Prostaglandin E2 Stimulates Human Lung Carcinoma Cell Growth through Induction of Integrin-Linked Kinase: The Involvement of EP4 and Sp1

Prostaglandin E2 mediates the late phase of ischemic preconditioning in the heart via its receptor subtype EP4

Ischemic preconditioning (IPC) describes a phenomenon wherein brief ischemia of the heart induces a potent cardioprotective mechanism against succeeding ischemic insult. Cyclooxygenase-2 (COX-2), a rate-limiting enzyme in prostanoid biosynthesis, is upregulated in the ischemic heart and contributes to IPC. Prostaglandin E₂ (PGE₂) protects the heart from ischemia-reperfusion (I/R) injury via its receptor subtype EP₄. We sought to clarify the role of the PGE₂/EP₄ system in the late phase of IPC. Mice were subjected to four IPC treatment cycles, consisting of 5 min of occlusion of the left anterior descending coronary artery (LAD). We found that COX-2 mRNA was significantly upregulated in wild-type hearts at 6 h after IPC treatment. Cardiac PGE₂ levels at 24 h after IPC treatment were significantly increased in both wild-type mice and mice lacking EP₄ (EP₄^-/-). At 24 h after IPC treatment, I/R injury was induced by 30 min of LAD occlusion followed by 2 h of reperfusion and the cardiac infarct size was determined. The infarct size was significantly reduced by IPC treatment in wild-type mice; a reduction was not observed in EP₄^-/- mice. AE1-329, an EP₄ agonist, significantly reduced infarct size and significantly ameliorated deterioration of cardiac function in wild-type mice subjected to I/R without IPC treatment. Furthermore, AE1-329 significantly enhanced the I/R-induced activation of Akt, a pro-survival kinase. We demonstrated that the PGE₂/EP₄ system in the heart plays a critical role in the late phase of IPC, partly by augmenting Akt-mediated signaling. These findings clarify the mechanism of IPC and may contribute to the development of therapeutic strategies for ischemic heart disease.

Pharmacological targeting of MTHFD2 suppresses NSCLC via the regulation of ILK signaling pathway

Lung cancer is the most common cause of cancer related deaths worldwide with the highest mortality rate. Non-small cell lung cancer (NSCLC) accounts for about 85 % of lung cancers. Mitochondrial methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) is a bifunctional enzyme and is the most differentially expressed metabolic enzyme in various tumors including lung cancer. However, little is known about how MTHFD2 functions in NSCLC. Integrin-linked kinase (ILK) signaling plays key a role in tumor progression including metastasis, proliferation and migration. Here, we show that MTHFD2 inhibition results in suppression of cell growth, migration, invasion and epithelial-mesenchymal transition (EMT) in NSCLC. Microarray analysis suggests that MTHFD2 is positively associated with ILK signaling based on western blotting results. In addition, the phosphorylation of AMPKα plays an essential role in MTHFD2 regulation of ILK signaling. Further, the small-molecule compound C18 inhibits MTHFD2 with great efficiency. C18 blocks MTHFD2/ILK signaling pathway and restrains cell growth, migration, invasion, and EMT of NSCLC and induces apoptosis. In brief, our study found that the positive impact of MTHFD2 is mediated via ILK signaling pathway in NSCLC. Thus, blocking MTHFD2 represents a promising therapeutic strategy against NSCLC clinically.

Integrin-linked kinase (ILK): the known vs. the unknown and perspectives

Integrin-linked kinase (ILK) is a multifunctional molecular actor in cell-matrix interactions, cell adhesion, and anchorage-dependent cell growth. It combines functions of a signal transductor and a scaffold protein through its interaction with integrins, then facilitating further protein recruitment within the ILK-PINCH-Parvin complex. ILK is involved in crucial cellular processes including proliferation, survival, differentiation, migration, invasion, and angiogenesis, which reflects on systemic changes in the kidney, heart, muscle, skin, and vascular system, also during the embryonal development. Dysfunction of ILK underlies the pathogenesis of various diseases, including the pro-oncogenic activity in tumorigenesis. ILK localizes mostly to the cell membrane and remains an important component of focal adhesion. We do know much about ILK but a lot still remains either uncovered or unclear. Although it was initially classified as a serine/threonine-protein kinase, its catalytical activity is now questioned due to structural and functional issues, leaving the exact molecular mechanism of signal transduction by ILK unsolved. While it is known that the three isoforms of ILK vary in length, the presence of crucial domains, and modification sites, most of the research tends to focus on the main isoform of this protein while the issue of functional differences of ILK2 and ILK3 still awaits clarification. The activity of ILK is regulated on the transcriptional, protein, and post-transcriptional levels. The crucial role of phosphorylation and ubiquitylation has been investigated, but the functions of the vast majority of modifications are still unknown. In the light of all those open issues, here we present an extensive literature survey covering a wide spectrum of latest findings as well as a past-to-present view on controversies regarding ILK, finishing with pointing out some open questions to be resolved by further research.

Prostaglandin E2 induced cardiac hypertrophy through EP2 receptor-dependent activation of β-catenin in 5/6 nephrectomy rats

Aims

Prostaglandin E₂ (PGE2) is involved in the development of cardiac hypertrophy. However, whether PGE2 regulates the chronic kidney disease‐associated cardiac hypertrophy and the tentative mechanism remains to be elucidated.

Methods and results

We explored the effect of PGE2 receptor inhibitors on cardiac hypertrophy in vitro and in a 5/6 nephrectomy (5/6NT) rat model using quantitative reverse transcription polymerase chain reaction, western blotting, enzyme‐linked immunosorbent assay, immunohistochemical staining, and immunofluorescence staining assays. The result showed that EP2 and EP4 receptors were both up‐regulated in the PGE2‐treated cardiomyocyte cells. PGE2 treatment enhanced active β‐catenin (non‐phosphorylated) signalling through mediating EP2 and EP4 receptors. Interestingly, inhibition of EP2 receptor suppressed PGE2‐induced cardiomyocyte hypertrophy and cardiac fibrosis‐related proteins in vitro. In the 5/6NT rat model, the increased secretion PGE2 was identified in the 5/6NT rat model for 2 weeks (P = 0.0251). EP2 receptor inhibitor administration significantly improved the cardiac function and fibrosis in 5/6NT rats.

Conclusions

Our study demonstrated that inhibition of EP2 receptor could improve PGE2‐induced cardiac hypertrophy in 5/6NT rats. The exploration of these mechanisms may contribute to the optimization of therapy in chronic kidney disease accompanied cardiac hypertrophy in clinic.

Effects of prostaglandin E2 on gap junction protein alpha 1 in the rat epididymis

Gap junctions are responsible for intercellular communication. In the adult mammalian epididymis, gap junction protein alpha 1 (GJA1) is localized between basal and either principal or clear cells. GJA1 levels and localization change during the differentiation of basal cells. The present objective was to determine the role of basal cells and prostaglandin E2 (PGE2) on GJA1 in the rat epididymis. Prior to basal cell differentiation, GJA1 is colocalized with TJP1 at the apical lateral margins between adjacent epithelial cells. When basal cells are present, GJA1 becomes associated between basal and principal cells, where it is primarily immunolocalized until adulthood. Basal cells express TP63, differentiate from epithelial cells, and produce prostaglandin-endoperoxide synthase 1 by 21 days of age. Prior to day 21, GJA1and TP63 are not strongly associated at the apical region. However, by day 28, TP63-positive basal cells migrate to the base of the epithelium, and also express GJA1. To assess effects of PGE2 on GJA1, rat caput epididymal (RCE) cells were exposed to PGE2 (50 μM) for 3 h. PGE2 increased levels of Gja1 mRNA in RCE cells, while levels of Gjb1, Gjb2, Gjb4, and GjB5 were unaltered. Furthermore, PGE2 increased protein levels of GJA1, phospho-GJA1, phospho-AKT, CTNNB1, and phospho-CTNNB1. Total AKT and the tight junction protein claudin1 were also not altered by PGE2. Data suggest that development of the epididymal epithelium and differentiation of epididymal basal cells regulate the targeting of GJA1, and that this appears to be mediated by PGE2.

PPARβ/δ Agonist GW501516 Inhibits Tumorigenicity of Undifferentiated Nasopharyngeal Carcinoma in C666-1 Cells by Promoting Apoptosis

Activation of peroxisome proliferator-activated receptor β/δ (PPARβ/δ) had been linked to inhibition on the proliferation and apoptosis in a few cancer cell lines. However, limited data exists regarding the role of PPARβ/δ in nasopharyngeal carcinoma (NPC). This study was undertaken to determine the effect of PPARβ/δ on cell proliferation, anchorage-dependent clonogenicity, and ectopic xenografts in the human NPC cell lines. Gene and protein expression of PPARβ/δ were reduced specifically in the poor- and un-differentiated NPC cell lines as compared with the control NP-69 cells. Ligand activation of PPARβ/δ by GW501516, a specific PPARβ/δ selective agonist, inhibited cell proliferation and colony formation strikingly, and induced a G2/M phase arrest in the EBV positive undifferentiated NPC C666-1 cells relative to the control cells. Moreover, GW501516 induced C666-1 cell apoptosis in a caspase and BAX dependent manner. In accordance with the in vitro result, GW501516 significantly suppressed the ectopic NPC xenograft tumorigenicity that derived from the C666-1 NPC cells in BALB/c nu/nu mice. This effect is greatly associated with its inhibition on the gene and protein expression of integrin-linked kinase (ILK) through activation of the AMPKα-dependent signaling pathways. Collectively, we showed that PPARβ/δ expression is in reverse correlation with the degree of differentiation in the NPC cell lines, and revealed the anti-tumorigenic effects of GW501516 in NPC cells by activation of AMPKα. This study suggested that PPARβ/δ targeting molecules may be useful for the poor-, and particularly un-differentiated NPC chemoprevention.

HMGA1 participates in MHCC97H cell proliferation and invasion through the ILK/Akt/GSK3β signaling pathway

Hepatocellular carcinoma (HCC) is one of the major causes of cancer‑related mortality, and the prognosis of HCC patients is unsatisfactory. It is known that the occurrence and development of HCC involves numerous genes, as well as various steps and stages in the pathological process. High mobility group AT‑hook 1 (HMGA1) and integrin‑linked kinase (ILK) may be overexpressed in HCC and may serve important roles in the development of cancer; however, the relationship between HMGA1 and ILK in HCC has not been examined. The present study demonstrated that inhibition of HMGA1 expression significantly decreased the levels of expression of ILK and the downstream elements phosphorylated (p)‑Akt, p‑glycogen synthase kinase 3β (GSK3β), matrix metalloproteinase (MMP)2, MMP9, CyclinD1 and c‑Myc. Transfection with an ILK expression vector was able to recover the decreased expression of these downstream genes, and affected cell proliferation and apoptosis. In addition, results from Transwell and wound‑healing experiments indicated that HMGA1 participates cell invasion and migration through the ILK/Akt/GSK3β pathway. The present study aimed to improve our understanding about the regulatory pathway involved in HCC and provides the basis for exploring HMGA1 inhibition as a therapy for patients with HCC and a new treatment strategy to prevent the development of HCC.

Inhibition of integrin-linked kinase expression by emodin through crosstalk of AMPKα and ERK1/2 signaling and reciprocal interplay of Sp1 and c-Jun

Despite the anti-cancer effect of emodin observed in several cancers, the underlying molecular mechanism remains to be elucidated. In this study, we showed that emodin-inhibited NSCLC cell growth and increased phosphorylation of AMPKα and ERK1/2. In addition, emodin-inhibited ILK protein expression. The overexpression of ILK reversed the effect of emodin on cell growth inhibition. Furthermore, the blockade of AMPK by compound C abrogated, while metformin, an activator of AMPK, strengthened the effect of emodin on the inhibition of ILK expression. Interestingly, the inhibitor of MAPK extracellular signaling-regulated kinase (ERK) kinase (MEK)/ERK1/2 (PD98059) attenuated emodin-induced phosphorylation of AMPKα. Moreover, emodin reduced the protein expression of Sp1 and AP-1 subunit c-Jun. Exogenous expression of Sp1 and c-Jun diminished emodin-reduced ILK protein expression. Emodin suppressed ILK promoter activity, which was not observed in cells overexpression of Sp1 and treated with compound C. Intriguingly, exogenous expression of c-Jun overcame the emodin-inhibited Sp1 protein expression. Collectively, our results demonstrate that emodin inhibits ILK expression through AMPKα-mediated reduction of Sp1 and c-Jun. Metformin enhances the effects of emodin. Exogenous expression of Sp1 and c-Jun resists emodin-inhibited ILK promoter activity and protein expression. In addition, the overexpression of c-Jun diminishes emodin-induced AMPKα signaling. Thus, the crosstalk of AMPKα and MEK/ERK1/2 signaling and the reciprocal interaction between Sp1 and c-Jun proteins contribute to the overall responses of emodin. This novel signaling axis may be a therapeutic potential for prevention and treatment of NSCLC.

Beta-Lapachone Suppresses Non-small Cell Lung Cancer Proliferation through the Regulation of Specificity Protein 1

Lung cancer is the leading cause of cancer-related death worldwide, and non-small cell lung cancer (NSCLC) is the most common pathological type with a reported frequency of about 85% of all cases. Despite recent advances in therapeutic agents and targeted therapies, the prognosis for NSCLC remains poor, and therefore it is important to identify the biological targets of this complex disease since a blockade of such targets would affect multiple downstream signaling cascades. β-Lapachone (β-Lap) is an antiproliferative agent that selectively induces apoptosis-related cell death in a variety of human cancer cells. However, the mechanisms of its action require further investigation. In this study, we show that treatment with β-lap triggers apoptosis and cell-cycle arrest in two NSCLC cell lines: H1299 and NCI-H358. The transcription factor specificity protein 1 (Sp1) was markedly inhibited by β-lap in a dose- and time-dependent manner. Furthermore, β-lap modulated the protein expression levels of the Sp1 regulatory genes, including cell-cycle regulatory proteins and antiapoptotic proteins, resulting in apoptosis. Taken together, our results indicate that β-lap may be a potential antiproliferative agent candidate by inducing apoptotic cell death in NSCLC tissue through downregulation of Sp1.

A prostaglandin E (PGE) receptor EP4 antagonist protects natural killer cells from PGE2-mediated immunosuppression and inhibits breast cancer metastasis

Cyclooxygenase-2 is frequently upregulated in epithelial tumors and contributes to poor outcomes in multiple malignancies. The COX-2 product prostaglandin E₂ (PGE₂) promotes tumor growth and metastasis by acting on a family of four G protein-coupled receptors (EP1-4). Using a novel small molecule EP4 antagonist (RQ-15986) and a syngeneic murine model of metastatic breast cancer, we determined the effect of EP4 blockade on innate immunity and tumor biology. Natural killer (NK)-cell functions are markedly depressed in mice bearing murine mammary tumor 66.1 or 410.4 cells owing to the actions of PGE₂ on NK cell EP4 receptors. The EP4 agonist PGE₁-OH inhibits NK functions in vitro, and this negative regulation is blocked by RQ-15986. Likewise, the treatment of tumor-bearing mice with RQ-15986 completely protected NK cells from the immunosuppressive effects of the tumor microenvironment in vivo. RQ-15986 also has direct effects on EP4 expressed by tumor cells, inhibiting the PGE₂-mediated activation of adenylate cyclase and blocking PGE₂-induced tumor cell migration. The pretreatment of tumor cells with a non-cytotoxic concentration of RQ-15986 inhibited lung colonization, a beneficial effect that was lost in mice depleted of NK cells. The oral administration of RQ-15986 inhibited the growth of tumor cells implanted into mammary glands and their spontaneous metastatic colonization to the lungs, resulting in improved survival. Our findings reveal that EP4 antagonism prevents tumor-mediated NK-cell immunosuppression and demonstrates the anti-metastatic activity of a novel EP4 antagonist. These observations support the investigation of EP4 antagonists in clinical trials.

JMJD2A-dependent silencing of Sp1 in advanced breast cancer promotes metastasis by downregulation of DIRAS3

Specificity protein 1(Sp1) is a ubiquitous transcription factor and is highly expressed in breast cancer. However, its expression pattern and role in breast cancer progression remain unclear. The purpose of this study is to examine the expression pattern of Sp1 and determine its role in breast cancer progression. Immunohistochemistry (IHC) was performed on breast cancer tissues to reveal the expression pattern of Sp1. Spearman rank correlation was used for clinical statistics. Gene and protein expressions were monitored by IHC analysis, quantitative polymerase chain reaction, and Western blot. Wound-healing and Transwell assays were conducted to assess the role of Sp1 in breast cancer. Co-immunoprecipitation, deletion mutagenesis, chromatin immunoprecipitation, and dual luciferase reporter gene assays were used for investigation of the regulatory network. Sp1 expression was downregulated in late stage breast cancer and in highly invasive breast cancer cell lines. Expression of Sp1 was negatively correlated with TNM staging (P = 0.002) and metastasis status (P = 0.023). Overexpression of Sp1 inhibited breast cancer cell migratory and invasive abilities, whereas knockdown of GTP-binding RAS-like 3 (DIRAS3, also known as ARHI, NOEY2) attenuated the inhibitory effects. Moreover, re-expression of DIRAS3 abolished Sp1 knockdown-mediated cell migration and invasion. Jumonji domain containing 2A (JMJD2A) inhibited Sp1 autoregulation and explains Sp1 expression pattern in breast cancer. Sp1 negatively regulated breast cancer metastasis by transcriptional activation of DIRAS3. Inhibition of Sp1 autoregulation by JMJD2A contributed to Sp1 expression pattern in breast cancer. Our findings provided evidence that targeted therapy against Sp1 might be useful in early stage breast cancer. However, in late stages, development of Sp1 activator may be more promising for breast cancer treatments.

Interactions between neutrophils and non-small cell lung cancer cells: enhancement of tumor proliferation and inflammatory mediator synthesis

The inflammatory tumor microenvironment plays a crucial role in tumor progression. In lung cancer, both bacterial infections and neutrophilia are associated with a poor prognosis. In this study, we characterized the effect of isolated human neutrophils on proliferation of the non-small cell lung cancer (NSCLC) cell line A549 and analyzed the impact of A549–neutrophil interactions on inflammatory mediator generation in naive and lipopolysaccharide (LPS)-exposed cell cultures. Co-incubation of A549 cells with neutrophils induced proliferation of resting and LPS-exposed A549 cells in a dose-dependent manner. In transwell-experiments, this effect was demonstrated to depend on direct cell-to-cell contact. This pro-proliferative effect of neutrophils on A549 cells could be attenuated by inhibition of neutrophil elastase activity, but not by oxygen radical neutralization. Correspondingly, neutrophil elastase secretion, but not respiratory burst, was specifically enhanced in co-cultures of A549 cells and neutrophils. Moreover, interference with COX-2 activity by indomethacin or the specific COX-2 inhibitor NS-398 also blunted the increased A549 proliferation in the presence of neutrophils. In parallel, a massive amplification of COX-2-dependent prostaglandin E₂ synthesis was detected in A549–neutrophil co-cultures. These findings suggest that direct cell–cell interactions between neutrophils and tumor cells cause release of inflammatory mediators which, in turn, may enhance tumor growth in NSCLC.

The oncoprotein hepatitis B X-interacting protein promotes the migration of ovarian cancer cells through the upregulation of S-phase kinase-associated protein 2 by Sp1

Hepatitis B X-interacting protein (HBXIP) is a novel oncoprotein. We have previously reported that HBXIP promotes the proliferation and migration of breast cancer cells. S-phase kinase-associated protein 2 (Skp2) is another oncoprotein which is important for migration. In this study, we investigated whether Skp2 is involved in the migration enhanced by HBXIP in ovarian cancer. The expression of HBXIP and Skp2 in ovarian cancer tissues was examined by immunohistochemistry using tissue microarrays. The role of HBXIP and Skp2 in the migration of ovarian cancer cells was investigated by wound-healing assay and Transwell migration assay. The effect of HBXIP on Skp2 was assessed by reverse transcription polymerase chain reaction (RT-PCR), western blot analysis, luciferase reporter gene assays and chromatin immunoprecipitation in ovarian cancer cells (SKOV3 and CAOV3). We found that both HBXIP and Skp2 were highly expressed in ovarian cancer tissues. We observed that the overexpression of HBXIP enhanced the migration of ovarian cancer cells, while Skp2 siRNAs decreased the cell migration enhanced by HBXIP. The HBXIP siRNAs inhibited ovarian cancer cell migration and Skp2 rescued the migration inhibition induced by HBXIP siRNA. HBXIP could upregulate Skp2 at the levels of mRNA and protein in ovarian cancer cells. Moreover, HBXIP increased the activity of Skp2 promoter via binding to the transcription factor Sp1. HBXIP is highly expressed in ovarian cancer tissues. HBXIP enhances the migration of ovarian cancer cells. HBXIP was able to stimulate the activity of Skp2 promoter via transcription factor Sp1 thus promoting the migration of ovarian cancer cells.

Repression of phosphoinositide-dependent protein kinase 1 expression by ciglitazone via Egr-1 represents a new approach for inhibition of lung cancer cell growth

Background

Peroxisome proliferator-activated receptors gamma (PPARγ) ligands have been shown to inhibit the growth of non-small cell lung cancer (NSCLC) cells. However, the mechanisms underlying this effect remain incompletely elucidated.

Methods

Cell proliferation and apoptosis were measured by cell viability, MTT and caspase3/7 activity assays. Phosphorylation/protein expression and gene silence/overexpression of AMPKα, phosphoinositide-dependent protein kinase 1 (PDK1), Egr-1 and PPARγ were performed by Western blot and siRNA/transfection assays. Dual-Luciferase Reporter Kit was used to measure the PPAR response elements (PPRE) reporter and PDK1 promoter activities, and ChIP assay was used to detect the Egr-1 protein binding to the DNA site in the PDK1 gene promoter.

Results

We found that ciglitazone, one synthetic PPARγ ligand, inhibited growth and induced apoptosis of NSCLC cells through decreased expression of PDK1, which was not blocked by GW9662 (a specific PPARγ antagonist). Overexpression of PDK1 overcame the effect of ciglitazone on cell growth and caspase 3/7 activity. Ciglitazone increased the phosphorylation of AMPKα and c-Jun N-terminal kinase (JNK), and the inhibitor of AMPK (compound C), but not JNK (SP600125), reversed the effect of ciglitazone on PDK1 protein expression. Ciglitazone reduced PDK1 gene promoter activity, which was not observed in cells exposed to compound C, but not silenced of PPARγ siRNA. Combination of ciglitazone and metformin further reduced PDK1 expression and promoter activity. Furthermore, we showed that ciglitazone induced the protein expression of Egr-1, which was not observed in cells silencing of AMPKα. Moreover, silencing of Egr-1 abrogated the effect of ciglitazone on PDK1 promoter activity and cell growth. On the contrary, overexpression of Egr-1 enhanced the effect of ciglitazone on PDK1 gene promoter activity. ChIP assays demonstrated that ciglitazone induced Egr-1 protein bind to the specific DNA site in the PDK1 gene promoter.

Conclusion

Collectively, our results demonstrate that ciglitazone inhibits PDK1 expression through AMPKα-mediated induction of Egr-1 and Egr-1 binding to the specific DNA site in the PDK1 gene promoter, which is independent of PPARγ. Activation of AMPKα by metformin enhances the effect of ciglitazone. In turn, this leads to inhibition of NSCLC cell proliferation.

Ribonuclease inhibitor up-regulation inhibits the growth and induces apoptosis in murine melanoma cells through repression of angiogenin and ILK/PI3K/AKT signaling pathway

Human ribonuclease inhibitor (RI), a cytoplasmic protein, is constructed almost entirely of leucine rich repeats. RI could suppress activities of ribonuclease and angiogenin (ANG) through closely combining with them. ANG is a potent inducer of blood vessel growth and has been implicated in the establishment, growth, and metastasis of tumors. ILK/PI3K/AKT signaling pathway also plays important roles in cell growth, cell-cycle progression, tumor angiogenesis, and cell apoptosis. Our previous experiments demonstrated that RI might effectively inhibit some tumor growth and metastasis. Our recent study showed that ILK siRNA inhibited the growth and induced apoptosis in bladder cancer cells as well as increased RI expression, which suggest a correlation between RI and ILK. However, the exact molecular mechanism of RI in anti-tumor and in the cross-talk of ANG and ILK signaling pathway remains largely unknown. Here we investigated the effects of up-regulating RI on the growth and apoptosis in murine melanoma cells through angiogenin and ILK/PI3K/AKT signaling pathway. We demonstrated that up-regulating RI obviously decreased ANG expression and activity. We also discovered that RI overexpression could remarkably inhibit cell proliferation, regulate cell cycle and induce apoptosis. Furthermore, up-regulation of RI inhibited phosphorylation of ILK downstream signaling targets protein kinase B/Akt, glycogen synthase kinase 3-beta (GSK-3β), and reduced β-catenin expression in vivo and vitro. More importantly, RI significant inhibited the tumor growth and angiogenesis of tumor bearing C57BL/6 mice. In conclusion, our findings, for the first time, suggest that angiogenin and ILK signaling pathway plays a pivotal role in mediating the inhibitory effects of RI on melanoma cells growth. This study identifies that RI may be a useful molecular target for melanoma therapy.

Repression of integrin-linked kinase by antidiabetes drugs through cross-talk of PPARγ- and AMPKα-dependent signaling: role of AP-2α and Sp1

Nasopharyngeal carcinoma (NPC) is one of the most common cancers of the head and neck, particularly in Southern China and Southeast Asia with high treatment failure due to the development of local recurrence and distant metastasis. The molecular mechanisms related to the progression of NPC have not been fully understood. In this study, we showed that antidiabetes drugs rosiglitazone and metformin inhibit NPC cell growth through reducing the expression of integrin-linked kinase (ILK). Blockade of PPARγ and AMPKα overcame the effects of rosiglitazone and metformin on ILK protein. Importantly, overexpression of ILK abrogated the effect of rosiglitazone and metformin on NPC cell growth. Furthermore, these agents reduced ILK promoter activity, which was not observed in AP-2α, but not Sp1 site mutation in ILK gene promoter. In addition, silencing of AP-2α or overexpression of Sp1 reversed the effect of these agents on ILK protein expression and cell growth. Chromatin immunoprecipitation (ChIP) assay showed that rosiglitazone induced AP-2α, while metformin reduced Sp1 protein binding to the DNA sequences in the ILK gene promoter. Intriguingly, overexpression of Sp1 abolished the effect of rosiglitazone on AP-2α protein expression. Collectively, we show that rosiglitazone and metformin inhibit ILK gene expression through PPARγ- and AMPKα-dependent signaling pathways that are involved in the regulation of AP-2α and Sp1 protein expressions. The effect of combination of rosiglitazone and metformin demonstrates greater extent than single agent alone. The cross-talk of PPARγ and AMPKα signaling enhances the synergistic effects of rosiglitazone and metformin. This study unveils novel mechanisms by which oral antidiabetes drugs inhibit the growth of human NPC cells.

Prostaglandin E receptor EP4 is a therapeutic target in breast cancer cells with stem-like properties

The cyclooxygenase pathway is strongly implicated in breast cancer progression but the role of this pathway in the biology of breast cancer stem/progenitor cells has not been defined. Recent attention has focused on targeting the cyclooxygenase 2 (COX-2) pathway downstream of the COX-2 enzyme by blocking the activities of individual prostaglandin E (EP) receptors. Prostaglandin E receptor 4 (EP4) is widely expressed in primary invasive ductal carcinomas of the breast and antagonizing this receptor with small molecule inhibitors or shRNA directed to EP4 inhibits metastatic potential in both syngeneic and xenograft models. Breast cancer stem/progenitor cells are defined as a subpopulation of cells that drive tumor growth, metastasis, treatment resistance, and relapse. Mammosphere-forming breast cancer cells of human (MDA-MB-231, SKBR3) or murine (66.1, 410.4) origin of basal-type, Her-2 phenotype and/or with heightened metastatic capacity upregulate expression of both EP4 and COX-2 and are more tumorigenic compared to the bulk population. In contrast, luminal-type or non-metastatic counterparts (MCF7, 410, 67) do not increase COX-2 and EP4 expression in mammosphere culture. Treatment of mammosphere-forming cells with EP4 inhibitors (RQ-15986, AH23848, Frondoside A) or EP4 gene silencing, but not with a COX inhibitor (Indomethacin) reduces both mammosphere-forming capacity and the expression of phenotypic markers (CD44^hi/CD24^low, aldehyde dehydrogenase) of breast cancer stem cells. Finally, an orally delivered EP4 antagonist (RQ-08) reduces the tumor-initiating capacity and markedly inhibits both the size of tumors arising from transplantation of mammosphere-forming cells and phenotypic markers of stem cells in vivo. These studies support the continued investigation of EP4 as a potential therapeutic target and provide new insight regarding the role of EP4 in supporting a breast cancer stem cell/tumor-initiating phenotype.

Endotoxin induces proliferation of NSCLC in vitro and in vivo: role of COX-2 and EGFR activation

Lung cancer is frequently complicated by pulmonary infections which may impair prognosis of this disease. Therefore, we investigated the effect of bacterial lipopolysaccharides (LPS) on tumor proliferation in vitro in the non-small cell lung cancer (NSCLC) cell line A549, ex vivo in a tissue culture model using human NSCLC specimens and in vivo in the A549 adenocarcinoma mouse model. LPS induced a time- and dose-dependent increase in proliferation of A549 cells as quantified by MTS activity and cell counting. In parallel, an increased expression of the proliferation marker Ki-67 and cyclooxygenase (COX)-2 was detected both in A549 cells and in ex vivo human NSCLC tissue. Large amounts of COX-2-derived prostaglandin (PG)E(2) were secreted from LPS-stimulated A549 cells. Pharmacological interventions revealed that the proliferative effect of LPS was dependent on CD14 and Toll-like receptor (TLR)4. Moreover, blocking of the epidermal growth factor receptor (EGFR) also decreased LPS-induced proliferation of A549 cells. Inhibition of COX-2 activity in A549 cells severely attenuated both PGE(2) release and proliferation in response to LPS. Synthesis of PGE(2) was also reduced by inhibiting CD14, TLR4 and EGFR in A549 cells. The proliferative effect of LPS on A549 cells could be reproduced in the A549 adenocarcinoma mouse model with enhancement of tumor growth and Ki-67 expression in implanted tumors. In summary, LPS induces proliferation of NSCLC cells in vitro, ex vivo in human NSCLC specimen and in vivo in a mouse model of NSCLC. Pulmonary infection may thus directly induce tumor progression in NSCLC.

Involvement of β-arrestins in cancer progression

β-arrestins, including β-arrestin1 and β-arrestin2, are ubiquitous cytosolic proteins which localize in the cytoplasm and plasma membrane, initially be regarded as an potential character in G protein-coupled receptors (GPCR) desensitization, sequestration, and internalization. Besides, recent many studies increasingly revealed that β-arrestins served widely as versatile adapter proteins for scaffolding many intracellular signaling networks to modulate the strength and duration of signaling by diverse types of receptors and downstream kinases. As we known, the biologic and clinical behaviors of many tumors are largely determined by multiple molecular signal pathways. More recently, accumulating evidences established that β-arrestins got widely involved in many cancer developmental signaling events which responsible for tumor viability and metastasis, suggesting an impressive role of β-arrestins in tumor progression. Because of the regulation and biological output of β-arrestins is so complex, the role of β-arrestins in cancer development still remains enigmatic. However, the further understanding with the clinical prognosis and oncogenic potential of β-arrestins might facilitate the identification of diagnosis biomarkers and development of drug targets in cancer. In this article, we reviewed a comprehensive summary of the β-arrestins-mediated functions in human cancers.

Arachidonic acid derivatives and their role in peripheral nerve degeneration and regeneration

After peripheral nerve injury, a process of axonal degradation, debris clearance, and subsequent regeneration is initiated by complex local signaling, called Wallerian degeneration (WD). This process is in part mediated by neuroglia as well as infiltrating inflammatory cells and regulated by inflammatory mediators such as cytokines, chemokines, and the activation of transcription factors also related to the inflammatory response. Part of this neuroimmune signaling is mediated by the innate immune system, including arachidonic acid (AA) derivatives such as prostaglandins and leukotrienes. The enzymes responsible for their production, cyclooxygenases and lipooxygenases, also participate in nerve degeneration and regeneration. The interactions between signals for nerve regeneration and neuroinflammation go all the way down to the molecular level. In this paper, we discuss the role that AA derivatives might play during WD and nerve regeneration, and the therapeutic possibilities that arise.

Development of stable HSPA1A promoter-driven luciferase reporter HepG2 cells for assessing the toxicity of organic pollutants present in air

HSPA1A (HSP70-1) is a highly inducible heat shock gene up-regulated in response to environmental stresses and pollutants. The aim of our study was to evaluate the sensitivity of the stable metabolically competent HepG2 cells containing a human HSPA1A promoter-driven luciferase reporter (HepG2-luciferase cells) for assessing the toxicity of organic pollutants present in air. The HepG2-luciferase cells were validated by heat shock treatment and testing three organic compounds (pyrene, benzo[a]pyrene, and formaldehyde) that are ubiquitous in the air. The maximal level of HSPA1A (HSP70-1) and relative luciferase activity induced by heat shock were over three and nine times the control level, respectively. Pyrene, benzo[a]pyrene, and formaldehyde all induced significantly elevated levels of relative luciferase activity in a dose-dependent manner. Extractable organic matter (EOM) from urban traffic and coke oven emissions in ambient air were tested on the HepG2-luciferase cells. The traffic EOM induced significant increase in relative luciferase activity at concentrations of picogram per liter. The coke oven EOM produced a strong dose-dependent induction of relative luciferase activity up to six times the control value. Significant increases in relative luciferase activity were observed at concentrations that were as low, or lower than the concentrations that the tested organic pollutants decreased cell viability, and increased malondialdehyde concentration, Olive tail moment, and micronuclei frequency. Therefore, we conclude that the HepG2-luciferase cells are a valuable tool for rapid screening of the overall toxicity of organic pollutants present in air.

Cytochrome P450 2S1 depletion enhances cell proliferation and migration in bronchial epithelial cells, in part, through modulation of prostaglandin E(2) synthesis

Cytochromes P450 (P450s) contribute to the metabolic activation and inactivation of various endogenous substrates. Despite years of research, the physiological role of CYP2S1 remains unknown. CYP2S1 has demonstrated NADPH P450-reductase-independent metabolism of cyclooxygenase (COX)-derived prostaglandins [e.g., prostaglandin G(2) (PGG(2))] at nanomolar concentrations. Arachidonic acid is converted to prostaglandin precursors [PGG(2) and prostaglandin H(2) (PGH(2))] through COX. These precursors are used to synthesize numerous prostanoids, including PGE(2). Prostaglandin E(2) (PGE(2)) promotes cell proliferation and cell migration and inhibits apoptosis. CYP2S1 metabolism of PGG(2) presumably sequesters PGG(2) and PGH(2), making them unavailable for synthesis of prostanoids such as PGE(2). Whether CYP2S1 contributes to prostaglandin metabolism and influences cell physiological remains to be determined. The purpose of this study was to evaluate the physiological role of CYP2S1, if any, in human bronchial epithelial cells [SV40-derived bronchial epithelial cell line (BEAS-2B)]. To do this, we used small interfering RNA to deplete CYP2S1 mRNA and protein by approximately 75% and evaluated the impact of CYP2S1 depletion on cell proliferation and migration. CYP2S1 depletion enhanced both cell proliferation and migration in BEAS-2B cells. Consistent with the proposed role of CYP2S1 in PGE(2) synthesis, the reduction in CYP2S1 expression doubled intracellular PGE(2) levels. Pharmacological administration of PGE(2) enhanced cell proliferation in BEAS-2B cells but failed to promote migration. Our data reveal an important role for CYP2S1 in the regulation of cell proliferation and migration, occurring in part through modulation of prostaglandin synthesis.

Prostaglandin E₂ increases fibroblast gene-specific and global DNA methylation via increased DNA methyltransferase expression

Although alterations in DNA methylation patterns have been associated with specific diseases and environmental exposures, the mediators and signaling pathways that direct these changes remain understudied. The bioactive lipid mediator prostaglandin E(2) (PGE(2)) has been shown to exert a myriad of effects on cell survival, proliferation, and differentiation. Here, we report that PGE(2) also signals to increase global DNA methylation and DNA methylation machinery in fibroblasts. HumanMethylation27 BeadChip array analysis of primary fetal (IMR-90) and adult lung fibroblasts identified multiple genes that were hypermethylated in response to PGE(2). PGE(2), compared with nontreated controls, increased expression and activity (EC(50)∼10(7) M) of one specific isoform of DNA methyltransferase, DNMT3a. Silencing of DNMT3a negated the ability of PGE(2) to increase DNMT activity. The increase in DNMT3a expression was mediated by PGE(2) signaling via its E prostanoid 2 receptor and the second messenger cAMP. PGE(2), compared with the untreated control, increased the expression and activity of Sp1 and Sp3 (EC(50)∼3×10(7) M), transcription factors known to increase DNMT3a expression, and inhibition of these transcription factors abrogated the PGE(2) increase of DNMT3a expression. These findings were specific to fibroblasts, as PGE(2) decreased DNMT1 and DNMT3a expression in RAW macrophages. Taken together, these findings establish that DNA methylation is regulated by a ubiquitous bioactive endogenous mediator. Given that PGE(2) biosynthesis is modulated by environmental toxins, various disease states, and commonly used pharmacological agents, these findings uncover a novel mechanism by which alterations in DNA methylation patterns may arise in association with disease and certain environmental exposures.

Comparison of the bronchodilating effects of inhaled β₂-agonists after methacholine challenge in a human lung reperfusion model

The aim of the present investigation was to compare the onset of action and intrinsic activity of the long-acting β(2)-agonist GW597901 with the fast- and short-acting salbutamol as model compounds using an isolated human lung reperfusion model. Twelve resected human lung lobes were challenged with methacholine (MCh) and subsequently nebulised with either GW597901 or salbutamol. Prostaglandin E(2) (PGE(2)) concentrations in the perfusion fluid were compared with the dose of MCh that was required to induce a bronchoconstriction. After successful MCh provocation, nebulisation of GW597901 and salbutamol fully reversed any observed bronchoconstriction. The bronchodilating effect was more pronounced for GW597901. Salbutamol revealed an immediate onset of action while the effect of GW597901 was observed with an approximate delay of 6 min. Higher doses of MCh were required for a successful bronchial challenge in the presence of elevated PGE(2) levels (r=0.8171, p ≤ 0.05). For the first time, an isolated perfused human lung model has been established for comparing the onset of action and potency of a short- and long-acting β(2)-agonist. We therefore conclude that it is an alternative for determination of drug effect characteristics and suitable for supplementing or predicting clinical data.

Prostaglandin E2 EP receptors as therapeutic targets in breast cancer

Prostaglandins are lipid compounds that mediate many physiological effects. Prostaglandin E2 (PGE(2)) is the most abundant prostanoid in the human body, and synthesis of PGE(2) is driven by cyclooxygenase enzymes including COX-2. Both elevated expression of COX-2 and increased PGE(2) levels have been associated with many cancers including breast cancer. PGE(2) exerts its effect by binding to the E series of prostaglandin receptors (EP) which are G protein-coupled receptors. Four EP receptor subtypes exist, EP1-4, and each is coupled to different intracellular signaling pathways. As downstream effectors of the COX-2 pathway, EP receptors have been shown to play a role in breast and other malignancies and in cancer metastasis. The role of each EP receptor in malignant behavior is complex and involves the interplay of EP receptor signaling on the tumor cell, on stromal cells, and on host immune effector cells. While preclinical and epidemiological data support the use of nonsteroidal anti-inflammatory drugs and selective COX-2 inhibitors (COXibs) for the prevention and treatment of malignancy, toxicities due to COXibs as well as less than promising results from clinical trials have laboratories seeking alternative targets. As knowledge concerning the role of EP receptors in cancer grows, so does the potential for exploiting EP receptors as therapeutic targets for the treatment or prevention of cancer and cancer metastasis.

Prostanoids in tumor angiogenesis: therapeutic intervention beyond COX-2

Prostanoids regulate angiogenesis in carcinoma and chronic inflammatory disease progression. Although prostanoid biosynthetic enzymes and signaling have been extensively analyzed in inflammation, little is known about how prostanoids mediate tumor-induced angiogenesis. Targeted cyclooxygenase (COX)-2 inhibition in tumor, stromal and endothelial cells is an attractive antiangiogenic strategy; however, the associated cardiovascular side effects have led to the development of a new generation of nonsteroidal anti-inflammatory drugs (NSAIDs) acting downstream of COX. These agents target terminal prostanoid synthases and prostanoid receptors, which may also include several peroxisome proliferator-activated receptors (PPARs). Here, we discuss the role of prostanoids as modulators of tumor angiogenesis and how prostanoid metabolism reflects complex cell-cell crosstalk that determines tumor growth. Finally, we discuss the potential of new NSAIDs for the treatment of angiogenesis-dependent tumor development.

Sp1 expression regulates lung tumor progression

The role of specificity protein 1 (Sp1) in controlling gene expression in lung tumor development and metastasis is not well understood. In this study, we showed that the Sp1 level was highly increased and required for lung tumor growth in transgenic mice bearing Kras-induced lung tumors under the control of doxycycline. Furthermore, the Sp1 level was highly upregulated in lung adenocarcinoma cells with low invasiveness and in patients with stage I lung cancer. We also demonstrated that Sp1 was downregulated in lung adenocarcinoma cells with high invasiveness and in patients with stage IV lung adenocarcinoma. Moreover, Sp1 inversely regulated migration, invasion and metastasis of lung adenocarcinoma cells in vivo. In addition, a decrease in the Sp1 level in highly invasive lung adenocarcinoma cells resulted from instability of the Sp1 protein. Furthermore, overexpression of Sp1 in highly invasive lung adenocarcinoma cells increased expression of E-cadherin, a suppressor of metastasis, and attenuated the translocation of β-catenin into the cellular nucleus that leads to tumor malignancy. Taken together, Sp1 level accumulated strongly in early stage and then declined in late stage, which is important for lung cancer cell proliferation and metastasis during tumorigenesis.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Activation of telomerase by seminal plasma in malignant and normal cervical epithelial cells

Seminal fluids are involved in the development of cervical cancer but the underlying mechanism is unclear. Because cellular transformation requires telomerase activation by expression of the telomerase reverse transcriptase (hTERT) gene, we examined the role of seminal fluids in telomerase activation. Significantly elevated hTERT mRNA and telomerase activity were observed in cervical cell lines (HeLa, SiHa and Caski) treated with seminal plasma. Normal cervical epithelial cells expressed minimal levels of hTERT mRNA and telomerase activity, and seminal plasma substantially enhanced both expression and activity. The hTERT promoter activity was similarly increased in seminal plasma-treated HeLa cells and this effect was closely correlated with increased Sp1 expression and binding to the hTERT promoter. Cyclooxygenase-2 (COX-2) was simultaneously increased in HeLa cells exposed to seminal plasma, and blockade of COX-2 induction abolished seminal plasma stimulation of the hTERT promoter activity, hTERT expression and telomerase activity. Prostaglandin E2 (PGE2) mimics the effect of seminal plasma, stimulating Sp1 expression, enhancing Sp1 occupancy on the hTERT promoter and promoter activity. Moreover, tumour growth was robustly enhanced when HeLa cells together with seminal plasma were injected into nude-mice. Taken together, seminal plasma stimulates COX-2-PGE2-Sp1-dependent hTERT transcription, which provides insights into the putative mechanism underlying telomerase activation in cervical epithelial and cancer cells.

Hypoxia and prostaglandin E receptor 4 signalling pathways synergise to promote endometrial adenocarcinoma cell proliferation and tumour growth

The prostaglandin endoperoxide synthase (PTGS) pathway is a potent driver of tumour development in humans by enhancing the biosynthesis and signalling of prostaglandin (PG) E(2). PTGS2 expression and PGE(2) biosynthesis is elevated in endometrial adenocarcinoma, however the mechanism whereby PTGS and PGE(2) regulate endometrial tumour growth is unknown. Here we investigated (a) the expression profile of the PGE synthase enzymes (PTGES, PTGES-2, PTGES-3) and PGE receptors (PTGER1-4) in endometrial adenocarcinomas compared with normal endometrium and (b) the role of PTGER4 in endometrial tumorigenesis in vivo. We found elevated expression of PTGES2 and PTGER4 and suppression of PTGER1 and PTGER3 in endometrial adenocarcinomas compared with normal endometrium. Using WT Ishikawa endometrial adenocarcinoma cells and Ishikawa cells stably transfected with the full length PTGER4 cDNA (PTGER4 cells) xenografted in the dorsal flanks of nude mice, we show that PTGER4 rapidly and significantly enhances tumour growth rate. Coincident with enhanced PTGER4-mediated tumour growth we found elevated expression of PTGS2 in PTGER4 xenografts compared with WT xenografts. Furthermore we found that the augmented growth rate of the PTGER4 xenografts was not due to enhanced angiogenesis, but regulated by an increased proliferation index and hypoxia. In vitro, we found that PGE(2) and hypoxia independently induce expression of PTGER4 indicating two independent pathways regulating prostanoid receptor expression. Finally we have shown that PGE(2) and hypoxia synergise to promote cellular proliferation of endometrial adenocarcinoma cells.

Varied pathways of stage IA lung adenocarcinomas discovered by integrated gene expression analysis

BACKGROUND

Discovery of the progression-associated genes and pathways in lung adenocarcinoma (LAD) has important implications in understanding the molecular mechanism of tumor development. However, few studies had been performed to focus on the changes of pathways in lung adenocarcinoma development using microarray expression profile.

RESULT

We performed a meta-analysis of 4 LAD microarray datasets encompassing 353 patients to reveal differentially expressed genes (DEGs) between normal lung tissues and LAD of different stages. Overall, 1 838 genes were found to be dys-regulated, and the adipogenesis, circadian rhythm, and Id pathways were significantly changed. Interestingly, most of the genes from the same gene family (such as Interleukin receptor, Matrix metallopeptidase, Histone cluster and Minichromosome maintenance complex component families) were found to be up-regulated (or down-regulated). Real-time PCR (qRT-PCR) was applied to validate the expression of randomly selected 18 DEGs in LAD cell lines. In the pathway analysis among stages, Oxidative stress, Glycolysis/Gluconeogenesis and Integrin-mediated cell adhesion pathways, which were involved in cancer cell proliferation and metastasis, were showed to be significantly regulated in stages other than IA.

CONCLUSION

Genes involved in adipogenesis and Id pathways might play important roles in development of LADs. The similar trend of expression of the gene family members suggested coordinate regulation in tumor progression. Three pathways (Oxidative stress, Glycolysis/Gluconeogenesis and Integrin-mediated cell adhesion pathways) significantly regulated in stages other than stage IA suggested that genes and pathways conferring invasive character might be activated in the preinvasive stage IB, while the Oxidative stress and the Glycolysis/Gluconeogenesis pathways might have strong connections to cisplatin-based chemotherapy. The insignificantly regulated three pathways in stage IA might be used in early-stage detection of LAD.

Cyclooxygenase-2 up-regulates vascular endothelial growth factor via a protein kinase C pathway in non-small cell lung cancer

Background

Vascular endothelial growth factor (VEGF) expression is up-regulated via a cyclooxygenase-2 (COX-2)-dependent mechanism in non-small cell lung cancer (NSCLC), but the specific signaling pathway involved is unclear. Our aim was to investigate the signaling pathway that links COX-2 with VEGF up-regulation in NSCLC.

Material and methods

COX-2 expression in NSCLC samples was detected immunohistochemically, and its association with VEGF, microvessel density (MVD), and other clinicopathological characteristics was determined. The effect of COX-2 treatment on the proliferation of NSCLC cells (A549, H460 and A431 cell lines) was assessed using the tetrazolium-based MTT method, and VEGF expression in tumor cells was evaluated by flow cytometry. COX-2-induced VEGF expression in tumor cells was monitored after treatment with inhibitors of protein kinase C (PKC), PKA, prostaglandin E2 (PGE₂), and an activator of PKC.

Results

COX-2 over-expression correlated with MVD (P = 0.036) and VEGF expression (P = 0.001) in NSCLC samples, and multivariate analysis demonstrated an association of VEGF with COX-2 expression (P = 0.001). Exogenously applied COX-2 stimulated the growth of NSCLCs, exhibiting EC₅₀ values of 8.95 × 10^-3, 11.20 × 10^-3, and 11.20 × 10^-3 μM in A549, H460, and A431 cells, respectively; COX-2 treatment also enhanced tumor-associated VEGF expression with similar potency. Inhibitors of PKC and PGE₂ attenuated COX-2-induced VEGF expression in NLCSCs, whereas a PKC activator exerted a potentiating effect.

Conclusion

COX-2 may contribute to VEGF expression in NSCLC. PKC and downstream signaling through prostaglandin may be involved in these COX-2 actions.

Naphthalene/quinoline amides and sulfonylureas as potent and selective antagonists of the EP4 receptor

Two new series of EP(4) antagonists based on naphthalene/quinoline scaffolds have been identified as part of our on-going efforts to develop treatments for inflammatory pain. One series contains an acidic sulfonylurea pharmacophore, whereas the other is a neutral amide. Both series show subnanomolar intrinsic binding potency towards the EP(4) receptor, and excellent selectivity towards other prostanoid receptors. While the amide series generally displays poor pharmacokinetic parameters, the sulfonylureas exhibit greatly improved profile. MF-592, the optimal compound from the sulfonylurea series, has a desirable overall preclinical profile that suggests it is suitable for further development.

Cyclooxygenase-deficient pancreatic cancer cells use exogenous sources of prostaglandins

Genes that are differentially expressed in pancreatic cancers and under epigenetic regulation are of considerable biological and therapeutic interest. We used global gene expression profiling and epigenetic treatment of pancreatic cell lines including pancreatic cancer cell lines, pancreatic cancer-associated fibroblasts, and cell lines derived from nonneoplastic pancreata. We examined expression and epigenetic alterations of cyclooxygenase-1 (COX-1) and COX-2 in pancreatic cancers and normal pancreas and performed proliferation, knockdown, and coculture experiments to understand the role of stromal sources of prostaglandins for pancreatic cancers. We identify COX-1 as a gene under epigenetic regulation in pancreatic cancers. We find that COX-1 expression is absent in many pancreatic cancer cells and some of these cancers also lack COX-2 expression. Suspecting that such cancers must rely on exogenous sources of prostaglandins, we show that pancreatic cancer stromal cells, such as fibroblasts expressing COX-1 and COX-2, are a likely source of prostaglandins for pancreatic cancer cells deficient in COX. Knocking down the prostaglandin transporter multidrug resistance-associated protein-4 in fibroblasts suppresses the proliferation of cocultured pancreatic cancer cells lacking COX. Pancreatic cancers that lack COX can use exogenous sources of prostaglandins. Blocking multidrug resistance-associated protein-4 may be a useful therapeutic strategy to deplete COX-deficient pancreatic cancers of prostaglandins.

Prostaglandin E2 promotes lung cancer cell migration via EP4-betaArrestin1-c-Src signalsome

Many human cancers express elevated levels of cyclooxygenase-2 (COX-2), an enzyme responsible for the biosynthesis of prostaglandins. Available clinical data establish the protective effect of COX-2 inhibition on human cancer progression. However, despite these encouraging outcomes, the appearance of unwanted side effects remains a major hurdle for the general application of COX-2 inhibitors as effective cancer drugs. Hence, a better understanding of the molecular signals downstream of COX-2 is needed for the elucidation of drug targets that may improve cancer therapy. Here, we show that the COX-2 product prostaglandin E(2) (PGE(2)) acts on cognate receptor EP4 to promote the migration of A549 lung cancer cells. Treatment with PGE(2) enhances tyrosine kinase c-Src activation, and blockade of c-Src activity represses the PGE(2)-mediated lung cancer cell migration. PGE(2) affects target cells by activating four receptors named EP1 to EP4. Use of EP subtype-selective ligand agonists suggested that EP4 mediates prostaglandin-induced A549 lung cancer cell migration, and this conclusion was confirmed using a short hairpin RNA approach to specifically knock down EP4 expression. Proximal EP4 effectors include heterotrimeric Gs and betaArrestin proteins. Knockdown of betaArrestin1 expression with shRNA significantly impaired the PGE(2)-induced c-Src activation and cell migration. Together, these results support the idea that increased expression of the COX-2 product PGE(2) in the lung tumor microenvironment may initiate a mitogenic signaling cascade composed of EP4, betaArrestin1, and c-Src which mediates cancer cell migration. Selective targeting of EP4 with a ligand antagonist may provide an efficient approach to better manage patients with advanced lung cancer.

The role of prostacyclin in lung cancer

Prostanoids are bioactive lipids that interact with 7-membrane-spanning G-protein-coupled receptors on target cells to impart their biologic effects. They include prostaglandins, prostacyclin, and thromboxane. Prostanoids are widely distributed; mediate several diverse biologic effects like platelet aggregation and smooth-muscle contraction; and are known to be involved in allergies, acquired immunity, and cancer metastasis. Prostanoids have also been associated with breast and endometrial cancer promotion, and with the inhibition of melanoma. The role of prostanoids in the development of lung disease has been poorly understood. In particular, prostacyclin possesses significant anti-inflammatory and antimetastatic properties and is the main product of cyclooxygenase-2 activity in the lung. In fact, the balance of the various members of the prostanoids family, specifically the prostaglandins PGE(2) and prostacyclin (PGI(2)), seems to play an increasingly important role in the development of lung cancer. Gaining a better understanding of prostanoids and their associated pathways is critical to the future development of molecular-based and pharmaceutical treatments of lung disease.

Tolfenamic acid decreases c-Met expression through Sp proteins degradation and inhibits lung cancer cells growth and tumor formation in orthotopic mice

The nonsteroidal anti-inflammatory drug (NSAID), tolfenamic acid (TA) is emerging as a new anti-cancer agent. TA induces the degradation of specific Specificity protein (Sp) transcription factors, Sp1, Sp3 and Sp4 which are associated with tumor growth and metastasis. In this study we have evaluated the effect of TA on lung cancer using both in vitro and in vivo models. TA in a dose dependent manner inhibited proliferation and cell viability of two different lung cancer cells, A549 and CRL5803. TA treatment for 48 h significantly decreased the expression of Sp1, Sp3 and Sp4. The hepatocyte growth factor receptor, c-Met is overexpressed in a variety of cancers including lung cancer and Sp proteins mediate the regulation of c-Met. TA diminished the expression of c-Met protein and modulates its downstream signaling pathway. Furthermore, TA treatment significantly increased the number of apoptotic cells and pro-apoptotic markers c-PARP and Bax confirming the activation of apoptotic pathways. In vivo studies using the orthotopic mice model for lung cancer showed that TA (25 mg/kg/2 days and 50 mg/kg/2 days) resulted in a dose dependent decrease in tumor formation. The immunohistochemical staining of lung tissue showed high expression of Sp1, Sp3, Sp4, c-Met and phospho Met in control group and a dose dependent decrease in TA treated groups. The crucial findings of this study support that targeting c-Met with a potent inhibitor of Sp proteins is a robust strategy for the implications in lung cancer treatment and TA can serve as a therapeutic agent for this devastating disease.

Nicotine stimulates PPARbeta/delta expression in human lung carcinoma cells through activation of PI3K/mTOR and suppression of AP-2alpha

We previously showed that nicotine stimulates non-small cell lung carcinoma (NSCLC) cell proliferation through nicotinic acetylcholine receptor (nAChR)-mediated signals. Activation of peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) has also been shown to induce NSCLC cell growth. Here, we explore the potential link between nicotine and PPARbeta/delta and report that nicotine increases the expression of PPARbeta/delta protein; this effect was blocked by an alpha7 nAChR antagonist (alpha-bungarotoxin), by alpha7 nAChR short interfering RNA, and by inhibitors of phosphatidylinositol 3-kinase (PI3K; wortmannin and LY294002) and mammalian target of rapamycin (mTOR; rapamycin). In contrast, this effect was enhanced by PUN282987, an alpha7 nAChR agonist. Silencing of PPARbeta/delta attenuated the stimulatory effect of nicotine on cell growth, which was overcome by transfection of an exogenous PPARbeta/delta expression vector. Of note, nicotine induced complex formation between alpha7 nAChR and PPARbeta/delta protein and increased PPARbeta/delta gene promoter activity through inhibition of AP-2alpha as shown by reduced AP-2alpha binding using electrophoretic gel mobility shift and chromatin immunoprecipitation assays. In addition, silencing of Sp1 attenuated the effect of nicotine on PPARbeta/delta. Collectively, our results show that nicotine increases PPARbeta/delta gene expression through alpha7 nAChR-mediated activation of PI3K/mTOR signals that inhibit AP-2alpha protein expression and DNA binding activity to the PPARbeta/delta gene promoter. Sp1 seems to modulate this process. This study unveils a novel mechanism by which nicotine promotes human lung carcinoma cell growth.