Necrosis in DU145 prostate cancer spheroids induces COX‐2/mPGES‐1‐derived PGE2 to promote tumor growth and to inhibit T cell activation

Cyclooxygenase (COX)‐2‐derived prostaglandin E2 (PGE₂) supports the growth of a spectrum of cancers. The potential benefit of COX‐2‐inhibiting non‐steroidal anti‐inflammatory drugs (NSAIDs) for cancer treatment is however limited by their well‐known cardiovascular side‐effects. Therefore, targeting microsomal PGE synthase 1 (mPGES‐1), the downstream enzyme in the COX‐2‐dependent pathway of PGE₂ production might be attractive, although conflicting data regarding a potential tumor‐supporting function of mPGES‐1 were reported. We determined the impact of mPGES‐1 in human DU145 prostate cancer cell growth. Surprisingly, knockdown of mPGES‐1 did not alter growth of DU145 monolayer cells, but efficiently inhibited the growth of DU145 multicellular tumor spheroids (MCTS). Opposed to MCTS, monolayer cells did not secrete PGE₂ due to a lack of COX‐2 expression, which was induced during spheroid formation. Pharmacological inhibition of COX‐2 and mPGES‐1 supported the crucial role of PGE₂ for growth of MCTS. The functionality of spheroid‐derived PGE₂ was demonstrated by its ability to inhibit cytotoxic T cell activation. When investigating mechanisms of spheroid‐induced COX‐2 induction, we observed that among microenvironmental factors neither glucose deprivation, hypoxia nor tumor cell apoptosis enhanced COX‐2 expression. Interestingly, interfering with apoptosis in spheroids triggered a shift towards necrosis, thus augmenting COX‐2 expression. We went on to demonstrate that necrotic cells induced COX‐2 mRNA expression and PGE₂ secretion from live tumor cells. In conclusion, necrosis‐dependent COX‐2 upregulation in MCTS promoted PGE₂‐dependent tumor growth and inhibited activated cytotoxic T cells. Hence, blocking mPGES‐1 as a therapeutic option may be considered for COX‐2/mPGES‐1‐positive solid cancers.     

Inflammation in gastric cancer: Interplay of the COX‐2/prostaglandin E2 and Toll‐like receptor/MyD88 pathways

Cyclooxygenase‐2 (COX‐2) and its downstream product prostaglandin E₂ (PGE₂) play a key role in generation of the inflammatory microenvironment in tumor tissues. Gastric cancer is closely associated with Helicobacter pylori infection, which stimulates innate immune responses through Toll‐like receptors (TLRs), inducing COX‐2/PGE₂ pathway through nuclear factor‐κB activation. A pathway analysis of human gastric cancer shows that both the COX‐2 pathway and Wnt/β‐catenin signaling are significantly activated in tubular‐type gastric cancer, and basal levels of these pathways are also increased in other types of gastric cancer. Expression of interleukin‐11, chemokine (C‐X‐C motif) ligand 1 (CXCL1), CXCL2, and CXCL5, which play tumor‐promoting roles through a variety of mechanisms, is induced in a COX‐2/PGE₂ pathway‐dependent manner in both human and mouse gastric tumors. Moreover, the COX‐2/PGE₂ pathway plays an important role in the maintenance of stemness with expression of stem cell markers, including CD44, Prom1, and Sox9, which are induced in both gastritis and gastric tumors through a COX‐2/PGE₂‐dependent mechanism. In contrast, disruption of Myd88 results in suppression of the inflammatory microenvironment in gastric tumors even when the COX‐2/PGE₂ pathway is activated, indicating that the interplay of the COX‐2/PGE₂ and TLR/MyD88 pathways is needed for inflammatory response in tumor tissues. Furthermore, TLR2/MyD88 signaling plays a role in maintenance of stemness in normal stem cells as well as gastric tumor cells. Accordingly, these results suggest that targeting the COX‐2/PGE₂ pathway together with TLR/MyD88 signaling, which would suppress the inflammatory microenvironment and maintenance of stemness, could be an effective preventive or therapeutic strategy for gastric cancer.     

Microsomal prostaglandin E synthase‐1 inhibition blocks proliferation and enhances apoptosis in oesophageal adenocarcinoma cells without affecting endothelial prostacyclin production

Prostaglandins are important in the progression of various gastrointestinal cancers including oesophageal adenocarcinoma (OAC). Cyclo‐oxygenase (COX)‐2 inhibitors reduce OAC prostaglandin production but also have potentially detrimental effects on vascular endothelial function by reducing prostacyclin production and increasing the risk of cardiovascular events. We have examined the effects of inhibiting microsomal prostaglandin synthase‐1 (mPGES‐1), the enzyme downstream of COX‐2 in the prostaglandin synthetic cascade. In OAC cells, reduction of mPGES‐1 with RNA interference blocked PGE2 production, inhibited serum‐induced proliferation and enhanced apoptosis in the COX‐2 expressing cell lines (OE33 and FLO) but had no effect in COX‐2 deficient BIC‐1 cells. Three different methods of inhibiting mPGES‐1 (RNA interference, a novel small molecule inhibitor and the endogenous inhibitor 15‐deoxy‐Δ^12,14‐PGJ₂) also blocked leptin induced mPGES‐1 expression and PGE2 production and abolished the leptin‐induced proliferative and anti‐apoptotic effects in OE33 cells, without affecting COX‐2 expression. The anti‐proliferative effects were equivalent to those produced by COX‐2 inhibitory concentrations of celecoxib and NS‐398. However, unlike the two COX‐2 inhibitors, mPGES‐1 inhibition did not reduce endothelial prostacyclin production. In contrast to the effects of the COX‐2 inhibitor celecoxib, mPGES‐1 inhibition had no effects on Akt kinase activity in OAC cells. We conclude that inhibition of mPGES‐1 has potentially beneficial effects in OAC without the potentially detrimental effects on vascular endothelial prostacyclin synthesis. We have also confirmed that celecoxib has anticancer actions separate from the inhibition of COX‐2. Inhibition of mPGES‐1 may be therapeutically useful in the treatment and prevention of OAC.     

Mitochondrial uncoupler exerts a synthetic lethal effect against β‐catenin mutant tumor cells

The wingless/int‐1 (Wnt) signal transduction pathway plays a central role in cell proliferation, survival, differentiation and apoptosis. When β‐catenin: a component of the Wnt pathway, is mutated into an active form, cell growth signaling is hyperactive and drives oncogenesis. As β‐catenin is mutated in a wide variety of tumors, including up to 10% of all sporadic colon carcinomas and 20% of hepatocellular carcinomas, it has been considered a promising target for therapeutic interventions. Therefore, we screened an in‐house natural product library for compounds that exhibited synthetic lethality towards β‐catenin mutations and isolated nonactin, an antibiotic mitochondrial uncoupler, as a hit compound. Nonactin, as well as other mitochondrial uncouplers, induced apoptosis selectively in β‐catenin mutated tumor cells. Significant tumor regression was observed in the β‐catenin mutant HCT 116 xenograft model, but not in the β‐catenin wild type A375 xenograft model, in response to daily administration of nonactin in vivo. Furthermore, we found that expression of an active mutant form of β‐catenin induced a decrease in the glycolysis rate. Taken together, our results demonstrate that tumor cells with mutated β‐catenin depend on mitochondrial oxidative phosphorylation for survival. Therefore, they undergo apoptosis in response to mitochondrial dysfunction following the addition of mitochondrial uncouplers, such as nonactin. These results suggest that targeting mitochondria is a potential chemotherapeutic strategy for tumor cells that harbor β‐catenin mutations.     

Transgenic insulin-like growth factor-1 stimulates activation of COX-2 signaling in mammary glands

Studies show that elevated insulin‐like growth factor‐1 (IGF‐1) levels are associated with an increased risk of breast cancer; however, mechanisms through which IGF‐1 promotes mammary tumorigenesis in vivo have not been fully elucidated. To assess the possible involvement of COX‐2 signaling in the pro‐tumorigenic effects of IGF‐1 in mammary glands, we used the unique BK5.IGF‐1 mouse model in which transgenic (Tg) mice have significantly increased incidence of spontaneous and DMBA‐induced mammary cancer compared to wild type (WT) littermates. Studies revealed that COX‐2 expression was significantly increased in Tg mammary glands and tumors, compared to age‐matched WTs. Consistent with this, PGE₂ levels were also increased in Tg mammary glands. Analysis of expression of the EP receptors that mediate the effects of PGE₂ showed that among the four G‐protein‐coupled receptors, EP3 expression was elevated in Tg glands. Up‐regulation of the COX‐2/PGE₂/EP3 pathway was accompanied by increased expression of VEGF and a striking enhancement of angiogenesis in IGF‐1 Tg mammary glands. Treatment with celecoxib, a selective COX‐2 inhibitor, caused a 45% reduction in mammary PGE₂ levels, attenuated the influx of mast cells and reduced vascularization in Tg glands. These findings indicate that the COX‐2/PGE₂/EP3 signaling pathway is involved in IGF‐1‐stimulated mammary tumorigenesis and that COX‐2‐selective inhibitors may be useful in the prevention or treatment of breast cancer associated with elevated IGF‐1 levels in humans. © 2011 Wiley Periodicals, Inc.     

Tumor inhibition by sodium selenite is associated with activation of c‐Jun NH2‐terminal kinase 1 and suppression of β‐catenin signaling

Epidemiological and clinical studies suggest that an increased intake of dietary selenium significantly reduces overall cancer risk, but the anticancer mechanism of selenium is not clear. In this study, we fed intestinal cancer mouse model. Muc2/p21 double mutant mice with a selenium‐enriched (sodium selenite) diet for 12 or 24 weeks, and found that sodium selenite significantly inhibited intestinal tumor formation in these animals (p < 0.01), which was associated with phosphorylation of JNK1 and suppression of β‐catenin and COX2. In vitro studies showed that sodium selenite promoted cell apoptosis and inhibited cell proliferation in human colon cancer cell lines HCT116 and SW620. These effects were dose‐ and time course‐dependent, and were also linked to an increase of JNK1 phosphorylation and suppression of β‐catenin signaling. Reduced JNK1 expression by small RNA interference abrogated sufficient activation of JNK1 by sodium selenite, leading to reduced inhibition of the β‐catenin signaling, resulting in reduced efficacy of inhibiting cell proliferation. Taken together, our data demonstrate that sodium selenite inhibits intestinal carcinogenesis in vivo and in vitro through activating JNK1 and suppressing β‐catenin signaling, a novel anticancer mechanism of selenium.     

Epidermal growth factor‐induced COX‐2 regulates metastasis of head and neck squamous cell carcinoma through upregulation of angiopoietin‐like 4

Epidermal growth factor receptor (EGFR) expression and activation are the major causes of metastasis in cancers such as head and neck squamous cell carcinoma (HNSCC). However, the reciprocal effect of EGF‐induced COX‐2 and angiopoietin‐like 4 (ANGPTL4) on HNSCC metastasis remains unclear. In this study, we revealed that the expression of ANGPTL4 is essential for COX‐2‐derived prostaglandin E₂ (PGE₂)‐induced tumor cell metastasis. We showed that EGF‐induced ANGPTL4 expression was dramatically inhibited with the depletion and inactivation of COX‐2 by knockdown of COX‐2 and celecoxib treatment, respectively. Prostaglandin E₂ induced ANGPTL4 expression in a time‐ and dose‐dependent manners in various HNSCC cell lines through the ERK pathway. In addition, the depletion of ANGPTL4 and MMP1 significantly impeded the PGE₂‐induced transendothelial invasion ability of HNSCC cells and the binding of tumor cells to endothelial cells. The induction of molecules involved in the regulation of epithelial‐mesenchymal transition was also dependent on ANGPTL4 expression in PGE₂‐treated cells. The depletion of ANGPTL4 further blocked PGE₂‐primed tumor cell metastatic seeding of lungs. These results indicate that the EGF‐activated PGE₂/ANGPTL4 axis enhanced HNSCC metastasis. The concurrent expression of COX‐2 and ANGPTL4 in HNSCC tumor specimens provides insight into potential therapeutic targets for the treatment of EGFR‐associated HNSCC metastasis.     

Intratumoral COX‐2 inhibition enhances GM‐CSF immunotherapy against established mouse GL261 brain tumors

Immunotherapy has shown effectiveness against experimental malignant brain tumors, but the clinical results have been less convincing most likely due to immunosuppression. Prostaglandin E₂ (PGE₂) is the key immunosuppressive product of cyclooxygenase‐2 (COX‐2) and increased levels of PGE₂ and COX‐2 have been shown in several tumor types, including brain tumors. In the current study, we report enhanced cure rate of mice with established mouse GL261 brain tumors when immunized with granulocyte macrophage‐colony stimulating factor (GM‐CSF) secreting tumor cells and simultaneously treated with the selective COX‐2 inhibitors parecoxib systemically (5 mg/kg/day; 69% cure rate) or valdecoxib intratumorally (5.3 µg/kg/day; 63% cure rate). Both combined therapies induced a systemic antitumor response of proliferating CD4⁺ and CD8⁺ T cells, and further analysis revealed T helper 1 (T_h1) cell supremacy. The GL261 tumor cell line produced low levels of PGE₂ in vitro, and co‐staining at the tumor site demonstrated that a large fraction of the COX‐2⁺ cells were derived from CD45⁺ immune cells and more specifically macrophages (F4/80⁺), indicating that tumor‐infiltrating immune cells constitute the primary source of COX‐2 and PGE₂ in this model. We conclude that intratumoral COX‐2 inhibition potentiates GM‐CSF immunotherapy against established brain tumors at substantially lower doses than systemic administration. These findings underscore the central role of targeting COX‐2 during immunotherapy and implicate intratumoral COX‐2 as the primary target.     

Prostaglandin E2 receptor EP4 as the common target on cancer cells and macrophages to abolish angiogenesis,lymphangiogenesis, metastasis,and stem‐like cell functions

We previously established that COX‐2 overexpression promotes breast cancer progression and metastasis. As long‐term use of COX‐2 inhibitors (COX‐2i) can promote thrombo‐embolic events, we tested an alternative target, prostaglandin E2 receptor EP4 subtype (EP4), downstream of COX‐2. Here we used the highly metastatic syngeneic murine C3L5 breast cancer model to test the role of EP4‐expressing macrophages in vascular endothelial growth factor (VEGF)‐C/D production, angiogenesis, and lymphangiogenesis in situ, the role of EP4 in stem‐like cell (SLC) functions of tumor cells, and therapeutic effects of an EP4 antagonist RQ‐15986 (EP4A). C3L5 cells expressed all EP receptors, produced VEGF‐C/D, and showed high clonogenic tumorsphere forming ability in vitro, functions inhibited with COX‐2i or EP4A. Treating murine macrophage RAW 264.7 cell line with COX‐2i celecoxib and EP4A significantly reduced VEGF‐A/C/D production in vitro, measured with quantitative PCR and Western blots. Orthotopic implants of C3L5 cells in C3H/HeJ mice showed rapid tumor growth, angiogenesis, lymphangiogenesis (CD31/LYVE‐1 and CD31/PROX1 immunostaining), and metastasis to lymph nodes and lungs. Tumors revealed high incidence of EP4‐expressing, VEGF‐C/D producing macrophages identified with dual immunostaining of F4/80 and EP4 or VEGF‐C/D. Celecoxib or EP4A therapy at non‐toxic doses abrogated tumor growth, lymphangiogenesis, and metastasis to lymph nodes and lungs. Residual tumors in treated mice revealed markedly reduced VEGF‐A/C/D and phosphorylated Akt/ERK proteins, VEGF‐C/D positive macrophage infiltration, and proliferative/apoptotic cell ratios. Knocking down COX‐2 or EP4 in C3L5 cells or treating cells in vitro with celecoxib or EP4A and treating tumor‐bearing mice in vivo with the same drug reduced SLC properties of tumor cells including preferential co‐expression of COX‐2 and SLC markers ALDH1A, CD44, OCT‐3/4, β‐catenin, and SOX‐2. Thus, EP4 is an excellent therapeutic target to block stem‐like properties, angiogenesis, and lymphangiogenesis induced by VEGF‐A/C/D secreted by cancer cells and tumor infiltrating macrophages.     

Targeting the EP1 receptor reduces Fas ligand expression and increases the antitumor immune response in an in vivo model of colon cancer

Despite studies demonstrating that inhibition of cyclooxygenase‐2 (COX‐2)‐derived prostaglandin E₂ (PGE₂) has significant chemotherapeutic benefits in vitro and in vivo, inhibition of COX enzymes is associated with serious gastrointestinal and cardiovascular side effects, limiting the clinical utility of these drugs. PGE₂ signals through four different receptors (EP1–EP4) and targeting individual receptor(s) may avoid these side effects, while retaining significant anticancer benefits. Here, we show that targeted inhibition of the EP1 receptor in the tumor cells and the tumor microenvironment resulted in the significant inhibition of tumor growth in vivo. Both dietary administration and direct injection of the EP1 receptor‐specific antagonist, ONO‐8713, effectively reduced the growth of established CT26 tumors in BALB/c mice, with suppression of the EP1 receptor in the tumor cells alone less effective in reducing tumor growth. This antitumor effect was associated with reduced Fas ligand expression and attenuated tumor‐induced immune suppression. In particular, tumor infiltration by CD4⁺CD25⁺Foxp3⁺ regulatory T cells was decreased, whereas the cytotoxic activity of isolated splenocytes against CT26 cells was increased. F4/80⁺ macrophage infiltration was also decreased; however, there was no change in macrophage phenotype. These findings suggest that the EP1 receptor represents a potential target for the treatment of colon cancer.     

Association between activation of atypical NF‐κB1 p105 signaling pathway and nuclear β‐catenin accumulation in colorectal carcinoma

Recent studies have demonstrated that increased expression of coding region determinant‐binding protein (CRD‐BP) in response to β‐catenin signaling leads to the stabilization of β‐TrCP1, a substrate‐specific component of SCF E3 ubiquitin ligase complex, resulting in an accelerated degradation of IκBα and activation of canonical nuclear factor‐κB (NF‐κB) pathway. Here, we show that the noncanonical NF‐κB1 p105 pathway is constitutively activated in colorectal carcinoma specimens, being particularly associated with β‐catenin‐mediated increased expression of CRD‐BP and β‐TrCP1. In the carcinoma tissues exhibiting high levels of nuclear β‐catenin the phospho‐p105 levels were increased and total p105 amounts were decreased in comparison to that of normal tissue indicating an activation of this NF‐κB pathway. Knockdown of CRD‐BP in colorectal cancer cell line SW620 resulted in significantly higher basal levels of both NF‐κB inhibitory proteins, p105 and IκBα. Furthermore decreased NF‐κB binding activity was observed in CRD‐BP siRNA‐transfected SW620 cells as compared with those transfected with control siRNA. Altogether, our findings suggest that activation of NF‐κB1 p105 signaling in colorectal carcinoma might be attributed to β‐catenin‐mediated induction of CRD‐BP and β‐TrCP1. © 2009 Wiley‐Liss, Inc.     

CDK8 expression in 470 colorectal cancers in relation to β‐catenin activation,other molecular alterations and patient survival

Alterations in the Wnt/β‐catenin pathway define a key event in the pathogenesis of colon cancer. We have recently shown that CDK8, the gene encoding a cyclin‐dependent kinase (CDK) component of the Mediator complex, acts as a colon cancer oncogene that is necessary for β‐catenin activity. Here, we tested the hypothesis that colorectal cancers with CDK8 expression have distinct clinical, prognostic and molecular attributes. Among 470 colorectal cancers identified in 2 prospective cohort studies, CDK8 expression was detected in 329 (70%) tumors by immunohistochemistry. Cox proportional hazards model and backward stepwise elimination were used to compute hazard ratio (HR) of deaths according to CDK8 status, initially adjusted for various patient and molecular features, including β‐catenin, p53, p21, p27 (CDK inhibitors), cyclin D1, fatty acid synthase (FASN), cyclooxygenase‐2 (COX‐2), microsatellite instability (MSI), CpG island methylator phenotype (CIMP), LINE‐1 methylation, and mutations in KRAS, BRAF and PIK3CA. CDK8 expression in colorectal cancer was independently associated with β‐catenin activation (p = 0.0002), female gender (p < 0.0001) and FASN overexpression (p = 0.0003). Among colon cancer patients, CDK8 expression significantly increased colon cancer‐specific mortality in both univariate analysis [HR 1.70; 95% confidence interval (CI), 1.03–2.83; p = 0.039] and multivariate analysis (adjusted HR 2.05; 95% CI, 1.18–3.56; p = 0.011) that was adjusted for potential confounders including β‐catenin, COX‐2, FASN, LINE‐1 hypomethylation, CIMP and MSI. CDK8 expression was unrelated with clinical outcome among rectal cancer patients. These data support a potential link between CDK8 and β‐catenin, and suggest that CDK8 may identify a subset of colon cancer patients with a poor prognosis.     

Timosaponin AIII inhibits melanoma cell migration by suppressing COX‐2 and in vivo tumor metastasis

Melanoma is the leading cause of death from skin disease, due in large part to its propensity to metastasize. We examined the effects of timosaponin AIII, a compound isolated from Anemarrhena asphodeloides Bunge, on melanoma cancer cell migration and the molecular mechanisms underlying these effects using B16‐F10 and WM‐115 melanoma cells lines. Overexpression of COX‐2, its metabolite prostaglandin E₂ (PGE₂), and PGE₂ receptors (EP2 and EP4) promoted cell migration in vitro. Exposure to timosaponin AIII resulted in concentration‐dependent inhibition of cell migration, which was associated with reduced levels of COX‐2, PGE₂, and PGE₂ receptors. Transient transfection of COX‐2 siRNA also inhibited cell migration. Exposure to 12‐O‐tetradecanoylphorbal‐13‐acetate enhanced cell migration, whereas timosaponin AIII inhibited 12‐O‐tetradecanoylphorbal‐13‐acetate‐induced cell migration and reduced basal levels of EP2 and EP4. Moreover, timosaponin AIII inhibited activation of nuclear factor‐kappa B (NF‐κB), an upstream regulator of COX‐2 in B16‐F10 cells. Consistent with our in vitro findings, in vivo studies showed that timosaponin AIII treatment significantly reduced the total number of metastatic nodules in the mouse lung and improved histological alterations in B16‐F10‐injected C57BL/6 mice. In addition, C57BL/6 mice treated with timosaponin AIII showed reduced expression of COX‐2 and NF‐κB in the lung. Together, these results indicate that timosaponin AIII has the capacity to inhibit melanoma cell migration, an essential step in the process of metastasis, by inhibiting expression of COX‐2, NF‐κB, PGE_2, and PGE₂ receptors.     

Tetraspanin CD63 acts as a pro‐metastatic factor via β‐catenin stabilization

The tetraspanin CD63 is implicated in pro‐metastatic signaling pathways but, so far, it is unclear, how CD63 levels affect the tumor cell phenotype. Here, we investigated the effect of CD63 modulation in different metastatic tumor cell lines. In vitro, knock down of CD63 induced a more epithelial‐like phenotype concomitant with increased E‐cadherin expression, downregulation of its repressors Slug and Zeb1, and decreased N‐cadherin. In addition, β‐catenin protein was markedly reduced, negatively affecting expression of the target genes MMP‐2 and PAI‐1. β‐catenin inhibitors mimicked the epithelial phenotype induced by CD63 knock down. Inhibition of β‐catenin upstream regulators PI3K/AKT or GSK3β could rescue the mesenchymal phenotype underlining the importance of the β‐catenin pathway in CD63‐regulated cell plasticity. CD63 knock down‐induced phenotypical changes correlated with a decrease of experimental metastasis whereas CD63 overexpression enhanced the tumor cell‐intrinsic metastatic potential. Taken together, our data show that CD63 is a crucial player in the regulation of the tumor cell‐intrinsic metastatic potential by affecting cell plasticity.     

Differences in the localization of the adenomatous polyposis coli‐Asef/Asef2 complex between adenomatous polyposis coli wild‐type and mutant cells

The tumor suppressor adenomatous polyposis coli (APC) is mutated in familial adenomatous polyposis and in many sporadic colorectal tumors. Adenomatous polyposis coli is known to negatively regulate Wnt signaling by inducing the degradation of β‐catenin. Adenomatous polyposis coli also interacts with the guanine nucleotide exchange factors Asef and Asef2 and stimulates their activity, thereby regulating cell adhesion and migration. Here we show that in confluent, non‐motile MDCK II cells, Asef/Asef2 are colocalized with APC at the sites of cell–cell adhesion at the apical and junctional levels. In contrast, in colorectal tumor cells containing mutated APC, significant amounts of Asef/Asef2 and the truncated mutant APCs are localized mainly in the cytoplasm. These results suggest that localization of the Asef/Asef2‐APC complex at the sites of cell–cell contact is critical for the regulation of cell adhesion, and that the aberrant subcellular localization of these complexes in colorectal tumor cells may contribute to the cell's aberrant adhesive and migratory properties.     

Tristetraprolin regulates interleukin-6, which is correlated with tumor progression in patients with head and neck squamous cell carcinoma

BACKGROUND:

Tumor‐derived cytokines play a significant role in the progression of head and neck squamous cell carcinoma (HNSCC). Targeting proteins, such as tristetraprolin (TTP), that regulate multiple inflammatory cytokines may inhibit the progression of HNSCC. However, TTP's role in cancer is poorly understood. The goal of the current study was to determine whether TTP regulates inflammatory cytokines in patients with HNSCC.

METHODS:

TTP messenger RNA (mRNA) and protein expression were determined by quantitative real‐time–polymerase chain reaction (Q‐RT‐PCR) and Western blot analysis, respectively. mRNA stability and cytokine secretion were evaluated by quantitative RT‐PCR and enzyme‐linked immunoadsorbent assay, respectively, after overexpression or knockdown of TTP in HNSCC. HNSCC tissue microarrays were immunostained for interleukin‐6 (IL‐6) and TTP.

RESULTS:

TTP expression in HNSCC cell lines was found to be inversely correlated with the secretion of IL‐6, vascular endothelial growth factor (VEGF), and prostaglandin E2 (PGE₂)_. Knockdown of TTP increased mRNA stability and the secretion of cytokines. Conversely, overexpression of TTP in HNSCC cells led to decreased secretion of IL‐6, VEGF, and PGE₂. Immunohistochemical staining of tissue microarrays for IL‐6 demonstrated that staining intensity is prognostic for poor disease‐specific survival (P = .023), tumor recurrence and development of second primary tumors (P = .014), and poor overall survival (P = .019).

CONCLUSIONS:

The results of the current study demonstrated that down‐regulation of TTP in HNSCC enhances mRNA stability and promotes secretion of IL‐6, VEGF, and PGE₂. Furthermore, high IL‐6 secretion in HNSCC tissue is a biomarker for poor prognosis. In as much as enhanced cytokine secretion is associated with poor prognosis, TTP may be a therapeutic target to reduce multiple cytokines concurrently in patients with HNSCC. Cancer 2011. © 2011 American Cancer Society.