cAMP-responsive element-binding protein regulates vascular endothelial growth factor expression: implication in human prostate cancer bone metastasis

cAMP response element-binding protein: A credible cancer drug target

Despite advancements in radiotherapy, chemotherapy, endocrine therapy, targeted therapy, and immunotherapy, resistance to therapy remains a pervasive challenge in oncology, in part owing to tumor heterogeneity. Identifying new therapeutic targets is key to addressing this challenge because it can both diversify and enhance existing treatment options, particularly through combination regimens. The cAMP response element-binding protein (CREB) is a transcription factor involved in various biological processes. It is aberrantly activated in several aggressive cancer types, including breast cancer. Clinically, high CREB expression is associated with increased breast tumor aggressiveness and poor prognosis. Functionally, CREB promotes breast cancer cell proliferation, survival, invasion, metastasis, as well as therapy resistance by deregulating genes related to apoptosis, cell cycle, and metabolism. Targeting CREB with small molecule inhibitors has demonstrated promise in preclinical studies. This review summarizes the current understanding of CREB mechanisms and their potential as a therapeutic target. SIGNIFICANCE STATEMENT: cAMP response element-binding protein (CREB) is a master regulator of multiple biological processes, including neurodevelopment, metabolic regulation, and immune response. CREB is a putative proto-oncogene in breast cancer that regulates the cell cycle, apoptosis, and cellular migration. Preclinical development of CREB-targeting small molecules is underway.

Disruption of oncogenic pathways in mucoepidermoid carcinoma: CREB inhibitor 666.15 as a potential therapeutic agent

OBJECTIVES

Mucoepidermoid carcinoma (MEC) is the most common malignant salivary gland tumour with around 50 % of cases carrying the CRTC1-MAML2 translocation. The CREB pathway has been associated with the transforming activity of this translocation. The aim of this study was to determine the effects of CREB inhibition on MEC cell behaviour in vitro.

MATERIAL AND METHODS

Two translocation-positive (UM-HMC-2 and H292) and one translocation-negative (H253) MEC cell lines were treated with 666.15, a CREB inhibitor. Drug IC50 doses were determined for each cell line. Clonogenic and spheroid assays were used to assess survival, including percentage of cancer stem cells, and transwell and scratch assays evaluated invasive and migratory capacities, respectively. Immunofluorescence staining was used to determine E-cadherin expression.

RESULTS

CREB inhibition significantly reduced the number of surviving colonies and spheroids and delayed cell invasion in all cell lines, but this was more significant in the fusion positive, UM-HMC-2 cells. The expression of E-cadherin was significantly higher in treated UM-HMC-2 and H292 cells.

CONCLUSION

CREB inhibition with 666.15 impaired key MEC oncogenic behaviours associated with metastasis and drug resistance, including cell invasion and survival.

CREB1 contributes colorectal cancer cell plasticity by regulating lncRNA CCAT1 and NF-κB pathways

The CREB1 gene encodes an exceptionally pleiotropic transcription factor that frequently dysregulated in human cancers. CREB1 can regulate tumor cell status of proliferation and/or migration; however, the molecular basis for this switch involvement in cell plasticity has not fully been understood yet. Here, we first show that knocking out CREB1 triggers a remarkable effect of epithelial-mesenchymal transition (EMT) and leads to the occurrence of inhibited proliferation and enhanced motility in HCT116 colorectal cancer cells. By monitoring 45 cellular signaling pathway activities, we find that multiple growth-related pathways decline significantly while inflammatory pathways including NF-κB are largely upregulated in comparing between the CREB1 wild-type and knocked out cells. Mechanistically, cells with CREB1 knocked out show downregulation of MYC as a result of impaired CREB1-dependent transcription of the oncogenic lncRNA CCAT1. Interestingly, the unbalanced competition between the coactivator CBP/p300 for CREB1 and p65 leads to the activation of the NF-κB pathway in cells with CREB1 disrupted, which induces an obvious EMT phenotype of the cancer cells. Taken together, these studies identify previously unknown mechanisms of CREB1 in CRC cell plasticity via regulating lncRNA CCAT1 and NF-κB pathways, providing a critical insight into a combined strategy for CREB1-targeted tumor therapies.

The Machine-Learning-Mediated Interface of Microbiome and Genetic Risk Stratification in Neuroblastoma Reveals Molecular Pathways Related to Patient Survival

Currently, most neuroblastoma patients are treated according to the Children's Oncology Group (COG) risk group assignment; however, neuroblastoma's heterogeneity renders only a few predictors for treatment response, resulting in excessive treatment. Here, we sought to couple COG risk classification with tumor intracellular microbiome, which is part of the molecular signature of a tumor. We determine that an intra-tumor microbial gene abundance score, namely M-score, separates the high COG-risk patients into two subpopulations (Mhigh and Mlow) with higher accuracy in risk stratification than the current COG risk assessment, thus sparing a subset of high COG-risk patients from being subjected to traditional high-risk therapies. Mechanistically, the classification power of M-scores implies the effect of CREB over-activation, which may influence the critical genes involved in cellular proliferation, anti-apoptosis, and angiogenesis, affecting tumor cell proliferation survival and metastasis. Thus, intracellular microbiota abundance in neuroblastoma regulates intracellular signals to affect patients' survival.

SS18-SSX drives CREB activation in synovial sarcoma

Purpose

Synovial sarcoma (SySa) is a rare soft tissue tumor characterized by a reciprocal t(X;18) translocation. The chimeric SS18-SSX fusion protein represents the major driver of the disease, acting as aberrant transcriptional dysregulator. Oncogenic mechanisms whereby SS18-SSX mediates sarcomagenesis are incompletely understood, and strategies to selectively target SySa cells remain elusive. Based on results of Phospho-Kinase screening arrays, we here investigate the functional and therapeutic relevance of the transcription factor CREB in SySa tumorigenesis.

Methods

Immunohistochemistry of phosphorylated CREB and its downstream targets (Rb, Cyclin D1, PCNA, Bcl-xL and Bcl-2) was performed in a large cohort of SySa. Functional aspects of CREB activity, including SS18-SSX driven circuits involved in CREB activation, were analyzed in vitro employing five SySa cell lines and a mesenchymal stem cell model. CREB mediated transcriptional activity was modulated by RNAi-mediated knockdown and small molecule inhibitors (666-15, KG-501, NASTRp and Ro 31-8220). Anti-proliferative effects of the CREB inhibitor 666-15 were tested in SySa avian chorioallantoic membrane and murine xenograft models in vivo.

Results

We show that CREB is phosphorylated and activated in SySa, accompanied by downstream target expression. Human mesenchymal stem cells engineered to express SS18-SSX promote CREB expression and phosphorylation. Conversely, RNAi-mediated knockdown of SS18-SSX impairs CREB phosphorylation in SySa cells. Inhibition of CREB activity reduces downstream target expression, accompanied by suppression of SySa cell proliferation and induction of apoptosis invitro and in vivo.

Conclusion

In conclusion, our data underline an essential role of CREB in SySa tumorigenesis and provides evidence for molecular targeted therapies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13402-022-00673-w.

Gab2 promotes acute myeloid leukemia growth and migration through the SHP2-Erk-CREB signaling pathway

Acute myeloid leukemia (AML) is a hematologic malignant disease largely affecting older adults with poor outcomes. Lack of effective targeted treatment is a major challenge in managing the disease in the clinic. Scaffolding adaptor Gab2 is amplified in a subset of AML. However, the causative role of Gab2 in AML remains to be explored. In this study, it was found that Gab2 was expressed at high levels in AML patient samples and AML cell lines. Experiments by knocking down Gab2 expression using shRNA showed that Gab2 promoted AML cell growth and migration in vitro and in vivo. Further studies using Gab2 mutants and pharmacological inhibitors revealed that Gab2 increased CREB phosphorylation via the SHP-2/Erk signaling pathway. CREB phosphorylation contributed to Gab2-induced cell migration by increasing MMP2 and MMP9 expression. This research indicates that high Gab2 expression promotes AML progression through the SHP2-Erk-CREB signaling pathway. CREB suppression may help treat AML with high Gab2 expression.

Multi-Omics Analysis Identifying Key Biomarkers in Ovarian Cancer

Ovarian cancer is one of the most common malignant tumors. Here, we aimed to study the expression and function of the CREB1 gene in ovarian cancer via the bioinformatic analyses of multiple databases. Previously, the prognosis of ovarian cancer was based on single-factor or single-gene studies. In this study, different bioinformatics tools (such as TCGA, GEPIA, UALCAN, MEXPRESS, and Metascape) have been used to assess the expression and prognostic value of the CREB1 gene. We used the Reactome and cBioPortal databases to identify and analyze CREB1 mutations, copy number changes, expression changes, and protein-protein interactions. By analyzing data on the CREB1 differential expression in ovarian cancer tissues and normal tissues from 12 studies collected from the "Human Protein Atlas" database, we found a significantly higher expression of CREB1 in normal ovarian tissues. Using this database, we collected information on the expression of 25 different CREB-related proteins, including TP53, AKT1, and AKT3. The enrichment of these factors depended on tumor metabolism, invasion, proliferation, and survival. Individualized tumors based on gene therapy related to prognosis have become a new possibility. In summary, we established a new type of prognostic gene profile for ovarian cancer using the tools of bioinformatics.

Molecular Characterization of NDL1-AGB1 Mediated Salt Stress Signaling: Further Exploration of the Role of NDL1 Interacting Partners

Salt stress is considered to be the most severe abiotic stress. High soil salinity leads to osmotic and ionic toxicity, resulting in reduced plant growth and crop production. The role of G-proteins during salt stresses is well established. AGB1, a G-protein subunit, not only plays an important role during regulation of Na⁺ fluxes in roots, but is also involved in the translocation of Na⁺ from roots to shoots. N-Myc Downregulated like 1 (NDL1) is an interacting partner of G protein βγ subunits and C-4 domain of RGS1 in Arabidopsis. Our recent in-planta expression analysis of NDL1 reported changes in patterns during salt stress. Based on these expression profiles, we have carried out functional characterization of the AGB1-NDL1 module during salinity stress. Using various available mutant and overexpression lines of NDL1 and AGB1, we found that NDL1 acts as a negative regulator during salt stress response at the seedling stage, an opposite response to that of AGB1. On the other hand, during the germination phase of the plant, this role is reversed, indicating developmental and tissue specific regulation. To elucidate the mechanism of the AGB1-NDL1 module, we investigated the possible role of the three NDL1 stress specific interactors, namely ANNAT1, SLT1, and IDH-V, using yeast as a model. The present study revealed that NDL1 acts as a modulator of salt stress response, wherein it can have both positive as well as negative functions during salinity stress. Our findings suggest that the NDL1 mediated stress response depends on its developmental stage-specific expression patterns as well as the differential presence and interaction of the stress-specific interactors.

Pharmacological inhibition of noncanonical EED-EZH2 signaling overcomes chemoresistance in prostate cancer

Rationale: Chemoresistance is a major obstacle in prostate cancer (PCa) treatment. We sought to understand the underlying mechanism of PCa chemoresistance and discover new treatments to overcome docetaxel resistance. Methods: We developed a novel phenotypic screening platform for the discovery of specific inhibitors of chemoresistant PCa cells. The mechanism of action of the lead compound was investigated using computational, molecular and cellular approaches. The in vivo toxicity and efficacy of the lead compound were evaluated in clinically-relevant animal models. Results: We identified LG1980 as a lead compound that demonstrates high selectivity and potency against chemoresistant PCa cells. Mechanistically, LG1980 binds embryonic ectoderm development (EED), disrupts the interaction between EED and enhancer of zeste homolog 2 (EZH2), thereby inducing the protein degradation of EZH2 and inhibiting the phosphorylation and activity of EZH2. Consequently, LG1980 targets a survival signaling cascade consisting of signal transducer and activator of transcription 3 (Stat3), S-phase kinase-associated protein 2 (SKP2), ATP binding cassette B 1 (ABCB1) and survivin. As a lead compound, LG1980 is well tolerated in mice and effectively suppresses the in vivo growth of chemoresistant PCa and synergistically enhances the efficacy of docetaxel in xenograft models. Conclusions: These results indicate that pharmacological inhibition of EED-EZH2 interaction is a novel strategy for the treatment of chemoresistant PCa. LG1980 and its analogues have the potential to be integrated into standard of care to improve clinical outcomes in PCa patients.

Targeting Intercellular Communication in the Bone Microenvironment to Prevent Disseminated Tumor Cell Escape from Dormancy and Bone Metastatic Tumor Growth

Metastasis to the bone is a common feature of many cancers including those of the breast, prostate, lung, thyroid and kidney. Once tumors metastasize to the bone, they are essentially incurable. Bone metastasis is a complex process involving not only intravasation of tumor cells from the primary tumor into circulation, but extravasation from circulation into the bone where they meet an environment that is generally suppressive of their growth. The bone microenvironment can inhibit the growth of disseminated tumor cells (DTC) by inducing dormancy of the DTC directly and later on following formation of a micrometastatic tumour mass by inhibiting metastatic processes including angiogenesis, bone remodeling and immunosuppressive cell functions. In this review we will highlight some of the mechanisms mediating DTC dormancy and the complex relationships which occur between tumor cells and bone resident cells in the bone metastatic microenvironment. These inter-cellular interactions may be important targets to consider for development of novel effective therapies for the prevention or treatment of bone metastases.

Suppression of beta 2 adrenergic receptor actions prevent UVB mediated cutaneous squamous cell tumorigenesis through inhibition of VEGF-A induced angiogenesis

Although beta 2 adrenergic receptors (β2 ADR) are present in the keratinocytes, their role in cutaneous squamous cell tumorigenesis needs to be ascertained. For the first time, we report here that selective β2 ADR antagonists by inhibiting β2 ADR actions significantly retarded the progression of ultraviolet B (UVB) induced premalignant cutaneous squamous cell lesions. These antagonists acted by inhibiting vascular endothelial growth factor-A (VEGF) mediated angiogenesis to prevent UVB radiation-induced squamous cell carcinoma of the skin.

CREB-binding protein (CREBBP) and preeclampsia: a new promising target gene

Preeclampsia (PE) is a major complication of pregnancy and remains a leading cause of neonatal and maternal mortality worldwide. Several studies have revealed that the incidence of preeclampsia is high in mothers who carried a fetus with Rubinstein-Taybi Syndrome due to the mutation in CREBBP. We aimed to compare the expression level of the CERBBP gene between preeclamptic and healthy placenta in our study. The expression level of CREBBP gene was evaluated in a total of one hundred placental biopsies from PE patients and healthy pregnant women after delivery using quantitative real-time polymerase chain reaction (qRT-PCR). Moreover, the differential expression of CREBBP was assessed between the maternal and fetal sides of the placenta. Expression of the CREBBP gene was higher in preeclampsia patients compared with the controls (Fold change = 2.158; P = 0.018). Moreover, the gene expression was slightly higher in the fetal side of the placenta, although it was not significantly different (Fold change = 1.713, P = 0.254). Our findings show a role for CREBBP in the pathogenesis of PE. Due to the important role of CREBBP in angiogenesis and hypoxia, the gene may serve as a promising target in future studies.

Abiraterone Acetate Induces CREB1 Phosphorylation and Enhances the Function of the CBP-p300 Complex, Leading to Resistance in Prostate Cancer Cells

PURPOSE

Abiraterone acetate (AA), an inhibitor of cytochrome P450 17alpha-hydroxylase/17, 20 lyase, is an FDA-approved drug for advanced prostate cancer. However, not all patients respond to AA, and AA resistance ultimately develops in patients who initially respond. We aimed to identify AA resistance mechanisms in prostate cancer cells.

EXPERIMENTAL DESIGN

We established several AA-resistant cell lines and performed a comprehensive study on mechanisms involved in AA resistance development. RNA sequencing and phospho-kinase array screenings were performed to discover that the cAMP-response element CRE binding protein 1 (CREB1) was a critical molecule in AA resistance development.

RESULTS

The drug-resistant cell lines are phenotypically stable without drug selection, and exhibit permanent global gene expression changes. The phosphorylated CREB1 (pCREB1) is increased in AA-resistant cell lines and is critical in controlling global gene expression. Upregulation of pCREB1 desensitized prostate cancer cells to AA, while blocking CREB1 phosphorylation resensitized AA-resistant cells to AA. AA treatment increases intracellular cyclic AMP (cAMP) levels, induces kinases activity, and leads to the phosphorylation of CREB1, which may subsequently augment the essential role of the CBP/p300 complex in AA-resistant cells because AA-resistant cells exhibit a relatively higher sensitivity to CBP/p300 inhibitors. Further pharmacokinetics studies demonstrated that AA significantly synergizes with CBP/p300 inhibitors in limiting the growth of prostate cancer cells.

CONCLUSIONS

Our studies suggest that AA treatment upregulates pCREB1, which enhances CBP/p300 activity, leading to global gene expression alterations, subsequently resulting in drug resistance development. Combining AA with therapies targeting resistance mechanisms may provide a more effective treatment strategy.

A novel miRNA inhibits metastasis of prostate cancer via decreasing CREBBP-mediated histone acetylation

BACKGROUND

To identify novel miRNAs implicated in prostate cancer metastasis.

METHODS

Sixty-five prostate cancer tissues and paired pan-cancer tissues were sequenced. Novel miRNAs were re-analyzed by MIREAP program. Biological functions of miR-N5 were transwell experiment and colony formation. Target genes of miR-N5 were analyzed by bioinformatic analysis. Downstream of target gene was analyzed by The Cancer Genome Atlas (TCGA) and Memorial Sloan Kettering Cancer Center (MSKCC) databases and confirmed by CHIP experiment.

RESULTS

We identified a novel miRNA-miR-N5, which was downregulated in PCa cells, PCa tissue, and in the serum of patients with PCa. Knockout of miR-N5 enhanced migration and invasiveness in vitro. miR-N5 specified targeted CREBBP 3'-UTR and inhibited CREBBP expression, which mediated H3K56 acetylation at the promoter of EGFR, β-catenin and CDH1.

CONCLUSION

This study may shed the light on miR-N5 which influences metastasis via histone acetylation.

Arginine vasopressin receptor 1a is a therapeutic target for castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) recurs after androgen deprivation therapy (ADT) and is incurable. Reactivation of androgen receptor (AR) signaling in the low androgen environment of ADT drives CRPC. This AR activity occurs through a variety of mechanisms, including up-regulation of AR coactivators such as VAV3 and expression of constitutively active AR variants such as the clinically relevant AR-V7. AR-V7 lacks a ligand-binding domain and is linked to poor prognosis. We previously showed that VAV3 enhances AR-V7 activity to drive CRPC progression. Gene expression profiling after depletion of either VAV3 or AR-V7 in CRPC cells revealed arginine vasopressin receptor 1a (AVPR1A) as the most commonly down-regulated gene, indicating that this G protein-coupled receptor may be critical for CRPC. Analysis of publicly available human PC datasets showed that AVPR1A has a higher copy number and increased amounts of mRNA in advanced PC. Depletion of AVPR1A in CRPC cells resulted in decreased cell proliferation and reduced cyclin A. In contrast, androgen-dependent PC, AR-negative PC, or nontumorigenic prostate epithelial cells, which have undetectable AVPR1A mRNA, were minimally affected by AVPR1A depletion. Ectopic expression of AVPR1A in androgen-dependent PC cells conferred castration resistance in vitro and in vivo. Furthermore, treatment of CRPC cells with the AVPR1A ligand, arginine vasopressin (AVP), activated ERK and CREB, known promoters of PC progression. A clinically safe and selective AVPR1A antagonist, relcovaptan, prevented CRPC emergence and decreased CRPC orthotopic and bone metastatic growth in mouse models. Based on these preclinical findings, repurposing AVPR1A antagonists is a promising therapeutic approach for CRPC.

Sofosbuvir Activates EGFR-Dependent Pathways in Hepatoma Cells with Implications for Liver-Related Pathological Processes

Direct acting antivirals (DAAs) revolutionized the therapy of chronic hepatitis C infection. However, unexpected high recurrence rates of hepatocellular carcinoma (HCC) after DAA treatment became an issue in patients with advanced cirrhosis and fibrosis. In this study, we aimed to investigate an impact of DAA treatment on the molecular changes related to HCC development and progression in hepatoma cell lines and primary human hepatocytes. We found that treatment with sofosbuvir (SOF), a backbone of DAA therapy, caused an increase in EGFR expression and phosphorylation. As a result, enhanced translocation of EGFR into the nucleus and transactivation of factors associated with cell cycle progression, B-MYB and Cyclin D1, was detected. Serine/threonine kinase profiling identified additional pathways, especially the MAPK pathway, also activated during SOF treatment. Importantly, the blocking of EGFR kinase activity by erlotinib during SOF treatment prevented all downstream events. Altogether, our findings suggest that SOF may have an impact on pathological processes in the liver via the induction of EGFR signaling. Notably, zidovudine, another nucleoside analogue, exerted a similar cell phenotype, suggesting that the observed effects may be induced by additional members of this drug class.

CREB1 is affected by the microRNAs miR-22-3p, miR-26a-5p, miR-27a-3p, and miR-221-3p and correlates with adverse clinicopathological features in renal cell carcinoma

The transcription factor cAMP response element-binding protein (CREB1) has been shown to be involved in diverse biological pathways including the regulation of cell proliferation, apoptosis, cell cycle progression, and metastasis. In this context, aberrant expression of CREB1 and the functional consequences are well investigated in a number of hematopoietic and solid tumors. However, CREB1 expression and underlying control mechanisms are only poorly analyzed in renal cell carcinoma (RCC). The present study confirmed a deregulation of CREB1 protein in the clear cell type of RCC (ccRCC) and analysis of in-house ccRCC cell lines suggested a post-transcriptional control. The combination of miRNA enrichment assay, in silico analysis and molecular biological approaches revealed four novel CREB1-regulating miRNAs, namely miR-22-3p, miR-26a-5p, miR-27a-3p, and miR-221-3p. Categorizing RCC samples as CREB1 negative or positive, respectively, the expression of these miRNAs was found to be inversely correlated with CREB1 protein levels. Analyzing 453 consecutive RCC tumors by immunohistochemistry, weakly negative, but significant correlations of CREB1 with tumor stage and grade, vascular invasion (V1) and lymphovascular invasion (L1) were found. In this respect, ccRCC might differ from other solid tumors like esophageal squamous-cell carcinoma or glioma.

Arabidopsis NDL-AGB1 modules Play Role in Abiotic Stress and Hormonal Responses Along with Their Specific Functions

Arabidopsis N-MYC Downregulated Like Proteins (NDLs) are interacting partners of G-Protein core components. Animal homologs of the gene family N-myc downstream regulated gene (NDRG) has been found to be induced during hypoxia, DNA damage, in presence of reducing agent, increased intracellular calcium level and in response to metal ions like nickel and cobalt, which indicates the involvement of the gene family during stress responses. ArabidopsisNDL gene family contains three homologs NDL1, NDL2 and NDL3 which share up to 75% identity at protein level. Previous studies on NDL proteins involved detailed characterization of the role of NDL1; roles of other two members were also established in root and shoot development using miRNA knockdown approach. Role of entire family in development has been established but specific functions of NDL2 and NDL3 if any are still unknown. Our in-silico analysis of NDLs promoters reveled that all three members share some common and some specific transcription factors (TFs) binding sites, hinting towards their common as well as specific functions. Based on promoter elements characteristics, present study was designed to carry out comparative analysis of the Arabidopsis NDL family during different stages of plant development, under various abiotic stresses and plant hormonal responses, in order to find out their specific and combined roles in plant growth and development. Developmental analysis using GUS fusion revealed specific localization/expression during different stages of development for all three family members. Stress analysis after treatment with various hormonal and abiotic stresses showed stress and tissue-specific differential expression patterns for all three NDL members. All three NDL members were collectively showed role in dehydration stress along with specific responses to various treatments. Their specific expression patterns were affected by presence of interacting partner the Arabidopsis heterotrimeric G-protein β subunit 1 (AGB1). The present study will improve our understanding of the possible molecular mechanisms of action of the independent NDL–AGB1 modules during stress and hormonal responses. These findings also suggest potential use of this knowledge for crop improvement.

Extracellular lipid loading augments hypoxic paracrine signaling and promotes glioma angiogenesis and macrophage infiltration

BACKGROUND

Primary brain tumors, in particular glioblastoma (GBM), remain among the most challenging cancers. Like most malignant tumors, GBM is characterized by hypoxic stress that triggers paracrine, adaptive responses, such as angiogenesis and macrophage recruitment, rescuing cancer cells from metabolic catastrophe and conventional oncological treatments. The unmet need of strategies to efficiently target tumor "stressness" represents a strong clinical motivation to better understand the underlying mechanisms of stress adaptation. Here, we have investigated how lipid loading may be involved in the paracrine crosstalk between cancer cells and the stromal compartment of the hypoxic tumor microenvironment.

METHODS

Regions from patient GBM tumors with or without the lipid loaded phenotype were isolated by laser capture microdissection and subjected to comparative gene expression analysis in parallel with cultured GBM cells with or without lipid loading. The potential involvement of extracellular lipids in the paracrine crosstalk with stromal cells was studied by immunoprofiling of the secretome and functional studies in vitro as well as in various orthotopic GBM mouse models, including hyperlipidemic ApoE-/- mice. Statistical analyses of quantitative experimental methodologies were performed using unpaired Student's T test. For survival analyses of mouse experiments, log-rank test was used, whereas Kaplan-Meier was performed to analyze patient survival.

RESULTS

We show that the lipid loaded niche of GBM patient tumors exhibits an amplified hypoxic response and that the acquisition of extracellular lipids by GBM cells can reinforce paracrine activation of stromal cells and immune cells. At the functional level, we show that lipid loading augments the secretion of e.g. VEGF and HGF, and may potentiate the cross-activation of endothelial cells and macrophages. In line with these data, in vivo studies suggest that combined local tumor lipid loading and systemic hyperlipidemia of ApoE-/- mice receiving a high fat diet induces tumor vascularization and macrophage recruitment, and was shown to significantly decrease animal survival.

CONCLUSIONS

Together, these data identify extracellular lipid loading as a potentially targetable modulator of the paracrine adaptive response in the hypoxic tumor niche and suggest the contribution of the distinct lipid loaded phenotype in shaping the glioma microenvironment.

Müller cells in pathological retinal angiogenesis

Müller cells are the major glial cells spanning the entire layer of the retina and maintaining retinal structure. Under pathological conditions, Müller cells are involved in retinal angiogenesis, a process of growing new blood vessels from pre-existing capillaries. In response to hypoxia, high glucose, and inflammation conditions, multiple signaling pathways are activated in Müller cells, followed by the increased production of proangiogenic factors including vascular endothelial growth factor, basic fibroblast growth factor, matrix metalloproteinases, Netrin-4, and angiopoietin-like 4. Expression of antiangiogenic factors is also downregulated in Müller cells. Besides, proliferation and dedifferentiation of Müller cells facilitates retinal angiogenesis. In this review, we summarized molecular mechanisms of Müller cells-related retinal angiogenesis. The potential of Müller cells as a therapeutic target for retinal angiogenesis was also discussed.

Cyclic nucleotide signaling in sensory neuron hyperexcitability and chronic pain after nerve injury

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Activation of cAMP-PKA and cGMP-PKG pathways contributes to injury-induced sensory neuron hyperexcitability.

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Activation of cAMP and cGMP contributes to the development of bone cancer pain.

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PAR2 activation mediates injury-induced cAMP-dependent sensory neuron hyperexcitability.

The cyclic nucleotide signaling, including cAMP-PKA and cGMP-PKG pathways, has been well known to play critical roles in regulating cellular growth, metabolism and many other intracellular processes. In recent years, more and more studies have uncovered the roles of cAMP and cGMP in the nervous system. The cAMP and cGMP signaling mediates chronic pain induced by different forms of injury and stress. Here we summarize the roles of cAMP-PKA and cGMP-PKG signaling pathways in the pathogenesis of chronic pain after nerve injury. In addition, acute dissociation and chronic compression of the dorsal root ganglion (DRG) neurons, respectively, leads to neural hyperexcitability possibly through PAR2 activation-dependent activation of cAMP-PKA pathway. Clinically, radiotherapy can effectively alleviate bone cancer pain at least partly through inhibiting the cancer cell-induced activation of cAMP-PKA pathway. Roles of cyclic nucleotide signaling in neuropathic and inflammatory pain are also seen in many other animal models and are involved in many pro-nociceptive mechanisms including the activation of hyperpolarization-activated cyclic nucleotide (HCN)-modulated ion channels and the exchange proteins directly activated by cAMP (EPAC). Further understanding the roles of cAMP and cGMP signaling in the pathogenesis of chronic pain is theoretically significant and clinically valuable for treatment of chronic pain.

Small molecule nAS-E targeting cAMP response element binding protein (CREB) and CREB-binding protein interaction inhibits breast cancer bone metastasis

Bone is the most common metastatic site for breast cancer. The excessive osteoclast activity in the metastatic bone lesions often produces osteolysis. The cyclic-AMP (cAMP)-response element binding protein (CREB) serves a variety of biological functions including the transformation and immortalization of breast cancer cells. In addition, evidence has shown that CREB plays a key role in osteoclastgenesis and bone resorption. Small organic molecules with good pharmacokinetic properties and specificity, targeting CREB-CBP (CREB-binding protein) interaction to inhibit CREB-mediated gene transcription have attracted more considerations as cancer therapeutics. We recently identified naphthol AS-E (nAS-E) as a cell-permeable inhibitor of CREB-mediated gene transcription through inhibiting CREB-CBP interaction. In this study, we tested the effect of nAS-E on breast cancer cell proliferation, survival, migration as well as osteoclast formation and bone resorption in vitro for the first time. Our results demonstrated that nAS-E inhibited breast cancer cell proliferation, migration, survival and suppressed osteoclast differentiation as well as bone resorption through inhibiting CREB-CBP interaction. In addition, the in vivo effect of nAS-E in protecting against breast cancer-induced osteolysis was evaluated. Our results indicated that nAS-E could reverse bone loss induced by MDA-MB-231 tumour. These results suggest that small molecules targeting CREB-CBP interaction to inhibit CREB-mediated gene transcription might be a potential approach for the treatment of breast cancer bone metastasis.

Adrb2 controls glucose homeostasis by developmental regulation of pancreatic islet vasculature

A better understanding of processes controlling the development and function of pancreatic islets is critical for diabetes prevention and treatment. Here, we reveal a previously unappreciated function for pancreatic β2-adrenergic receptors (Adrb2) in controlling glucose homeostasis by restricting islet vascular growth during development. Pancreas-specific deletion of Adrb2 results in glucose intolerance and impaired insulin secretion in mice, and unexpectedly, specifically in females. The metabolic phenotypes were recapitulated by Adrb2 deletion from neonatal, but not adult, β-cells. Mechanistically, Adrb2 loss increases production of Vascular Endothelial Growth Factor-A (VEGF-A) in female neonatal β-cells and results in hyper-vascularized islets during development, which in turn, disrupts insulin production and exocytosis. Neonatal correction of islet hyper-vascularization, via VEGF-A receptor blockade, fully rescues functional deficits in glucose homeostasis in adult mutant mice. These findings uncover a regulatory pathway that functions in a sex-specific manner to control glucose metabolism by restraining excessive vascular growth during islet development.

Repositioning Dopamine D2 Receptor Agonist Bromocriptine to Enhance Docetaxel Chemotherapy and Treat Bone Metastatic Prostate Cancer

Docetaxel resistance remains a major obstacle in the treatment of prostate cancer bone metastasis. In this study, we demonstrate that the dopamine D2 receptor (DRD2) agonist bromocriptine effectively enhances docetaxel efficacy and suppresses skeletal growth of prostate cancer in preclinical models. DRD2 is ubiquitously expressed in prostate cancer cell lines and significantly reduced in prostate cancer tissues with high Gleason score. Bromocriptine has weak to moderate cytotoxicity in prostate cancer cells, but effectively induces cell-cycle arrest. At the molecular level, bromocriptine inhibits the expression of c-Myc, E2F-1, and survivin and increases the expression of p53, p21, and p27. Intriguingly, bromocriptine markedly reduces androgen receptor levels, partially through Hsp90-mediated protein degradation. The combination of bromocriptine and docetaxel demonstrates enhanced in vitro cytotoxicity in prostate cancer cells and significantly retards the skeletal growth of C4-2-Luc tumors in mice. Collectively, these results provide the first experimental evidence for repurposing bromocriptine as an effective adjunct therapy to enhance docetaxel efficacy in prostate cancer. Mol Cancer Ther; 17(9); 1859-70. ©2018 AACR.

Tolerance to sustained activation of the cAMP/Creb pathway activity in osteoblastic cells is enabled by loss of p53

The loss of p53 function is a central event in the genesis of osteosarcoma (OS). How mutation of p53 enables OS development from osteoblastic lineage cells is poorly understood. We and others have reported a key role for elevated and persistent activation of the cAMP/PKA/Creb1 pathway in maintenance of OS. In view of the osteoblast lineage being the cell of origin of OS, we sought to determine how these pathways interact within the context of the normal osteoblast. Normal osteoblasts (p53 WT) rapidly underwent apoptosis in response to acute elevation of cAMP levels or activity, whereas p53-deficient osteoblasts tolerated this aberrant cAMP/Creb level and activity. Using the p53 activating small-molecule Nutlin-3a and cAMP/Creb1 activator forskolin, we addressed the question of how p53 responds to the activation of cAMP. We observed that p53 acts dominantly to protect cells from excessive cAMP accumulation. We identify a Creb1-Cbp complex that functions together with and interacts with p53. Finally, translating these results we find that a selective small-molecule inhibitor of the Creb1-Cbp interaction demonstrates selective toxicity to OS cells where this pathway is constitutively active. This highlights the cAMP/Creb axis as a potentially actionable therapeutic vulnerability in p53-deficient tumors such as OS. These results define a mechanism through which p53 protects normal osteoblasts from excessive or abnormal cAMP accumulation, which becomes fundamentally compromised in OS.

Acquired SETD2 mutation and impaired CREB1 activation confer cisplatin resistance in metastatic non-small cell lung cancer

Resistance to chemotherapy remains a critical barrier to effective cancer treatment. Although cisplatin is one of the most commonly used chemotherapeutic agents in the treatment of non-small cell lung cancer (NSCLC), mechanisms of resistance to this drug are not fully understood. Here, we report a novel cisplatin-resistance mechanism involving SET Domain Containing 2 (SETD2), a histone H3 lysine 36 (H3K36) trimethyltransferase, and cAMP-responsive element-binding protein 1 (CREB1). A549 cells selected in vivo to give brain metastases exhibited cisplatin resistance and decreased expression of phosphorylated CREB1. Next-generation sequencing (NGS) analysis identified a missense mutation in SETD2 (p.T1171K), and we demonstrated that SETD2-mediated trimethylation of H3K36 (H3K36me3) and CREB1 phosphorylation are critical for cellular sensitivity to cisplatin. Moreover, we showed that suppression of SETD2 or CREB1 and ectopic expression of mutant SETD2 conferred cisplatin resistance through inhibition of H3K36me3 and ERK activation in NSCLC cells. Our results provide evidence that SETD2 and CREB1 contribute to cisplatin cytotoxicity via regulation of the ERK signaling pathway, and their inactivation may lead to cisplatin resistance.

Chemical modulation of transcription factors

Transcription factors (TFs) constitute a diverse class of sequence-specific DNA-binding proteins, which are key to the modulation of gene expression. TFs have been associated with human diseases, including cancer, Alzheimer's and other neurodegenerative diseases, which makes this class of proteins attractive targets for chemical biology and medicinal chemistry research. Since TFs lack a common binding site or structural similarity, the development of small molecules to efficiently modulate TF biology in cells and in vivo is a challenging task. This review highlights various strategies that are currently being explored for the identification and development of modulators of Myc, p53, Stat, Nrf2, CREB, ER, AR, HIF, NF-κB, and BET proteins.

Inhibition of ER stress-related IRE1α/CREB/NLRP1 pathway promotes the apoptosis of human chronic myelogenous leukemia cell

Endoplasmic reticulum (ER) stress is induced in chronic myelogenous leukemia (CML) cells. As an important sensor of ER stress, inositol-requiring protein-1α (IRE1α) promotes the survival of acute myeloid leukemia. NLRP1 inflammasome activation promotes metastatic melanoma growth and that IRE1α can increase NLRP1 inflammasome gene expression. This study aimed to investigate the role and molecular mechanism of IRE1α in CML cell growth. We found that overexpression of IRE1α or NLRP1 significantly promoted the proliferation and decreased the apoptosis of CML cells, whereas downregulation of these two genes showed the opposite effects. 4-phenylbutyric acid (4-PBA), an ER stress inhibitor, reduced the expression of IRE1α and NLRP1. IRE1α elevated NLRP1 expression via cAMP responsive element binding protein (CREB) phosphorylation. NLRP1 inflammasome was activated in CML cells and its activation partly reversed ER stress inhibitor-induced cell apoptosis. Furthermore, inhibition of IRE1α/NLRP1 pathway sensitized CML cells to imatinib-mediated apoptosis. Additionally, IRE1α expression was elevated and NLRP1 inflammasome was activated in primary cells from CML patients. Downregulation of IRE1α or NLRP1 suppressed the proliferation and elevated the apoptosis of primary CML cells. Collectively, this study demonstrated that the IRE1α/CREB/NLRP1 pathway contributes to the progression of CML and the development of imatinib resistance. Hence, targeting ER stress-related IRE1α expression or NLRP1 inflammasome activation may block CML development.

Expression of Hypoxia Inducible Factor 1alpha Is Protein Kinase A-dependent in Primary Cortical Astrocytes Exposed to Severe Hypoxia

The hypoxia inducible factor 1 (HIF-1) and the cyclic AMP-responsive element binding protein (CREB) are two transcription factors that have been studied in the context of neuronal survival and neurodegeneration. HIF-1 upregulation and CREB activation have been observed not only in neurons but also in astrocytes under conditions of hypoxia. We hypothesized that activation of CREB regulate HIF-1α expression in the nucleus of cortical astrocytes under in vitro ischemic condition. To test the hypothesis, we determined the effects of inhibiting the CREB activation pathway on the expression of HIF-1α protein in astrocytes exposed to CoCl₂ and severe hypoxia (near anoxia, 0.1% O₂). The results demonstrated that inhibition of CaMKII and CaMKIV had no effect on both HIF-1α and pCREB expression in cortical astrocytes exposed to CoCl₂ and anoxia. In contrast, PKA inhibition lowered the expression of HIF-1α and pCREB expression. Furthermore, the inhibition of PKA but not CaMKII or CaMKIV increased cell death of astrocytes exposed to near anoxia. The results suggest that PKA plays an important role in the cell survival signaling pathways in astrocytes.

Dendritic cell-derived VEGF-A plays a role in inflammatory angiogenesis of human secondary lymphoid organs and is driven by the coordinated activation of multiple transcription factors

Lymph node expansion during inflammation is essential to establish immune responses and relies on the development of blood and lymph vessels. Previous work in mice has shown that this process depends on the presence of VEGF-A produced by B cells, macrophages and stromal cells. In humans, however, the cell types and the mechanisms regulating the intranodal production of VEGF-A remain elusive. Here we show that CD11c⁺ cells represent the main VEGF-A-producing cell population in human reactive secondary lymphoid organs. In addition we find that three transcription factors, namely CREB, HIF-1α and STAT3, regulate the expression of VEGF-A in inflamed DCs. Both HIF-1α and STAT3 are activated by inflammatory agonists. Conversely, CREB phosphorylation represents the critical contribution of endogenous or exogenous PGE₂. Taken together, these results propose a crucial role for DCs in lymph node inflammatory angiogenesis and identify novel potential cellular and molecular targets to limit inflammation in chronic diseases and tumors.

c-Met, CREB1 and EGFR are involved in miR-493-5p inhibition of EMT via AKT/GSK-3β/Snail signaling in prostate cancer

miR-493-5p downregulation has emerged as a critical player in cancer progression yet, the underlying mechanisms of miR-493-5p expression pattern and its function in prostate cancer remains to be elucidated. Here, we illustrate that miR-493-5p is frequently downregulated in prostate cancer, at least partially due to altered DNA methylation. miR-493-5p functions as a tumor suppressor in prostate cancer cells. c-Met, CREB1 and EGFR are downstream target genes of miR-493-5p. miR-493-5p inhibits EMT via AKT/GSK-3β/Snail signaling in prostate cancer. Taken together, our study identified c-Met, CREB1, EGFR and miR-493-5p establish a regulatory loop in prostate cancer, which could prove useful in the development of effective and therapies against prostate cancer.

Functional consequence of the p53 codon 72 polymorphism in colorectal cancer

BACKGROUND

The codon 72 polymorphism in p53 has been implicated in colorectal cancer (CRC) risk, prognosis and CRC health disparities. We examined the functional consequence of this polymorphism in CRC.

EXPERIMENTAL DESIGN

Plasmids (pCMV6) that express different phenotypes of p53 [p53 wild type (wt) at codon 72 (R72wt), R72wt with mutation at codon 273 cysteine (R72273Cys), p53 mutation at codon 72 (P72wt) and P72wt with mutation at codon 273 (P72273Cys)] were constructed. The CRC cell line Caco2, which does not express p53 for in vitro studies, was used as host. CRC xenografts were established in severe combined immunodeficient (SCID) mice using established cell lines. CRC surgical specimens, corresponding normal colon, and tumor xenografts were sequenced for codon 72 polymorphism of p53. Proteins signaling mechanisms were evaluated to assess the functional consequence of P72 phenotype of p53.

RESULTS

This study demonstrated a significantly increased survival of cells expressing P72wt, mutant phenotype, versus R72wt phenotype. WB analyses revealed that P72wt induced activation of p38 and RAF/MEK/ extracellular signal-regulated kinase (ERK) MAP kinases. Activation of CREB was found to be higher in tumors that exhibit P72 phenotype. Metastatic lesions of CRC expressed more phospho-CREB than non-metastatic lesions. The expression of P72wt promoted CRC metastasis.

CONCLUSIONS

P72 contributes to the aggressiveness of CRC. Because P72 is over-expressed in CRC, specifically in African-American patients, this suggests a role for P72 in cancer health disparities. This work was supported by NIH/NCI Workforce Diversity Grant R21-CA171251 & U54CA118948.

CREB1 regulates glucose transport of glioma cell line U87 by targeting GLUT1

Glioma is stemmed from the glial cells in the brain, which is accounted for about 45% of all intracranial tumors. The characteristic of glioma is invasive growth, as well as there is no obvious boundary between normal brain tissue and glioma tissue, so it is difficult to resect completely with worst prognosis. The metabolism of glioma is following the Warburg effect. Previous researches have shown that GLUT1, as a glucose transporter carrier, affected the Warburg effect, but the molecular mechanism is not very clear. CREB1 (cAMP responsive element-binding protein1) is involved in various biological processes, and relevant studies confirmed that CREB1 protein regulated the expression of GLUT1, thus mediating glucose transport in cells. Our experiments mainly reveal that the CREB1 could affect glucose transport in glioma cells by regulating the expression of GLUT1, which controlled the metabolism of glioma and affected the progression of glioma.

α-Tocopheryl Phosphate Induces VEGF Expression via CD36/PI3Kγ in THP-1 Monocytes

The CD36 scavenger receptor binds several ligands and mediates ligand uptake and ligand-dependent signal transduction and gene expression, events that may involve CD36 internalization. Here we show that CD36 internalization in THP-1 monocytes is triggered by α-tocopherol (αT) and more strongly by α-tocopheryl phosphate (αTP) and EPC-K1, a phosphate diester of αTP and L-ascorbic acid. αTP-triggered CD36 internalization is prevented by the specific covalent inhibitor of selective lipid transport by CD36, sulfo-N-succinimidyl oleate (SSO). Moreover, SSO inhibited the CD36-mediated uptake of 14C-labelled αTP suggesting that αTP binding and internalization of CD36 is involved in cellular αTP uptake, whereas the uptake of αT was less affected. Similar to that, inhibition of selective lipid transport of the SR-BI scavenger receptor resulted mainly in reduction of αTP and not αT uptake. In contrast, uptake of αT was mainly inhibited by Dynasore, an inhibitor of clathrin-mediated endocytosis, suggesting that the differential regulatory effects of αTP and αT on signaling may be influenced by their different routes of uptake. Interestingly, αTP and EPC-K1 also reduced the neutral lipid content of THP-1 cells and the phagocytosis of fluorescent Staphylococcus aureus bioparticles. Moreover, induction of the vascular endothelial growth factor (VEGF) promoter activity by αTP occurred via CD36/PI3Kγ/Akt, as it could be inhibited by specific inhibitors of this pathway (SSO, Wortmannin, AS-605240). These results suggest that αTP activates PI3Kγ/Akt signaling leading to VEGF expression in monocytes after binding to and/or transport by CD36, a receptor known to modulate angiogenesis in response to amyloid beta, oxLDL, and thrombospondin. J. Cell. Biochem. 118: 1855-1867, 2017. © 2017 Wiley Periodicals, Inc.

Roles of p300 and cyclic adenosine monophosphate response element binding protein in high glucose-induced hypoxia-inducible factor 1α inactivation under hypoxic conditions

Aims/Introduction

Given the high prevalence of diabetes and burn injuries worldwide, it is essential to dissect the underlying mechanism of delayed burn wound healing in diabetes patients, especially the high glucose‐induced hypoxia‐inducible factor 1 (HIF‐1)‐mediated transcription defects.

Materials and Methods

Human umbilical vein endothelial cells were cultured with low or high concentrations of glucose. HIF‐1α‐induced vascular endothelial growth factor (VEGF) transcription was measured by luciferase assay. Immunofluorescence staining was carried out to visualize cyclic adenosine monophosphate response element binding protein (CREB) localization. Immunoprecipitation was carried out to characterize the association between HIF‐1α/p300/CREB. To test whether p300, CREB or p300+CREB co‐overexpression was sufficient to rescue the HIF‐1‐mediated transcription defect after high glucose exposure, p300, CREB or p300+CREB co‐overexpression were engineered, and VEGF expression was quantified. Finally, in vitro angiogenesis assay was carried out to test whether the high glucose‐induced angiogenesis defect is rescuable by p300 and CREB co‐overexpression.

Results

Chronic high glucose treatment resulted in impaired HIF‐1‐induced VEGF transcription and CREB exclusion from the nucleus. P300 or CREB overexpression alone cannot rescue high glucose‐induced HIF‐1α transcription defects. In contrast, co‐overexpression of p300 and CREB dramatically ameliorated high glucose‐induced impairment of HIF‐1‐mediated VEGF transcription, as well as in vitro angiogenesis. Finally, we showed that co‐overexpression of p300 and CREB rectifies the dissociation of HIF‐1α‐p300‐CREB protein complex in chronic high glucose‐treated cells.

Conclusion

Both p300 and CREB are required for the function integrity of HIF‐1α transcription machinery and subsequent angiogenesis, suggesting future studies to improve burn wound healing might be directed to optimization of the interaction between p300, CREB and HIF‐1α.

Understanding the CREB1-miRNA feedback loop in human malignancies

cAMP response element binding protein 1 (CREB1, CREB) is a key transcription factor that mediates transcriptional responses to a variety of growth factors and stress signals. CREB1 has been shown to play a critical role in development and progression of tumors. MicroRNAs (miRNAs) are a class of non-coding RNAs. They post-transcriptionally regulate gene expression through pairing with the 3'-UTR of their target mRNAs and thus regulate initiation and progression of various types of human cancers. Recent studies have demonstrated that a number of miRNAs can be transcriptionally regulated by CREB1. Interestingly, CREB1 expression can also be modulated by miRNAs, thus forming a feedback loop. This review outlines the functional roles of CREB1, miRNA, and their interactions in human malignancies. This will help to define a relationship between CREB1 and miRNA in human cancer and develop novel therapeutic strategies.

Activation of PKA leads to mesenchymal-to-epithelial transition and loss of tumor-initiating ability

The epithelial-to-mesenchymal transition enables carcinoma cells to acquire malignancy-associated traits and the properties of tumor-initiating cells (TICs). TICs have emerged in recent years as important targets for cancer therapy, owing to their ability to drive clinical relapse and enable metastasis. Here, we propose a strategy to eliminate mesenchymal TICs by inducing their conversion to more epithelial counterparts that have lost tumor-initiating ability. We report that increases in intracellular levels of the second messenger, adenosine 3',5'-monophosphate, and the subsequent activation of protein kinase A (PKA) induce a mesenchymal-to-epithelial transition (MET) in mesenchymal human mammary epithelial cells. PKA activation triggers epigenetic reprogramming of TICs by the histone demethylase PHF2, which promotes their differentiation and loss of tumor-initiating ability. This study provides proof-of-principle for inducing an MET as differentiation therapy for TICs and uncovers a role for PKA in enforcing and maintaining the epithelial state.

Regulator of G Protein Signaling 17 as a Negative Modulator of GPCR Signaling in Multiple Human Cancers

Regulators of G protein signaling (RGS) proteins modulate G protein-coupled receptor (GPCR) signaling networks by terminating signals produced by active Gα subunits. RGS17, a member of the RZ subfamily of RGS proteins, is typically only expressed in appreciable amounts in the human central nervous system, but previous works have shown that RGS17 expression is selectively upregulated in a number of malignancies, including lung, breast, prostate, and hepatocellular carcinoma. In addition, this upregulation of RGS17 is associated with a more aggressive cancer phenotype, as increased proliferation, migration, and invasion are observed. Conversely, decreased RGS17 expression diminishes the response of ovarian cancer cells to agents commonly used during chemotherapy. These somewhat contradictory roles of RGS17 in cancer highlight the need for selective, high-affinity inhibitors of RGS17 to use as chemical probes to further the understanding of RGS17 biology. Based on current evidence, these compounds could potentially have clinical utility as novel chemotherapeutics in the treatment of lung, prostate, breast, and liver cancers. Recent advances in screening technologies to identify potential inhibitors coupled with increasing knowledge of the structural requirements of RGS-Gα protein-protein interaction inhibitors make the future of drug discovery efforts targeting RGS17 promising. This review highlights recent findings related to RGS17 as both a canonical and atypical RGS protein, its role in various human disease states, and offers insights on small molecule inhibition of RGS17.

Artesunate suppresses tumor growth and induces apoptosis through the modulation of multiple oncogenic cascades in a chronic myeloid leukemia xenograft mouse model

Artesunate (ART), a semi-synthetic derivative of artemisinin, is one of the most commonly used anti-malarial drugs. Also, ART possesses anticancer potential albeit through incompletely understood molecular mechanism(s). Here, the effect of ART on various protein kinases, associated gene products, cellular response, and apoptosis was investigated. The in vivo effect of ART on the growth of human CML xenograft tumors in athymic nu/nu mice was also examined. In our preliminary experiments, we first observed that phosphorylation of p38, ERK, CREB, Chk-2, STAT5, and RSK proteins were suppressed upon ART exposure. Interestingly, ART induced the expression of SOCS-1 protein and depletion of SOCS-1 using siRNA abrogated the STAT5 inhibitory effect of the drug. Also various dephosphorylations caused by ART led to the suppression of various survival gene products and induced apoptosis through caspase-3 activation. Moreover, ART also substantially potentiated the apoptosis induced by chemotherapeutic agents. Finally, when administered intraperitoneally, ART inhibited p38, ERK, STAT5, and CREB activation in tumor tissues and the growth of human CML xenograft tumors in mice without exhibiting any significant adverse effects. Overall, our results suggest that ART exerts its anti-proliferative and pro-apoptotic effects through suppression of multiple signaling cascades in CML both in vitro and in vivo.

c-Met and CREB1 are involved in miR-433-mediated inhibition of the epithelial-mesenchymal transition in bladder cancer by regulating Akt/GSK-3β/Snail signaling

Emerging evidence has suggested that microRNAs (miRNAs) have an important role in tumor development and progression by regulating diverse cellular pathways. Here we describe the function and regulation network of miR-433 in bladder cancer (BCa). miR-433 is frequently downregulated in BCa tissues compared with adjacent non-cancerous tissues. Epigenetic mechanisms may be involved in the regulation of miR-433 expression. Enforced expression of miR-433 significantly inhibits proliferation, colony formation, migration, and invasion in BCa cells. In addition, miR-433 inhibits the epithelial-mesenchymal transition (EMT) in BCa cells by regulating c-Met/Akt/GSK-3β/Snail signaling pathway. Both c-Met and CREB1 are downstream target genes of miR-433. CREB1 can also indirectly regulate c-Met/Akt/GSK-3β/Snail signaling via MITF. Furthermore, CREB1 expression is an independent prognostic factor for overall survival in patients with BCa. Finally, there appears to exist a reciprocal regulation between c-Met and miR-433/miR-409-3p. Taken together, this study reveals that miR-433-c-MET/CREB1-Akt/GSK-3β/Snail signaling is critical to EMT in BCa. Targeting the pathway described here may open up new prospects to restrict metastatic progression of BCa.

Integrative analysis identifies targetable CREB1/FoxA1 transcriptional co-regulation as a predictor of prostate cancer recurrence

Identifying prostate cancer-driving transcription factors (TFs) in addition to the androgen receptor promises to improve our ability to effectively diagnose and treat this disease. We employed an integrative genomics analysis of master TFs CREB1 and FoxA1 in androgen-dependent prostate cancer (ADPC) and castration-resistant prostate cancer (CRPC) cell lines, primary prostate cancer tissues and circulating tumor cells (CTCs) to investigate their role in defining prostate cancer gene expression profiles. Combining genome-wide binding site and gene expression profiles we define CREB1 as a critical driver of pro-survival, cell cycle and metabolic transcription programs. We show that CREB1 and FoxA1 co-localize and mutually influence each other's binding to define disease-driving transcription profiles associated with advanced prostate cancer. Gene expression analysis in human prostate cancer samples found that CREB1/FoxA1 target gene panels predict prostate cancer recurrence. Finally, we showed that this signaling pathway is sensitive to compounds that inhibit the transcription co-regulatory factor MED1. These findings not only reveal a novel, global transcriptional co-regulatory function of CREB1 and FoxA1, but also suggest CREB1/FoxA1 signaling is a targetable driver of prostate cancer progression and serves as a biomarker of poor clinical outcomes.

Cyclic AMP Response Element Binding Protein Mediates Pathological Retinal Neovascularization via Modulating DLL4-NOTCH1 Signaling

Retinal neovascularization is the most common cause of moderate to severe vision loss in all age groups. Despite the use of anti-VEGFA therapies, this complication continues to cause blindness, suggesting a role for additional molecules in retinal neovascularization. Besides VEGFA and VEGFB, hypoxia induced VEGFC expression robustly. Based on this finding, we tested the role of VEGFC in pathological retinal angiogenesis. VEGFC induced proliferation, migration, sprouting and tube formation of human retinal microvascular endothelial cells (HRMVECs) and these responses require CREB-mediated DLL4 expression and NOTCH1 activation. Furthermore, down regulation of VEGFC levels substantially reduced tip cell formation and retinal neovascularization in vivo. In addition, we observed that CREB via modulating the DLL4-NOTCH1 signaling mediates VEGFC-induced tip cell formation and retinal neovascularization. In regard to upstream mechanism, we found that down regulation of p38β levels inhibited hypoxia-induced CREB-DLL4-NOTCH1 activation, tip cell formation, sprouting and retinal neovascularization. Based on these findings, it may be suggested that VEGFC besides its role in the regulation of lymphangiogenesis also plays a role in pathological retinal angiogenesis and this effect depends on p38β and CREB-mediated activation of DLL4-NOTCH1 signaling.

NKCC1 mediates traumatic brain injury-induced hippocampal neurogenesis through CREB phosphorylation and HIF-1α expression

Traumatic brain injury (TBI) is one of the most prevalent causes of worldwide mortality and morbidity. We previously had evidenced that TBI induced Na-K-2Cl co-transporter (NKCC1) upregulation in hippocampus. Here, we aim to investigate the role of NKCC1 in TBI-induced neurogenesis and the detailed mechanisms. The TBI-associated alternations in the expression of NKCC1, HIF-1α, VEGF, MAPK cascade, and CREB phosphorylation were analyzed by Western blot. TBI-induced neurogenesis was determined by immuno-fluorescence labeling. Chromatin immunoprecipitation was used to elucidate whether HIF-1α would activate VEGF gene after TBI. We found that the level of hippocampal NKCC1 and VEGF began to rise 8 h after TBI, and both of them reached maxima at day 7. Along with the upregulation of NKCC1 and VEGF, MAPK cascade was activated and hippocampal neurogenesis was promoted. Administration of CREB antisense oligonucleotide significantly attenuated the expression of HIF-1α, while HIF-1α antisense oligonucleotide exhibited little effect on the expression of CREB. However, HIF-1α antisense oligonucleotide administration did effectively suppress the expression of VEGF. Our results of the chromosome immunoprecipitation also indicated that HIF-1α could directly act on the VEGF promoter and presumably would elevate the VEGF expression after TBI. All these results have illustrated the correlation between NKCC1 upregulation and TBI-associated neurogenesis. The pathway involves the activation of Raf/MEK/ERK cascade, CREB phosphorylation, and HIF-1α upregulation, and finally leads to the stimulation of VEGF expression and the induction of neurogenesis.

Identification of a Potent Inhibitor of CREB-Mediated Gene Transcription with Efficacious in Vivo Anticancer Activity

Recent studies have shown that nuclear transcription factor cyclic adenosine monophosphate response element binding protein (CREB) is overexpressed in many different types of cancers. Therefore, CREB has been pursued as a novel cancer therapeutic target. Naphthol AS-E and its closely related derivatives have been shown to inhibit CREB-mediated gene transcription and cancer cell growth. Previously, we identified naphthamide 3a as a different chemotype to inhibit CREB’s transcription activity. In a continuing effort to discover more potent CREB inhibitors, a series of structural congeners of 3a was designed and synthesized. Biological evaluations of these compounds uncovered compound 3i (666-15) as a potent and selective inhibitor of CREB-mediated gene transcription (IC₅₀ = 0.081 ± 0.04 μM). 666-15 also potently inhibited cancer cell growth without harming normal cells. In an in vivo MDA-MB-468 xenograft model, 666-15 completely suppressed the tumor growth without overt toxicity. These results further support the potential of CREB as a valuable cancer drug target.

Pathological hypertrophy reverses β2-adrenergic receptor-induced angiogenesis in mouse heart

β-adrenergic activation and angiogenesis are pivotal for myocardial function but the link between both events remains unclear. The aim of this study was to explore the cardiac angiogenesis profile in a mouse model with cardiomyocyte-restricted overexpression of β₂-adrenoceptors (β₂-TG), and the effect of cardiac pressure overload. β₂-TG mice had heightened cardiac angiogenesis, which was essential for maintenance of the hypercontractile phenotype seen in this model. Relative to controls, cardiomyocytes of β₂-TGs showed upregulated expression of vascular endothelial growth factor (VEGF), heightened phosphorylation of cAMP-responsive-element-binding protein (CREB), and increased recruitment of phospho-CREB, CREB-binding protein (CBP), and p300 to the VEGF promoter. However, when hearts were subjected to pressure overload by transverse aortic constriction (TAC), angiogenic signaling in β₂-TGs was inhibited within 1 week after TAC. β₂-TG hearts, but not controls, exposed to pressure overload for 1–2 weeks showed significant increases from baseline in phosphorylation of Ca²⁺/calmodulin-dependent kinase II (CaMKIIδ) and protein expression of p53, reduction in CREB phosphorylation, and reduced abundance of phospho-CREB, p300 and CBP recruited to the CREB-responsive element (CRE) site of VEGF promoter. These changes were associated with reduction in both VEGF expression and capillary density. While non-TG mice with TAC developed compensatory hypertrophy, (₂-TGs exhibited exaggerated hypertrophic growth at week-1 post-TAC, followed by LV dilatation and reduced fractional shortening measured by serial echocardiography. In conclusion, angiogenesis was enhanced by the cardiomyocyte (₂AR/CREB/VEGF signaling pathway. Pressure overload rapidly inhibited this signaling, likely as a consequence of activated CaMKII and p53, leading to impaired angiogenesis and functional decompensation.

Vascular endothelial growth factor is an autocrine growth factor, signaling through neuropilin-1 in non-small cell lung cancer

Background

The VEGF pathway has become an important therapeutic target in lung cancer, where VEGF has long been established as a potent pro-angiogenic growth factor expressed by many types of tumors. While Bevacizumab (Avastin) has proven successful in increasing the objective tumor response rate and in prolonging progression and overall survival in patients with NSCLC, the survival benefit is however relatively short and the majority of patients eventually relapse. The current use of tyrosine kinase inhibitors alone and in combination with chemotherapy has been underwhelming, highlighting an urgent need for new targeted therapies. In this study, we examined the mechanisms of VEGF-mediated survival in NSCLC cells and the role of the Neuropilin receptors in this process.

Methods

NSCLC cells were screened for expression of VEGF and its receptors. The effects of recombinant VEGF and its blockade on lung tumor cell proliferation and cell cycle were examined. Phosphorylation of Akt and Erk1/2 proteins was examined by high content analysis and confocal microscopy. The effects of silencing VEGF on cell proliferation and survival signaling were also assessed. A Neuropilin-1 stable-transfected cell line was generated. Cell growth characteristics in addition to pAkt and pErk1/2 signaling were studied in response to VEGF and its blockade. Tumor growth studies were carried out in nude mice following subcutaneous injection of NP1 over-expressing cells.

Results

Inhibition of the VEGF pathway with anti-VEGF and anti-VEGFR-2 antibodies or siRNA to VEGF, NP1 and NP2 resulted in growth inhibition of NP1 positive tumor cell lines associated with down-regulation of PI3K and MAPK kinase signaling. Stable transfection of NP1 negative cells with NP1 induced proliferation in vitro, which was further enhanced by exogenous VEGF. In vivo, NP1 over-expressing cells significantly increased tumor growth in xenografts compared to controls.

Conclusions

Our data demonstrate that VEGF is an autocrine growth factor in NSCLC signaling, at least in part, through NP1. Targeting this VEGF receptor may offer potential as a novel therapeutic approach and also support the evaluation of the role of NP1 as a biomarker predicting sensitivity or resistance to VEGF and VEGFR-targeted therapies in the clinical arena.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0310-8) contains supplementary material, which is available to authorized users.

Functional cyclic AMP response element in the breast cancer resistance protein (BCRP/ABCG2) promoter modulates epidermal growth factor receptor pathway- or androgen withdrawal-mediated BCRP/ABCG2 transcription in human cancer cells

Phosphorylated cyclic-AMP (cAMP) response element binding protein (p-CREB) is a downstream effector of a variety of important signaling pathways. We investigated whether the human BCRP promoter contains a functional cAMP response element (CRE). 8Br-cAMP, a cAMP analogue, increased the activity of a BCRP promoter reporter construct and BCRP mRNA in human carcinoma cells. Epidermal growth factor receptor (EGFR) pathway activation also led to an increase in p-CREB and in BCRP promoter reporter activity via two major downstream EGFR signaling pathways: the phosphotidylinositol-3-kinase (PI3K)/AKT pathway and the mitogen-activated protein kinase (MAPK) pathway. EGF treatment increased the phosphorylation of EGFR, AKT, ERK and CREB, while simultaneously enhancing BCRP mRNA and functional protein expression. EGF-stimulated CREB phosphorylation and BCRP induction were diminished by inhibition of EGFR, PI3K/AKT or RAS/MAPK signaling. CREB silencing using RNA interference reduced basal levels of BCRP mRNA and diminished the induction of BCRP by EGF. Chromatin immunoprecipitation assays confirmed that a putative CRE site on the BCRP promoter bound p-CREB by a point mutation of the CRE site abolished EGF-induced stimulation of BCRP promoter reporter activity. Furthermore, the CREB co-activator, cAMP-regulated transcriptional co-activator (CRTC2), is involved in CREB-mediated BCRP transcription: androgen depletion of LNCaP human prostate cancer cells increased both CREB phosphorylation and CRTC2 nuclear translocation, and enhanced BCRP expression. Silencing CREB or CRTC2 reduced basal BCRP expression and BCRP induction under androgen-depletion conditions. This novel CRE site plays a central role in mediating BCRP gene expression in several human cancer cell lines following activation of multiple cancer-relevant signaling pathways.

p-CREB expression in human meningiomas: correlation with angiogenesis and recurrence risk

Despite total surgical resection, a percentage of meningiomas do unexpectedly recur. At present the prediction of recurrence risk and the management of recurrent tumours represent major issues in the patients affected by meningiomas. The present study aims at investigating the prognostic value of the expression of the phosphorylated transcription factor cyclic AMP responsive element binding protein (p-CREB) in a series of meningiomas of different histotype and grade. While no p-CREB expression was found in specimens of normal leptomeninges, 71 % of meningiomas in our cohort expressed p-CREB. In addition, nuclear expression of p-CREB was present in the endothelia of tumor vessels in all of the meningiomas, but not in the vessels of the non-neoplastic meninges. High expression of p-CREB was significantly more frequent in meningiomas showing atypical, chordoid or microcystic histotype (P = 0.0003), high histological grade (P < 0.0001), high Ki-67 labeling index (P = 0.0001), high microvessel density counts (P < 0.0001) and high vascular endothelial growth factor expression (P = 0.0113). In addition, high p-CREB expression was significantly associated with the development of recurrences (P = 0.0031) and it was a significant negative, albeit not independent, prognostic factor for disease free survival in patients with meningiomas submitted to complete surgical removal (P = 0.0019). In conclusion, we showed that p-CREB is expressed in human meningiomas and that it represents a significant predictor of recurrence risk in these tumors. Due to its high expression in more aggressive tumors and in the tumor vessels, it may represent a novel therapeutic target in meningiomas.

Salt-inducible kinase 2 regulates mitotic progression and transcription in prostate cancer

Salt-inducible kinase 2 (SIK2) is a multifunctional kinase of the AMPK family that plays a role in CREB1-mediated gene transcription and was recently reported to have therapeutic potential in ovarian cancer. The expression of this kinase was investigated in prostate cancer clinical specimens. Interestingly, auto-antibodies against SIK2 were increased in the plasma of patients with aggressive disease. Examination of SIK2 in prostate cancer cells found that it functions both as a positive regulator of cell-cycle progression and a negative regulator of CREB1 activity. Knockdown of SIK2 inhibited cell growth, delayed cell-cycle progression, induced cell death, and enhanced CREB1 activity. Expression of a kinase-dead mutant of SIK2 also inhibited cell growth, induced cell death, and enhanced CREB1 activity. Treatment with a small-molecule SIK2 inhibitor (ARN-3236), currently in preclinical development, also led to enhanced CREB1 activity in a dose- and time-dependent manner. Because CREB1 is a transcription factor and proto-oncogene, it was posited that the effects of SIK2 on cell proliferation and viability might be mediated by changes in gene expression. To test this, gene expression array profiling was performed and while SIK2 knockdown or overexpression of the kinase-dead mutant affected established CREB1 target genes; the overlap with transcripts regulated by forskolin (FSK), the adenylate cyclase/CREB1 pathway activator, was incomplete.

IMPLICATIONS

This study demonstrates that targeting SIK2 genetically or therapeutically will have pleiotropic effects on cell-cycle progression and transcription factor activation, which should be accounted for when characterizing SIK2 inhibitors.

Upregulation of CREM/ICER suppresses wound endothelial CRE-HIF-1α-VEGF-dependent signaling and impairs angiogenesis in type 2 diabetes

Impaired angiogenesis and endothelial dysfunction in type 2 diabetes constitute dominant risk factors for non-healing wounds and most forms of cardiovascular disease. We propose that diabetes shifts the ‘angiogenic balance’ in favor of an excessive anti-angiogenic phenotype. Herein, we report that diabetes impairs in vivo sponge angiogenic capacity by decreasing VEGF expression and fibrovascular invasion, and reciprocally enhances the formation of angiostatic molecules, such as thrombospondins, NFκB and FasL. Defective in vivo angiogenesis prompted cellular studies in cultured endothelial cells derived from subcutaneous sponge implants (SIECs) of control and Goto-Kakizaki rats. Ensuing data from diabetic SIECs demonstrated a marked upregulation in cAMP-PKA-CREB signaling, possibly stemming from increased expression of adenylyl cyclase isoforms 3 and 8, and decreased expression of PDE3. Mechanistically, we found that oxidative stress and PKA activation in diabetes enhanced CREM/ICER expression. This reduces IRS2 cellular content by inhibiting cAMP response element (CRE) transcriptional activity. Consequently, a decrease in the activity of Akt-mTOR ensued with a concomitant reduction in the total and nuclear protein levels of HIF-1α. Limiting HIF-1α availability for the specific hypoxia response elements in diabetic SIECs elicited a marked reduction in VEGF expression, both at the mRNA and protein levels. These molecular abnormalities were illustrated functionally by a defect in various pro-angiogenic properties, including cell proliferation, migration and tube formation. A genetic-based strategy in diabetic SIECs using siRNAs against CREM/ICER significantly augmented the PKA-dependent VEGF expression. To this end, the current data identify the importance of CREM/ICER as a negative regulator of endothelial function and establish a link between CREM/ICER overexpression and impaired angiogenesis during the course of diabetes. Moreover, it could also point to CREM/ICER as a potential therapeutic target in the treatment of pathological angiogenesis.