Sp1 deacetylation induced by phorbol ester recruits p300 to activate 12(S)-lipoxygenase gene transcription

Sp4/HD11 and Sp1/HAT-p300 complexes induce apoptotic cell death in CuCl2-treated neurons by modulating histone acetylation on BCL-W and BAX promoters

Copper is a metal physiologically present in the brain that becomes neurotoxic at high concentrations; on the other hand, pharmacological inhibition of Histone Deacetylases (HDs) or of Histone Acetyltransferases (HATs) reduce neuronal death caused by several neurotoxicants. Herein, we found that CuCl2 (300 μM in SH-SY5Y cells or 100 μM in cortical neurons) determined apoptotic cell death, that was counteracted by the class IV HDs inhibitor Mocetinostat (MOCE) and by the HAT-p300 inhibitor C646, but not by the class I and II HDs inhibitors. Interestingly, HD11 and HAT-p300 protein levels increased after both 12 and 24 h of CuCl2 exposure and their silencing partially limited CuCl2-neurodetrimental effect. Furthermore, in CuCl2-treated cells the transcriptional factor Sp4 co-localized with HD11 on the promoter of anti-apoptotic gene BCL-W, determining histone H3 hypo-acetylation, a marker of gene repression. Contrarily, Sp1 co-localized with HAT-p300 on the pro-apoptotic gene BAX, determining histone H4 hyper-acetylation, a hallmark of transcriptional activation. In addition, siRNA against Sp4 prevented HD11 binding on BCL-W promoter and its consequent down-regulation, whereas Sp1 knocking-down, by reducing HAT-p300 interaction on BAX gene promoter counteracted its up-regulation. Importantly, while the single knocking-down of Sp1, Sp4, HD11 and HAT-p300 partially mitigated CuCl2-induced cell death, the double-transfection of siRNAs for Sp1 and Sp4, or for HD11 and HAT-p300, completely reverted the neurotoxic effect of CuCl2. Collectively, we found that CuCl2-induced neuronal apoptosis is determined by the binding of Sp1/HAT-p300 and of Sp4/HD11 transcriptional complexes on the BAX and BCL-W gene, respectively, unraveling a new pathway involved in Copper-induced neurotoxicity.

HDAC6 inhibition upregulates endothelial SOD3 expression via Sp1 acetylation and attenuates angiotensin II-induced hypertension

Extracellular superoxide dismutase (SOD3) plays an important role in maintaining vascular redox homeostasis by eliminating superoxides. The angiotensin II (AngII) peptide mediates vasoconstriction in part via reactive oxygen species (ROS) but has pathologic effects when elevated in adults. Histone deacetylase 6 (HDAC6) modulates the acetylation of non-histone substrates and is associated with hypertensive disorders. Here, we investigated the potential regulation of SOD3 by HDAC6 in human aortic endothelial cells (HAECs) and its implications for AngII-induced oxidative stress and hypertension. HDAC6 inhibition (via the specific inhibitor tubastatin A (TubA), gene knockdown, or a deacetylase activity-deficient mutant) significantly increased SOD3 protein and mRNA expression but did not affect SOD1 or SOD2 protein levels. Conversely, AngII downregulated SOD3 levels and increased ROS and superoxide levels; these effects were antagonized by TubA. We confirmed that the transcription factor Sp1 mediates TubA-induced as well as basal SOD3 expression. Notably, TubA strongly augmented Sp1 acetylation at lysine 703, which activated Sp1 binding to the proximal SOD3 promoter region and, consequently, SOD3 expression. Alternatively, AngII decreased Sp1 acetylation, and TubA-mediated SOD3 induction was reduced upon overexpression of an acetylation-resistant Sp1 mutant (K703R) compared to that by the wild-type protein. Consistent with these findings, aortic SOD3 expression was significantly higher in HDAC6-deficient mice than in wild-type mice. Moreover, AngII infusion-mediated blood pressure elevation was reduced in HDAC6-deficient mice compared with that in wild-type mice. Collectively, our results suggest that HDAC6 inhibition leads to SOD3 upregulation by enhancing Sp1 acetylation in HAECs, thereby mitigating AngII-induced oxidative stress and hypertension.

Inhibition of HDAC6 elicits anticancer effects on head and neck cancer cells through Sp1/SOD3/MKP1 signaling axis to downregulate ERK phosphorylation

Oxidative stress caused by reactive oxygen species (ROS) and superoxides is linked to various cancer-related biological events. Extracellular superoxide dismutase (SOD3), an antioxidant enzyme that removes superoxides, contributes to redox homeostasis and has the potential to regulate tumorigenesis. Histone deacetylase 6 (HDAC6), a major HDAC isoform responsible for mediating the deacetylation of non-histone protein substrates, also plays a role in cancer progression. In this study, we examined the potential effects of HDAC6 inhibition on SOD3 expression in head and neck cancer (HNC) cells and its impact on cell proliferation, which remains unaddressed. We found that functional inactivation of HDAC6, through the use of chemical inhibitors such as tubastatin A (TubA), gene knockdown, or overexpression of an inactive mutant, strongly upregulated protein and mRNA levels of SOD3 in HNC cell lines FaDu and Detroit562. Mechanistically, TubA induced acetylation of the transcription factor Sp1 at Lys703, which consequently enhanced its binding to the SOD3 proximal promoter region and increased SOD3 expression. An acetylation-defective Sp1 mutant (K703R) was much less effective in inducing SOD3 expression compared to wild-type Sp1. TubA reduced intracellular ROS and superoxide levels, and this antioxidative effect was attenuated in SOD3 knockdown cells. Similar to the changes in ROS levels, HDAC6 inhibition as well as SOD3 overexpression suppressed cell proliferation and the stimulatory phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), whereas SOD3 knockdown produced opposite effects in both resting and TubA-treated conditions. In addition, SOD3 overexpression prevented ROS-induced ERK1/2 phosphorylation and enhanced the protein stability of mitogen-activated protein kinase phosphatase 1 (MKP1), thereby counteracting ERK1/2 phosphorylation. We further showed that SOD3-mediated ERK1/2 dephosphorylation was moderated in MKP1 knockdown cells. Collectively, these results suggest that HDAC6 inhibition elicits anticancer effects on HNC cells by promoting Sp1 acetylation-dependent SOD3 upregulation, leading to MKP1 stabilization and subsequent ERK1/2 inactivation.

Acetylation-enhanced Sp1 transcriptional activity suppresses Mlph expression

Melanosome transport is regulated by major proteins, including Rab27a, Melanophilin (Mlph), and Myosin Va (Myo-Va), that form a tripartite complex. Mutation of these proteins causes melanosome aggregation around the nucleus. Among these proteins, Mlph is a linker between Rab27a and Myo-Va. There are some studies about the regulation of Mlph transcriptional expression. However, its regulation by post-translational modifications remains unclear. In this study, inhibition of HDACs by SAHA and TSA disrupted melanosome transport, causing melanosome aggregation. Specifically, we identified a novel mechanism in which HDAC5 regulates Mlph expression via Sp1. Knockdown of HDAC5 increased the acetylation of Sp1 and the binding to the Mlph promoter, thereby modulating its expression. This study highlights the crucial role of HDAC5 in melanosome transport through its interaction with Sp1. These findings suggest that HDAC5-mediated deacetylation is pivotal in the post-translational modification of melanosome transport, providing insights into the molecular mechanisms underlying this process.

O-GlcNAc transferase congenital disorder of glycosylation (OGT-CDG): Potential mechanistic targets revealed by evaluating the OGT interactome

O-GlcNAc transferase (OGT) is the sole enzyme responsible for the post-translational modification of O-GlcNAc on thousands of target nucleocytoplasmic proteins. To date, nine variants of OGT that segregate with OGT Congenital Disorder of Glycosylation (OGT-CDG) have been reported and characterized. Numerous additional variants have been associated with OGT-CDG, some of which are currently undergoing investigation. This disorder primarily presents with global developmental delay and intellectual disability (ID), alongside other variable neurological features and subtle facial dysmorphisms in patients. Several hypotheses aim to explain the etiology of OGT-CDG, with a prominent hypothesis attributing the pathophysiology of OGT-CDG to mutations segregating with this disorder disrupting the OGT interactome. The OGT interactome consists of thousands of proteins, including substrates as well as interactors that require noncatalytic functions of OGT. A key aim in the field is to identify which interactors and substrates contribute to the primarily neural-specific phenotype of OGT-CDG. In this review, we will discuss the heterogenous phenotypic features of OGT-CDG seen clinically, the variable biochemical effects of mutations associated with OGT-CDG, and the use of animal models to understand this disorder. Furthermore, we will discuss how previously identified OGT interactors causal for ID provide mechanistic targets for investigation that could explain the dysregulated gene expression seen in OGT-CDG models. Identifying shared or unique altered pathways impacted in OGT-CDG patients will provide a better understanding of the disorder as well as potential therapeutic targets.

Discovery of a novel hybrid coumarin-hydroxamate conjugate targeting the HDAC1-Sp1-FOSL2 signaling axis for breast cancer therapy

BACKGROUND

Breast cancer is one of the most lethal cancers in women. Despite significant advances in the diagnosis and treatment of breast cancer, many patients still succumb to this disease, and thus, novel effective treatments are urgently needed. Natural product coumarin has been broadly investigated since it reveals various biological properties in the medicinal field. Accumulating evidence indicates that histone deacetylase inhibitors (HDACIs) are promising novel anti-breast cancer agents. However, most current HDACIs exhibit only moderate effects against solid tumors and are associated with severe side effects. Thus, to develop more effective HDACIs for breast cancer therapy, hydroxamate of HDACIs was linked to coumarin core, and coumarin-hydroxamate hybrids were designed and synthesized.

METHODS

A substituted coumarin moiety was incorporated into the classic hydroxamate HDACIs by the pharmacophore fusion strategy. ZN444B was identified by using the HDACI screening kit and cell viability assay. Molecular docking was performed to explore the binding mode of ZN444B with HDAC1. Western blot, immunofluorescent staining, cell viability, colony formation and cell migration and flow cytometry assays were used to analyze the anti-breast cancer effects of ZN444B in vitro. Orthotopic studies in mouse models were applied for preclinical evaluation of efficacy and toxicity in vivo. Proteomic analysis, dual-luciferase reporter assay, chromatin immunoprecipitation, co-immunoprecipitation, immunofluorescent staining assays along with immunohistochemical (IHC) analysis were used to elucidate the molecular basis of the actions of ZN444B.

RESULTS

We synthesized and identified a novel coumarin-hydroxamate conjugate, ZN444B which possesses promising anti-breast cancer activity both in vitro and in vivo. A molecular docking model showed that ZN444B binds to HDAC1 with high affinity. Further mechanistic studies revealed that ZN444B specifically decreases FOS-like antigen 2 (FOSL2) mRNA levels by inhibiting the deacetylase activity of HDAC1 on Sp1 at K703 and abrogates the binding ability of Sp1 to the FOSL2 promoter. Furthermore, FOSL2 expression positively correlates with breast cancer progression and metastasis. Silencing FOSL2 expression decreases the sensitivity of breast cancer cells to ZN444B treatment. In addition, ZN444B shows no systemic toxicity in mice.

CONCLUSIONS

Our findings highlight the potential of FOSL2 as a new biomarker and therapeutic target for breast cancer and that targeting the HDAC1-Sp1-FOSL2 signaling axis with ZN444B may be a promising therapeutic strategy for breast cancer.

Cancer-associated fibroblast-derived acetate promotes pancreatic cancer development by altering polyamine metabolism via the ACSS2-SP1-SAT1 axis

The ability of tumour cells to thrive in harsh microenvironments depends on the utilization of nutrients available in the milieu. Here we show that pancreatic cancer-associated fibroblasts (CAFs) regulate tumour cell metabolism through the secretion of acetate, which can be blocked by silencing ATP citrate lyase (ACLY) in CAFs. We further show that acetyl-CoA synthetase short-chain family member 2 (ACSS2) channels the exogenous acetate to regulate the dynamic cancer epigenome and transcriptome, thereby facilitating cancer cell survival in an acidic microenvironment. Comparative H3K27ac ChIP-seq and RNA-seq analyses revealed alterations in polyamine homeostasis through regulation of SAT1 gene expression and enrichment of the SP1-responsive signature. We identified acetate/ACSS2-mediated acetylation of SP1 at the lysine 19 residue that increased SP1 protein stability and transcriptional activity. Genetic or pharmacologic inhibition of the ACSS2-SP1-SAT1 axis diminished the tumour burden in mouse models. These results reveal that the metabolic flexibility imparted by the stroma-derived acetate enabled cancer cell survival under acidosis via the ACSS2-SP1-SAT1 axis.

HDAC6 Enhances Endoglin Expression through Deacetylation of Transcription Factor SP1, Potentiating BMP9-Induced Angiogenesis

Histone deacetylase 6 (HDAC6) plays a crucial role in the acetylation of non-histone proteins and is notably implicated in angiogenesis, though its underlying mechanisms were previously not fully understood. This study conducted transcriptomic and proteomic analyses on vascular endothelial cells with HDAC6 knockdown, identifying endoglin (ENG) as a key downstream protein regulated by HDAC6. This protein is vital for maintaining vascular integrity and plays a complex role in angiogenesis, particularly in its interaction with bone morphogenetic protein 9 (BMP9). In experiments using human umbilical vein endothelial cells (HUVECs), the pro-angiogenic effects of BMP9 were observed, which diminished following the knockdown of HDAC6 and ENG. Western blot analysis revealed that BMP9 treatment increased SMAD1/5/9 phosphorylation, a process hindered by HDAC6 knockdown, correlating with reduced ENG expression. Mechanistically, our study indicates that HDAC6 modulates ENG transcription by influencing promoter activity, leading to increased acetylation of transcription factor SP1 and consequently altering its transcriptional activity. Additionally, the study delves into the structural role of HDAC6, particularly its CD2 domain, in regulating SP1 acetylation and subsequently ENG expression. In conclusion, the present study underscores the critical function of HDAC6 in modulating SP1 acetylation and ENG expression, thereby significantly affecting BMP9-mediated angiogenesis. This finding highlights the potential of HDAC6 as a therapeutic target in angiogenesis-related processes.

Colchicine inhibits the proliferation and promotes the apoptosis of papillary thyroid carcinoma cells likely due to the inhibitory effect on HDAC1

Although the prognosis for papillary thyroid carcinoma (PTC) is generally good, a certain proportion of patients show recurrent or advanced disease, indicating the need for further development of targeted medications. The purpose of this study was to explore the interventional effects of colchicine on PTC and the potential mechanisms or targets. We obtained PTC-related targets from the database and colchicine targets by predicting them. We screened the common targets of colchicine and the PTC-related target histone deacetylase 1 (HDAC1) and verified through molecular docking that colchicine has a good affinity for HDAC1, i.e., colchicine may act on PTC by affecting HDAC1. We then used CCK-8, colony formation, mitochondrial membrane potential and apoptosis assays to confirm that colchicine could inhibit the proliferation and promote the apoptosis of PTC cells and verified by RT‒qPCR, Western blot, and cellular immunofluorescence assays that colchicine could inhibit the expression of HDAC1 in PTC cells. The cytotoxicity and inhibitory effect of colchicine on HDAC1 in PTC cells was stronger than that in normal thyroid cells. We then applied an HDAC1 inhibitor, pyroxamide, to verify that inhibition of HDAC1 inhibits proliferation and promotes apoptosis in PTC cells. Therefore, we conclude that colchicine can inhibit the proliferation and promote the apoptosis of PTC cells likely due to its inhibitory effect on HDAC1. This finding implies that colchicine may be helpful for therapeutic intervention in PTC and that HDAC1 may be a promising clinical therapeutic target.

Damage-mediated macrophage polarization in sterile inflammation

Most of the leading causes of death, such as cardiovascular diseases, cancer, dementia, neurodegenerative diseases, and many more, are associated with sterile inflammation, either as a cause or a consequence of these conditions. The ability to control the progression of inflammation toward tissue resolution before it becomes chronic holds significant clinical potential. During sterile inflammation, the initiation of inflammation occurs through damage-associated molecular patterns (DAMPs) in the absence of pathogen-associated molecules. Macrophages, which are primarily localized in the tissue, play a pivotal role in sensing DAMPs. Furthermore, macrophages can also detect and respond to resolution-associated molecular patterns (RAMPs) and specific pro-resolving mediators (SPMs) during sterile inflammation. Macrophages, being highly adaptable cells, are particularly influenced by changes in the microenvironment. In response to the tissue environment, monocytes, pro-inflammatory macrophages, and pro-resolution macrophages can modulate their differentiation state. Ultimately, DAMP and RAMP-primed macrophages, depending on the predominant subpopulation, regulate the balance between inflammatory and resolving processes. While sterile injury and pathogen-induced reactions may have distinct effects on macrophages, most studies have focused on macrophage responses induced by pathogens. In this review, which emphasizes available human data, we illustrate how macrophages sense these mediators by examining the expression of receptors for DAMPs, RAMPs, and SPMs. We also delve into the signaling pathways induced by DAMPs, RAMPs, and SPMs, which primarily contribute to the regulation of macrophage differentiation from a pro-inflammatory to a pro-resolution phenotype. Understanding the regulatory mechanisms behind the transition between macrophage subtypes can offer insights into manipulating the transition from inflammation to resolution in sterile inflammatory diseases.

TRRAP-mediated acetylation on Sp1 regulates adult neurogenesis

The adult hippocampal neurogenesis plays a vital role in the function of the central nervous system (CNS), including memory consolidation, cognitive flexibility, emotional function, and social behavior. The deficiency of adult neural stem cells (aNSCs) in maintaining the quiescence and entering cell cycle, self-renewal and differentiation capacity is detrimental to the functional integrity of neurons and cognition of the adult brain. Histone acetyltransferase (HAT) and histone deacetylase (HDAC) have been shown to modulate brain functionality and are important for embryonic neurogenesis via regulation of gene transcription. We showed previously that Trrap, an adapter for several HAT complexes, is required for Sp1 transcriptional control of the microtubule dynamics in neuronal cells. Here, we find that Trrap deletion compromises self-renewal and differentiation of aNSCs in mice and in cultures. We find that the acetylation status of lysine residues K16, K19, K703 and K639 all fail to overcome Trrap-deficiency-incurred instability of Sp1, indicating a scaffold role of Trrap. Interestingly, the deacetylation of Sp1 at K639 and K703 greatly increases Sp1 binding to the promoter of target genes, which antagonizes Trrap binding, and thereby elevates Sp1 activity. However, only deacetylated K639 is refractory to Trrap deficiency and corrects the differentiation defects of Trrap-deleted aNSCs. We demonstrate that the acetylation pattern at K639 by HATs dictates the role of Sp1 in the regulation of adult neurogenesis.

FRA1:c-JUN:HDAC1 complex down-regulates filaggrin expression upon TNFα and IFNγ stimulation in keratinocytes

Filaggrin (FLG), an essential structural protein for skin barrier function, is down-regulated under chronic inflammatory conditions, leading to disruption of the skin barrier. However, the detailed molecular mechanisms of how FLG changes in the context of chronic inflammation are poorly understood. Here, we identified the molecular mechanisms by which inflammatory cytokines inhibit FLG expression in the skin. We found that the AP1 response element within the -343/+25 of the FLG promoter was necessary for TNFα + IFNγ-induced down-regulation of FLG promoter activity. Using DNA affinity precipitation assay, we observed that AP1 subunit composition binding to the FLG promoter was altered from c-FOS:c-JUN (at the early time) to FRA1:c-JUN (at the late time) in response to TNFα + IFNγ stimulation. Knockdown of FRA1 or c-JUN abrogated TNFα + IFNγ-induced FLG suppression. Histone deacetylase (HDAC) 1 interacted with FRA1:c-JUN under TNFα + IFNγ stimulation. Knockdown of HDAC1 abrogated the inhibitory effect of TNFα + IFNγ on FLG expression. The altered expression of FLG, FRA1, c-JUN, and HDAC1 was confirmed in mouse models of 2,4-dinitrochlorobenzene-induced atopic dermatitis and imiquimod-induced psoriasis. Thus, the current study demonstrates that TNFα + IFNγ stimulation suppresses FLG expression by promoting the FRA1:c-JUN:HDAC1 complex. This study provides insight into future therapeutic strategies targeting the FRA1:c-JUN:HDAC1 complex to restore impaired FLG expression in chronic skin inflammation.

Transcription factor Sp1 regulates mitotic chromosome assembly and segregation

Aneuploidy is a pervasive feature of cancer cells that results from chromosome missegregation. Several transcription factors have been associated with aneuploidy; however, no studies to date have demonstrated that mammalian transcription factors directly regulate chromosome segregation during mitosis. Here, we demonstrate that the ubiquitously expressed transcription factor specificity protein 1 (Sp1), which we have previously linked to aneuploidy, has a mitosis-specific role regulating chromosome segregation. We find that Sp1 localizes to mitotic centromeres and auxin-induced rapid Sp1 degradation at mitotic onset results in chromosome segregation errors and aberrant mitotic progression. Furthermore, rapid Sp1 degradation results in anomalous mitotic chromosome assembly characterized by loss of condensin complex I localization to mitotic chromosomes and chromosome condensation defects. Consistent with these defects, Sp1 degradation results in reduced chromosome passenger complex activity and histone H3 serine 10 phosphorylation during mitosis, which is essential for condensin complex I recruitment and chromosome condensation. Together, these data provide the first evidence of a mammalian transcription factor acting specifically during mitosis to regulate chromosome segregation.

Lyon IARC Polyomavirus Displays Transforming Activities in Primary Human Cells

Several studies reported the presence of a recently discovered polyomavirus (PyV), Lyon IARC PyV (LIPyV), in human and domestic animal specimens. LIPyV has some structural similarities to well-established animal and human oncogenic PyVs, such as raccoon PyV and Merkel cell PyV (MCPyV), respectively. In this study, we demonstrate that LIPyV early proteins immortalize human foreskin keratinocytes. LIPyV LT binds pRb, accordingly cell cycle checkpoints are altered in primary human fibroblasts and keratinocytes expressing LIPyV early genes. Mutation of the pRb binding site in LT strongly affected the ability of LIPyV ER to induced HFK immortalization. LIPyV LT also binds p53 and alters p53 functions activated by cellular stresses. Finally, LIPyV early proteins activate telomerase reverse transcriptase (hTERT) gene expression, via accumulation of the Sp1 transcription factor. Sp1 recruitment to the hTERT promoter is controlled by its phosphorylation, which is mediated by ERK1 and CDK2. Together, these data highlight the transforming properties of LIPyV in in vitro experimental models, supporting its possible oncogenic nature. IMPORTANCE Lyon IARC PyV is a recently discovered polyomavirus that shows some structural similarities to well-established animal and human oncogenic PyVs, such as raccoon PyV and Merkel cell PyV, respectively. Here, we show the capability of LIPyV to efficiently promote cellular transformation of primary human cells, suggesting a possible oncogenic role of this virus in domestic animals and/or humans. Our study identified a novel virus-mediated mechanism of activation of telomerase reverse transcriptase gene expression, via accumulation of the Sp1 transcription factor. In addition, because the persistence of infection is a key event in virus-mediated carcinogenesis, it will be important to determine whether LIPyV can deregulate immune-related pathways, similarly to the well-established oncogenic viruses.

Histone Deacetylases and Their Potential as Targets to Enhance Tumour Radiosensitisation

In mammalian cells, genomic DNA is packaged with histone proteins and condensed into chromatin. To gain access to the DNA, chromatin remodelling is required that is enhanced through histone post-translational modifications, which subsequently stimulate processes including DNA repair and transcription. Histone acetylation is one of the most well understood modifications and is controlled by histone acetyltransferases (HATs) and histone deacetylases (HDACs). These enzymes play critical roles in normal cellular functioning, and the dysregulation of HDAC expression in particular has been linked with the development of a number of different cancer types. Conversely, tumour cell killing following radiotherapy is triggered through DNA damage and HDACs can help co-ordinate the cellular DNA damage response which promotes radioresistance. Consequently, HDAC inhibitors have been investigated as potential radiosensitizers in vitro and in vivo to improve the efficacy or radiotherapy in specific tumour types. In this review, we provide an up-to-date summary of HDACs and their cellular functions, including in DNA damage repair. We also review evidence demonstrating that HDAC inhibitors can effectively enhance tumour radiosensitisation, and which therefore show potential for translation into the clinic for cancer patient benefit.

Beyond HAT Adaptor: TRRAP Liaisons with Sp1-Mediated Transcription

The members of the phosphatidylinositol 3-kinase-related kinase (PIKK) family play vital roles in multiple biological processes, including DNA damage response, metabolism, cell growth, mRNA decay, and transcription. TRRAP, as the only member lacking the enzymatic activity in this family, is an adaptor protein for several histone acetyltransferase (HAT) complexes and a scaffold protein for multiple transcription factors. TRRAP has been demonstrated to regulate various cellular functions in cell cycle progression, cell stemness maintenance and differentiation, as well as neural homeostasis. TRRAP is known to be an important orchestrator of many molecular machineries in gene transcription by modulating the activity of some key transcription factors, including E2F1, c-Myc, p53, and recently, Sp1. This review summarizes the biological and biochemical studies on the action mode of TRRAP together with the transcription factors, focusing on how TRRAP-HAT mediates the transactivation of Sp1-governing biological processes, including neurodegeneration.

Deacetylated Sp1 improves β-glycerophosphate-induced calcification in vascular smooth muscle cells

The aging of the population has led to an annual increase in the incidence of vascular calcification (VC). Specific protein 1 (Sp1) is a transcriptional activator that serves an important role in VC. The deacetylation of transcription factors represses their binding to the promoters of downstream genes, thereby causing their downregulation. The present study aimed to investigate the role of deacetylated Sp1 in the development of VC. In the present study, western blotting and immunoprecipitation (IP) were performed to detect the protein levels of acetylated Sp1. Western blotting and immunofluorescence staining were used to analyze phenotypic switching in vascular smooth muscle cells (VSMCs). Alizarin red S, alkaline phosphatase (ALP) activity and calcium content assays were used to assess calcium deposition in VSMCs. Western blotting, flow cytometry, TUNEL staining and caspase3 activity assay were used to evaluate apoptosis of VSMCs. Chromatin immunoprecipitation (ChIP) assay was used to detect Sp1 binding to the BMP2 promoter. The results indicated that, in a β-glycerophosphate (β-GP)-induced VSMC calcification model, the level of acetylated Sp1 was increased. Western blotting and immunofluorescence staining results showed that, compared with the Sp1 overexpression group (Sp1-WT), deacetylated Sp1 (Sp1-K704A) downregulated the expression of osteogenic markers runt-related transcription factor 2 (Runx2) and bone morphogenetic protein 2 (BMP2), and upregulated the expression of contraction marker α-smooth muscle actin (α-SMA) and calponin 1. In addition, deacetylated Sp1 also reduced the ALP activity and calcium content of calcified VSMCs, and the Alizarin red S assay revealed that the calcium crystallization of Sp1-K704A group was markedly decreased. Western blotting, flow cytometry, TUNEL staining and caspase-3 activity assay were detected to indicate that the B-cell lymphoma 2 (Bcl-2)/Bcl-2-associated X protein ratio was increased, and caspase-3 activity and the apoptotic rate of VSMCs were decreased, in the Sp1-K704A group, as compared with the Sp1-WT group. ChIP assay revealed that Sp1 binding to the BMP2 promoter was downregulated in the Sp1-K704A group, compared with that in theSp1-WT group. In conclusion, a deacetylated mutant of Sp1 decreased Sp1 binding to the BMP2 promoter, thus decreasing apoptosis, phenotypic switching and calcium deposition in calcified VSMCs. This finding may indicate potential therapeutic targets for VC.

Selective inhibition of HDAC6 regulates expression of the oncogenic driver EWSR1-FLI1 through the EWSR1 promoter in Ewing sarcoma

Ewing sarcoma (EWS) is an aggressive bone and soft tissue tumor of children and young adults in which the principal driver is a fusion gene, EWSR1-FLI1. Although the essential role of EWSR1-FLI1 protein in the regulation of oncogenesis, survival, and tumor progression processes has been described in-depth, little is known about the regulation of chimeric fusion-gene expression. Here, we demonstrate that the active nuclear HDAC6 in EWS modulates the acetylation status of specificity protein 1 (SP1), consequently regulating the SP1/P300 activator complex binding to EWSR1 and EWSR1-FLI1 promoters. Selective inhibition of HDAC6 impairs binding of the activator complex SP1/P300, thereby inducing EWSR1-FLI1 downregulation and significantly reducing its oncogenic functions. In addition, sensitivity of EWS cell lines to HDAC6 inhibition is higher than other tumor or non-tumor cell lines. High expression of HDAC6 in primary EWS tumor samples from patients correlates with a poor prognosis in two independent series accounting 279 patients. Notably, a combination treatment of a selective HDAC6 and doxorubicin (a DNA damage agent used as a standard therapy of EWS patients) dramatically inhibits tumor growth in two EWS murine xenograft models. These results could lead to suitable and promising therapeutic alternatives for patients with EWS.

Treatment with 2-methoxyestradiol increases endothelial nitric oxide synthase activity via scavenger receptor class BI in human umbilical vein endothelial cells

Concentrations of 2-methoxyestradiol (2ME2), a principal metabolite of estradiol, are significantly lower in women with severe preeclampsia. Nitric oxide (NO) released by endothelial nitric oxide synthase (eNOS) plays an important role in regulating cardiovascular homeostasis. Importantly, high-density lipoprotein (HDL) stimulates eNOS activity via endothelial human scavenger receptor class B type I (hSR-BI/CLA-1). Here, we aimed to determine the effect of 2ME2 on hSR-BI/CLA-1 expression in human umbilical vein endothelial cells (HUVECs). hSR-BI/CLA-1 expression was measured by real-time PCR, western blotting and reporter gene assays; eNOS activity was assessed by the measurement of eNOS phosphorylation. Both the mRNA and protein concentrations of hSR-BI/CLA-1 were significantly increased by 2ME2 in HUVECs. 2ME2 also dose-dependently increased the transcriptional activity of the hSR-BI/CLA-1 promoter. The effect of 2ME2 treatment on the promoter activity of hSR-BI/CLA-1 was abrogated by treatment with LY294002, a specific inhibitor of phosphatidylinositol 3-kinase, as was the increase in HDL-induced eNOS activation. Notably, constitutively active Akt increased the activity of the hSR-BI/CLA-1 promoter, whereas dominant-negative Akt abolished the effect of 2ME2 treatment on hSR-BI/CLA-1 promoter activity. The nuclear Sp1 protein concentration was significantly increased by exposure to 2ME2 and Sp1 overexpression increased the promoter activity of the hSR-BI/CLA gene. Furthermore, knockdown of Sp1 inhibited the effect of 2ME2 treatment on hSR-BI/CLA-1 protein expression. These results indicate that 2ME2 treatment increases HDL-dependent eNOS phosphorylation by upregulating endothelial hSR-BI/CLA-1 expression, suggesting that 2ME2 has a potential therapeutic value in the treatment of preeclampsia.

Promoter G-quadruplex favours epigenetic reprogramming-induced atypical expression of ZEB1 in cancer cells

BACKGROUND

Aberrant expression of Zinc-finger E-box binding homeobox 1 (ZEB1), which remains repressed in normal cells, is frequently associated with cancer aggressiveness. However, transcriptional mechanism underlying such atypical ZEB1 expression in cancer is not yet well-understood.

METHODS

ZEB1 promoter G-quadruplexes were studied and modeled extensively using circular dichroism, fluorescence spectroscopy, ITC and DMS protection assay. Luciferase assay, qPCR, FAIRE, ChIP, western blotting, confocal microscopy was used to access the regulation of ZEB1 transcription.

RESULTS

Our study unravels the occupancy of nucleolin to ZEB1 promoter as a crucial determinant which facilitates the binding of SP1 transcription factor to chromatin, by locally remodelling the region. SP1, subsequently, recruits P300 acetyl transferase leading to enriched acetyl-histone H3 at promoter and activates ZEB1 transcription. ZEB1 promoter analysis identifies presence of four putative G-quadruplex (G4) forming motifs within 700 bp of TSS; each quadruplex is characterized structurally in details with an array of biophysical techniques. Surprisingly, stabilization of G4 with cationic porphyrin TMPyP4 represses its transcription and eventually impedes cell invasiveness.

CONCLUSIONS

TMPyP4 binding to a selected G4 motif (5' -534/-511-3' from TSS), where nucleolin/SP1/P300 co-occupies, prevents the association of nucleolin which consequently hinders SP1 binding, leading to chromatin compactness and transcriptional repression.

GENERAL SIGNIFICANCE

Our findings demonstrate an epigenetic mechanism of ZEB1 reactivation where dynamic occupancy of transcription regulators encompassing a G4 motif is crucial and thus, small molecule induced G-quadruplex stabilization may act as a potential molecular switch to turn-off gene expression.

Increased activation of HDAC1/2/6 and Sp1 underlies therapeutic resistance and tumor growth in glioblastoma

BACKGROUND

Glioblastoma is associated with poor prognosis and high mortality. Although the use of first-line temozolomide can reduce tumor growth, therapy-induced stress drives stem cells out of quiescence, leading to chemoresistance and glioblastoma recurrence. The specificity protein 1 (Sp1) transcription factor is known to protect glioblastoma cells against temozolomide; however, how tumor cells hijack this factor to gain resistance to therapy is not known.

METHODS

Sp1 acetylation in temozolomide-resistant cells and stemlike tumorspheres was analyzed by immunoprecipitation and immunoblotting experiments. Effects of the histone deacetylase (HDAC)/Sp1 axis on malignant growth were examined using cell proliferation-related assays and in vivo experiments. Furthermore, integrative analysis of gene expression with chromatin immunoprecipitation sequencing and the recurrent glioblastoma omics data were also used to further determine the target genes of the HDAC/Sp1 axis.

RESULTS

We identified Sp1 as a novel substrate of HDAC6, and observed that the HDAC1/2/6/Sp1 pathway promotes self-renewal of malignancy by upregulating B cell-specific Mo-MLV integration site 1 (BMI1) and human telomerase reverse transcriptase (hTERT), as well as by regulating G2/M progression and DNA repair via alteration of the transcription of various genes. Importantly, HDAC1/2/6/Sp1 activation is associated with poor clinical outcome in both glioblastoma and low-grade gliomas. However, treatment with azaindolyl sulfonamide, a potent HDAC6 inhibitor with partial efficacy against HDAC1/2, induced G2/M arrest and senescence in both temozolomide-resistant cells and stemlike tumorspheres.

CONCLUSION

Our study uncovers a previously unknown regulatory mechanism in which the HDAC6/Sp1 axis induces cell division and maintains the stem cell population to fuel tumor growth and therapeutic resistance.

Suppression of complement component 2 expression by hepatitis B virus contributes to the viral persistence in chronic hepatitis B patients

Previously, we identified rare missense mutations of complement component 2 (C2) to be associated with chronic hepatitis B (CHB) by exome sequencing. However, up to now, little is known about the role of C2 in CHB. In the present study, we aimed to perform preliminary exploration about the underlying role of C2 in CHB. Serum samples from 113 CHB patients and 30 healthy controls, and liver biopsy samples from 5 CHB patients and 3 healthy controls were obtained from the Third Affiliated Hospital of Sun Yat-sen University between January 2018 and January 2020. HepG2.2.15 and HepG2-NTCP cells infected with HBV were used to examine the influence of HBV infection on C2 expression. IFN-treated HepG2.2.15 cells were used to assess the effect of IFN on C2 expression. C2-overexpressing or C2-silencing HepG2.2.15 cells were constructed to evaluate the effect of C2 on HBV infection. Western blot and RT-qPCR were used to measure C2 expression in biopsy samples. HBeAg and HBsAg in culture medium and C2 of serum samples were measured by ELISA. HBV-DNA was measured by RT-qPCR. GSE84044, GSE54747 and GSE27555 were downloaded from GEO. C2 expression in liver tissue and serum was significantly lower in CHB patients compared to healthy controls, and significantly higher C2 expression was found in CHB patients with lower ALT, AST, Scheuer grade and stages compared to CHB patients with higher ALT, AST, Scheuer grades and Scheuer stage. Besides, HBV infection could decrease C2 expression by increasing expression of Sp1 and reducing expression of HDAC4. Moreover, C2 could enhance the anti-virus effect of IFN on HepG2.2.15 cells and also inhibit HBV replication in HepG2.2.15 cells by inhibition of p38-MAPK signalling pathway. In conclusion, HBV may promote viral persistence in CHB patients by inhibiting C2 expression.

cAMP regulates 11β-hydroxysteroid dehydrogenase-2 and Sp1 expression in MLO-Y4/MC3T3-E1 cells

11β-hydroxysteroid dehydrogenase-2 (11β-HSD2) is one of the key enzymes in glucocorticoid metabolism, which can inactivate local corticosterone and regulate the level of active glucocorticoid in tissues. The expression of 11β-HSD2 and its regulatory pathway serve an important role in the apoptosis of steroid induced osteonecrosis of the femoral head (SANFH). The present study aimed to identify the regulatory effects of cAMP on the expression of Sp1 transcription factor (Sp1) and 11β-HSD2 in osteocytes at the cellular level. Murine long bone osteocyte Y4 (MLO-Y4) clone cells and mouse embryo osteoblast-like (MC3T3-E1) cells were cultured in vitro with adenylate cyclase activator or inhibitor (forskolin and SQ22536, respectively) to investigate the effects of alterations to intracellular cAMP levels. mRNA and protein expression levels of Sp1 and 11β-HSD2 were detected by reverse transcription-quantitative PCR and western blotting, respectively. Compared with the negative control group, the mRNA and protein expression levels of Sp1 were significantly increased in the activation group, whereas Sp1 expression levels were significantly decreased in the inhibition group. Similarly, compared with the negative control group, the mRNA and protein expression levels of 11β-HSD2 were significantly increased in the activator group, but significantly decreased in the inhibitor group. The aforementioned results indicated that intracellular cAMP levels significantly regulated the expression of Sp1 and 11β-HSD2 in mouse osteocytes and osteoblasts. Therefore, the present study suggested a potential therapeutic strategy for the prevention of osteonecrosis of the femoral head.

Intrauterine RAS programming alteration-mediated susceptibility and heritability of temporal lobe epilepsy in male offspring rats induced by prenatal dexamethasone exposure

Partial temporal lobe epilepsy (TLE) has an intrauterine developmental origin. This study was aimed at elucidating the heritable effects and programming mechanism of TLE in offspring rats induced by prenatal dexamethasone exposure (PDE). Pregnant Wistar rats were injected subcutaneously with dexamethasone (0.2 mg/kg day) from gestational day 9 to 20. The F1 and F2 generations of male offspring were administered lithium pilocarpine (LiPC) for electroencephalography and video monitoring in epilepsy or behavioral tests. Results showed that the PDE + LiPC group exhibited TLE susceptibility, which continued throughout F2 generation. Expression of hippocampal glucocorticoid receptor (GR), CCAAT enhancer-binding protein α (C/EBPα), intrauterine renin-angiotensin system (RAS) classical pathway related genes, the H3K27ac level in angiotensin-converting enzyme (ACE) promoter, as well as high mobility group box 1 (HMGB1) and toll-like receptor 4 (TLR4) were increased, but glutamate dehydrogenase (GLUD) 1/2 expression were decreased, accompanied by increased glutamate levels in PDE fetal and adult rats, as well as in F1 and F2 offspring of the PDE + LiPC group. These consistent changes were also observed by treating the H19-7 fetal hippocampal cell line with dexamethasone and were reversed by GR inhibitor (RU486) and ACE inhibitor (enalaprilat). Our results confirmed that PDE-induced H3K27ac enrichment in the ACE promoter and enhanced the RAS classic pathway via activating GR-C/EBPα-p300 in utero, which caused changes of the HMGB1 pathway and glutamate excitatory damage. Intrauterine programming mediated by abnormal histone modification of hippocampal ACE could continue to adulthood and even F2 generation, which induced the heritability of TLE in male offspring rats.

Sp1 participates in the cadmium-induced imbalance of the placental glucocorticoid barrier by suppressing 11β-HSD2 expression

Cadmium (Cd) is widely present in the environment as a heavy metal poison. Prenatal Cd exposure can damage the placental glucocorticoid barrier, leading to foetal growth restriction (FGR), but the molecular mechanism is unknown. We aimed to study the effects of prenatal Cd exposure on 11β-HSD2 and its possible involvement in Cd induced damage in the placental glucocorticoid barrier. Pregnant rats were treated with CdCl2 (1.0 mg/kg/day) by gavage from gestational day (GD) 9-19. Maternal exposure to Cd increased the FGR rate of the offspring, and the levels of corticosterone in the placenta, maternal and foetal serum. Further in vitro experiments with placenta or JEG3 cells indicated that Cd was able to decrease 11β-HSD2 and Sp1 expression in trophoblast cells but did not affect 11β-HSD1. Additionally, decreased p300 and Sp1 enrichment at the 11β-HSD2 promoter region was observed in the cells treated with Cd. Decreasing or increasing Sp1 expression accordingly inhibited or promoted the expression of 11β-HSD2 and further decreased or increased p300 and Sp1 enrichment at the 11β-HSD2 promoter region. In conclusion, Cd inhibits the expression of 11β-HSD2 by affecting the binding of p300 to 11β-HSD2 via a decrease in Sp1 expression, which damages the placental glucocorticoid barrier and exposes the foetus to excessive glucocorticoids, resulting in FGR. These findings reveal a possible underlying molecular mechanism by which Cd exposure leads to FGR.

The transcription factor Sp1 modulates RNA polymerase III gene transcription by controlling BRF1 and GTF3C2 expression in human cells

Specificity protein 1 (Sp1) is an important transcription factor implicated in numerous cellular processes. However, whether Sp1 is involved in the regulation of RNA polymerase III (Pol III)-directed gene transcription in human cells remains unknown. Here, we first show that filamin A (FLNA) represses Sp1 expression as well as expression of TFIIB-related factor 1 (BRF1) and general transcription factor III C subunit 2 (GTF3C2) in HeLa, 293T, and SaOS2 cell lines stably expressing FLNA-silencing shRNAs. Both BRF1 promoter 4 (BRF1P4) and GTF3C2 promoter 2 (GTF3C2P2) contain putative Sp1-binding sites, suggesting that Sp1 affects Pol III gene transcription by regulating BRF1 and GTF3C2 expression. We demonstrate that Sp1 knockdown inhibits Pol III gene transcription, BRF1 and GTF3C2 expression, and the proliferation of 293T and HeLa cells, whereas Sp1 overexpression enhances these activities. We obtained a comparable result in a cell line in which both FLNA and Sp1 were depleted. These results indicate that Sp1 is involved in the regulation of Pol III gene transcription independently of FLNA expression. Reporter gene assays showed that alteration of Sp1 expression affects BRF1P4 and GTF3C2P2 activation, suggesting that Sp1 modulates Pol III-mediated gene transcription by controlling BRF1 and GTF3C2 gene expression. Further analysis revealed that Sp1 interacts with and thereby promotes the occupancies of TATA box-binding protein, TFIIAα, and p300 at both BRF1P4 and GTF3C2P2. These findings indicate that Sp1 controls Pol III-directed transcription and shed light on how Sp1 regulates cancer cell proliferation.

Reciprocal Role Of DNA Methylation And Sp1 Binding In Ki-67 Gene Transcription

Purpose

DNA methylation plays major regulatory roles in gene transcription. Our previous studies confirmed that Ki-67 promoter is hypomethylated and Sp1 is a transcriptional activator of Ki-67 gene in cancer cells. However, whether Sp1-mediated transcriptional activation of Ki-67 is related to its methylation has not been studied yet.

Materials and methods

In this study, we confirmed that methylated CpG binding protein 2 (MBD2) binding to methylated DNA hindered the binding of Sp1 to Ki-67 promoter and then repressed Ki-67 transcription through chromatin immunoprecipitation (ChIP) and quantitative real-time PCR (qRT-PCR). Co-immunoprecipitation (Co-IP), ChIP, methylation-specific PCR (MS-PCR) and Western blot were utilized to analyze the effects of Sp1 binding to Ki-67 promoter on its methylation status.

Results

Less DNA methyltransferase 1 (DNMT1) bound to the Ki-67 promoter in MKN45 cells than in HK-2 cells. Histone acetyltransferase p300 that was recruited by Sp1 to Ki-67 promoter could attenuate the methylation level of Ki-67 promoter. Furthermore, higher expression of Sp1 and Ki-67 was related to the overall survival (OS), first progression (FP) and post-progression survival (PPS) in gastric cancer by scrutinizing bioinformatics datasets.

Conclusion

Taken together, our findings suggested that hypomethylation of Ki-67 promoter enhanced the binding of Sp1, which in turn maintained hypomethylation of promoter, leading to increase Ki-67 expression in cancer cells. Sp1 and Ki-67 could act promising prognostic biomarkers for clinical diagnosis and treatment of cancer.

MKK7 transcription positively or negatively regulated by SP1 and KLF5 depends on HDAC4 activity in glioma

JNK activity has been implicated in the malignant proliferation, invasion and drug-resistance of glioma cells (GCs), but the molecular mechanisms underlying JNK activation are currently unknown. Here, we reported that MKK7, not MKK4, directly activates JNK in GCs and exerts oncogenic effects on tumor formation. Notably, MKK7 expression in glioma tissues was closely correlated with the grade of the glioma and JNK/c-Jun activation. Mechanistically, MKK7 transcription critically depends on the complexes formed by HDAC4 and the transcriptional factors SP1 and Krüppel-like factor-5 (KLF5), wherein HDAC4 directly deacetylates both SP1 and KLF5 and synergistically upregulates MKK7 transcription through two SP1 sites located on its promoter. In contrast, the increases in acetylated-SP1 and acetylated-KLF5 after HDAC4 inhibition switched to transcriptionally suppress MKK7. Selective inhibition of HDAC4 by LMK235, siRNAs or blockage of SP1 and KLF5 by the ectopic dominant-negative SP1 greatly reduced the malignant capacity of GCs. Furthermore, suppression of both MKK7 expression and JNK/c-Jun activities was involved in the tumor-growth inhibitory effects induced by LMK235 in U87-xenograft mice. Interestingly, HDAC4 is highly expressed in glioma tissues, and the rate of HDAC4 nuclear import is closely correlated with glioma grade, as well as with MKK7 expression. Collectively, these findings demonstrated that highly expressed MKK7 contributes to JNK/c-Jun signaling-mediated glioma formation. MKK7 transcription, regulated by SP1 and KLF5, critically depends on HDAC4 activity, and inhibition of HDAC4 presents a potential strategy for suppressing the oncogenic roles of MKK7/JNK/c-Jun signaling in GCs.

Tributyrin Inhibits Ethanol-Induced Epigenetic Repression of CPT-1A and Attenuates Hepatic Steatosis and Injury

Ethanol-mediated down-regulation of carnitine palmitoyltransferase-1 (CPT-1A) gene expression plays a major role in the development of hepatic steatosis; however, the underlying mechanisms are not completely elucidated. Tributyrin, a butyrate prodrug that can inhibit histone deacetylase (HDAC) activity, attenuates hepatic steatosis and injury. The present study examined the beneficial effect of tributyrin/butyrate in attenuating ethanol-induced pathogenic epigenetic mechanisms affecting CPT-1A promoter-histone modifications and gene expression and hepatic steatosis/injury.

METHODS

Mice were fed a liquid Lieber-DeCarli diet (Research Diet Inc, New Brunswick, NJ) with or without ethanol for 4 weeks. In a subset of mice, tributyrin (2 g/kg) was administered orally by gavage. Primary rat hepatocytes were treated with 50 mmol/L ethanol and/or 2 mmol/L butyrate. Gene expression and epigenetic modifications at the CPT-1A promoter were analyzed by chromatin immunoprecipitation analysis.

RESULTS

In vivo, ethanol induced hepatic CPT-1A promoter histone H3K9 deacetylation, which is indicative of a repressive chromatin state, and decreased CPT-1A gene expression. Our data identified HDAC1 as the predominant HDAC causing CPT-1A promoter histone H3K9 deacetylation and epigenetic down-regulation of gene expression. Significantly, Specificity Protein 1 (SP1) and Hepatocyte Nuclear Factor 4 Alpha (HNF4α) participated in the recruitment of HDAC1 to the proximal and distal regions of CPT-1A promoter, respectively, and mediated transcriptional repression. Importantly, butyrate, a dietary HDAC inhibitor, attenuated ethanol-induced recruitment of HDAC1 and facilitated p300-HAT binding by enabling SP1/p300 interaction at the proximal region and HNF4α/peroxisomal proliferator-activated receptor-γ coactivator-1α/p300 interactions at the distal region, leading to promoter histone acetylation and enhanced CPT-1A transcription.

CONCLUSIONS

This study identifies HDAC1-mediated repressive epigenetic mechanisms that underlie an ethanol-mediated decrease in CPT-1A expression. Importantly, tributyrin/butyrate inhibits HDAC1, rescues CPT-1A expression, and attenuates ethanol-mediated hepatic steatosis and injury, suggesting its potential use in therapeutic strategies for alcoholic liver disease.

Elevated histone H3 acetylation and loss of the Sp1-HDAC1 complex de-repress the GM2-synthase gene in renal cell carcinoma

GM2-synthase produces sialic acid-containing glycosphingolipids called gangliosides, and its mRNA overexpression and the gangliosides it generates are linked to tumor progression, migration, and suppression of tumor-specific host immune responses. However, the mechanism underlying GM2-synthase de-repression in renal cell carcinoma (RCC) is poorly understood. Here, we demonstrate that higher GM2-synthase mRNA expression levels in various cancer cells and in human RCC tumors correlate with higher histone acetylation levels (H3K9, H3K14, or both) at region +38/+187 relative to the transcription start site (TSS) of the GM2-synthase gene than in normal kidney epithelial (NKE) cells or healthy adjacent tissues. An increase in GM2-synthase mRNA expression in cells treated with a histone deacetylase (HDAC) inhibitor was accompanied by increased histone acetylation levels at this promoter region. DNA methylation around the TSS was absent in both RCC cell lines and NKE cells. Of note, both the transcription factor Sp1 and corepressor HDAC1 associated with the +38/+187 region when the GM2-synthase gene was repressed in NKE and tumor-adjacent tissues, indicating plausible site-specific repressive roles of HDAC1 and Sp1 in GM2-synthase mRNA expression. Site-directed mutagenesis of the Sp1-binding site within the +38/+187 region relieved repressed luciferase activity of this region by limiting HDAC1 recruitment. Moreover, Sp1 or HDAC1 knock down increased GM2-synthase transcription, and butyrate-mediated activation of GM2-synthase mRNA expression in SK-RC-45 cells was accompanied by Sp1 and HDAC1 loss from the +38/+187 region. Taken together, we have identified an epigenetic mechanism for the de-repression of the GM2-synthase gene in RCC.

Silencing of Transcription Factor Sp1 Promotes SN1 Transporter Regulation by Ammonia in Mouse Cortical Astrocytes

The involvement of the astrocytic SN1 (SNAT3) transporter in ammonia-induced l-glutamine retention was recently documented in mouse-cultured astrocytes. Here we investigated the involvement of specificity protein 1 (Sp1) transcription factor in SN1 regulation in ammonium chloride (“ammonia”)-treated astrocytes. Sp1 expression and its cellular localization were determined using real-time qPCR, Western blot, and confocal microscopy. Sp1 binding to Snat3 promoter was analyzed by chromatin immunoprecipitation. The role of Sp1 in SN1 expression and SN1-mediated [³H]glutamine uptake in ammonia-treated astrocytes was verified using siRNA and mithramycin A. The involvement of protein kinase C (PKC) isoforms in Sp1 level/phosphorylation status was verified using siRNA technology. Sp1 translocation to the nuclei and its enhanced binding to the Snat3 promoter, along with Sp1 dependence of system N-mediated [³H]glutamine uptake, were observed in astrocytes upon ammonia exposure. Ammonia decreased the level of phosphorylated Sp1, and the effect was reinforced by long-term incubation with PKC modulator, phorbol 12-myristate 13-acetate, which is a treatment likely to dephosphorylate Sp1. Furthermore, silencing of the PKCδ isoform appears to enhance the ammonia effect on the Sp1 level. Collectively, the results demonstrate the regulatory role of Sp1 in regulation of SN1 expression and activity in ammonia-treated astrocytes and implicate altered Sp1 phosphorylation status in this capacity.

Epigenetic Study in Parkinson's Disease: A Pilot Analysis of DNA Methylation in Candidate Genes in Brain

Efforts have been made to understand the pathophysiology of Parkinson’s disease (PD). A significant number of studies have focused on genetics, despite the fact that the described pathogenic mutations have been observed only in around 10% of patients; this observation supports the fact that PD is a multifactorial disorder. Lately, differences in miRNA expression, histone modification, and DNA methylation levels have been described, highlighting the importance of epigenetic factors in PD etiology. Taking all this into consideration, we hypothesized that an alteration in the level of methylation in PD-related genes could be related to disease pathogenesis, possibly due to alterations in gene expression. After analysing promoter regions of five PD-related genes in three brain regions by pyrosequencing, we observed some differences in DNA methylation levels (hypo and hypermethylation) in substantia nigra in some CpG dinucleotides that, possibly through an alteration in Sp1 binding, could alter their expression.

Inhibition of HDACs-EphA2 Signaling Axis with WW437 Demonstrates Promising Preclinical Antitumor Activity in Breast Cancer

Histone deacetylase inhibitors (HDACi) are small molecules targeting epigenetic enzymes approved for hematologic neoplasms, which have also demonstrated clinical activities in solid tumors. In our present study, we screened our internal compound library and discovered a novel HDACi, WW437, with potent anti-breast cancer ability in vitro and in vivo. WW437 significantly inhibited phosphorylated EphA2 and EphA2 expression. Further study demonstrated WW437 blocked HDACs-EphA2 signaling axis in breast cancer. In parallel, we found that EphA2 expression positively correlates with breast cancer progression; and combined use of WW437 and an EphA2 inhibitor (ALW-II-41-27) exerted more remarkable effect on breast cancer growth than either drug alone. Our findings suggested inhibition of HDACs-EphA2 signaling axis with WW437 alone or in combination with other agents may be a promising therapeutic strategy for advanced breast cancer.

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WW437 is a novel HDACi, which displays potent anticancer activity in breast cancer.

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HDACs-EphA2 signaling axis represents a novel target in breast cancer.

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WW437 is a promising therapeutic agent for advanced breast cancer, alone or in combination with EphA2 inhibitor.

Histone deacetylase inhibitors (HDACi) are small molecules targeting epigenetic enzymes approved for cutaneous T-cell lymphoma (CTCL), peripheral T-cell lymphoma (PTCL) and multiple myeloma (MM) treatment, which have also demonstrated clinical activities in solid tumors, including lung cancer and breast cancer. Herein we report a novel HDACi WW437, which displays potent anticancer activity in both cultured cancer cells and xenograft models. Importantly, our work reveals WW437 significantly blocked the HDACs-EphA2 signaling axis in breast cancer. WW437 exhibited significant inhibitory effects on tumor growth and metastases with little toxicity, and tumors from treated mice showed decreased EphA2 expression, suggesting that EphA2 may be a useful biomarker of response to WW437. We also found that EphA2 expression positively correlates with tumor progression in aggressive breast cancer.

Two intrauterine programming mechanisms of adult hypercholesterolemia induced by prenatal nicotine exposure in male offspring rats

Epidemiologic studies showed that low birth weight is associated with high cholesterol and an increased risk of cardiovascular diseases in adulthood. This study aimed to elucidate the intrauterine programming mechanisms of adult hypercholesterolemia. The results showed that prenatal nicotine exposure (PNE) caused intrauterine growth retardation and hypercholesterolemia in male adult offspring rats. Hepatic cholesterol synthesis and output were deceased in utero but increased in adults; hepatic reverse cholesterol transport (RCT) persistently deceased before and after birth. Meanwhile, PNE elevated serum corticosterone level and decreased hepatic IGF1 pathway activity in male fetuses, whereas converse changes were observed in male adults. The chronic stress model and cortisol-treated HepG2 cells verified that excessive glucocorticoid (GC)-induced GC-IGF1 axis programming enhanced hepatic cholesterol synthesis and output. In addition, PNE decreased the expression of specific protein 1 and P300 enrichment and H3K27 acetylation at the promoter region of genes responsible for RCT both in fetal and adult, male livers and reduced expression of those genes, similar alterations were also confirmed in cortisol-treated HepG2 cells, suggesting that excessive GC-related programming induced continuous RCT reduction by epigenetic modification. Taken together, the "2-programming" approach discussed above may ultimately contribute to the development of hypercholesterolemia in male adult offspring.-Zhou, J., Zhu, C., Luo, H., Shen, L., Gong, J., Wu, Y., Magdalou, J., Chen, L., Guo, Y., Wang, H. Two intrauterine programming mechanisms of adult hypercholesterolemia induced by prenatal nicotine exposure in male offspring rats.

The interferon-stimulated gene TRIM22: A double-edged sword in HIV-1 infection

Infection of target cells by the human immunodeficiency virus type-1 (HIV-1) is hampered by constitutively expressed host cell proteins preventing or curtailing virus replication and therefore defined as "restriction factors". Among them, members of the tripartite motif (TRIM) family have emerged as important players endowed with both antiviral effects and modulatory capacity of the innate immune response. TRIM5α and TRIM19 (i.e. promyelocytic leukemia, PML) are among the best-characterized family members; however, in this review we will focus on the potential role of another family member, i.e. TRIM22, a factor strongly induced by interferon stimulation, in HIV infection in vivo and in vitro in the context of its broader antiviral effects. We will also focus on the potential role of TRIM22 in HIV-1-infected individuals speculating on its dual role in controlling virus replication and more complex role in chronic infection. At the molecular levels, we will review the evidence in favor of a relevant role of TRIM22 as epigenetic inhibitor of HIV-1 transcription acting by preventing the binding of the host cell transcription factor Sp1 to the viral promoter. These evidences suggest that TRIM22 should be considered a potential new player in either the establishment or maintenance of HIV-1 reservoirs of latently infected cells unaffected by combination antiretroviral therapy.

Lysine Acetylation Goes Global: From Epigenetics to Metabolism and Therapeutics

Post-translational acetylation of lysine residues has emerged as a key regulatory mechanism in all eukaryotic organisms. Originally discovered in 1963 as a unique modification of histones, acetylation marks are now found on thousands of nonhistone proteins located in virtually every cellular compartment. Here we summarize key findings in the field of protein acetylation over the past 20 years with a focus on recent discoveries in nuclear, cytoplasmic, and mitochondrial compartments. Collectively, these findings have elevated protein acetylation as a major post-translational modification, underscoring its physiological relevance in gene regulation, cell signaling, metabolism, and disease.

TIP60 represses telomerase expression by inhibiting Sp1 binding to the TERT promoter

HIV1-TAT interactive protein (TIP60) is a haploinsufficient tumor suppressor. However, the potential mechanisms endowing its tumor suppressor ability remain incompletely understood. It plays a vital role in virus-induced cancers where TIP60 down-regulates the expression of human papillomavirus (HPV) oncoprotein E6 which in turn destabilizes TIP60. This intrigued us to identify the role of TIP60, in the context of a viral infection, where it is targeted by oncoproteins. Through an array of molecular biology techniques such as Chromatin immunoprecipitation, expression analysis and mass spectrometry, we establish the hitherto unknown role of TIP60 in repressing the expression of the catalytic subunit of the human telomerase complex, TERT, a key driver for immortalization. TIP60 acetylates Sp1 at K639, thus inhibiting Sp1 binding to the TERT promoter. We identified that TIP60-mediated growth suppression of HPV-induced cervical cancer is mediated in part due to TERT repression through Sp1 acetylation. In summary, our study has identified a novel substrate for TIP60 catalytic activity and a unique repressive mechanism acting at the TERT promoter in virus-induced malignancies.

Stimulation of Pol III-dependent 5S rRNA and U6 snRNA gene expression by AP-1 transcription factors

RNA polymerase III transcribes structurally diverse group of essential noncoding RNAs including 5S ribosomal RNA (5SrRNA) and U6 snRNA. These noncoding RNAs are involved in RNA processing and ribosome biogenesis, thus, coupling Pol III activity to the rate of protein synthesis, cell growth, and proliferation. Even though a few Pol II-associated transcription factors have been reported to participate in Pol III-dependent transcription, its activation by activator protein 1 (AP-1) factors, c-Fos and c-Jun, has remained unexplored. Here, we show that c-Fos and c-Jun bind to specific sites in the regulatory regions of 5S rRNA (type I) and U6 snRNA (type III) gene promoters and stimulate their transcription. Our chromatin immunoprecipitation studies suggested that endogenous AP-1 factors bind to their cognate promoter elements during the G1/S transition of cell cycle apparently synchronous with Pol III transcriptional activity. Furthermore, the interaction of c-Jun with histone acetyltransferase p300 promoted the recruitment of p300/CBP complex on the promoters and facilitated the occupancy of Pol III transcriptional machinery via histone acetylation and chromatin remodeling. The findings of our study, together, suggest that AP-1 factors are novel regulators of Pol III-driven 5S rRNA and U6 snRNA expression with a potential role in cell proliferation.

Specificity protein 1: Its role in colorectal cancer progression and metastasis

Specificity protein 1 (Sp1) is a widely expressed transcription factor that plays an important role in the promotion of oncogenes required for tumor survival, progression and metastasis. Sp1 is highly expressed in several cancers including colorectal cancer (CRC) and is related to poor prognosis. Therefore, targeting Sp1 is a rational for CRC therapy. In this review, we will recapitulate the current understanding of Sp1 signaling, its molecular mechanisms, and its potential involvement in CRC growth, progression and metastasis. We will also discuss the current therapeutic drugs for CRC and their mechanism of action via Sp1.

The cellular senescence of leukemia-initiating cells from acute lymphoblastic leukemia is postponed by β-Arrestin1 binding with P300-Sp1 to regulate hTERT transcription

Although we previously reported that the self-renewal of leukemia-initiating cells of B-lineage acute lymphoblastic leukemia (B-ALL LICs) was regulated by β-Arrestin1, a multiple-function protein, the cellular senescence is critical for LICs fate and leukemia progress, and worthy for further investigation. Here we found that depletion of β-Arrestin1 extended the population doubling time and the percentage of senile cells, the signatures of cellular senescence, of B-ALL LICs. Moreover, lack of β-Arrestin1 enhanced the expression of proteins (CBX, HIRA) and genes (P53, P16) related to senescence in leukemic Reh cells and B-ALL-LICs-derived leukemic mice. Further results showed that loss of β-Arrestin1 induced senescence of Reh cells through mediating hTERT-telomerase-telomere axis, which was reversed by BIBR1532, the telomerase activity inhibitor. Importantly, depletion of β-Arrestin1 decreased the binding of Sp1 to hTERT promoter at the region of −28 to −36 bp. The anti-sense oligonucleotide of this key region downregulated the transcription of hTERT and aggravated the senescence of Reh cells. Further data demonstrated that the depleted β-Arrestin1 reduced the interaction of P300 with Sp1, thus to reduce Sp1 binding to hTERT promoter, downregulate hTERT transcription, decrease telomerase activity, shorten telomere length, and promote Reh cell senescence. Interestingly, the percentage of senile cells in B-ALL LICs was decreased, which was negatively correlated to good prognosis and β-Arrestin1 mRNA expression in childhood B-ALL patients. Our study shed a light on the senescence of B-ALL LICs and is regulated by β-Arrestin1, providing the potential therapeutic target of leukemia by promoting cellular senescence with a key region of hTERT promoter.

The transcriptional modulator Ifrd1 controls PGC-1α expression under short-term adrenergic stimulation in brown adipocytes

Sympathetic tone activates the function of classical brown adipocytes, which constitutively exist in the brown adipose tissue (BAT), and inducible brown adipocytes (so-called beige adipocytes), which sporadically reside within the white adipose tissue (WAT). Here we identified the transcriptional modulator interferon-related developmental regulator 1 (Ifrd1) as a negative regulator of thermogenic and mitochondrial gene expression in brown adipocytes. Ifrd1 expression was markedly induced by cold exposure and administration of CL-316243 (a β3 adrenergic agonist) in interscapular brown adipose and inguinal subcutaneous WATs, but not in epididymal visceral WAT, in vivo. Adrenergic stimulation also induced Ifrd1 expression in brown adipocytes in a cAMP responsive element binding protein-dependent manner in vitro. CL-316243 injection markedly elevated thermogenic and mitochondrial gene expression, including peroxisome proliferator-activated receptor γ coactivator 1α (Pgc1a) in the subcutaneous WAT of Ifrd1 knockout mice compared with gene expression in wild-type mice. Pgc1a promoter activity enhanced by the transcription factor specificity protein 1 (Sp1) was markedly repressed by co-introduction of Ifrd1 in brown adipocytes, whereas the repression was markedly prevented by the addition of trichostatin A, a histone deacetylase inhibitor. Moreover, adrenergic stimulation induced complex formation between Ifrd1, Sp1 and mSIN3B, which is a component of the SIN complex containing histone deacetylase, in brown adipocytes. These findings, therefore, suggest that Ifrd1 could be a pivotal negative regulator of sympathetic regulation of thermogenic and mitochondrial gene expression in brown adipocytes by interacting with Sp1 and the mSIN3 complex.

The Role of the Ubiquitously Expressed Transcription Factor Sp1 in Tissue-specific Transcriptional Regulation and in Disease

Sp1 belongs to the 26 member strong Sp/KLF family of transcription factors. It is a paradigm for a ubiquitously expressed transcription factor and is involved in regulating the expression of genes associated with a wide range of cellular processes in mammalian cells. Sp1 can interact with a range of proteins, including other transcription factors, members of the transcription initiation complex and epigenetic regulators, enabling tight regulation of its target genes. In this review, we discuss the mechanisms involved in Sp1-mediated transcriptional regulation, as well as how a ubiquitous transcription factor can be involved in establishing a tissue-specific pattern of gene expression and mechanisms by which its activity may be regulated. We also consider the role of Sp1 in human diseases, such as cancer.

A calcium-sensitive feed-forward loop regulating the expression of the ATP-gated purinergic P2X7 receptor via specificity protein 1 and microRNA-22

Cells have developed complex transcriptional regulatory mechanisms to maintain intracellular homeostasis and withstand pathophysiological stressors. Feed-forward loops comprising transcription factors that drive expression of both target gene and a microRNA as negative regulator, are gaining increasing recognition as key regulatory elements of cellular homeostasis. The ATP-gated purinergic P2X7 receptor (P2X7R) is an important driver of inflammation and has been implicated in the pathogenesis of numerous brain diseases including epilepsy. Changes in P2X7R expression have been reported in both experimental models and in epilepsy patients but the mechanism(s) controlling P2X7R levels remain incompletely understood. The specificity protein 1 (Sp1) has been shown to induce P2X7R transcription in vitro and recent data has identified microRNA-22 as a post-transcriptional repressor of P2X7R expression after seizures. In the present study we show that Sp1 can induce the transcription of both microRNA-22 and P2X7R in vitro during increased neuronal activity and in vivo in a mouse model of status epilepticus. We further show that Sp1-driven microRNA-22 transcription is calcium-sensitive and Sp1 occupancy of the microRNA-22 promoter region is blocked under conditions of seizure activity sufficient to elicit neuronal death. Taken together, our results suggest a neuronal activity-dependent P2X7R expression which is induced by the transcription factor Sp1 and repressed in a calcium-dependent manner by microRNA-22.

The role of mitogen-activated protein kinases and sterol receptor coactivator-1 in TGF-β-regulated expression of genes implicated in macrophage cholesterol uptake

The anti-atherogenic cytokine TGF-β inhibits macrophage foam cell formation by suppressing the expression of key genes implicated in the uptake of modified lipoproteins. We have previously shown a critical role for p38 MAPK and JNK in the TGF-β-mediated regulation of apolipoprotein E expression in human monocytes. However, the roles of these two MAPK pathways in the control of expression of key genes involved in the uptake of modified lipoproteins in human macrophages is poorly understood and formed the focus of this study. TGF-β activated both p38 MAPK and JNK, and knockdown of p38 MAPK or c-Jun, a key downstream target of JNK action, demonstrated their requirement in the TGF-β-inhibited expression of several key genes implicated in macrophage lipoprotein uptake. The potential role of c-Jun and specific co-activators in the action of TGF-β was investigated further by studies on the lipoprotein lipase gene. c-Jun did not directly interact with the minimal promoter region containing the TGF-β response elements and a combination of transient transfection and knock down assays revealed an important role for SRC-1. These studies provide novel insights into the mechanisms underlying the TGF-β-mediated inhibition of macrophage gene expression associated with the control of cholesterol homeostasis.

Low-density lipoprotein upregulate SR-BI through Sp1 Ser702 phosphorylation in hepatic cells

Scavenger receptor class B type I (SR-BI) is one of the key proteins in the process of reverse cholesterol transport (RCT), and its major function is to uptake high density lipoprotein (HDL) cholesterol from plasma into liver cells. The regulation of SR-BI expression is important for controlling serum lipid content and reducing the risks of cardiovascular diseases. Here we found that SR-BI expression was significantly increased by LDL in vivo and in vitro, and the transcription factor specific protein 1 (Sp1) plays a critical role in this process. Results from co-immunoprecipitation experiments indicate that the activation of SR-BI was associated with Sp1-recruited protein complexes in the promoter region of SR-BI, where histone acetyltransferase p300 was recruited and histone deacetylase HDAC1 was dismissed. As a result, histone acetylation increased, leading to activation of SR-BI transcription. With further investigation, we found that LDL phosphorylated Sp1 through ERK1/2 pathway, which affected Sp1 protein complexes formation in SR-BI promoter. Using mass spectrometry and site directed mutagenesis, a new Sp1 phosphorylation site Ser702 was defined to be associated with Sp1-HDAC1 interaction and may be important in SR-BI activation, shedding light on the knowledge of delicate mechanism of hepatic HDL receptor SR-BI gene modulation by LDL.

Sp1-mediated ectopic expression of T-cell lymphoma invasion and metastasis 2 in hepatocellular carcinoma

T-cell lymphoma invasion and metastasis 2 (TIAM2) is a neuron-specific protein that has been found ectopically expressed in hepatocellular carcinoma (HCC). Results from clinical specimens and cellular and animal models have shown that the short form of TIAM2 (TIAM2S) functions as an oncogene in the tumorigenesis of liver cancer. However, the regulation of TIAM2S ectopic expression in HCC cells remains largely unknown. This study aimed to identify the mechanism underlying the ectopic expression of TIAM2S in liver cancer cells. In this report, we provide evidence illustrating that Sp1 binds directly to the GC box located in the TIAM2S core promoter. We further demonstrated that overexpression of Sp1 in HepaRG cells promotes endogenous TIAM2S mRNA and protein expressions, and knockdown of Sp1 in 2 HCC cell lines, HepG2 and PLC/PRF/5, led to a substantial reduction in TIAM2S mRNA and protein in these cells. Of 60 paired HCC samples, 70% showed a significant increase (from 1.1- to 3.6-fold) in Sp1 protein expression in the tumor cells. The elevated Sp1 expression was highly correlated with both TIAM2S mRNA and protein expressions in these samples. Together, these results illustrate that Sp1 positively controls TIAM2S transcription and that Sp1-mediated transcriptional activation is essential for TIAM2S ectopic expression in liver cancer cells.

SENP3 regulates the global protein turnover and the Sp1 level via antagonizing SUMO2/3-targeted ubiquitination and degradation

SUMOylation is recently found to function as a targeting signal for the degradation of substrates through the ubiquitin-proteasome system. RNF4 is the most studied human SUMO-targeted ubiquitin E3 ligase. However, the relationship between SUMO proteases, SENPs, and RNF4 remains obscure. There are limited examples of the SENP regulation of SUMO2/3-targeted proteolysis mediated by RNF4. The present study investigated the role of SENP3 in the global protein turnover related to SUMO2/3-targeted ubiquitination and focused in particular on the SENP3 regulation of the stability of Sp1. Our data demonstrated that SENP3 impaired the global ubiquitination profile and promoted the accumulation of many proteins. Sp1, a cancer-associated transcription factor, was among these proteins. SENP3 increased the level of Sp1 protein via antagonizing the SUMO2/3-targeted ubiquitination and the consequent proteasome-dependent degradation that was mediated by RNF4. De-conjugation of SUMO2/3 by SENP3 attenuated the interaction of Sp1 with RNF4. In gastric cancer cell lines and specimens derived from patients and nude mice, the level of Sp1 was generally increased in parallel to the level of SENP3. These results provided a new explanation for the enrichment of the Sp1 protein in various cancers, and revealed a regulation of SUMO2/3 conjugated proteins whose levels may be tightly controlled by SENP3 and RNF4.

Nucleotides in neuroregeneration and neuroprotection

Brain injury generates the release of a multitude of factors including extracellular nucleotides, which exhibit bi-functional properties and contribute to both detrimental actions in the acute phase and also protective and reparative actions in the later recovery phase to allow neuroregeneration. A promising strategy toward restoration of neuronal function is based on activation of endogenous adult neural stem/progenitor cells. The implication of purinergic signaling in stem cell biology, including regulation of proliferation, differentiation, and cell death has become evident in the last decade. In this regard, current strategies of acute transplantation of ependymal stem/progenitor cells after spinal cord injury restore altered expression of P2X4 and P2X7 receptors and improve functional locomotor recovery. The expression of both receptors is transcriptionally regulated by Sp1 factor, which plays a key role in the startup of the transcription machinery to induce regeneration-associated genes expression. Finally, general signaling pathways triggered by nucleotide receptors in neuronal populations converge on several intracellular kinases, such as PI3K/Akt, GSK3 and ERK1,2, as well as the Nrf-2/heme oxigenase-1 axis, which specifically link them to neuroprotection. In this regard, regulation of dual specificity protein phosphatases can become novel mechanism of actions for nucleotide receptors that associate them to cell homeostasis regulation. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Oncogenic STRAP functions as a novel negative regulator of E-cadherin and p21(Cip1) by modulating the transcription factor Sp1

We have previously reported the identification of a novel WD-domain protein, STRAP that plays a role in maintenance of mesenchymal morphology by regulating E-cadherin and that enhances tumorigenicity partly by downregulating CDK inhibitor p21(Cip1). However, the functional mechanism of regulation of E-cadherin and p21(Cip1) by STRAP is unknown. Here, we have employed STRAP knock out and knockdown cell models (mouse embryonic fibroblast, human cancer cell lines) to show how STRAP downregulates E-cadherin and p21(Cip1) by abrogating the binding of Sp1 to its consensus binding sites. Moreover, ChIP assays suggest that STRAP recruits HDAC1 to Sp1 binding sites in p21(Cip1) promoter. Interestingly, loss of STRAP can stabilize Sp1 by repressing its ubiquitination in G1 phase, resulting in an enhanced expression of p21(Cip1) by >4.5-fold and cell cycle arrest. Using Bioinformatics and Microarray analyses, we have observed that 87% mouse genes downregulated by STRAP have conserved Sp1 binding sites. In NSCLC, the expression levels of STRAP inversely correlated with that of Sp1 (60%). These results suggest a novel mechanism of regulation of E-cadherin and p21(Cip1) by STRAP by modulating Sp1-dependent transcription, and higher expression of STRAP in lung cancer may contribute to downregulation of E-cadherin and p21(Cip1) and to tumor progression.