Cooperation between Myc and YY1 provides novel silencing transcriptional targets of alpha3beta1-integrin in tumour cells

GCIP and SIRT6 cooperatively suppress ITGAV gene expression by modulating c-myc transcription ability

Grap2 and CyclinD1 interacting protein (GCIP) has been suggested to function as a tumor suppressor and acts as a transcriptional regulator that negatively controls cancer cell growth, invasion, and migration. Knockdown of GCIP reportedly enhances cancer cell migration and invasion, but no previous study has examined the mechanism(s) by which GCIP suppresses migration/invasion in cancer cells. Here, we report that cDNA microarray-based expression profiling of A549 cells without and with knockdown of GCIP reveals that the expression levels of ITGAV and ICAM-1 are negatively regulated by GCIP. In vitro co-immunoprecipitation and in vivo proximity ligation assays reveal that GCIP interacts with c-Myc. Sequence analyses reveal the presence of two c-Myc regulatory motifs (E-boxes) within the ITGAV promoter. Luciferase reporter and ChIP assays indicate that GCIP represses ITGAV transcription by interacting with c-Myc on the E-box binding sites of the ITGAV promoter region. Furthermore, GCIP interacts with SIRT6 in vitro and in vivo and cooperates with SIRT6, thereby linking its activity, to negatively regulate transcription at the E-box by modulating c-Myc transcription ability. Taken together, these findings contribute to our understanding of GCIP in tumorigenesis and identify a previously unrecognized function of GCIP: It can interact with c-Myc and SIRT6 at E-box binding sites of the ITGAV promoter region. Our data collectively reveal a regulatory network involving GCIP, SIRT6, c-Myc, and ITGAV, and suggest that the SIRT6-GCIP complex negatively regulates the oncogenic function of c-Myc in cell proliferation and migration.

The oncogenic axis YAP/MYC/EZH2 impairs PTEN tumor suppression activity enhancing lung tumorigenicity

The tumor suppressor PTEN (phosphatase and tensin homolog deleted in chromosome 10) is genetically deleted or downregulated in many cancer types. Loss of PTEN protein expression is frequently found in lung cancer while genetic alterations are less abundant. PTEN expression is regulated at multiple genetic and epigenetic levels and even partial reduction of its expression increases cancer occurrence. We show that YAP and TAZ cooperate with EZH2, and MYC to transcriptionally repress onco-suppressor genes, including PTEN, in non-small cell lung cancer (NSCLC) cells. YAP/TAZ-EZH2-MYC transcriptional regulators form a nuclear complex that represses PTEN transcription, while their combinatorial targeting restores PTEN expression, attenuates NSCLC cell growth, and prevents compensatory responses induced by single treatments. Datasets analysis of NSCLC patients revealed that PTEN expression is negatively correlated to YAP/TAZ, EZH2 and MYC and that low expression of PTEN is predictive of poor prognosis, especially at earlier stages of the disease. These findings highlight the repressive role of the YAP/TAZ-EZH2-MYC axis on tumor-suppressor genes and offer a potential therapeutic strategy for lung cancer patients with low PTEN levels.

KIF18A inactivates hepatic stellate cells and alleviates liver fibrosis through the TTC3/Akt/mTOR pathway

Activation of hepatic stellate cells (HSCs) has been demonstrated to play a pivotal role in the process of liver fibrogenesis. In this study, we observed a decrease in the expression of KIF18A in fibrotic liver tissues compared to healthy liver tissues, which exhibited a negative correlation with the activation of HSCs. To elucidate the molecular mechanisms underlying the involvement of KIF18A, we performed in vitro proliferation experiments and established a CCl4-induced liver fibrosis model. Our results revealed that KIF18A knockdown enhanced HSCs proliferation and reduced HSCs apoptosis in vitro. Mouse liver fibrosis grade was evaluated with Masson's trichrome and alpha-smooth muscle actin (α-SMA) staining. In addition, the expression of fibrosis markers Col1A1, Stat1, and Timp1 were detected. Animal experiments demonstrated that knockdown of KIF18A could promote liver fibrosis, whereas overexpression of KIF18A alleviated liver fibrosis in a CCl4-induced mouse model. Mechanistically, we found that KIF18A suppressed the AKT/mTOR pathway and exhibited direct binding to TTC3. Moreover, TTC3 was found to interact with p-AKT and could promote its ubiquitination and degradation. Our findings provide compelling evidence that KIF18A enhances the protein binding between TTC3 and p-AKT, promoting TTC3-mediated ubiquitination and degradation of p-AKT. These results refine the current understanding of the mechanisms underlying the pathogenesis of liver fibrosis and may offer new targets for treating this patient population.

Zinc Ions Modulate YY1 Activity: Relevance in Carcinogenesis

YY1 is widely recognized as an intrinsically disordered transcription factor that plays a role in development of many cancers. In most cases, its overexpression is correlated with tumor progression and unfavorable patient outcomes. Our latest research focusing on the role of zinc ions in modulating YY1's interaction with DNA demonstrated that zinc enhances the protein's multimeric state and affinity to its operator. In light of these findings, changes in protein concentration appear to be just one element relevant to modulating YY1-dependent processes. Thus, alterations in zinc ion concentration can directly and specifically impact the regulation of gene expression by YY1, in line with reports indicating a correlation between zinc ion levels and advancement of certain tumors. This review concentrates on other potential consequences of YY1 interaction with zinc ions that may act by altering charge distribution, conformational state distribution, or oligomerization to influence its interactions with molecular partners that can disrupt gene expression patterns.

Integrins in cancer: Emerging mechanisms and therapeutic opportunities

Integrins are vital surface adhesion receptors that mediate the interactions between the extracellular matrix (ECM) and cells and are essential for cell migration and the maintenance of tissue homeostasis. Aberrant integrin activation promotes initial tumor formation, growth, and metastasis. Recently, many lines of evidence have indicated that integrins are highly expressed in numerous cancer types and have documented many functions of integrins in tumorigenesis. Thus, integrins have emerged as attractive targets for the development of cancer therapeutics. In this review, we discuss the underlying molecular mechanisms by which integrins contribute to most of the hallmarks of cancer. We focus on recent progress on integrin regulators, binding proteins, and downstream effectors. We highlight the role of integrins in the regulation of tumor metastasis, immune evasion, metabolic reprogramming, and other hallmarks of cancer. In addition, integrin-targeted immunotherapy and other integrin inhibitors that have been used in preclinical and clinical studies are summarized.

Depletion of enhancer zeste homolog 2 (EZH2) directs transcription factors associated with T cell differentiation through epigenetic regulation of Yin Yang 1(YY1) in combating non-small cell lung cancer (NSCLC)

Non-Small Cell Lung Cancer (NSCLC) is the leading cause of death in all countries alike. In the current study, we have found out that Histone H3Lys4trimethylation is abnormal on YY1 in CD4⁺T Helper (T_H) cells of NSCLC patients which is evident by Histone H3Lys27 trimethylation mediated via EZH2. We investigated the status of Yin Yang 1 (YY1) and the involvement of certain transcription factors that lead to tumorigenesis after depleting endogenous EZH2 in vitro by CRISPR/Cas9 in the CD4⁺T_H1-or-T_H2-polarized cells isolated initially as CD4⁺T_H0 cells from the PBMC of the control subjects and patients suffering from NSCLC. After depletion of endogenous EZH2, RT-qPCR based mRNA expression analysis showed that there was an increase in the expression of T_H1 specific genes and a decrease in the expression of T_H2 specific genes in NSCLC patients CD4⁺T_H cells. We can conclude that this group of NSCLC patients may have the tendency at least in vitro to elucidate adaptive/protective immunity through the depletion of endogenous EZH2 along with the reduction in the expression of YY1. Moreover, depletion of EZH2 not only suppressed the CD4⁺CD25⁺FOXP3⁺Regulatory T cells (Treg) but also it aided the generation of CD8⁺Cytotoxic T Lymphocytes (CTL) which were involved in killing of the NSCLC cells. Thus the transcription factors involved in EZH2 mediated T cell differentiation linked to malignancies offers us an appealing avenue of targeted therapeutic intervention for NSCLC.

In silico strategies to identify protein-protein interaction modulator in cell-to-cell transmission of SARS CoV2

RNA sequence data from SARS CoV2 patients helps to construct a gene network related to this disease. A detailed analysis of the human host response to SARS CoV2 with expression profiling by high-throughput sequencing has been accomplished with primary human lung epithelial cell lines. Using this data, the clustered gene annotation and gene network construction are performed with the help of the String database. Among the four clusters identified, only 1 with 44 genes could be annotated. Interestingly, this corresponded to basal cells with p = 1.37e - 05, which is relevant for respiratory tract infection. Functional enrichment analysis of genes present in the gene network has been completed using the String database and the Network Analyst tool. Among three types of cell-cell communication, only the anchoring junction between the basal cell membrane and the basal lamina in the host cell is involved in the virus transmission. In this junction point, a hemidesmosome structure plays a vital role in virus spread from one cell to basal lamina in the respiratory tract. In this protein complex structure, different integrin protein molecules of the host cell are used to promote the spread of virus infection into the extracellular matrix. So, small molecular blockers of different anchoring junction proteins, such as integrin alpha 3, integrin beta 1, can provide efficient protection against this deadly viral disease. ORF8 from SARS CoV2 virus can interact with both integrin proteins of human host. By using molecular docking technique, a ternary complex of these three proteins is modelled. Several oligopeptides are predicted as modulators for this ternary complex. In silico analysis of these modulators is very important to develop novel therapeutics for the treatment of SARS CoV2.

MicroRNA-206 enhances antitumor immunity by disrupting the communication between malignant hepatocytes and regulatory T cells in c-Myc mice

BACKGROUND AND AIMS

Intertumoral accumulation of regulatory T cells (Tregs) has been implicated in the pathogenesis of HCC. Because of poor understanding of the immunosuppression mechanism(s) in HCC, immunotherapy is largely unsuccessful for the treatment of HCC.

APPROACH AND RESULTS

Hydrodynamic injection (HDI) of c-Myc into mice resulted in enlarged spleens and lethal HCC associated with an increase in hepatic Tregs and depletion of CTLs (cytotoxic T lymphocytes). Malignant hepatocytes in c-Myc mice overproduced TGFβ1, which enhanced the suppressor function of Tregs and impaired the proliferation and cytotoxicity of CTLs. In addition to activating TGFβ signaling, c-Myc synergized with Yin Yang 1 to impair microRNA-206 (miR-206) biogenesis. HDI of miR-206 fully prevented HCC and the associated enlargement of the spleen, whereas 100% of control mice died from HCC within 5-9 weeks postinjection. Mechanistically, by directly targeting errant kirsten ras oncogene (KRAS) signaling, miR-206 impeded the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) axis that drives expression of Tgfb1. By blocking the KRAS/MEK/ERK axis, miR-206 prevented TGFβ1 overproduction, thereby impairing the suppressor function and expansion of Tregs, but enhancing the expansion and cytotoxic program of CTLs. Disrupting the interaction between miR-206 and Kras offset the roles of miR-206 in inhibiting immunosuppression and HCC. Depletion of CD8⁺ T cells impaired the ability of miR-206 to inhibit HCC.

CONCLUSIONS

c-Myc-educated hepatocytes promoted immunosuppression by overproducing TGFβ1, which promoted HCC development. miR-206, by attenuating TGFβ1 overproduction, disrupted the communication of malignant hepatocytes with CTLs and Tregs, which prevented HCC. miR-206 represents a potential immunotherapeutic agent against HCC.

Transcription factor YY1 contributes to human melanoma cell growth through modulating the p53 signaling pathway

BACKGROUND

Melanoma has a higher mortality rate than any other skin cancer, and its cases are increasing. The transcription factor YY1 has been proven to be involved in tumor progression; however, the role of YY1 in melanoma is not well understood.

METHODS

This study investigates how YY1 functions in melanoma progression, and it also elucidates the underlying mechanisms involved.

RESULTS

We have found that in clinical human melanoma tissues, YY1 is overexpressed compared to YY1 expression in normal melanocytes and skin tissues. Cellular immunofluorescence shows that YY1 is mainly located in the nucleus. YY1 knockdown reduces proliferation, migration, and invasion of melanoma cell lines. Moreover, the apoptosis rate of cells is significantly increased in low-YY1 environments. The overexpression of YY1 resulted in decreased apoptotic rates in melanoma cells. YY1 also affects the expression of EMT-related proteins. Additional experiments reveal that YY1 knockdown disrupts the interaction of MDM2-p53, and that it both stabilizes and increases p53 activity. The upregulation of p53 expression in turn stimulates p21 expression just as it suppresses CDK4 expression, which then induces cells that were arrested in the G1 phase. The effect then is to constrain cell proliferation in melanoma cells. Upon activation of the p53 pathway, Bax, a pro-apoptotic protein, is upregulated, and Bcl-2, an anti-apoptotic protein, was downregulated in A375 cells.

CONCLUSIONS

The findings of this study provide novel insights into the pathology of melanoma as well as the role that YY1 plays in tumor progression. The findings also suggest that targeting YY1 has the potential to improve the diagnosis and treatment of melanoma.

Effect of the transcription factor YY1 on the development of pancreatic endocrine and exocrine tumors: a narrative review

Pancreatic tumors are classified into endocrine and exocrine types, and the clinical manifestations in patients are nonspecific. Most patients, especially those with pancreatic ductal adenocarcinoma (PDAC), have lost the opportunity to receive for the best treatment at the time of diagnosis. Although chemotherapy and radiotherapy have shown good therapeutic results in other tumors, their therapeutic effects on pancreatic tumors are minimal. A multifunctional transcription factor, Yin-Yang 1 (YY1) regulates the transcription of a variety of important genes and plays a significant role in diverse tumors. Studies have shown that targeting YY1 can improve the survival time of patients with tumors. In this review, we focused on the mechanism by which YY1 affects the occurrence and development of pancreatic tumors. We found that a YY1 mutation is specific for insulinomas and has a role in driving the degree of malignancy. In addition, changes in the circadian network are a key causative factor of PDAC. YY1 promotes pancreatic clock progression and induces malignant changes, but YY1 seems to act as a tumor suppressor in PDAC and affects many biological behaviors, such as proliferation, migration, apoptosis and metastasis. Our review summarizes the progress in understanding the role of YY1 in pancreatic endocrine and exocrine tumors and provides a reasonable assessment of the potential for therapeutic targeting of YY1 in pancreatic tumors.

Role of the Transcription Factor Yin Yang 1 and Its Selectively Identified Target Survivin in High-Grade B-Cells Non-Hodgkin Lymphomas: Potential Diagnostic and Therapeutic Targets

B-cell non-Hodgkin lymphomas (B-NHLs) are often characterized by the development of resistance to chemotherapeutic drugs and/or relapse. During drug-induced apoptosis, Yin Yang 1 (YY1) transcription factor might modulate the expression of apoptotic regulators genes. The present study was aimed to: (1) examine the potential oncogenic role of YY1 in reversing drug resistance in B-NHLs; and (2) identify YY1 transcriptional target(s) that regulate the apoptotic pathway in B-NHLs. Predictive analyses coupled with database-deposited data suggested that YY1 binds the promoter of the BIRC5/survivin anti-apoptotic gene. Gene Expression Omnibus (GEO) analyses of several B-NHL repositories revealed a conserved positive correlation between YY1 and survivin, both highly expressed, especially in aggressive B-NHLs. Further validation experiments performed in Raji Burkitt’s lymphomas cells, demonstrated that YY1 silencing was associated with survivin downregulation and sensitized the cells to apoptosis. Overall, our results revealed that: (1) YY1 and survivin are positively correlated and overexpressed in B-NHLs, especially in BLs; (2) YY1 strongly binds to the survivin promoter, hence survivin may be suggested as YY1 transcriptional target; (3) YY1 silencing sensitizes Raji cells to drug-induced apoptosis via downregulation of survivin; (4) both YY1 and survivin are potential diagnostic markers and therapeutic targets for the treatment of resistant/relapsed B-NHLs.

YY1 control of mitochondrial-related genes does not account for regulation of immunoglobulin class switch recombination in mice

Immunoglobulin class switch recombination (CSR) occurs in activated B cells with increased mitochondrial mass and membrane potential. Transcription factor Yin Yang 1 (YY1) is critical for CSR and for formation of the DNA loops involved in this process. We therefore sought to determine if YY1 knockout impacts mitochondrial gene expression and mitochondrial function in murine splenic B cells, providing a potential mechanism for regulating CSR. We identified numerous genes in splenic B cells differentially regulated when cells are induced to undergo CSR. YY1 conditional knockout caused differential expression of 1129 genes, with 59 being mitochondrial-related genes. ChIP-seq analyses showed YY1 was directly bound to nearly half of these mitochondrial-related genes. Surprisingly, at the time when YY1 knockout dramatically reduces DNA loop formation and CSR, mitochondrial mass and membrane potential were not significantly impacted, nor was there a significant change in mitochondrial oxygen consumption, extracellular acidification rate, or mitochondrial complex I or IV activities. Our results indicate that YY1 regulates numerous mitochondrial-related genes in splenic B cells, but this does not account for the impact of YY1 on CSR or long-distance DNA loop formation.

Knockdown of Yin Yang 1 enhances anticancer effects of cisplatin through protein phosphatase 2A-mediated T308 dephosphorylation of AKT

Cisplatin is still one of the first-line drugs for chemotherapy of head and neck squamous cell carcinoma (HNSCC) and shows a survival advantage for HNSCC. However, a substantial proportion of HNSCC eventually becomes resistance to cisplatin and the underlying mechanisms remain to be fully understood. Yin Yang 1 (YY1) is a multifunctional protein regulating both gene transcription and protein modifications and also plays a role in chemotherapy resistance. Here, we reported that knockdown of YY1 by lentivirus-mediated short hairpin RNA or tetracycline-inducible short hairpin RNA enhanced cisplatin-induced apoptosis and inhibition of cell proliferation, migration and invasion in the HNSCC cell lines, and inhibition of the xenograft tumor growth. The underlying mechanisms were revealed that knockdown of YY1 downregulated both S473 and T308 phosphorylation of AKT (protein kinase B), which was mainly responsible for cisplatin resistance, whereas overexpression of YY1 upregulated both S473 and T308 phosphorylation. Cisplatin upregulated YY1 mRNA and protein expression and both S473 and T308 phosphorylation of AKT. In the presence of cisplatin, knockdown of YY1 not only blocked cisplatin-induced increase in S473 and T308 phosphorylation of AKT, but still downregulated T308 phosphorylation. Moreover, protein phosphatase 2A (PP2A) antagonist, okadaic acid, upregulated T308, but not S473, phosphorylation, and simultaneously abolished YY1 knockdown-mediated enhancement of cisplatin-induced inhibition of cell proliferation. In addition, knockdown of YY1 promoted PP2A activity through upregulating mRNA and protein expressions of PP2A catalytic subunit alpha (PPP2CA) through the binding of YY1 in the promoter of PPP2CA. Conversely, activating PP2A by forskolin also promoted YY1 degradation and subsequently inhibited T308 phosphorylation. These results suggested that knockdown of YY1 enhanced anticancer effects of cisplatin through PP2A mediating T308 dephosphorylation of AKT, and that targeting YY1 or PP2A would enhance the efficiency of cisplatin chemotherapy in treatment of HNSCC.

Post-surgery fluids promote transition of cancer stem cell-to-endothelial and AKT/mTOR activity, contributing to relapse of giant cell tumors of bone

Giant cell tumors of bone (GCTB) are rare sarcomas with a high rate of unpredictable local relapse. Studies suggest that surgical methods affect recurrence, supporting the idea that local disease develops from re-growth of residual cancer cells. To identify early prognostic markers of individual risk of recurrence, we evaluated the effect of post-surgery fluids from a cohort of GCTB patients on growth of primary and established sarcoma cell lines, and mice xenograph. Post-surgery fluids increased cell growth and enhanced expression of CD44⁺⁺, the principal receptor for the extracellular matrix component hyaluronan and the mesenchymal stem marker CD117⁺. Cancer cells became highly invasive and tumorigenic, acquiring stemness properties, and activated AKT/mTOR pathway. Prolonged stimulation with post-surgery fluids down-regulated the mesenchymal gene TWIST1 and Vimentin protein, and transdifferentiated cells into tubule-like structures positive to the endothelial markers VE-Cadherin and CD31⁺. In mice, post-surgery fluids gave rise to larger and more vascularized tumors than control, while in patients AKT/mTOR pathway activation was associated with recurrence by logistic regression (Kaplan-Meier; P<0.001). These findings indicate that post-surgery fluids are an adjuvant in mechanisms of tumor regrowth, increasing stem cell growth and AKT/mTOR activity.

New Cross-Talk Layer between Ultraconserved Non-Coding RNAs, MicroRNAs and Polycomb Protein YY1 in Bladder Cancer

MicroRNAs (miRNAs) are highly conserved elements in mammals, and exert key regulatory functions. Growing evidence shows that miRNAs can interact with another class of non-coding RNAs, so-called transcribed ultraconserved regions (T-UCRs), which take part in transcriptional, post-transcriptional and epigenetic regulation processes. We report here the interaction of miRNAs and T-UCRs as a network modulating the availability of these non-coding RNAs in bladder cancer cells. In our cell system, antagomiR-596 increased the expression of T-UCR 201+. Moreover, T-UCR 8+ silencing increased miR-596 expression, which in turn reduced total T-UCR 283+, showing that the perturbation of one element in this network changes the expression of other interactors. In addition, we identify the polycomb protein Yin Yang 1 (YY1) as mediator of binding between miR-596 and T-UCR 8+. These new findings describe for the first time a network between T-UCRs, miRNAs and YY1 protein, highlighting the existence of an additional layer of gene expression regulation.

Nicotine Suppressed Fetal Adrenal StAR Expression via YY1 Mediated-Histone Deacetylation Modification Mechanism

Steroidogenic acute regulatory (StAR) protein plays a pivotal role in steroidogenesis. Previously, we have demonstrated that prenatal nicotine exposure suppressed fetal adrenal steroidogenesis via steroidogenic factor 1 deacetylation. This study further explored the potential role of the transcriptional repressor Yin Yang 1 (YY1) in nicotine-mediated StAR inhibition. Nicotine was subcutaneously administered (1.0 mg/kg) to pregnant rats twice per day and NCI-H295A cells were treated with nicotine. StAR and YY1 expression were analyzed by real-time PCR, immunohistochemistry, and Western blotting. Histone modifications and the interactions between the YY1 and StAR promoter were assessed using chromatin immunoprecipitation (ChIP). Prenatal nicotine exposure increased YY1 expression and suppressed StAR expression. ChIP assay showed that there was a decreasing trend for histone acetylation at the StAR promoter in fetal adrenal glands, whereas H3 acetyl-K14 at the YY1 promoter presented an increasing trend following nicotine exposure. Furthermore, in nicotine-treated NCI-H295A cells, nicotine enhanced YY1 expression and inhibited StAR expression. ChIP assay showed that histone acetylation decreased at the StAR promoter in NCI-H295A cells and that the interaction between the YY1 and StAR promoter increased. These data indicated that YY1-medicated histone deacetylation modification in StAR promoters might play an important role in the inhibitory effect of nicotine on StAR expression.

Epigenetic regulators: Polycomb-miRNA circuits in cancer

Polycomb group (PcG) proteins belong to a family of epigenetic modifiers and play a key role in dynamic control of their target genes. Several reports have found that aberrations in PcG-microRNA (miRNA) interplay in various cancer types often associated with poor clinical prognosis. This review discusses important PcG-miRNA molecular networks which act as critical interfaces between chromatin remodeling, and transcriptional and post-transcriptional regulation of their target genes in cancer. Moreover, here are discussed several compounds influencing the activity of PcG proteins entered in clinical arena for the treatment of solid tumors, multiple myeloma and B lymphomas, thus highlighting the therapeutic potential of targeting this protein family.

Polycomb YY1 is a critical interface between epigenetic code and miRNA machinery after exposure to hypoxia in malignancy

Yin Yang 1 (YY1) is a member of polycomb protein family involved in epigenetic modifications and transcriptional controls. We have shown that YY1 acts as positive regulator of tumor growth and angiogenesis by interfering with the VEGFA network. Yet, the link between polycomb chromatin complex and hypoxia regulation of VEGFA is still poorly understood. Here, we establish that hypoxia impairs YY1 binding to VEGFA mRNA 3'UTR (p<0.001) in bone malignancy. Moreover, RNA immunoprecipitation reveals the formation of triplex nuclear complexes among YY1, VEGFA DNA, mRNA, and unreached about 200 fold primiRNA 200b and 200c via Dicer protein. In this complex, YY1 is necessary to maintain the steady-state level of VEGFA expression while its silencing increases VEGFA mRNA half-life at 4 h and impairs the maturation of miRNA 200b/c. Hypoxia promotes histone modification through ubiquitination both of YY1 and Dicer proteins. Hypoxia-mediated down-regulation of YY1 and Dicer changes post-transcriptional VEGFA regulation by resulting in the accumulation of primiRNA200b/c in comparison to mature miRNAs (p<0.001). Given the regulatory functions of VEGFA on cellular activities to promote neoangiogenesis, we conclude that YY1 acts as novel critical interface between epigenetic code and miRNAs machinery under chronic hypoxia in malignancy.

MYC is an early response regulator of human adipogenesis in adipose stem cells

Adipose stem cell (ASC) differentiation is necessary for the proper maintenance and function of adipose tissue. The procurement and characterization of multipotent ASCs has enabled investigation into the molecular determinants driving human adipogenesis. Here, the transcription factor MYC was identified as a significant regulator of ASC differentiation. Expression of MYC transcript and protein was found to accumulate during the initial course of differentiation. Loss-of-function analysis using siRNA mediated knockdown of MYC demonstrated inhibition of hormonally stimulated adipogenesis. MYC exhibited an early and sustained expression pattern that preceded down regulation of key suppressor genes, as well as induction of transcriptional and functional effectors. Glucocorticoid stimulation was identified as a necessary component for MYC induction and was found to impact adipogenesis in a concentration-dependent manner. Global gene expression analysis of MYC knockdown in ASC enriched for functional pathways related to cell adhesion, cytoskeletal remodeling, and transcriptional components of adipogenesis. These results identify a functional role for MYC in promotion of multipotent ASC to the adipogenic lineage.

MYC cofactors: molecular switches controlling diverse biological outcomes

The transcription factor MYC has fundamental roles in proliferation, apoptosis, tumorigenesis, and stem cell pluripotency. Over the last 30 years extensive information has been gathered on the numerous cofactors that interact with MYC and the target genes that are regulated by MYC as a means of understanding the molecular mechanisms controlling its diverse roles. Despite significant advances and perhaps because the amount of information learned about MYC is overwhelming, there has been little consensus on the molecular functions of MYC that mediate its critical biological roles. In this perspective, the major MYC cofactors that regulate the various transcriptional activities of MYC, including canonical and noncanonical transactivation and transcriptional repression, will be reviewed and a model of how these transcriptional mechanisms control MYC-mediated proliferation, apoptosis, and tumorigenesis will be presented. The basis of the model is that a variety of cofactors form dynamic MYC transcriptional complexes that can switch the molecular and biological functions of MYC to yield a diverse range of outcomes in a cell-type- and context-dependent fashion.

Osteosarcoma cells induce endothelial cell proliferation during neo-angiogenesis

Understanding the mechanisms inducing endothelial cell (EC) proliferation following tumor microenvironment stimuli may be important for the development of antiangiogenic therapies. Here, we show that cyclin-dependent kinase 2 and 5 (Cdk2, Cdk5) are important mediators of neoangiogenesis in in vitro and in vivo systems. Furthermore, we demonstrate that a specific Yin Yang 1 (YY1) protein-dependent signal from osteosarcoma (SaOS) cells determines proliferation of human aortic endothelial cells (HAECs). Following tumor cell stimuli, HAECs overexpress Cdk2 and Cdk5, display increased Cdk2 activity, undergo enhanced proliferation, and form capillary-like structures. Moreover, Roscovitine, an inhibitor of Cdks, blunted overexpression of Cdk2 and Cdk5 and Cdk2 activity induced by the YY1-dependent signal secreted by SaOS cells. Furthermore, Roscovitine decreased HAEC proliferation and angiogenesis (the latter by 70% in in vitro and 50% in in vivo systems; P < 0.01 vs. control). Finally, the finding that Roscovitine triggers apoptosis in SaOS cells as well as in HAECs by activating caspase-3/7 indicates multiple mechanisms for the potential antitumoral effect of Roscovitine. Present work suggests that Cdk2 and Cdk5 might be pharmacologically accessible targets for both antiangiogenic and antitumor therapy.

Sequence features and chromatin structure around the genomic regions bound by 119 human transcription factors

Chromatin immunoprecipitation coupled with high-throughput sequencing (ChIP-seq) has become the dominant technique for mapping transcription factor (TF) binding regions genome-wide. We performed an integrative analysis centered around 457 ChIP-seq data sets on 119 human TFs generated by the ENCODE Consortium. We identified highly enriched sequence motifs in most data sets, revealing new motifs and validating known ones. The motif sites (TF binding sites) are highly conserved evolutionarily and show distinct footprints upon DNase I digestion. We frequently detected secondary motifs in addition to the canonical motifs of the TFs, indicating tethered binding and cobinding between multiple TFs. We observed significant position and orientation preferences between many cobinding TFs. Genes specifically expressed in a cell line are often associated with a greater occurrence of nearby TF binding in that cell line. We observed cell-line-specific secondary motifs that mediate the binding of the histone deacetylase HDAC2 and the enhancer-binding protein EP300. TF binding sites are located in GC-rich, nucleosome-depleted, and DNase I sensitive regions, flanked by well-positioned nucleosomes, and many of these features show cell type specificity. The GC-richness may be beneficial for regulating TF binding because, when unoccupied by a TF, these regions are occupied by nucleosomes in vivo. We present the results of our analysis in a TF-centric web repository Factorbook (http://factorbook.org) and will continually update this repository as more ENCODE data are generated.

A genome-wide approach to comparative oncology: high-resolution oligonucleotide aCGH of canine and human osteosarcoma pinpoints shared microaberrations

Molecular cytogenetic evaluation of human osteosarcoma (OS) has revealed the characteristically high degree of genomic reorganization that is the hallmark of this cancer. The extent of genomic disorder in OS has hindered identification of the genomic aberrations driving disease progression. With pathophysiological similarities to its human counterpart, canine OS represents an ideal model for comparison of conserved regions of genomic instability that may be disease-associated rather than genomic passengers. This study used high-resolution oligonucleotide array comparative genomic hybridization and a variety of informatics tools to aid in the identification of disease-associated genome-wide DNA copy number aberrations in canine and human OS. Our findings support and build upon the high level of cytogenetic complexity, through the identification of shared regions of microaberration (<500 kb) and functional analysis of possible orthologous OS-associated genes to pinpoint the cellular processes most commonly affected by aberration in human and canine OS. Aberrant regions contained previously reported genes such as CDC5L, MYC, RUNX2, and CDKN2A/CDKN2B, while expanding the gene of interest list to include ADAM15, CTC1, MEN1, CDK7, and others. Such regions of instability may thus have functional significance in the etiology of OS, the most common primary bone tumor in both species.

Transcription factor co-localization patterns affect human cell type-specific gene expression

BACKGROUND

Cellular development requires the precise control of gene expression states. Transcription factors are involved in this regulatory process through their combinatorial binding with DNA. Information about transcription factor binding sites can help determine which combinations of factors work together to regulate a gene, but it is unclear how far the binding data from one cell type can inform about regulation in other cell types.

RESULTS

By integrating data on co-localized transcription factor binding sites in the K562 cell line with expression data across 38 distinct hematopoietic cell types, we developed regression models to describe the relationship between the expression of target genes and the transcription factors that co-localize nearby. With K562 binding sites identifying the predictors, the proportion of expression explained by the models is statistically significant only for monocytic cells (p-value< 0.001), which are closely related to K562. That is, cell type specific binding patterns are crucial for choosing the correct transcription factors for the model. Comparison of predictors obtained from binding sites in the GM12878 cell line with those from K562 shows that the amount of difference between binding patterns is directly related to the quality of the prediction. By identifying individual genes whose expression is predicted accurately by the binding sites, we are able to link transcription factors FOS, TAF1 and YY1 to a sparsely studied gene LRIG2. We also find that the activity of a transcription factor may be different depending on the cell type and the identity of other co-localized factors.

CONCLUSION

Our approach shows that gene expression can be explained by a modest number of co-localized transcription factors, however, information on cell-type specific binding is crucial for understanding combinatorial gene regulation.

MYC suppresses cancer metastasis by direct transcriptional silencing of αv and β3 integrin subunits

Over-expression of MYC transforms cells in culture, elicits malignant tumors in experimental animals and is found in many human tumors. We now report the paradoxical finding that this powerful oncogene can also act as a suppressor of cell motility, invasiveness and metastasis. Overexpression of MYC stimulated proliferation of breast cancer cells both in culture and in vivo as expected, but inhibited motility and invasiveness in culture, and lung and liver metastases in xenografted tumors. We show further that MYC represses transcription of both subunits of αvβ3 integrin, and that exogenous expression of β3 integrin in human breast cancer cells that do not express this integrin rescues invasiveness and migration when MYC is downregulated. These data uncover an unexpected function of MYC, provide an explanation for the hitherto puzzling literature on the relationship between MYC and metastasis and reveal a variable that should influence the development of therapeutics that target MYC.

Oncogenic potential of yin yang 1 mediated through control of imprinted genes

The transcription factor Yin Yang (YY) 1 is one of the most evolutionarily well-conserved DNA binding proteins that is ubiquitously expressed among different tissue types. YY1 functions as a critical regulator for a diverse set of genes, making its role in the cancerous environment elusive. Recent studies have demonstrated that clusters of YY1 binding sites are overrepresented in imprinted gene loci. These clustered binding sites may function as a molecular rheostat with respect to YY1 protein levels. YY1 levels were documented to be altered in various tumor tissues in conjunction with the transcriptional levels of the imprinted genes it regulates. This review highlights the unexplored mechanism through which fluctuations in YY1 protein levels alter the transcriptional status of imprinted genes containing clustered YY1 binding sites, which potentially could affect cancer development and/or progression.

The oncogenic role of Yin Yang 1

Yin Yang 1 (YY1) is a transcription factor with diverse and complex biological functions. YY1 either activates or represses gene transcription, depending on the stimuli received by the cells and its association with other cellular factors. Since its discovery, a biological role for YY1 in tumor development and progression has been suggested because of its regulatory activities toward multiple cancer-related proteins and signaling pathways and its overexpression in most cancers. In this review, we primarily focus on YY1 studies in cancer research, including the regulation of YY1 as a transcription factor, its activities independent of its DNA binding ability, the functions of its associated proteins, and mechanisms regulating YY1 expression and activities. We also discuss the correlation of YY1 expression with clinical outcomes of cancer patients and its target potential in cancer therapy. Although there is not a complete consensus about the role of YY1 in cancers based on its activities of regulating oncogene and tumor suppressor expression, most of the currently available evidence supports a proliferative or oncogenic role of YY1 in tumorigenesis.

Different expression of CD146 in human normal and osteosarcoma cell lines

The CD146 cell membrane adhesion molecule is highly expressed on the cell surface of several tumours. The level of its expression has been found to correlate directly with tumour progression and metastatic potential, thus establishing CD146 as an important candidate of tumour growth and metastasis. In order to characterize its expression in human osteosarcoma (OS) cell lines, we have examined the CD146 expression at protein and RNA levels in both normal and tumour osteoblast-like cell lines by several methods. Our results indicate that CD146 protein is expressed at low levels in normal osteoblast cells whereas it is highly expressed in all OS cell lines analysed, (SaOS, MG-63, U-2OS). Moreover, CD146 overexpression was partially reduced in shYY1 cells, where the Yin Yang 1 transcription factor, also found over-expressed in human OS cells, has been silenced.

Regulation of gene transcription by the oncoprotein MYC

The proteins of the MYC/MAX/MAD network are central regulators of many key processes associated with basic cell physiology. These include the regulation of protein biosynthesis, energy metabolism, proliferation, and apoptosis. Molecularly the MYC/MAX/MAD network achieves these broad activities by controlling the expression of many target genes, which are primarily responsible for the diverse physiological consequences elicited by the network. The MYC proteins of the network possess oncogenic activity and their functional deregulation is associated with the majority of human tumors. Over the last years we have witnessed the accumulation of a considerable number of molecular observations that suggest many different biochemical means and tools by which MYC controls gene expression. We will summarize the more recent findings and discuss how these different building blocks might come together to explain how MYC regulates gene transcription. We note that despite the many molecular details known, we do not have an integrated view of how MYC uses the different tools, neither in a spatial nor in a temporal order.

YY1 overexpression is associated with poor prognosis and metastasis-free survival in patients suffering osteosarcoma

Background

The polycomb transcription factor Yin Yang 1 (YY1) overexpression can be causally implicated in experimental tumor growth and metastasization. To date, there is no clinical evidence of YY1 involvement in outcome of patients with osteosarcoma. Prognosis of osteosarcoma is still severe and only few patients survive beyond five years. We performed a prospective immunohistochemistry analysis to correlate YY1 immunostaining with metastatic development and survival in a selected homogeneous group of patients with osteosarcoma.

Methods

We studied 41 patients suffering from osteosarcoma (stage II-IVa). Multivariate analysis was performed using Cox proportional hazard regression to evaluate the correlation between YY1 expression and both metastasis development and mortality.

Results

YY1 protein is not usually present in normal bone; in contrast, a high number of patients (61%) showed a high score of YY1 positive cells (51-100%) and 39% had a low score (10-50% positive cells). No statistical difference was found in histology, anatomic sites, or response to chemotherapy between the two degrees of YY1 expression. Cox regression analysis demonstrated that the highest score of YY1 expression was predictive of both low metastasis-free survival (HR = 4.690, 95%CI = 1.079-20.396; p = 0.039) and poor overall survival (HR = 8.353, 95%CI = 1.863-37.451 p = 0.006) regardless of the effects of covariates such as age, gender, histology and chemonecrosis.

Conclusion

Overexpression of YY1 in primary site of osteosarcoma is associated with the occurrence of metastasis and poor clinical outcome.

Yin Yang 1 contains G-quadruplex structures in its promoter and 5'-UTR and its expression is modulated by G4 resolvase 1

Yin Yang 1 (YY1) is a multifunctional protein with regulatory potential in tumorigenesis. Ample studies demonstrated the activities of YY1 in regulating gene expression and mediating differential protein modifications. However, the mechanisms underlying YY1 gene expression are relatively understudied. G-quadruplexes (G4s) are four-stranded structures or motifs formed by guanine-rich DNA or RNA domains. The presence of G4 structures in a gene promoter or the 5′-UTR of its mRNA can markedly affect its expression. In this report, we provide strong evidence showing the presence of G4 structures in the promoter and the 5′-UTR of YY1. In reporter assays, mutations in these G4 structure forming sequences increased the expression of Gaussia luciferase (Gluc) downstream of either YY1 promoter or 5′-UTR. We also discovered that G4 Resolvase 1 (G4R1) enhanced the Gluc expression mediated by the YY1 promoter, but not the YY1 5′-UTR. Consistently, G4R1 binds the G4 motif of the YY1 promoter in vitro and ectopically expressed G4R1 increased endogenous YY1 levels. In addition, the analysis of a gene array data consisting of the breast cancer samples of 258 patients also indicates a significant, positive correlation between G4R1 and YY1 expression.

Characterization of canine osteosarcoma by array comparative genomic hybridization and RT-qPCR: signatures of genomic imbalance in canine osteosarcoma parallel the human counterpart

Osteosarcoma (OS) is the most commonly diagnosed malignant bone tumor in humans and dogs, characterized in both species by extremely complex karyotypes exhibiting high frequencies of genomic imbalance. Evaluation of genomic signatures in human OS using array comparative genomic hybridization (aCGH) has assisted in uncovering genetic mechanisms that result in disease phenotype. Previous low-resolution (10-20 Mb) aCGH analysis of canine OS identified a wide range of recurrent DNA copy number aberrations, indicating extensive genomic instability. In this study, we profiled 123 canine OS tumors by 1 Mb-resolution aCGH to generate a dataset for direct comparison with current data for human OS, concluding that several high frequency aberrations in canine and human OS are orthologous. To ensure complete coverage of gene annotation, we identified the human refseq genes that map to these orthologous aberrant dog regions and found several candidate genes warranting evaluation for OS involvement. Specifically, subsequenct FISH and qRT-PCR analysis of RUNX2, TUSC3, and PTEN indicated that expression levels correlated with genomic copy number status, showcasing RUNX2 as an OS associated gene and TUSC3 as a possible tumor suppressor candidate. Together these data demonstrate the ability of genomic comparative oncology to identify genetic abberations which may be important for OS progression. Large scale screening of genomic imbalance in canine OS further validates the use of the dog as a suitable model for human cancers, supporting the idea that dysregulation discovered in canine cancers will provide an avenue for complementary study in human counterparts.

CXCR4/YY1 inhibition impairs VEGF network and angiogenesis during malignancy

Tumor growth requires neoangiogenesis. VEGF is the most potent proangiogenic factor. Dysregulation of hypoxia-inducible factor (HIF) or cytokine stimuli such as those involving the chemokine receptor 4/stromal-derived cell factor 1 (CXCR4/SDF-1) axis are the major cause of ectopic overexpression of VEGF in tumors. Although the CXCR4/SDF-1 pathway is well characterized, the transcription factors executing the effector function of this signaling are poorly understood. The multifunctional Yin Yang 1 (YY1) protein is highly expressed in different types of cancers and may regulate some cancer-related genes. The network involving CXCR4/YY1 and neoangiogenesis could play a major role in cancer progression. In this study we have shown that YY1 forms an active complex with HIF-1alpha at VEGF gene promoters and increases VEGF transcription and expression observed by RT-PCR, ELISA, and Western blot using two different antibodies against VEGFB. Long-term treatment with T22 peptide (a CXCR4/SDF-1 inhibitor) and YY1 silencing can reduce in vivo systemic neoangiogenesis (P < 0.01 and P < 0.05 vs. control, respectively) during metastasis. Moreover, using an in vitro angiogenesis assay, we observed that YY1 silencing led to a 60% reduction in branches (P < 0.01) and tube length (P < 0.02) and a 75% reduction in tube area (P < 0.001) compared with control cells. A similar reduction was observed using T22 peptide. We demonstrated that T22 peptide determines YY1 cytoplasmic accumulation by reducing its phosphorylation via down-regulation of AKT, identifying a crosstalk mechanism involving CXCR4/YY1. Thus, YY1 may represent a crucial molecular target for antiangiogenic therapy during cancer progression.

Glycogen synthase kinase 3 beta: can it be a target for oral cancer

Despite progress in treatment approaches for oral cancer, there has been only modest improvement in patient outcomes in the past three decades. The frequent treatment failure is due to the failure to control tumor recurrence and metastasis. These failures suggest that new targets should be identified to reverse oral epithelial dysplastic lesions. Recent developments suggest an active role of glycogen synthase kinase 3 beta (GSK3 β) in various human cancers either as a tumor suppressor or as a tumor promoter. GSK3β is a Ser/Thr protein kinase, and there is emerging evidence that it is a tumor suppressor in oral cancer. The evidence suggests a link between key players in oral cancer that control transcription, accelerated cell cycle progression, activation of invasion/metastasis and anti-apoptosis, and regulation of these factors by GSK3β. Moreover, the major upstream kinases of GSK3β and their oncogenic activation by several etiological agents of oral cancer support this hypothesis. In spite of all this evidence, a detailed analysis of the role of GSK3β in oral cancer and of its therapeutic potential has yet to be conducted by the scientific community. The focus of this review is to discuss the multitude of roles of GSK3β, its possible role in controlling different oncogenic events and how it can be targeted in oral cancer.

Biochemical characterization of Yin Yang 1-RNA complexes

YY1 (Yin Yang 1) is present in the Xenopus oocyte cytoplasm as a constituent of messenger ribonucleoprotein complexes (mRNPs). Association of YY1 with mRNPs requires direct RNA-binding activity. Previously, we have shown YY1 has a high affinity for U-rich RNA; however, potential interactions with plausible in vivo targets have not been investigated. Here we report a biochemical characterization of the YY1-RNA interaction including an investigation of the stability, potential 5'-methylguanosine affinity, and specificity for target RNAs. The formation of YY1-RNA complexes in vitro was highly resistant to thermal, ionic, and detergent disruption. The endogenous oocyte YY1-mRNA interactions were also found to be highly stable. Specific YY1-RNA interactions were observed with selected mRNA and 5S RNA probes. The affinity of YY1 for these substrates was within an order of magnitude of that for its cognate DNA element. Experiments aimed at determining the potential role of the 7-methylguanosine cap on RNA-binding reveal no significant difference in the affinity of YY1 for capped or uncapped mRNA. Taken together, the results show that the YY1-RNA interaction is highly stable, and that YY1 possesses the ability to interact with structurally divergent RNA substrates. These data are the first to specifically document the interaction between YY1 and potential in vivo targets.

Molecular mechanisms of the antiangiogenic and antitumor effects of mycophenolic acid

The relative risk for the development of malignancies following solid organ transplantation seems to be decreased in patients treated with the immunosuppressive agent mycophenolic acid (MPA). However, the molecular mechanisms of the antineoplastic effects of MPA are not completely understood. Here, we report that human endothelial cells and fibroblasts are highly sensitive to MPA treatment. We found that U87 glioblastoma cells were resistant to MPA treatment in vitro. However, U87 tumor growth was markedly inhibited in vivo in BALB/c nude mice, suggesting that MPA exerted its antitumor effects via modulation of the tumor microenvironment. Accordingly, microvascular density and pericyte coverage were markedly reduced in MPA-treated tumors in vivo. Using functional in vitro assays, we showed that MPA potently inhibited endothelial cell and fibroblast proliferation, invasion/migration, and endothelial cell tube formation. To identify the genetic participants governing the antiangiogenic and antifibrotic effects of MPA, we performed genome-wide transcriptional analysis in U87, endothelial and fibroblast cells at 6 and 12 h after MPA treatment. Network analysis revealed a critical role for MYC signaling in endothelial cells treated with MPA. Moreover, we found that the antiangiogenic effects of MPA were organized by coordinated communications between MYC and NDRG1, YYI, HIF1A, HDAC2, CDC2, GSK3B, and PRKACB signaling. The regulation of these "hub nodes" was confirmed by real-time quantitative reverse transcription-PCR and protein analysis. The critical involvement of MYC in the antiangiogenic signaling of MPA was further shown by gene knockdown experiments. Together, these data provide a molecular basis for the antiangiogenic and antifibrotic effects of MPA, which warrants further clinical investigations.

Deletion of Yin Yang 1 protein in osteosarcoma cells on cell invasion and CXCR4/angiogenesis and metastasis

We know that the Yin Yang 1 protein (YY1) overexpression is positively and strongly correlated with the degree of malignancy of bone tumors. Therefore, we questioned whether we could influence cell invasiveness by deleting YY1 in human osteosarcoma cells (SaOs-2), as tested in Matrigel-coated filters and metastasis implantation of such osteosarcoma cells in vivo, by serial analysis with nuclear magnetic resonance. Moreover, we focused our work on the chemokine receptor CXCR4 and its inhibition by T22 antibody, as well as on systemic (direct in vivo assay) and computer-assisted imaging of angiogenesis-related metastasis. Results showed that cell invasiveness and metastasis implantation by wild-type SaOs-2 cells, as evaluated by histology and immunohistochemistry, are associated with up-regulation of CXCR4 expression, which in turn was significantly reduced by T22. In addition, deletion of YY1 (siRNAYY1-SaOs-2) induced a significant decrease of cell invasion and metastasis growth. This phenomenon was associated with decreased vascular endothelial growth factor (VEGF)/angiogenesis and a complex rearrangement of the gene expression profile as evaluated by microarray analysis. In conclusion, YY1 and VEGF/CXCR4 seem to intervene in the pathogenesis of the malignant phenotype of osteosarcoma by acting on cell invasiveness and metastasis growth.

Expression of integrin α3 in colon cancer and its relationship with invasion and metastasis

AIM: To investigate the expression of integrin α3 in colon cancer and its biological significance.

METHODS: Eighty specimens (male: 47 cases; female: 33 cases) of excised colon cancer, 60 lymph nodes, 40 lymph node metastasis tissues (40 cases) and 20 non-metastatic lymph nodes (20 cases) were selected. All specimens were examined through pathological method. Twelve non-tumorous colon mucosal tissues were chosen as controls. Immunohistochemical assay was used to determine the expression of integrin α3.

RESULTS: The positive rates of integrin α3 expression in the primary lesions of colon cancer and lymph node metastasis tissues were obviously lower than those in the non-tumorous colon mucosa and non-metastatic lymph nodes (52/80 vs 12/12; 24/40 vs 18/20, P < 0.05). The expression of integrin α3 in colon cancer had no correlation with the sex and age of patients, but it was weakened gradually with the increasing of Dukes staging and decreasing of tumor differentiation (P < 0.05). In addition, integrin α3 expression in the primary cases with the metastases of lymph node or liver was significantly weaker than that without metastases (25/49 vs 27/31; 1/16 vs 51/64, P < 0.05).

CONCLUSION: The expression of integrinα3 is correlated with the biological behavior of colon cancer.

Prostaglandin F2alpha suppresses rat steroidogenic acute regulatory protein expression via induction of Yin Yang 1 protein and recruitment of histone deacetylase 1 protein

Prostaglandin F2alpha (PGF2alpha) plays a pivotal role in ovarian luteolysis by inhibiting the expression of steroidogenic acute regulatory (StAR) protein, leading to a decrease in intracellular cholesterol transport and luteal steroid production. Previously we have demonstrated that the transcription factor Yin Yang 1 (YY1) bound to three regions in the StAR promoter in vitro and repressed promoter activity. This study further defined the YY1-mediated PGF2alpha effect on the inhibition of StAR protein expression through YY1 interaction with a single region in the StAR promoter in vivo. PGF2alpha consistently suppressed StAR mRNA and protein expression in cultured luteal cells in a dose-dependent manner. PGF2alpha also enhanced YY1 protein expression and binding to its cis-element in a time-dependent pattern that preceded the decline in StAR protein levels. The StAR promoter region bound by YY1 was also associated with histone deacetylase 1 (HDAC1). PGF2alpha treatment promoted HDAC1 binding to and suppressed the histone H3 acetylation in this region. On the contrary, YY1 knockdown decreased HDAC1 binding, increased histone H3 acetylation, enhanced StAR protein expression, and negated PGF2alpha effect on StAR protein expression. Luciferase assays showed that YY1 overexpression inhibited StAR promoter activity and the addition of a HDAC inhibitor, trichostatin A, abrogated the effect of YY1. Trichostatin A-treated luteal cells displayed increased StAR protein expression. These data indicate that PGF2alpha enhances a direct YY1/StAR promoter interaction and the recruitment of HDAC1 to the promoter, thereby preventing transcriptional activation of the StAR gene.