Cyclic AMP response element-binding protein overexpression: a feature associated with negative prognosis in never smokers with non-small cell lung cancer

The CREB1/WNK1 axis promotes the tumorigenesis of ovarian cancer via regulating HIF-1

The aim of this study was to explore the functions and molecular mechanisms of the WNK lysine deficient protein kinase 1 (WNK1) in the development of ovarian cancer. Firstly, loss- and gain-of-function assays were carried out and subsequently cell proliferation, apoptosis, invasion and migration were detected. Furthermore, WNK1 action on glucose uptake, lactate production and adenosine triphosphate (ATP) level were assessed. The roles of WNK1 on cisplatin resistance were explored using CCK-8, colony formation, and flow cytometry in vitro. Immunohistochemistry, Western blot and qRT-PCR were conducted to determine the protein and mRNA expression. Additionally, tumor growth in vivo was also monitored. We found that the overexpression of WNK1 predicted a bad prognosis of ovarian cancer patients. WNK1 enhanced the malignant behavior and facilitated glycolysis of ovarian cancer cells. Moreover, WNK1 increased cisplatin resistance in ovarian cancer cells. Mechanistically, we found that WNK1 expression was promoted by CREB1 at the transcriptional level. And CREB1 could facilitate ovarian cancer cells malignant behavior through target upregulating WNK1. Besides, we also showed that WNK1 facilitated the malignant behavior by accelerating HIF-1 expression. In xenograft tumor tissues, the downregulation of WNK1 significantly reduced HIF-1α expression. These data demonstrated that the CREB1/WNK1 axis could promote the tumorigenesis of ovarian cancer via accelerating HIF-1 expression, suggesting that the CREB1/WNK1 axis could be a potential target during the therapy of ovarian cancer.

Unlocking the role of EIF5A: A potential diagnostic marker regulating the cell cycle and showing negative correlation with immune infiltration in lung adenocarcinoma

BACKGROUND

Despite EIF5A upregulation related to tumor progression in LUAD (lung adenocarcinoma), the underlying mechanisms remain elusive. In addition, there are few comprehensive analyses of EIF5A in LUAD.

METHODS

We investigated the EIF5A expression level in LUAD patients using data from the TCGA and GEO databases. We employed qRT-PCR and western blot to verify EIF5A expression in cell lines, while immunohistochemistry was utilized for clinical sample analysis. We analyzed EIF5A expression in tumor-infiltrating immune cells using the TISCH database and assessed its association with immune infiltration in LUAD using the "ESTIMATE" R package. Bioinformatics approaches were developed to discover the EIF5A-related genes and explore EIF5A potential mechanisms in LUAD. Proliferation ability was verified through CCK-8, clone formation, and EdU assays, while flow cytometry assessed apoptosis and cell cycle. Western blot was used to detect the expression of pathway-related proteins.

RESULTS

EIF5A was significantly upregulated in LUAD. Moreover, we constructed a MAZ-hsa-miR-424-3p-EIF5A transcriptional network. We explored the potential mechanism of EIF5A in LUAD and further investigated the cAMP signaling pathway and the cell cycle. Finally, we proved that EIF5A silencing induced G1/S Cell Cycle arrest, promoted apoptosis, and inhibited proliferation via the cAMP/PKA/CREB signaling pathway.

CONCLUSION

EIF5A serves as a prognostic biomarker with a negative correlation to immune infiltrates in LUAD. It regulated the cell cycle in LUAD by inhibiting the cAMP/PKA/CREB signaling pathway.

Inhibition of PKA/CREB1 pathway confers sensitivity to ferroptosis in non-small cell lung cancer

Ferroptosis is a type of regulated cell death characterized by iron accumulation and lipid peroxidation. The molecular mechanisms underlying ferroptosis regulation in non-small cell lung cancer (NSCLC) are poorly understood. In this study, we found that protein kinase A (PKA) inhibition enhanced ferroptosis susceptibility in NSCLC cells, as evidenced by reduced cell viability and increased lipid peroxidation. We further identified cAMP-responsive element protein 1 (CREB1), a transcription factor and a substrate of PKA, as a key regulator of ferroptosis. Knockdown of CREB1 sensitized NSCLC cells to ferroptosis inducers (FINs) and abolished the effects of PKA inhibitor and agonist, revealing the pivotal role of CREB1 in ferroptosis regulation. Using a high-throughput screening approach and subsequent validation by chromatin immunoprecipitation (ChIP) and dual-luciferase assays, we discovered that CREB1 transcriptionally activated stearoyl-CoA desaturase (SCD), an enzyme that catalyzes the conversion of saturated fatty acids to monounsaturated fatty acids. SCD conferred ferroptosis resistance by decreasing the availability of polyunsaturated fatty acids for lipid peroxidation, and its overexpression rescued the effect of CREB1 knockdown on ferroptosis in vitro. Besides, CREB1 knockdown suppressed xenograft tumor growth in the presence of Imidazole Ketone Erastin (IKE), a potent FIN, and this effect was reversed by SCD. Finally, we showed that high expression of CREB1 was associated with poor prognosis in NSCLC patients from public datasets and our institution. Collectively, this study illustrates the effect of PKA/CREB1/SCD axis in regulating ferroptosis of NSCLC, targeting this pathway may provide new strategies for treating NSCLC patients.

ZNRF2 as an oncogene is transcriptionally regulated by CREB1 in breast cancer models

E3 ubiquitin ligase Zinc and Ring Finger 2 (ZNRF2) has been demonstrated to be engaged in the development of multiple cancers. Nevertheless, the function of ZNRF2 in breast cancer (BC) still unclear. In this work, we firstly analyzed the differentially expressed genes in BC by bioinformatics and found that ZNRF2 was highly expressed in BC. Consistently, we further confirmed that ZNRF2 was upregulated in BC tissues compared with adjacent normal tissues, and this was positively correlated with the poor prognosis and the higher pathological grades of patients with BC. Functional assays performed on HCC1937 and MCF-7 cells indicated that silencing of ZNRF2 suppressed cell proliferation, as evidenced by the decrease in the expression of cyclin A, PCNA and cyclin D1. Flow cytometry and Hoechst staining showed that knockdown of ZNRF2 induced cell apoptosis, which was verified by the upregulation of apoptosis genes such as Bax, cleaved PARP and Bim. ZNRF2 knockdown also inhibited in vivo tumor growth. But, instead, ZNRF2-overexpressed BC cells exhibited obvious malignant phenotypes. Additionally, we observed that cAMP response element binding protein 1 (CREB1) directly bound to the promoter sequence of ZNRF2 and thus activating its transcription, suggesting that ZNRF2 is transcriptionally regulated by CREB1. Additionally, ZNRF2 knockdown could reverse the proliferation-promoting action of CREB1 on BC cells, Hence, this study demonstrated that ZNRF2 might serve as a prospective therapeutic target for BC.

Ensemble learning based assessment of the role of transcription factors in gene expression

Cancer cells are formed when the associated, active genes fail to function the way they are meant to function. Multiple genes collectively control cell growth by activating a proper set of genes. Regulation of gene expression is controlled through the combined effort of multiple regulatory elements. Transcription of each gene is affected differently according to the combinatorial patterns of regulatory elements bound in the nearby regions. Identifying and analysing such patterns will give a better insight into the cell function. The main focus of this study is on developing a computational model to predict the functional role of transcriptional factors residing between divergent gene pairs. Acute Myeloid Leukaemia (AML) gene expression data from GEO and the two TFs EP300 and CTCF binding data calibrated in k562 cell line from ENCODE consortium are taken as a case study.

microRNA-206 prevents hepatocellular carcinoma growth and metastasis via down-regulating CREB5 and inhibiting the PI3K/AKT signaling pathway

Hepatocellular carcinoma (HCC) is one of the most common cancers and has continued to increase in incidence worldwide. Moreover, the involvement of microRNAs (miRs) has been reported in the development and progression of HCC. Here, we investigated the role of miR-206 in HCC growth and metastasis. HCC-related microarray datasets were harvested to screen differentially expressed miRNAs in HCC samples followed by prediction of downstream target genes. The dual-luciferase reporter assay verified the target-binding relationship between miR-206 and CREB5. The human HCC cell line MHCC97-H was cultured in vitro and transfected with miR-206 mimic/inhibitor or sh-/oe-CREB5 for analyzing MHCC97-H cell biological functions. The orthotopic xenograft model of HCC mice was constructed to observe the tumorigenic ability of HCC cells in vivo. Bioinformatics analysis found that miR-206 may be involved in HCC growth and metastasis by targeting CREB5 and regulating PI3K/AKT signaling pathway. In vivo animal experiments found that CREB5 was significantly overexpressed in mouse HCC tissues. In HCC cells, miR-206 can target down-regulate the expression of CREB5, thereby inhibiting the activation of PI3K/AKT signaling pathway. Furthermore, in vitro cell experiments confirmed that overexpression of miR-206 could inhibit the PI3K/AKT signaling pathway by down-regulating CREB5 expression, thereby inhibiting the proliferation, migration and invasion of HCC cells. In conclusion, our results revealed that miR-206 could down-regulate the expression of CREB5 and inhibit the activation of PI3K/AKT signaling pathway, thereby preventing HCC growth and metastasis.Abbreviations: HCC: hepatocellular carcinoma; HBV or HCV: hepatitis B or C virus; miRNAs: microRNAs; CREB: cAMP response element-binding protein; CRE: cAMP response elements.

The Bile Acid Membrane Receptor TGR5 in Cancer: Friend or Foe?

The G-protein-coupled bile acid receptor, Gpbar1 or TGR5, is characterized as a membrane receptor specifically activated by bile acids. A series of evidence shows that TGR5 induces protein kinase B (AKT), nuclear factor kappa-B (NF-κB), extracellular regulated protein kinases (ERK1/2), signal transducer and activator of transcription 3 (STAT3), cyclic adenosine monophosphate (cAMP), Ras homolog family member A (RhoA), exchange protein activated by cAMP (Epac), and transient receptor potential ankyrin subtype 1 protein (TRPA1) signaling pathways, thereby regulating proliferation, inflammation, adhesion, migration, insulin release, muscle relaxation, and cancer development. TGR5 is widely distributed in the brain, lung, heart, liver, spleen, pancreas, kidney, stomach, jejunum, ileum, colon, brown adipose tissue (BAT), white adipose tissue (WAT), and skeletal muscle. Several recent studies have demonstrated that TGR5 exerts inconsistent effects in different cancer cells upon activating via TGR5 agonists, such as INT-777, ursodeoxycholic acid (UDCA), and taurolithocholic acid (TLCA). In this review, we discuss both the ‘friend’ and ‘foe’ features of TGR5 by summarizing its tumor-suppressing and oncogenic functions and mechanisms.

Activation of the CREB Coactivator CRTC2 by Aberrant Mitogen Signaling promotes oncogenic functions in HPV16 positive head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) is the 6th most common cancer worldwide and incidence rates are continuing to rise globally. Patients often present with locally advanced disease and a staggering 50% chance of relapse following treatment. Aberrant activation of adaptive response signaling pathways, such as the cAMP/PKA pathway, induce an array of genes associated with known cancer pathways that promote tumorigenesis and drug resistance. We identified the cAMP Regulated Transcription Coactivator 2 (CRTC2) to be overexpressed and constitutively activated in HNSCCs and this confers poor prognosis. CRTCs are regulated through their subcellular localization and we show that CRTC2 is exclusively nuclear in HPV(+) HNSCC, thus constitutively active, due to non-canonical Mitogen-Activated Kinase Kinase 1 (MEKK1)-mediated activation via a MEKK1-p38 signaling axis. Loss-of-function and pharmacologic inhibition experiments decreased CRTC2/CREB transcriptional activity by reducing nuclear CRTC2 via nuclear import inhibition and/or by eviction of CRTC2 from the nucleus. This shift in localization was associated with decreased proliferation, migration, and invasion. Our results suggest that small molecules that inhibit nuclear CRTC2 and p38 activity may provide therapeutic benefit to patients with HPV(+) HNSCC.

cAMP Signaling in Cancer: A PKA-CREB and EPAC-Centric Approach

Cancer is one of the most common causes of death globally. Despite extensive research and considerable advances in cancer therapy, the fundamentals of the disease remain unclear. Understanding the key signaling mechanisms that cause cancer cell malignancy may help to uncover new pharmaco-targets. Cyclic adenosine monophosphate (cAMP) regulates various biological functions, including those in malignant cells. Understanding intracellular second messenger pathways is crucial for identifying downstream proteins involved in cancer growth and development. cAMP regulates cell signaling and a variety of physiological and pathological activities. There may be an impact on gene transcription from protein kinase A (PKA) as well as its downstream effectors, such as cAMP response element-binding protein (CREB). The position of CREB downstream of numerous growth signaling pathways implies its oncogenic potential in tumor cells. Tumor growth is associated with increased CREB expression and activation. PKA can be used as both an onco-drug target and a biomarker to find, identify, and stage tumors. Exploring cAMP effectors and their downstream pathways in cancer has become easier using exchange protein directly activated by cAMP (EPAC) modulators. This signaling system may inhibit or accelerate tumor growth depending on the tumor and its environment. As cAMP and its effectors are critical for cancer development, targeting them may be a useful cancer treatment strategy. Moreover, by reviewing the material from a distinct viewpoint, this review aims to give a knowledge of the impact of the cAMP signaling pathway and the related effectors on cancer incidence and development. These innovative insights seek to encourage the development of novel treatment techniques and new approaches.

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.

The Patient-Derived Cancer Organoids: Promises and Challenges as Platforms for Cancer Discovery

The cancer burden is rapidly increasing in most countries, and thus, new anticancer drugs for effective cancer therapy must be developed. Cancer model systems that recapitulate the biological processes of human cancers are one of the cores of the drug development process. PDCO has emerged as a unique model that preserves the genetic, physiological, and histologic characteristics of original cancer, including inter- and intratumoral heterogeneities. Due to these advantages, the PCDO model is increasingly investigated for anticancer drug screening and efficacy testing, preclinical patient stratification, and precision medicine for selecting the most effective anticancer therapy for patients. Here, we review the prospects and limitations of PDCO compared to the conventional cancer models. With advances in culture success rates, co-culture systems with the tumor microenvironment, organoid-on-a-chip technology, and automation technology, PDCO will become the most promising model to develop anticancer drugs and precision medicine.

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.

Increased phosphorylated CREB1 protein correlates with poor prognosis in clear cell renal cell carcinoma

Background

This study aims to investigate the level of cAMP response element-binding protein 1 (phospho S133) (p-CREB1) protein in clear cell renal cell carcinoma (ccRCC) and evaluates its prognosis significance.

Methods

Immunohistochemistry (IHC) method was performed to detect p-CREB1 staining in 233 ccRCC patients. Three or more high-power fields per tissue section were equally captured by a Leica DMRXA microphotographic system, and average staining intensity (optical density, OD) was analyzed by Leica Qwin Standard V2.6 system. Univariate and multivariate Cox proportional regression model was performed to assess the correlation of p-CREB1 staining and clinical outcomes.

Results

IHC proved that the level of p-CREB1 protein was significantly higher in tumor tissues than in adjacent normal tissues, and gradually increased from normal to tumor sections. On the basis of the receiver operating characteristic curve, patients were divided into low p-CREB1 staining (OD ≤0.28) and high p-CREB1 staining subgroup (OD >0.28) according to p-CREB1 protein staining intensity of tumor cells. Multivariate analyses showed that high p-CREB1staining was an independent risk factor for cancer-specific free survival, overall survival and progression-free survival.

Conclusions

p-CREB1 protein is an independent prognostic biomarker for ccRCC patients.

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.

Role of NRF2 in immune modulator expression in developing lung

After birth, the alveolar epithelium is exposed to environmental pathogens and high O₂ tensions. The alveolar type II cells may protect this epithelium through surfactant production. Surfactant protein, SP-A, an immune modulator, is developmentally upregulated in fetal lung with surfactant phospholipid synthesis. Herein, we observed that the redox-regulated transcription factor, NRF2, and co-regulated C/EBPβ and PPARγ, were markedly induced during cAMP-mediated differentiation of cultured human fetal lung (HFL) epithelial cells. This occurred with enhanced expression of immune modulators, SP-A, TDO2, AhR, and NQO1. Like SP-A, cAMP induction of NRF2 was prevented when cells were exposed to hypoxia. NRF2 knockdown inhibited induction of C/EBPβ, PPARγ, and immune modulators. Binding of endogenous NRF2 to promoters of SP-A and other immune modulator genes increased during HFL cell differentiation. In mouse fetal lung (MFL), a developmental increase in Nrf2, SP-A, Tdo2, Ahr, and Nqo1 and decrease in Keap1 occurred from 14.5 to 18.5 dpc. Developmental induction of Nrf2 in MFL was associated with increased nuclear localization of NF-κB p65, a decline in p38 MAPK phosphorylation, increase in the MAPK phosphatase, DUSP1, induction of the histone acetylase, CBP, and decline in the histone deacetylase, HDAC4. Thus, together with surfactant production, type II cells protect the alveolar epithelium through increased expression of NRF2 and immune modulators to prevent inflammation and oxidative stress. Our findings further suggest that lung cancer cells have usurped this developmental pathway to promote immune tolerance and enhance survival.

Comprehensive functional annotation of susceptibility variants identifies genetic heterogeneity between lung adenocarcinoma and squamous cell carcinoma

Although genome-wide association studies have identified more than eighty genetic variants associated with non-small cell lung cancer (NSCLC) risk, biological mechanisms of these variants remain largely unknown. By integrating a large-scale genotype data of 15 581 lung adenocarcinoma (AD) cases, 8350 squamous cell carcinoma (SqCC) cases, and 27 355 controls, as well as multiple transcriptome and epigenomic databases, we conducted histology-specific meta-analyses and functional annotations of both reported and novel susceptibility variants. We identified 3064 credible risk variants for NSCLC, which were overrepresented in enhancer-like and promoter-like histone modification peaks as well as DNase I hypersensitive sites. Transcription factor enrichment analysis revealed that USF1 was AD-specific while CREB1 was SqCC-specific. Functional annotation and gene-based analysis implicated 894 target genes, including 274 specifics for AD and 123 for SqCC, which were overrepresented in somatic driver genes (ER = 1.95, P = 0.005). Pathway enrichment analysis and Gene-Set Enrichment Analysis revealed that AD genes were primarily involved in immune-related pathways, while SqCC genes were homologous recombination deficiency related. Our results illustrate the molecular basis of both well-studied and new susceptibility loci of NSCLC, providing not only novel insights into the genetic heterogeneity between AD and SqCC but also a set of plausible gene targets for post-GWAS functional experiments.

Dipyridamole induces the phosphorylation of CREB to promote cancer cell proliferation

Dipyridamole, a traditional anti-platelet drug, has been reported to inhibit the proliferation of cancer cells. The present study aimed to investigate the possibility of dipyridamole as an adjuvant of chemotherapy by enhancing the cytotoxicity of an anti-cancer drug. The cytotoxicity of colorectal cancer cells (HCT-8), CD133⁺/CD44⁺ stem-like subpopulation of HCT-8 cells and lymphoma cells (U937) to dipyridamole and/or doxorubicin was evaluated using MTT proliferation and colony forming assays. The expression levels of phosphorylated cAMP-regulatory element-binding protein (pCREB) and poly(ADP-ribose) polymerase-1 (PARP-1) in cells were analyzed via western blotting and immunofluorescence. The present study reported controversial data regarding the anti-cancer effect of dipyridamole. Dipyridamole increased, rather than inhibited, the proliferation of HCT-8 and U937 cells in a dose-dependent manner. Furthermore, it was found that dipyridamole significantly increased the expression levels of pCREB and PARP-1. However, the combined usage of dipyridamole significantly enhanced the cytotoxicity of doxorubicin to HCT-8 cells at particular doses. Based on the current findings, dipyridamole likely induces the phosphorylation of CREB to promote the proliferation of cancer cells, but may enhance the cytotoxicity of anti-cancer drugs at particular doses.

Transcription factors in colorectal cancer: molecular mechanism and therapeutic implications

Colorectal cancer (CRC) is a major cause of cancer mortality worldwide, however, the molecular mechanisms underlying the pathogenesis of CRC remain largely unclear. Recent studies have revealed crucial roles of transcription factors in CRC development. Transcription factors essential for the regulation of gene expression by interacting with transcription corepressor/enhancer complexes and they orchestrate downstream signal transduction. Deregulation of transcription factors is a frequent occurrence in CRC, and the accompanying drastic changes in gene expression profiles play fundamental roles in multistep process of tumorigenesis, from cellular transformation, disease progression to metastatic disease. Herein, we summarized current and emerging key transcription factors that participate in CRC tumorigenesis, and highlighted their oncogenic or tumor suppressive functions. Moreover, we presented critical transcription factors of CRC, emphasized the major molecular mechanisms underlying their effect on signal cascades associated with tumorigenesis, and summarized of their potential as molecular biomarkers for CRC prognosis therapeutic response, as well as drug targets for CRC treatment. A better understanding of transcription factors involved in the development of CRC will provide new insights into the pathological mechanisms and reveal novel prognostic biomarkers and therapeutic strategies for CRC.

Complex roles of cAMP-PKA-CREB signaling in cancer

Cyclic adenosine monophosphate (cAMP) is the first discovered second messenger, which plays pivotal roles in cell signaling, and regulates many physiological and pathological processes. cAMP can regulate the transcription of various target genes, mainly through protein kinase A (PKA) and its downstream effectors such as cAMP-responsive element binding protein (CREB). In addition, PKA can phosphorylate many kinases such as Raf, GSK3 and FAK. Aberrant cAMP-PKA signaling is involved in various types of human tumors. Especially, cAMP signaling may have both tumor-suppressive and tumor-promoting roles depending on the tumor types and context. cAMP-PKA signaling can regulate cancer cell growth, migration, invasion and metabolism. This review highlights the important roles of cAMP-PKA-CREB signaling in tumorigenesis. The potential strategies to target this pathway for cancer therapy are also discussed.

MicroRNA‑138 modulates glioma cell growth, apoptosis and invasion through the suppression of the AKT/mTOR signalling pathway by targeting CREB1

Alterations in the expression of microRNA (miR)-138 have been demonstrated to result in the development of several malignant tumours. However, the possible function of miR-138 in human glioma cells remains unclear. The present study demonstrated that miR-138 was significantly downregulated in 48 human glioma specimens by quantitative PCR analysis. The upregulation of miR-138 exerted significant antiproliferative and anti-invasive effects on glioma cells and promoted their apoptosis. In addition, cAMP response element-binding protein 1 (CREB1) was confirmed as a direct target gene of miR-138 by luciferase gene reporter assay, and the antitumour effect of miR-138 on glioma cells was significantly reversed by CREB1 overexpression. Moreover, the molecular mechanisms underlying the tumour-suppressive role of miR-138 in malignant glioma may be associated with the dephosphorylation of AKT/mTOR caused by the miR-138 upregulation-induced decrease in CREB1 expression in glioma cells. The results of the present study indicated that miR-138 may affect CREB1/AKT/mTOR signalling to regulate the proliferation, apoptosis and invasion of glioma cells and the malignant progression of glioma, thereby suggesting that miR-138 may be a potential target for the treatment of gliomas.

What turns CREB on? And off? And why does it matter?

Altered expression and function of the transcription factor cyclic AMP response-binding protein (CREB) has been identified to play an important role in cancer and is associated with the overall survival and therapy response of tumor patients. This review focuses on the expression and activation of CREB under physiologic conditions and in tumors of distinct origin as well as the underlying mechanisms of CREB regulation by diverse stimuli and inhibitors. In addition, the clinical relevance of CREB is summarized, including its use as a prognostic and/or predictive marker as well as a therapeutic target.

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.

MSK1 promotes cell proliferation and metastasis in uveal melanoma by phosphorylating CREB

INTRODUCTION

Uveal melanoma is known as a frequent intraocular tumor, with high metastasis and poor prognosis. Mitogen- and stress-activated protein kinase 1 (MSK1) is a serine/threonine kinase that has been reported to be associated with tumor progression in several types of human cancer. However, the role of MSK1 has rarely been studied in uveal melanoma and the underlying mechanism remained unclear.

MATERIAL AND METHODS

The expression level of MSK1 in human uveal melanoma tissues and normal uveal tissues was determined by qRT-PCR analysis, western blotting and immunohistochemistry (IHC). Subsequently, MTT assay, colony formation assay and flow cytometry assay were performed to assess the effects of MSK1 on cell proliferation. Wound-healing and transwell chamber assays were adopted to clarify the role of MSK1 in cell metastasis. Finally, the function of MSK1 was confirmed in vivo in a tumor-bearing mouse model.

RESULTS

The expression levels of MSK1 and p-cyclic AMP-responsive element binding protein (CREB) were strongly up-regulated in human uveal melanoma tissues. MSK1 overexpression facilitated cell viability and clone formation, and promoted migration and invasion of uveal melanoma cells. However, mutation of cyclic AMP-responsive element binding protein (CREB) at Ser133 residues reversed the effect of MSK1 on uveal melanoma cell proliferation and metastasis. The in vivo experiment suggested that the tumor weight was lower and the tumor mass grew more slowly in the shMSK1 group as compared to the shNC group.

CONCLUSIONS

MSK1 promotes proliferation and metastasis of uveal melanoma cells by phosphorylated CREB at Ser133 residues. Therefore, MSK1 could be a promising candidate for uveal melanoma therapy and especially has tremendous potential in the treatment of cancers in which the MSK1-CREB pathway is abnormally active.

Increased 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 activity in response to EGFR signaling contributes to non-small cell lung cancer cell survival

Constitutive activation of the epidermal growth factor receptor (EGFR) because of somatic mutations of the EGFR gene is commonly observed in tumors of non-small cell lung cancer (NSCLC) patients. Consequently, tyrosine kinase inhibitors (TKI) targeting the EGFR are among the most effective therapies for patients with sensitizing EGFR mutations. Clinical responses to the EGFR-targeting TKIs are evaluated through 2-[¹⁸F]fluoro-2-deoxy-glucose (¹⁸FDG)-PET uptake, which is decreased in patients responding favorably to therapy and is positively correlated with survival. Recent studies have reported that EGFR signaling drives glucose metabolism in NSCLC cells; however, the precise downstream effectors required for this EGFR-driven metabolic effect are largely unknown. 6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB3) is an essential glycolytic regulator that is consistently overexpressed in lung cancer. Here, we found that PFKFB3 is an essential target of EGFR signaling and that PFKFB3 activation is required for glycolysis stimulation upon EGFR activation. We demonstrate that exposing NSCLC cells harboring either WT or mutated EGFR to EGF rapidly increases PFKFB3 phosphorylation, expression, and activity and that PFKFB3 inhibition markedly reduces the EGF-mediated increase in glycolysis. Furthermore, we found that prolonged NSCLC cell exposure to the TKI erlotinib drives PFKFB3 expression and that chemical PFKFB3 inhibition synergizes with erlotinib in increasing erlotinib's anti-proliferative activity in NSCLC cells. We conclude that PFKFB3 has a key role in mediating glucose metabolism and survival of NSCLC cells in response to EGFR signaling. These results support the potential clinical utility of using PFKFB3 inhibitors in combination with EGFR-TKIs to manage NSCLC.

ILF2 Directly Binds and Stabilizes CREB to Stimulate Malignant Phenotypes of Liver Cancer Cells

Cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB) is overexpressed and has an oncogenic role in hepatocellular carcinoma (HCC). Interleukin enhancer binding factor 2 (ILF2) has become research hotspot in liver cancer recently. However, it is still unclear whether and how CREB and ILF2 interact with each other. And how this interaction exerts its role in occurrence and development of liver cancer is still unclear. Here, we found that ILF2 directly bound with CREB, and this binding was essential for the malignant phenotypes of liver cancer cells. Moreover, we found that ILF2 acted as one of the upstream proteins of CREB and promoted CREB only in the protein level, whereas ILF2 expression was not regulated by CREB. Mechanistically, ILF2 bound to the pKID domain of CREB and stimulated its phosphorylation at Ser133. Taken together, our study finds a novel interaction between CREB and ILF2 in liver cancer, and this interaction might play a role in the diagnosis and remedy of liver cancer.

GATA6 suppresses migration and metastasis by regulating the miR-520b/CREB1 axis in gastric cancer

Transcription factors (TFs) and microRNAs (miRNAs) are tightly linked to each other in tumor development and progression, but their interactions in gastric cancer (GC) metastasis remain elusive. Here we report a novel suppressive role of GATA6 in inhibiting GC metastasis by transactivating miR-520b. We found that GATA6 expression was significantly downregulated in metastatic GC cells and tissues and that its downregulation was correlated with a poor GC prognosis. Overexpression of GATA6 suppressed GC cell migration, invasion and metastasis both in vitro and in vivo. Luciferase reporter assays and chromatin immunoprecipitation assays demonstrated that miR-520b is a direct transcriptional target of GATA6. Moreover, miR-520b expression was positively correlated with GATA6 expression in GC tissues, and ectopic expression of miR-520b inhibited the migration and invasion of GC cells. Furthermore, cAMP responsive element binding protein 1 (CREB1) was identified as a direct and functional target of miR-520b, and GATA6 could suppress GC cell migration and metastasis via miR-520b-mediated repression of CREB1. Downregulation of GATA6 and miR-520b may partly account for the overexpression of CREB1 in GC. In conclusion, our results provide novel insight into the TF-miRNA regulatory network involved in GC metastasis. Targeting the GATA6/miR-520b/CREB1 axis may be an effective approach for GC treatment.

CREB5 promotes cell proliferation and correlates with poor prognosis in hepatocellular carcinoma

CAMP responsive element binding protein 5 (CREB5) has been reported to be overexpressed in several types of human cancers and has crucial roles in regulating cell growth, proliferation, differentiation, and the cell cycle. However, the expression and function of CREB5 in hepatocellular carcinoma (HCC) remains unclear. The purpose of this study was to investigate the role of CREB5 in HCC, and its prognostic significance. We measured the expression of CREB5 in 91 specimens of paraffin-embedded HCC tissue by immunohistochemistry and performed a clinicopathological analysis. Gain of function and loss of function assays were used to evaluate the effect of CREB5 on cell proliferation in vitro. We found that up-regulation of CREB5 was associated with a poor prognosis, and CREB5 status was an independent prognostic factor. The overexpression of CREB5 increased the proliferation of SMMC-7721 cells, but the knockdown of CREB5 had the opposite effect. The results indicate that CREB5 may be useful when determining a treatment strategy for patients with HCC.

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.

Targeting CREB-binding protein overrides LPS induced radioresistance in non-small cell lung cancer cell lines

Non-small cell lung cancer (NSCLC) has a very poor prognosis even when treated with the best therapies available today often including radiation. NSCLC is frequently complicated by pulmonary infections which appear to impair prognosis as well as therapy, whereby the underlying mechanisms are still not known. It was investigated here, whether the bacterial lipopolysaccharides (LPS) might alter the tumor cell radiosensitivity. LPS were found to induce a radioresistance but solely in cells with an active TLR-4 pathway. Proteome profiling array revealed that LPS combined with irradiation resulted in a strong phosphorylation of cAMP response element-binding protein (CREB). Inhibition of CREB binding protein (CBP) by the specific inhibitor ICG-001 not only abrogated the LPS-induced radioresistance but even led to an increase in radiosensitivity. The sensitization caused by ICG-001 could be attributed to a reduction of DNA double-strand break (DSB) repair.

It is shown that in NSCLC cells LPS leads to a CREB dependent radioresistance which is, however, reversible through CBP inhibition by the specific inhibitor ICG-001. These findings indicate that the combined treatment with radiation and CBP inhibition may improve survival of NSCLC patients suffering from pulmonary infections.

Hypoxia-mediated alterations and their role in the HER-2/neuregulated CREB status and localization

The cAMP-responsive element-binding protein (CREB) is involved in the tumorigenicity of HER-2/neu-overexpressing murine and human tumor cells, but a link between the HER-2/neu-mediated CREB activation, its posttranslational modification and localization and changes in the cellular metabolism, due to an altered (tumor) microenvironment remains to be established. The present study demonstrated that shRNA-mediated silencing of CREB in HER-2/neu-transformed cells resulted in decreased tumor formation, which was associated with reduced angiogenesis, but increased necrotic and hypoxic areas in the tumor. Hypoxia induced pCREBSer133, but not pCREBSer121 expression in HER-2/neu-transformed cells. This was accompanied by upregulation of the hypoxia-inducible genes GLUT1 and VEGF, increased cell migration and matrix metalloproteinase-mediated invasion. Treatment of HER-2/neu+ cells with signal transduction inhibitors targeting in particular HER-2/neu was able to revert hypoxia-controlled CREB activation. In addition to changes in the phosphorylation, hypoxic response of HER-2/neu+ cells caused a transient ubiquitination and SUMOylation as well as a co-localization of nuclear CREB to the mitochondrial matrix. A mitochondrial localization of CREB was also demonstrated in hypoxic areas of HER-2/neu+ mammary carcinoma lesions. This was accompanied by an altered gene expression pattern, activity and metabolism of mitochondria leading to an increased respiratory rate, oxidative phosphorylation and mitochondrial membrane potential and consequently to an enhanced apoptosis and reduced cell viability. These data suggest that the HER-2/neu-mediated CREB activation caused by a hypoxic tumor microenvironment contributes to the neoplastic phenotype of HER-2/neu+ cells at various levels.

Control of CREB expression in tumors: from molecular mechanisms and signal transduction pathways to therapeutic target

The cyclic AMP response element binding (CREB) protein has pleiotropic activities in physiologic processes. Due to its central position downstream of many growth signaling pathways CREB has the ability to influence cell survival, growth and differentiation of normal, but also of tumor cells suggesting an oncogenic potential of CREB. Indeed, increased CREB expression and activation is associated with tumor progression, chemotherapy resistance and reduced patients' survival. We summarize here the different cellular functions of CREB in tumors of distinct histology as well as its use as potential prognostic marker. In addition, the underlying molecular mechanisms to achieve constitutive activation of CREB including structural alterations, such as gene amplification and chromosomal translocation, and deregulation, which could occur at the transcriptional, post-transcriptional and post-translational level, will be described. Since downregulation of CREB by different strategies resulted in inhibition of cell proliferation, invasion and induction of apoptosis, the role of CREB as a promising target for cancer therapy will be also discussed.

Analysis of the oncogene BRAF mutation and the correlation of the expression of wild-type BRAF and CREB1 in endometriosis

B-Raf proto-oncogene, serine/threonine kinase (BRAF) has previously been identified as a candidate target gene in endometriosis. Wild-type and mutated BRAF serve important roles in different diseases. The aim of the present study was to explore BRAF mutation, the mRNA and protein expression of wild-type BRAF (^wtBRAF) in endometriosis, and the association between the expression levels of ^wtBRAF and the predicted transcription factor cAMP responsive element binding protein 1 (CREB1). In the present study, BRAF mutation was detected using Sanger sequencing among 30 ectopic and matched eutopic endometrium samples of patients with endometriosis as well as 25 normal endometrium samples, and no BRAF mutation was detected in exons 11 or 15. A region of ~2,000 bp upstream of the BRAF gene was then screened using NCBI and UCSC databases, and CREB1 was identified as a potential transcription factor of BRAF by analysis with the JASPAR and the TRANSFAC databases. Quantitative polymerase chain reaction was used to analysis the mRNA expression levels of ^wtBRAF and CREB1, and the corresponding protein expression levels were evaluated using immunohistochemistry and western blot analysis. The results revealed that the mRNA and protein expression levels of ^wtBRAF and CREB1 were significantly upregulated in the eutopic endometrial tissues of patients with endometriosis compared with normal endometrial tissues (P<0.05) and no significant difference in ^wtBRAF and CREB1 levels was detected between the ectopic and eutopic endometrium (P>0.05). In addition, correlation analysis revealed that the protein expression of CREB1 was positively correlated with the transcript level and protein expression of ^wtBRAF. It is reasonable to speculate that CREB1 may activate the transcription of ^wtBRAF through directly binding to its promoter, increasing BRAF expression and regulating the cell proliferation, migration and invasion of endometriosis.

Cyclic AMP responsive element-binding protein promotes renal cell carcinoma proliferation probably via the expression of spindle and kinetochore-associated protein 2

Emerging evidence shows that the aberrantly expressed cyclic AMP responsive element-binding protein (CREB) is associated with tumor development and progression in several cancers. Spindle and kinetochore-associated protein 2 (SKA2) is essential for regulating the progress of mitosis. In this study, we evaluate in vitro and in vivo the functional relationship between CREB and SKA2 in renal cell carcinoma (RCC). Suppressing and replenishing CREB levels were used to manipulate SKA2 expression, observing the effects on RCC cell lines. Computational prediction and ChIP assay identified that CREB targeted ska2 by binding its CRE sequence in the human genome. Overexpression of CREB reversed the inhibited cell growth following siSKA2 treatment, and reduced the number of cells holding in mitosis. Decreased expression of CREB suppressed RCC cell growth and xenograft tumor formation, accompanied by reduced expression of SKA2. In RCC tumor samples from patients, mRNA for SKA2 were plotted near those of CREB in each sample, with significantly increased immunohistochemical staining of higher SKA2 and CREB in the higher TNM stages. The study adds evidence that CREB, a tumor oncogene, promotes RCC proliferation. It probably achieves this by increasing SKA2 expression.

Linking CREB function with altered metabolism in murine fibroblast-based model cell lines

The cAMP-responsive element binding protein CREB is frequently overexpressed and activated in tumors of distinct histology, leading to enhanced proliferation, migration, invasion and angiogenesis as well as reduced apoptosis. The de-regulated expression of CREB might be linked with transcriptional as well as post-transcriptional regulation mechanisms. We show here that altered CREB expression levels and function are associated with changes in the cellular metabolism. Using comparative proteome-based analysis an altered expression pattern of proteins involved in the cellular metabolism in particular in glycolysis was found upon CREB down-regulation in HER-2/neu-transfected cell lines. This was associated with diminished expression levels of the glucose transporter 1, reduced glucose uptake and reduced glycolytic activity in HER-2/neu-transfected cells with down-regulated CREB when compared to HER-2/neu⁺ cells. Furthermore, hypoxia-induced CREB activity resulted in changes of the metabolism in HER-2/neu transfected cells. Low pH values in the supernatant of HER-2/neu transformants were restored by CREB down-regulation, but further decreased by hypoxia. The altered intracellular pH values were associated with a distinct expression of lactate dehydrogenase, and its substrate lactate. Moreover, enhanced phosphorylation of CREB on residue Ser133 was accompanied by a down-regulation of pERK and an up-regulation of pAKT. CREB promotes the detoxification of ROS by catalase, therefore protecting the mitochondrial activity under oxidative stress. These data suggest that there might exists a link between CREB function and the altered metabolism in HER-2/neu-transformed cells. Thus, targeting these altered metabolic pathways might represent an attractive therapeutic approach at least for the treatment of patients with HER-2/neu overexpressing tumors.

CREB5 promotes tumor cell invasion and correlates with poor prognosis in epithelial ovarian cancer

CAMP responsive element binding protein 5 (CREB5) has crucial roles in regulating cell growth, proliferation, differentiation and cell cycle regulation. CREB5 has been identified to be overexpressed in several types of human cancer. However, the expression characteristics of CREB5 in epithelial ovarian cancer remains unknown, and its potential clinical prognostic significance has not yet been elucidated. In the present study, quantitative polymerase chain reaction (qPCR) and western blot analysis were performed to detect CREB5 mRNA and protein expression levels in 10 fresh tissue and cell lines epithelial ovarian cancer. Furthermore, CREB5 expression was analyzed using immunohistochemical analysis in 125 clinicopathologically characterized ovarian cancers: Stage I+II (n=31), stage III (n=70), stage IV (n=24). The patient survival rate was evaluated using Kaplan-Meier analysis. CREB5 was significantly overexpressed at both the mRNA and protein levels in epithelial ovarian cancer cells. There was a significant positive correlation between high CREB5 expression and increasing the International Federation of Gynecology and Obstetrics (FIGO) stage and pelvic lymph node metastasis (P<0.05). Patients with high CREB5 expression had a shorter overall survival, whereas patients with low CREB5 expression had longer survival. In addition, patients with high CREB5 expression had shorter relapse-free survival whereas patients with low CREB5 expression had longer relapse-free survival. Univariate logistic regression analysis and stepwise multivariate analysis all revealed that the FIGO stage and high CREB5 expression were significant risk factors for epithelial ovarian cancer (P<0.001), which suggested that CREB5 upregulation may be associated with a poor prognosis; therefore, it may be an independent prognostic indicator of epithelial ovarian cancer and may serve as a tumor-aggressive gene.

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 (R72^wt), R72^wt with mutation at codon 273 cysteine (R72^273Cys), p53 mutation at codon 72 (P72^wt) and P72^wt with mutation at codon 273 (P72^273Cys)] 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 P72^wt, mutant phenotype, versus R72^wt phenotype. WB analyses revealed that P72^wt 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 P72^wt 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.

Crosstalk in competing endogenous RNA network reveals the complex molecular mechanism underlying lung cancer

We investigated the transcriptional mechanism underlying lung cancer development. RNA sequencing analysis was performed on blood samples from lung cancer cases and healthy controls. Differentially expressed microRNAs (miRNAs), circular RNAs (circRNAs), mRNAs (genes), and long non-coding RNAs (lncRNA) were identified, followed by pathway enrichment analysis. Based on miRNA target interactions, a competing endogenous network was established and significant nodes were screened. Differentially expressed transcriptional factors were retrieved from the TRRUST database and the transcriptional factor regulatory network was constructed. The expression of 59 miRNAs, 18,306 genes,232 lncRNAs, and 292 circRNAs were greatly altered in patients with lung cancer. miRNAs were closely associated with cancer-related pathways, such as pathways in cancer, colorectal cancer, and transcriptional misregulation in cancer. Two novel pathways, olfactory transduction and neuroactive ligand-receptor interactions, were significantly enriched by differentially expressed genes. The competing endogenous RNA network revealed 5 hub miRNAs. Hsa-miR-582-3p and hsa-miR-582-5p were greatly enriched in the Wnt signaling pathway. Hsa-miR-665 was closely related with the MAPK signaling pathway. Hsa-miR-582-3p and hsa-miR-582-5p were also present in the TF regulatory network. Transcriptional factors of WT1 (wilms tumor 1) and ETV1 (ETS variant 1) were regulated by hsa-miR-657 and hsa-miR-582-5p, respectively, and controlled androgen receptor gene expression. miR-582-5p, miRNA-582-3p, and miR-657 may play critical regulatory roles in lung tumor development. Our work may explore new mechanism of lung cancer and aid the development of novel therapy.

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.

Towards Targeting PI3K-Dependent Regulation of Gene Expression in Brain Cancer

The PI3K pathway is one of the most highly perturbed cell signaling pathways in human cancer, including the most common malignant brain tumors, gliomas, where either activating mutations of positive pathway effectors or loss/inactivation of pathway inhibitors occurs. Knowledge of the precise transcription factors modulated by PI3K in tumor cells remains elusive but there are numerous PI3K-responsive signaling factors, including kinases, which can activate many transcription factors. In the context of cancer, these transcription factors participate in the regulation of target genes expression networks to support cancer cell characteristics such as survival, proliferation, migration and differentiation. This review focuses on the role of PI3K signaling-regulated transcription in brain cancer cells from a series of recent investigations. A deeper understanding of this regulation is beginning to provide the hope of developing more sophisticated anti-cancer targeting approaches, where both upstream and downstream components of the PI3K pathway may be targeted by existing and novel drugs.

Cyclic AMP responsive element-binding protein induces metastatic renal cell carcinoma by mediating the expression of matrix metallopeptidase-2/9 and proteins associated with epithelial-mesenchymal transition

Renal cell carcinoma (RCC) is the most frequently occurring malignancy of the kidney worldwide. Anti-angiogenic targeted therapies inhibit the progression of RCC, however, limited effects on the invasion or metastasis of tumor cells have been observed. Cyclic AMP responsive element‑binding protein (CREB) is a serine/threonine kinase that has been implicated in the regulation of cell proliferation, apoptosis, cycle progression and metastasis, amongst others. Our previous research demonstrated that phosphorylated CREB (pCREB) was upregulated in human renal cancer cell lines and tissues, and decreased pCREB at the Ser133 site inhibited the growth and metastatic activity of OS‑RC‑2 cells. However, the role of CREB in RCC metastasis requires further investigation. Thus, the present study further investigated the role of CREB in RCC metastasis. The present study demonstrated that knockdown of CREB using small interfering RNA (siRNA) that targeted CREB (siCREB) significantly inhibited the migration and invasion of 786‑O and OS‑RC‑2 cells, however, the opposite effect was observed in ACHN cells. In addition, knockdown of CREB suppressed the expression of matrix metallopeptidase (MMP)‑2/9 and proteins associated with epithelial‑mesenchymal transition (EMT) in 786‑O and OS‑RC‑2 cells, and promoted expression in ACHN cells. Furthermore, the chromatin immunoprecipitation assay indicated that pCREB (Ser133) had a direct interaction with the fibronectin promoter, however, pCREB (Ser133) did not target the vimentin promoter in RCC. Therefore, the results of the present study indicate that CREB regulated metastatic RCC by mediating the expression of MMP‑2/9 and EMT‑associated proteins, however, CREB‑mediated MMP‑2/9 and EMT‑associated protein expression may be induced by different pathways in different RCC cells.

Xanthohumol inhibits the extracellular signal regulated kinase (ERK) signalling pathway and suppresses cell growth of lung adenocarcinoma cells

Aberrant activation of the Ras/MEK/ERK signaling pathway has been frequently observed in non-small-cell lung carcinoma (NSCLC) and its important role in cancer progression and malignant transformation has been documented. Hence, the ERK1/2 kinase cascade becomes a potential molecular target in cancer treatment. Xanthohumol (XN, a prenylated chalcone derived from hope cones) is known to possess a broad spectrum of chemopreventive and anticancer activities. In our studies, the MTT and BrdU assays revealed that XN demonstrated greater antiproliferative activity against A549 lung adenocarcinoma cells than against the lung adenocarcinoma H1563 cell line. We observed that XN was able to suppress the activities of ERK1/2 and p90RSK kinases, followed by inhibition of phosphorylation and activation of the CREB protein. Additionally, the XN treatment of the cancer cells caused upregulation of key cell cycle regulators p53 and p21 as well as downregulation of cyclin D1. As a result, the cytotoxic effect of XN was attributed to the cell cycle arrest at G1 phase and induction of apoptosis indicated by increased caspase-3 activity. Thus, XN might be a promising anticancer drug candidate against lung carcinomas.

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.

GSK-3α Is a Novel Target of CREB and CREB-GSK-3α Signaling Participates in Cell Viability in Lung Cancer

Overexpression or activation of cyclic AMP-response element-binding protein (CREB) has been known to be involved in several human malignancies, including lung cancer. Genes regulated by CREB have been reported to suppress apoptosis, induce cell proliferation, inflammation, and tumor metastasis. However, the critical target genes of CREB in lung cancer have not been well understood. Here, we identified GSK-3α as one of the CREB target genes which is critical for the viability of lung cancer cells. The CREB knockdown significantly reduced the expression of GSK-3α and the direct binding of CREB on the promoter of GSK3A was identified. Kaplan-Meier analysis with a public database showed a prognostic significance of aberrant GSK-3α expression in lung cancer. Inhibition of GSK-3α suppressed cell viability, colony formation, and tumor growth. For the first time, we demonstrated that GSK-3α is regulated by CREB in lung cancer and is required for the cell viability. These findings implicate CREB-GSK-3α axis as a novel therapeutic target for lung cancer treatment.

LncRNA-UCA1 enhances cell proliferation and 5-fluorouracil resistance in colorectal cancer by inhibiting miR-204-5p

Recent preliminary studies reported the in vitro tumor-promoting effects of long non-coding RNA urothelial carcinoma associated 1 (UCA1) in colorectal cancer (CRC). However, the in vivo functions and molecular mechanism of UCA1 in CRC remain unclear. Therefore, we investigated the detailed role and mechanism of UCA1 in CRC. We found that UCA1 was up-regulated in CRCs and negatively correlated with survival time in two CRC cohorts. Functional assays revealed the in vitro and in vivo growth-promoting function of UCA1 and revealed that UCA1 can decrease the sensitivity of CRC cells to 5-FU by attenuating apoptosis. Further mechanistic studies revealed that UCA1 could sponge endogenous miR-204-5p and inhibit its activity. We also identified CREB1 as a new target of miR-204-5p. The protein levels of CREB1 were significantly up-regulated in CRCs, negatively associated with survival time and positively correlated with the UCA1 expression. The present work provides the first evidence of a UCA1-miR-204-5p-CREB1/BCL2/RAB22A regulatory network in CRC and reveals that UCA1 and CREB1 are potential new oncogenes and prognostic factors for CRC.

Chemosensitizing effect of podophyllotoxin acetate on topoisomerase inhibitors leads to synergistic enhancement of lung cancer cell apoptosis

Podophyllotoxin acetate (PA) acts as a radiosensitizer against non-small cell lung cancer (NSCLC) in vitro and in vivo. In this study, we examined its potential role as a chemosensitizer in conjunction with the topoisomerase inhibitors etoposide (Eto) and camptothecin (Cpt). The effects of combinations of PA and Eto/Cpt were examined with CompuSyn software in two NSCLC cell lines, A549 and NCI-H1299. Combination index (CI) values indicated synergistic effects of PA and the topoisomerase inhibitors. The intracellular mechanism underlying synergism was further determined using propidium iodide uptake, immunoblotting and electrophoretic mobility shift assay (EMSA). Combination of PA with Eto/Cpt promoted disruption of the dynamics of actin filaments, leading to subsequent enhancement of apoptotic cell death via induction of caspase-3, -8, and -9, accompanied by increased phosphorylation of p38. Conversely, suppression of p38 phosphorylation blocked the apoptotic effect of the drug combinations. Notably, CREB-1, a transcription factor, was constitutively activated in both cell types, and synergistically inhibited upon combination treatment. Our results collectively indicate that PA functions as a chemosensitizer by enhancing apoptosis through activation of the p38/caspase axis and suppression of CREB-1.

Bacillus bombysepticus α-Toxin Binding to G Protein-Coupled Receptor Kinase 2 Regulates cAMP/PKA Signaling Pathway to Induce Host Death

Bacterial pathogens and their toxins target host receptors, leading to aberrant behavior or host death by changing signaling events through subversion of host intracellular cAMP level. This is an efficient and widespread mechanism of microbial pathogenesis. Previous studies describe toxins that increase cAMP in host cells, resulting in death through G protein-coupled receptor (GPCR) signaling pathways by influencing adenylyl cyclase or G protein activity. G protein-coupled receptor kinase 2 (GRK2) has a central role in regulation of GPCR desensitization. However, little information is available about the pathogenic mechanisms of toxins associated with GRK2. Here, we reported a new bacterial toxin-Bacillus bombysepticus (Bb) α-toxin that was lethal to host. We showed that Bb α-toxin interacted with BmGRK2. The data demonstrated that Bb α-toxin directly bound to BmGRK2 to promote death by affecting GPCR signaling pathways. This mechanism involved stimulation of G_αs, increase level of cAMP and activation of protein kinase A (PKA). Activated cAMP/PKA signal transduction altered downstream effectors that affected homeostasis and fundamental biological processes, disturbing the structural and functional integrity of cells, resulting in death. Preventing cAMP/PKA signaling transduction by inhibitions (NF449 or H-89) substantially reduced the pathogenicity of Bb α-toxin. The discovery of a toxin-induced host death specifically linked to GRK2 mediated signaling pathway suggested a new model for bacterial toxin action. Characterization of host genes whose expression and function are regulated by Bb α-toxin and GRK2 will offer a deeper understanding of the pathogenesis of infectious diseases caused by pathogens that elevate cAMP.

Interference with regulation of host signaling by pathogens can alter gene expression, leading to functional disarray in the host cells that causes abnormal division or death. Here, we propose a previously undescribed model for how bacterial toxins subvert host processes via interaction with GRK2 that influences cAMP/PKA signaling. Our findings provide new fundamental information about how bacterial pathogens regulate host signal transduction to cause death, which offers additional perspectives in host-pathogen systems. These findings will help to advance our understanding of bacteria pathogenic mechanism. Furthermore, these might extend to other microbial pathogenesis and assist in designing new or safer strategies against pathogens.

Experimental and molecular dynamics studies showed that CBP KIX mutation affects the stability of CBP:c-Myb complex

The coactivators CBP (CREBBP) and its paralog p300 (EP300), two conserved multi-domain proteins in eukaryotic organisms, regulate gene expression in part by binding DNA-binding transcription factors. It was previously reported that the CBP/p300 KIX domain mutant (Y650A, A654Q, and Y658A) altered both c-Myb-dependent gene activation and repression, and that mice with these three point mutations had reduced numbers of platelets, B cells, T cells, and red blood cells. Here, our transient transfection assays demonstrated that mouse embryonic fibroblast cells containing the same mutations in the KIX domain and without a wild-type allele of either CBP or p300, showed decreased c-Myb-mediated transcription. Dr. Wright's group solved a 3-D structure of the mouse CBP:c-Myb complex using NMR. To take advantage of the experimental structure and function data and improved theoretical calculation methods, we performed MD simulations of CBP KIX, CBP KIX with the mutations, and c-Myb, as well as binding energy analysis for both the wild-type and mutant complexes. The binding between CBP and c-Myb is mainly mediated by a shallow hydrophobic groove in the center where the side-chain of Leu302 of c-Myb plays an essential role and two salt bridges at the two ends. We found that the KIX mutations slightly decreased stability of the CBP:c-Myb complex as demonstrated by higher binding energy calculated using either MM/PBSA or MM/GBSA methods. More specifically, the KIX mutations affected the two salt bridges between CBP and c-Myb (CBP-R646 and c-Myb-E306; CBP-E665 and c-Myb-R294). Our studies also revealed differing dynamics of the hydrogen bonds between CBP-R646 and c-Myb-E306 and between CBP-E665 and c-Myb-R294 caused by the CBP KIX mutations. In the wild-type CBP:c-Myb complex, both of the hydrogen bonds stayed relatively stable. In contrast, in the mutant CBP:c-Myb complex, hydrogen bonds between R646 and E306 showed an increasing trend followed by a decreasing trend, and hydrogen bonds of the E665:R294 pair exhibited a fast decreasing trend over time during MD simulations. In addition, our data showed that the KIX mutations attenuate CBP's hydrophobic interaction with Leu302 of c-Myb. Furthermore, our 500-ns MD simulations showed that CBP KIX with the mutations has a slightly lower potential energy than wild-type CBP. The CBP KIX structures with or without its interacting protein c-Myb are different for both wild-type and mutant CBP KIX, and this is likewise the case for c-Myb with or without CBP, suggesting that the presence of an interacting protein influences the structure of a protein. Taken together, these analyses will improve our understanding of the exact functions of CBP and its interaction with c-Myb.

High expression of cAMP-responsive element-binding protein 1 (CREB1) is associated with metastasis, tumor stage and poor outcome in gastric cancer

cAMP responsive element binding protein 1 (CREB1) has been reported to be implicated in tumor development and progression of human cancers. However, the clinical significance and regulatory mechanisms of CREB1 expression in gastric cancer remain largely unknown. In the present study, immunohistochemistry was performed to detect the expression of CREB1 protein in 185 primary gastric cancer tissues, 50 secondary lymph node metastatic foci and 50 nontumorous gastric tissues. A prognostic model combining CREB1 expression with TNM tumor stage was constructed by logistic regression analysis. Regulation of CREB1 by miRNAs was investigated by luciferase reporter assay and Western blot. It was shown that CREB1 was highly expressed and correlated with lymph node metastasis, distant metastasis and tumor stage and poor outcome in gastric cancer. The prognostic model was proven to be an independent prognosis predictor and performed better than CREB1 or tumor stage alone. CREB1 was identified as a direct target of miR-27b and miR-200b, and down-regulated by miR-27b/miR-200b. We conclude that CREB1 is a promising biomarker to predict tumor metastasis and patient outcome in gastric cancer, and the miR-27b/miR-200b-CREB1 pathway may serve as a potential molecular target for the treatment of gastric cancer.