regulated miR-380-3p Blocks the Translation of Sp3 Protein and Its Mediation of Paraquat-Induced Toxicity in Mouse Neuroblastoma N2a Cells

Laboratorial and epidemiological research has established a relationship between paraquat (PQ) exposure and a risk for Parkinson's disease. Previously, we have investigated the effects of nuclear factor erythroid 2 related factor 2 (Nrf2) and microRNAs in PQ-induced neurotoxicity, addressing the function of miR-380-3p, a microRNA dysregulated by PQ, as well as Nrf2 deficiency. Nrf2 is known to mediate the expression of a variety of genes, including noncoding genes. By chromatin immunoprecipitation, we identified the relationship between Nrf2 and miR-380-3p in transcriptional regulation. qRT-PCR, Western blots, and dual-luciferase reporter gene assay showed that miR-380-3p blocked the translation of the transcription factor specificity protein-3 (Sp3) in the absence of degradation of Sp3 mRNA. Results based on cell counting analysis, annexin v-fluorescein isothiocyanate/propidium iodide double-staining assay, and propidium iodide staining showed that overexpression of miR-380-3p inhibited cell proliferation, increased the apoptotic rate, induced cell cycle arrest, and intensified the toxicity of PQ in mouse neuroblastoma (N2a [Neuro2a]) cells. Knockdown of Sp3 inhibited cell proliferation and eclipsed the alterations induced by miR-380-3p in cell proliferation. Two mediators of apoptosis and cell cycle identified in previous studies as Sp3-regulated, namely cyclin-dependent kinase inhibitor 1 (p21) and calmodulin (CaM), were dysregulated by PQ, but not Sp3 deficiency. In conclusion, Nrf2-regulated miR-380-3p inhibited cell proliferation and enhanced the PQ-induced toxicity in N2a cells potentially by blocking the translation Sp3 mRNA. We conclude that CaM and p21 were involved in PQ-induced toxicity.

Novel Survivin Inhibitor for Suppressing Pancreatic Cancer Cells Growth via Downregulating Sp1 and Sp3 Transcription Factors

BACKGROUND/AIMS

Targeting survivin, an anti-apoptotic protein and mitotic regulator, is considered as an effective therapeutic option for pancreatic cancer (PaCa). Tolfenamic acid (TA) showed anti-cancer activity in pre-clinical studies. A recent discovery demonstrated a copper(II) complex of TA (Cu-TA) can result in higher activity. In this study, the ability of Cu-TA to inhibit survivin and its transcription factors, Specificity protein (Sp) 1 and 3 in PaCa cell lines and tumor growth in mouse xenograft model were evaluated.

METHODS

Cell growth inhibition was measured in MIA PaCa-2 and Panc1 cells for 2 days using CellTiter-Glo kit. Sp1, Sp3 and survivin expression (by Western blot and qPCR), apoptotic cells and cell cycle phase distribution (by flow cytometry) were evaluated. A pilot study was performed using athymic nude mice [treated with vehicle/Cu-TA (25 or 50 mg/kg) 3 times/week for 4 weeks.

RESULTS

The IC50 value for Cu-TA was about half than TA.Both agents repressed the protein expression of Sp1/Sp3/survivin, Cu-TA was more effective than TA. Especially effect on survivin inhibition was 5.2 (MIA PaCa-2) or 6.4 (Panc1) fold higher and mRNA expression of only survivin was decreased. Apoptotic cells increased with Cu-TA treatment in both cell lines, while Panc1 showed both effect on apoptosis and cell cycle (G2/M) arrest. Cu-TA decreased the tumor growth in mouse xenografts (25 mg/kg: 48%; 50 mg/kg: 68%). Additionally, there was no change observed in mice body weights, indicating no overt toxicity was occurring.

CONCLUSION

These results show that Cu-TA can serve as an effective survivin inhibitor for inhibiting PaCa cell growth.

ZBP-89 and Sp1 contribute to Bak expression in hepatocellular carcinoma cells

Background

Kruppel family member zinc binding protein 89 (ZBP-89), also known as ZNF148, regulates Bak expression via binding to GC-rich promoter domain. It is not clear if other GC-rich binding factors, such as Sp family members, can interact with ZBPp-89 on Bak expression. This study aims to elucidate the mechanism of Bak expression regulation by ZBP-89 and Sp proteins, based on in vitro experiment and The Cancer Genome Atlas (TCGA) hepatocellular carcinoma (HCC) data cohort.

Methods

We downloaded TCGA hepatocellular carcinoma (HCC) cohort data to analysis the association of Bak transcription level with ZBP-89 and Sp proteins transcription level. HCC cell lines and liver immortal non-tumour cell lines were used for mechanism study, including western blotting analysis, expression vector mediated gene expression and siRNA interference.

Results

Results showed that cancer tissues have higher Bak transcription level compared with adjacent non-cancer tissues. Bak transcription level was correlated with Sp1 and Sp3 expression level, while no correlation was found in ZBP-89 and Bak, neither Sp2 nor Sp4. Mithramycin A (MMA) induced Bak expression in a dose-dependent manner. Western blotting results showed Sp1 overexpression increased Bak expression both in liver immortal non-tumour cells and HCC cells. Interference Sp1 expression could inhibit Bak expression alone. ZBP-89 siRNA suppressed Bak expression even in the presence of MMA treatment and S1 overexpression. Additionally, Bak and Sp1 level were associated with HCC patient survival.

Conclusions

Bak expression required ZBP-89 and Sp1 cooperative regulation simultaneously.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4349-y) contains supplementary material, which is available to authorized users.

The miR-491-3p/Sp3/ABCB1 axis attenuates multidrug resistance of hepatocellular carcinoma

As one of main obstacles in the treatment and prognosis of hepatocellular carcinoma (HCC), multidrug resistance (MDR) is usually associated with the overexpression of the drug efflux pump P-glycoprotein (P-gp/ABCB1) which is responsible for reducing the intracellular concentration of chemotherapeutic agents. In current work, we discovered the novel role of miR-491-3p in ABCB1-mediated multidrug resistance in HCC and revealed the underlying mechanism in which miR-491-3p downregulated the expression of ABCB1 and its transcription factor Sp3 by directly targeting their 3'-UTR. Moreover, overexpressing ABCB1 or Sp3 reversed the sensitivity to chemotherapeutics in Hep3B cells induced by miR-491-3p, confirming miR-491-3p/Sp3/ABCB1 regulatory loop plays an important role in enhancing the drugs sensitivity of HCC. Meanwhile, the discovery of that the expression level of miR-491-3p was inversely correlated with that of ABCB1 and Sp3 in HCC cell lines and clinical samples pointed out the possibility of miR-491-3p in clinical use. In summary, our results reveal a pivotal role of miR-491-3p in the regulation of MDR in HCC, and suggest the potential application of miR-491-3p as a therapeutic strategy for modulating MDR in cancer cells.

Monoamine oxidase B levels are highly expressed in human gliomas and are correlated with the expression of HiF-1α and with transcription factors Sp1 and Sp3

Monoamine oxidases A and B (MAOA and MAOB) are highly expressed in many cancers. Here we investigated the level of MAOB in gliomas and confirmed its high expression. We found that MAOB levels correlated with tumor grade and hypoxia-inducible factor 1-alpha (HiF-1α) expression. HiF-1α was localized to the nuclei in high-grade gliomas, but it was primarily cytosolic in low-grade gliomas and normal human astrocytes. Expression of both glial fibrillary acidic protein (GFAP) and MAOB are correlated to HiF-1α expression levels. Levels of MAOB are correlated by the levels of transcription factor Sp3 in the majority of GBM examined, but this control of MAOB expression by Sp3 in low grade astrocytic gliomas is significantly different from control in the in the majority of glioblastomas. The current findings support previous suggestions that MAOB can be exploited for the killing of cancer cells. Selective cell toxicity can be achieved by designing non-toxic prodrugs that require MAOB for their catalytic conversion into mature cytotoxic chemotherapeutics.

Brain in situ hybridization maps as a source for reverse-engineering transcriptional regulatory networks: Alzheimer's disease insights

Microarray data have been a valuable resource for identifying transcriptional regulatory relationships among genes. As an example, brain region-specific transcriptional regulatory events have the potential of providing etiological insights into Alzheimer Disease (AD). However, there is often a paucity of suitable brain-region specific expression data obtained via microarrays or other high throughput means. The Allen Brain Atlas in situ hybridization (ISH) data sets (Jones et al., 2009) represent a potentially valuable alternative source of high-throughput brain region-specific gene expression data for such purposes. In this study, Allen Brain Atlas mouse ISH data in the hippocampal fields were extracted, focusing on 508 genes relevant to neurodegeneration. Transcriptional regulatory networks were learned using three high-performing network inference algorithms. Only 17% of regulatory edges from a network reverse-engineered based on brain region-specific ISH data were also found in a network constructed upon gene expression correlations in mouse whole brain microarrays, thus showing the specificity of gene expression within brain sub-regions. Furthermore, the ISH data-based networks were used to identify instructive transcriptional regulatory relationships. Ncor2, Sp3 and Usf2 form a unique three-party regulatory motif, potentially affecting memory formation pathways. Nfe2l1, Egr1 and Usf2 emerge among regulators of genes involved in AD (e.g. Dhcr24, Aplp2, Tia1, Pdrx1, Vdac1, and Syn2). Further, Nfe2l1, Egr1 and Usf2 are sensitive to dietary factors and could be among links between dietary influences and genes in the AD etiology. Thus, this approach of harnessing brain region-specific ISH data represents a rare opportunity for gleaning unique etiological insights for diseases such as AD.

Differential effects of Sp cellular transcription factors on viral promoter activation by varicella-zoster virus (VZV) IE62 protein

The immediate early (IE) 62 protein is the major varicella-zoster virus (VZV) regulatory factor. Analysis of the VZV genome revealed 40 predicted GC-rich boxes within 36 promoters. We examined effects of ectopic expression of Sp1-Sp4 on IE62- mediated transactivation of three viral promoters. Ectopic expression of Sp3 and Sp4 enhanced IE62 activation of ORF3 and gI promoters while Sp3 reduced IE62 activation of ORF28/29 promoter and VZV DNA replication. Sp2 reduced IE62 transactivation of gI while Sp1 had no significant influence on IE62 activation with any of these viral promoters. Electrophoretic mobility shift assays (EMSA) confirmed binding of Sp1 and Sp3 but not Sp2 and Sp4 to the gI promoter. Sp1-4 bound to IE62 and amino acids 238-258 of IE62 were important for the interaction with Sp3 and Sp4 as well as Sp1. This work shows that Sp family members have differential effects on IE62-mediated transactivation in a promoter-dependent manner.

O-GlcNAc modification of Sp3 and Sp4 transcription factors negatively regulates their transcriptional activities

The addition of O-linked N-acetylglucosamine (O-GlcNAc) on serine or threonine modifies a myriad of proteins and regulates their function, stability and localization. O-GlcNAc modification is common among chromosome-associated proteins, such as transcription factors, suggesting its extensive involvement in gene expression regulation. In this study, we demonstrate the O-GlcNAc status of the Sp family members of transcription factors and the functional impact on their transcriptional activities. We highlight the presence of O-GlcNAc residues in Sp3 and Sp4, but not Sp2, as demonstrated by their enrichment in GlcNAc positive protein fractions and by detection of O-GlcNAc residues on Sp3 and Sp4 co-expressed in Escherichia coli together with O-GlcNAc transferase (OGT) using an O-GlcNAc-specific antibody. Deletion mutants of Sp3 and Sp4 indicate that the majority of O-GlcNAc sites reside in their N-terminal transactivation domain. Overall, using reporter gene assays and co-immunoprecipitations, we demonstrate a functional inhibitory role of O-GlcNAc modifications in Sp3 and Sp4 transcription factors. Thereby, our study strengthens the current notion that O-GlcNAc modification is an important regulator of protein interactome.

Transcriptional regulation of BNIP3 by Sp3 in prostate cancer

BACKGROUND

The transcription factors Sp3/Sp1 are expressed in a various types of cancers and BNIP3 is overexpressed in prostate cancer. Although it has been demonstrated that BNIP3 is transcriptionally regulated by HIF-1α and is post-transcriptionally regulated by miR145, our previous data indicated that there might be some other transcription factors regulating BNIP3 in prostate cancer. This study is conducted to investigate whether BNIP3 expression is directly regulated by Sp3/Sp1 or not.

MATERIALS AND METHODS

Bioinformatics analysis shows that BNIP3 promoter contains several potential Sp3/Sp1 binding sites. And then it is demonstrated that SP3 could regulate the BNIP3 transcriptionally by binding to the predicted sites by dual reporter gene assays, ChIP, and EMSA. The biological effects of SP3 regulating BNIP3 on prostate cancer cells proliferation are measured by MTT, TUNEL, and flow cytometry.

RESULTS

Our data show that Sp3 but not Sp1, is positively related to BNIP3 overexpression in prostate cancer. Sp3 can directly regulate BNIP3 transcription by mainly binding to the Sp3 binding sites (-624~-615 and -350~-343) of BNIP3 promoter. Knockdown of Sp3 by RNA interference could reduce cells growth and lead to cells apoptosis in PC-3 and DU145. Sp3-dependent BNIP3 overexpression might be an important mechanism to promote prostate cancer cells proliferation.

CONCLUSION

This is the first study to provide direct evidence of Sp3-dependent BNIP3 expression. Sp3 might be the major transcriptional regulator of BNIP3 in prostate cancer and it is worthy to further study. The regulation of BNIP3 by Sp3 may be a new cancer-specific therapeutic target in prostate cancer.

Sodium butyrate stimulates NHE8 expression via its role on activating NHE8 basal promoter activity

Butyrate is a major metabolite in colonic lumen. It is produced from bacterial fermentation of dietary fiber. Butyrate has been shown to stimulate electroneutral sodium absorption through its regulation on sodium/hydrogen exchanger 3 (NHE3). Although NHE8, the newest addition of intestinal NHE family, is involved in sodium absorption in the intestinal tract, whether butyrate modulates NHE8 expression in the intestinal epithelial cells is not known. In the current study, we showed that butyrate treatment strongly induced NHE8 protein and NHE8 mRNA expression in human intestinal epithelial cells. Transfection with the human NHE8 promoter reporter constructs showed that butyrate treatment stimulated reporter gene expression at an amount comparable with its stimulation of NHE8 mRNA expression. Interestingly, a similar result was also observed in human NHE8 promoter transfected cells after trichostatin (TSA) treatment. Gel mobility shift assay identified an enhanced Sp3 protein binding on the human NHE8 basal promoter region upon butyrate stimulation. Furthermore, Sp3 acetylation modification is involved in butyrate-mediated NHE8 activation in Caco-2 cells. Our findings suggest that the mechanism of butyrate action on NHE8 expression involves enhanced Sp3 interaction at the basal promoter region of the human NHE8 gene promoter to activate NHE8 gene transcription. Thus butyrate is involved in intestinal regulation of NHE8 resulting enhanced sodium absorption.

Sp1 transcription factor: A long-standing target in cancer chemotherapy

Sp1 (specificity protein 1) is a well-known member of a family of transcription factors that also includes Sp2, Sp3 and Sp4, which are implicated in an ample variety of essential biological processes and have been proven important in cell growth, differentiation, apoptosis and carcinogenesis. Sp1 activates the transcription of many cellular genes that contain putative CG-rich Sp-binding sites in their promoters. Sp1 and Sp3 proteins bind to similar, if not the same, DNA tracts and compete for binding, thus they can enhance or repress gene expression. Evidences exist that the Sp-family of proteins regulates the expression of genes that play pivotal roles in cell proliferation and metastasis of various tumors. In patients with a variety of cancers, high levels of Sp1 protein are considered a negative prognostic factor. A plethora of compounds can interfere with the trans-activating activities of Sp1 and other Sp proteins on gene expression. Several pathways are involved in the down-regulation of Sp proteins by compounds with different mechanisms of action, which include not only the direct interference with the binding of Sp proteins to their putative DNA binding sites, but also promoting the degradation of Sp protein factors. Down-regulation of Sp transcription factors and Sp1-regulated genes is drug-dependent and it is determined by the cell context. The acknowledgment that several of those compounds are safe enough might accelerate their introduction into clinical usage in patients with tumors that over-express Sp1.

MicroRNA-Specificity Protein (Sp) Transcription Factor Interactions and Significance in Carcinogenesis

Specificity protein (Sp) transcription factors (TFs) such as Sp1, Sp3 and Sp4 are overexpressed in tumors and Sp1 is a negative prognostic factor for multiple tumor types. Sp TFs regulate expression of pro-oncogenic factors important for cell proliferation, survival, angiogenesis, migration/invasion and inflammation and the high expression of Sp TFs in tumors is primarily due to miRNAs. For example, expression of tumor-suppressor-like miRNAs such as miR-200b/c, miR-335, miR-22, miR-149 and others that inactivate Sp1 expression is low in many tumor types. Research in our laboratory has also demonstrated that high expression of Sp TFs is also due to miRNA-dependent inhibition of the transcriptional repressors ZBTB10 and ZBTB4 by miR-27a and miR-20a/miR-17p, respectively. Thus, miRNAs play a critical role in maintaining high levels of Sp1, Sp3, Sp4 and pro-oncogenic Sp-regulated genes in tumors and cancer cells, and there is ample evidence that anticancer agents targeting the miRNASp TF axis can be highly effective for cancer chemotherapy.

Overexpression of histone deacetylases in cancer cells is controlled by interplay of transcription factors and epigenetic modulators

Histone deacetylases (HDACs) that deacetylate histone and nonhistone proteins play crucial roles in a variety of cellular processes. The overexpression of HDACs is reported in many cancer types and is directly linked to accelerated cell proliferation and survival. However, little is known about how HDAC expression is regulated in cancer cells. In this study, we found that HDAC1 and HDAC2 promoters are regulated through collaborative binding of transcription factors Sp1/Sp3 and epigenetic modulators, including histone H3K4 methyltransferase SET1 and histone acetyltransferase p300, whose levels are also elevated in colon cancer cell lines and patient samples. Interestingly, Sp1 and Sp3 differentially regulate HDAC1 and HDAC2 promoter activity. In addition, Sp1/Sp3 recruits SET1 and p300 to the promoters. SET1 knockdown (KD) results in a loss of the H3K4 trimethylation mark at the promoters, as well as destabilizes p300 at the promoters. Conversely, p300 also influences SET1 recruitment and H3K4me3 level, indicating a crosstalk between p300 and SET1. Further, SET1 KD reduces Sp1 binding to the HDAC1 promoter through the increase of Sp1 acetylation. These results indicate that interactions among transcription factors and epigenetic modulators orchestrate the activation of HDAC1 and HDAC2 promoter activity in colon cancer cells.

Alteration of gene expression profile in hepatocellular carcinoma HepG2 cells with Sp3 downregulation

AIM: To analyze the alteration of gene expression profile in hepatocellular carcinoma cell line HepG2 with Sp3 downregulation.

METHODS: RNA interference was performed to downregulate Sp3 mRNA in HepG2 cells and NimbleGen Human Gene Expression Microarray was used for gene expression profile analysis. Real-time quantitative PCR was employed to confirm the expression of several differentially expressed genes. The cell cycle was analyzed by flow cytometry.

RESULTS: A total of 1789 genes was found to be differentially expressed in HepG2 cells with Sp3 downregulation, including 1007 up-regulated and 782 down-regulated ones. These genes were involved in many cellular biological process such as proliferation, differentiation, programmed death, adhesion, and metabolic process. Real-time quantitative PCR confirmed the alteration of several cell cycle related genes (CCND1, CCNE2, TGFB1, and CDKN2A). Flow cytometry analysis showed that the percentage of cells in G₁ phase increased significantly after Sp3 downregulation.

CONCLUSION: Gene expression profile alters in HepG2 with Sp3 downregulation. Sp3 knockdown induces cell cycle arrest in G₀/G₁ phase in HepG2 cells. Sp3 may play an essential role in the pathogenesis of hepatocellular carcinoma as a transcription factor via regulating cell cycle progression.

Sp1 and Sp3 transcription factors regulate the basal expression of human microsomal epoxide hydrolase (EPHX1) through interaction with the E1b far upstream promoter

Microsomal epoxide hydrolase (mEH, EPHX1) is a critical biotransformation enzyme, catalyzing the metabolism of many xenobiotics. Human mEH is transcribed using alternative promoters. The upstream E1 promoter is active in liver while the far upstream E1b promoter drives the expression of mEH in all tissues, including liver. Although several liver-specific transcription factors have been identified in the regulation of E1 transcription, little is known regarding the mechanisms of E1b transcriptional regulation. Genome-wide mapping of DNase I hypersensitive sites revealed an open chromatin region between nucleotide -300 upstream and +400 downstream of E1b. This area coincides with a previously described promoter region responsible for maintaining high basal promoter activity. In silico analysis of this location revealed several Sp1/Sp3 binding sites. Site-directed mutagenesis of these motifs suppressed the transactivation activity of the E1b proximal promoter, indicating their importance as contributors to E1b promoter regulation. Further, E1b promoter activities were increased significantly following Sp1 and Sp3 overexpression, while Mithramycin A, a selective Sp1 inhibitor, reduced the promoter activities. EMSA studies demonstrated that Sp1 bound to two putative Sp1/Sp3 binding sites. ChIP analysis confirmed that both endogenous Sp1 and Sp3 were bound to the proximal promoter region of E1b. Knockdown of Sp1 expression using siRNA did not alter the endogenous E1b transcriptional level, while knockdown of Sp3 greatly decreased E1b expression in different human cell lines. Taken together, these results support the concept that Sp1 and Sp3 are functionally involved as transcriptional integrators regulating the basal expression of the derived mEH E1b variant transcript.

Enforcing the pause: transcription factor Sp3 limits productive elongation by RNA polymerase II

The transition of paused RNA polymerase II into productive elongation is a highly dynamic process that serves to fine-tune gene expression in response to changing cellular environments. We have recently reported that the transcription factor Sp3 inhibits the transition of paused RNA Pol II to productive elongation at the promoter of the cyclin-dependent kinase inhibitor p21(CIP1) and other Sp3-repressed genes. Our studies support the view that Sp3 has three modes of action: activation, SUMO-Sp3-mediated heterochromatin silencing and SUMO-independent inhibition of elongation. At the p21(CIP1) promoter, binding of the positive elongation factor P-TEFb kinase was not affected by Sp3. In contrast, Sp3 promoted binding of the protein phosphatase PP1 to the p21(CIP1) promoter, suggesting that Sp3-dependent regulation of the local balance between kinase and phosphatase activities may contribute to gene expression. Our findings show that the transition of paused RNA Pol II to productive elongation is an important step regulated by both promoter-specific activators and repressors to finely modulate mRNA expression levels.