Induction of retinoic acid receptor-beta suppresses cyclooxygenase-2 expression in esophageal cancer cells

Genetic analysis of potential biomarkers and therapeutic targets in neuroinflammation from sporadic Creutzfeldt-Jakob disease

This study aimed to identify hub genes and pathological mechanisms related to neuroinflammation in Sporadic Creutzfeldt-Jakob disease (SCJD) based on comprehensive bioinformatics. SCJD and normal samples were collected from GSE160208. Weighted gene co-expression network analysis (WGCNA) and Limma R package were used to obtain key genes, which were used for enrichment and immune cell infiltration analyses. Protein-protein interaction (PPI) network, cytoHubba, and machine learning were used to screen the central genes of SCJD. The chemicals related to hub genes were predicted and explored by molecular docking. 88 candidate genes were screened. Enrichment analysis showed they were mainly related to bacterial and viral infection and immune cell activation. Immune cell infiltration analysis suggested that immune cell activation and altered activity of the immune system are involved in the progression of SCJD. After identifying hub genes, KIT and SPP1 had higher diagnostic efficacy for SCJD (AUC > 0.9), so they were identified as central genes. The molecular docking results showed hub genes both docked well with Tretinoin. KIT, SPP1, and Tretinoin are essential in developing neuroinflammation in SCJD and may provide new ideas for diagnosing and treating SCJD.

Construction of a cuproptosis-associated long non-coding RNA risk prediction model for pancreatic adenocarcinoma based on the TCGA database

Cuproptosis is a recently identified controlled process of cell death that functions in tumor development and treatment. Long non-coding RNAs (lncRNAs) are RNA molecules longer than 200 nucleotides that bind to transcription factors and regulate tumor invasion, penetration, metastasis, and prognosis. However, there are limited data on the function of cuproptosis-associated lncRNAs in pancreatic adenocarcinoma. Utilizing data retrieved from the cancer genome atlas database, we devised a risk prediction model of cuproptosis-associated lncRNAs in pancreatic adenocarcinoma, determined their prognostic significance and relationship with tumor immunity, and screened potential therapeutic drugs. Overall, 178 patients were randomized to a training or test group. We then obtained 6 characteristic cuproptosis-associated lncRNAs from the training group, based on which we constructed the risk prediction model, calculated the risk score, and verified the test group results. Subsequently, we performed differential gene analysis, tumor immunoassays, functional enrichment analysis, and potential drug screening. Finally, we found that the prediction model was highly reliable for the prognostic assessment of pancreatic adenocarcinoma patients. Generally, low risk patients had better outcomes than high risk patients. A tumor immunoassay showed that immunotherapy may benefit high risk patients more as there is a greater likelihood that the tumors could escape the immune system in low-risk patients. Through drug screening, we identified ten drugs that may have therapeutic effects on patients with pancreatic adenocarcinoma. In conclusion, this study constructed a risk prediction model of cuproptosis-associated lncRNAs, which can reliably predict the prognosis of pancreatic adenocarcinoma patients, provided a clinical reference for determining treatment approach, and provided some insights into the associations between lncRNAs and cuproptosis. This provides useful insight to aid in the development of therapeutic drugs for pancreatic adenocarcinoma.

Demystifying the Functional Role of Nuclear Receptors in Esophageal Cancer

Esophageal cancer (EC), an aggressive and poorly understood disease, is one of the top causes of cancer-related fatalities. GLOBOCAN 2020 reports that there are 544,076 deaths and 604,100 new cases expected worldwide. Even though there are various advancements in treatment procedures, this cancer has been reported as one of the most difficult cancers to cure, and to increase patient survival; treatment targets still need to be established. Nuclear receptors (NRs) are a type of transcription factor, which has a key role in several biological processes such as reproduction, development, cellular differentiation, stress response, immunity, metabolism, lipids, and drugs, and are essential regulators of several diseases, including cancer. Numerous studies have demonstrated the importance of NRs in tumor immunology and proved the well-known roles of multiple NRs in modulating proliferation, differentiation, and apoptosis. There are surplus of studies conducted on NRs and their implications in EC, but only a few studies have demonstrated the diagnostic and prognostic potential of NRs. Therefore, there is still a paucity of the role of NRs and different ways to target them in EC cells to stop them from spreading malignancy. This review emphasizes the significance of NRs in EC by discussing their diverse agonists as well as antagonists and their response to tumor progression. Additionally, we emphasize NRs’ potential to serve as a novel therapeutic target and their capacity to treat and prevent EC.

The Effects of Lentivirus-Mediated Gene Silencing of RARβ on the Stemness Capability of Non-Small Cell Lung Cancer

Retinoic acid receptor beta is a nuclear receptor protein that binds to retinoic acid (RA) to mediate cellular signalling in embryogenic morphogenesis, cell growth, and differentiation. However, the function of RARβ in cancer stem cells (CSCs) has yet to be determined. This study aimed to understand the role of RARβ in regulating cell growth and differentiation of lung cancer stem cells. Based on the clonogenic assay, spheroid assay, mRNA levels of stem cell transcription factors, and cell cycle being arrested at the G0/G1 phase, the suppression of RARβ resulted in significant inhibition of A549 parental cell growth. This finding was contradictory to the results seen in CSCs, where RARβ inhibition enhanced the cell growth of putative and non-putative CSCs. These results suggest that RARβ suppression may act as an essential regulator in A549 parental cells, but not in the CSCs population. The findings in this study demonstrated that the loss of RARβ promotes tumorigenicity in CSCs. Microarray analysis revealed that various cancer pathways were significantly activated following the suppression of RARβ. The changes seen might compensate for the loss of RARβ function, CSCs population's aggressiveness, which led to the CSCs population's aggressiveness. Thus, understanding the role of RARβ in regulating the stemness of CSCs may lead to targeted therapy for lung CSCs.

Retinoic acid receptor-beta prevents cisplatin-induced proximal tubular cell death

Cisplatin's toxicity in renal tubular epithelial cells limits the therapeutic efficacy of this antineoplastic drug. In cultured human proximal tubular HK-2 cells (PTC) a prostaglandin uptake transporter (PGT)-dependent increase in intracellular prostaglandin E₂ (iPGE₂) mediates cisplatin's toxicity (i.e. increased cell death and loss of cell proliferation) so that it is prevented by PGT inhibitors. Here we found in cisplatin-treated PTC that 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), a PGT inhibitor, prevented cisplatin's toxicity but not the increase in iPGE₂. Because expression of retinoic acid receptor-β (RAR-β) is dependent on iPGE₂ and because RAR-β is a regulator of cell survival and proliferation, we hypothesized that RAR-β might mediate the protective effect of DIDS against cisplatin's toxicity in PTC. Our results confirmed this hypothesis because: i) protection of PTC by DIDS was abolished by RAR-β antagonist LE-135; ii) DIDS increased the expression of RAR-β in PTC and prevented its decrease in cisplatin-treated PTC but not in cisplatin-treated human cervical adenocarcinoma HeLa cells in which DIDS failed to prevent cisplatin's toxicity; iii) while RAR-β expression decreased in cisplatin-treated PTC, RAR-β over-expression prevented cisplatin's toxicity. RAR-β agonist CH55 or RAR pan-agonist all-trans retinoic acid did not prevent cisplatin's toxicity, which suggests that RAR-β does not protect PTC through activation of gene transcription. In conclusion, RAR-β might be a new player in cisplatin-induced proximal tubular injury and the preservation of its expression in proximal tubules through treatment with DIDS might represent a novel strategy in the prevention of cisplatin's nephrotoxicity without compromising cisplatin's chemotherapeutic effect on cancer cells.

Role of retinoids in the prevention and treatment of colorectal cancer

Vitamin A and its derivatives, retinoids, have been widely studied for their use as cancer chemotherapeutic agents. With respect to colorectal cancer (CRC), several critical mutations dysregulate pathways implicated in progression and metastasis, resulting in aberrant Wnt/β-catenin signaling, gain-of-function mutations in K-ras and phosphatidylinositol-3-kinase/Akt, cyclooxygenase-2 over-expression, reduction of peroxisome proliferator-activated receptor γ activation, and loss of p53 function. Dysregulation leads to increased cellular proliferation and invasion and decreased cell-cell interaction and differentiation. Retinoids affect these pathways by various mechanisms, many involving retinoic acid receptors (RAR). RAR bind to all-trans-retinoic acid (ATRA) to induce the transcription of genes responsible for cellular differentiation. Although most research concerning the chemotherapeutic efficacy of retinoids focuses on the ability of ATRA to decrease cancer cell proliferation, increase differentiation, or promote apoptosis; as CRC progresses, RAR expression is often lost, rendering treatment of CRCs with ATRA ineffective. Our laboratory focuses on the ability of dietary vitamin A to decrease CRC cell proliferation and invasion via RAR-independent pathways. This review discusses our research and others concerning the ability of retinoids to ameliorate the defective signaling pathways listed above and decrease tumor cell proliferation and invasion through both RAR-dependent and RAR-independent mechanisms.

Prenatal effects of retinoic acid on lumbar spinal cord development and liver antioxidants in rats

During embryonic and early postnatal development, retinoic acid (RA) regulates genes that control neuronal differentiation and neurite outgrowth from the neural tube. The effects of high levels of RA on the CNS can be detected via nitric oxide (NO), which plays a crucial role in neural transmission. The aim of the study was to investigate the prenatal influence of high levels of RA on postnatal development of nitrergic structures in lumbar spinal cord and antioxidant status. RA was administered orally at a dose of 10mg/kg body weight to pregnant female Wistar rats during days 8-10 of gestation. Neuronal nitric oxide synthase (nNOS) of lumbar spinal cord sections was processed for visualization via nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry on postnatal day one, day twenty-one and in adults. The results suggest that prenatal administration of high levels of RA is not associated with postnatal morphological changes in nNOS-positive neurons in the rat lumbar spinal cord. An estimation of the activity of enzymes related to the storage of retinoid in the liver showed possible side effects. Suppression and deepening of superoxide dismutase activity persisted into adulthood, and a concurrent downregulation of glutathione reductase was noted. A decrease in reduced glutathione persisted until adulthood when other compensatory mechanisms were probably active to maintain an appropriate level.

Inhibition of farnesoid X receptor controls esophageal cancer cell growth in vitro and in nude mouse xenografts

BACKGROUND

Gastroesophageal reflux is a risk factor for esophageal adenocarcinoma, and bile acid and its farnesoid X receptor (FXR) have been implicated in esophageal tumorigenesis. The authors investigated the role of FXR expression and activity in esophageal cancer initiation and growth.

METHODS

FXR expression in esophageal adenocarcinoma tissues was assessed by immunohistochemistry. Knockdown of FXR expression in esophageal cancer cells in vitro and in nude mice xenografts was suppressed by FXR small hairpin RNA (shRNA) and guggulsterone (a natural FXR inhibitor). Esophageal cancer cells were treated with bile acids to demonstrate their effects on growth-promoting genes.

RESULTS

FXR was expressed in 48 of 59 esophageal adenocarcinoma tissues (81.3%), and this overexpression was associated with higher tumor grade, larger tumor size, and lymph node metastasis; however, was inversely associated with retinoic acid receptor-β2 (RAR-β2 ) expression. Knockdown of FXR expression suppressed tumor cell growth in vitro and in nude mouse xenografts. Guggulsterone reduced the viability of esophageal cancer cells in a time-dependent and dose-dependent manner, whereas this effect was diminished after knockdown of FXR expression. Guggulsterone induced apoptosis through activation of caspase-8, caspase-9, and caspase-3 in tumor cells. FXR mediated bile acid-induced alterations of gene expression, eg, RAR-β2 and cyclooxygenase-2 (COX-2).

CONCLUSIONS

Inhibition of FXR by FXR shRNA or guggulsterone suppressed tumor cell viability and induced apoptosis in vitro, and it reduced tumor formation and growth in nude mouse xenografts. FXR also mediated bile acid-induced alterations of cell growth-related genes in esophageal cancer cells.

Retinoid receptors in human esophageal squamous cell carcinoma: retinoid X receptor as a potent prognostic factor

Retinoids regulate cell proliferation and differentiation in normal and neoplastic tissue. These effects are mainly mediated by two types of nuclear retinoid receptors, retinoic acid receptors (RAR) and retinoid X receptors (RXR). RXR have been demonstrated to play important roles in esophageal carcinoma, but the expression of RXRβ and RXRγ has not been examined in esophagus. Therefore, we examined the immunoreactivity of all subtypes of RAR and RXR in 53 non-neoplastic esophageal epithelium and 74 esophageal squamous cell carcinoma tissues. In non-neoplastic epithelium RARβ immunoreactivity was marked in the basal layer and weak in the suprabasal layer, but immunoreactivity of other retinoid receptors was detected in both of layers. In addition, the status of RARβ and RXRβ immunoreactivity inversely correlated with that of lymph node metastasis (P= 0.0477 and P= 0.0034, respectively); decreased RXRβ immunoreactivity of carcinoma cells was positively associated with adverse clinical outcome of the patients (P= 0.0187). These findings all indicate the important roles of retinoid receptors, especially, RXR in the esophageal squamous cell carcinoma.

Hypermethylation of tumor-related genes in Tunisian patients with gastric carcinoma: clinical and biological significance

BACKGROUND

Promoter hypermethylation is an alternative mechanism of gene silencing in cancers including gastric carcinoma (GC). Its affects genes with crucial functions as tumor suppressor.

METHODS

DNA methylation in the promoter of P16INK4a, DAPK, retinoic acid receptor β (RARβ2), RASSF1A, and CDH1 genes was investigated in 79 Tunisian patients with GC using methylation-specific PCR.

RESULTS

The methylation frequencies vary from 31.6% for P16INK4a to 65.8% for RARβ2. Hypermethylation of DAPK and CDH1 was associated with tumor grade and age (P = 0.04 and 0.034) respectively, while hypermethylation of RASSF1A correlated with TNM stage (P = 0.027). The distribution of the methylated DNA at P16INK4a, DAPK, and CDH1 promoters were different in the intestinal and diffuse histotypes of GC according to TNM. Moreover, the survival rate of patients with P16INK4a methylated status was shorter than that of patients with the unmethylated status (P log rank = 0.009). On the other hand, the hypermethylation of RARβ2 correlated with COX-2 expression (P = 0.001).

CONCLUSION

We showed that methylation of P16INK4a is predictive of poor prognosis and could be a useful marker. Moreover, the association between RARβ2 methylation and COX-2 expression suggests a functional link between these two proteins in gastric carcinogenesis.

Prognostic significance of differentially expressed miRNAs in esophageal cancer

Altered microRNA (miRNA) expression has been found to promote carcinogenesis, but little is known about the role of miRNAs in esophageal cancer. In this study, we selected 10 miRNAs and analyzed their expression in 10 esophageal cancer cell lines and 158 tissue specimens using Northern blotting and in situ hybridization, respectively. We found that Let-7g, miR-21 and miR-195p were expressed in all 10 cell lines, miR-9 and miR-20a were not expressed in any of the cell lines, and miR-16-2, miR-30e, miR-34a, miR-126 and miR-200a were expressed in some of the cell lines but not others. In addition, transient transfection of miR-34a inhibited c-Met and cyclin D1 expression and esophageal cancer cell proliferation, whereas miR-16-2 suppressed RAR-β(2) expression and increased tumor cell proliferation. Furthermore, we found that miR-126 expression was associated with tumor cell dedifferentiation and lymph node metastasis, miR-16-2 was associated with lymph node metastasis, and miR-195p was associated with higher pathologic disease stages in patients with esophageal adenocarcinoma. Kaplan-Meier analysis showed that miR-16-2 expression and miR-30e expression were associated with shorter overall and disease-free survival in all esophageal cancer patients. In addition, miR-16-2, miR-30e and miR-200a expression were associated with shorter overall and disease-free survival in patients with esophageal adenocarcinoma; however, miR-16-2, miR-30e and miR-200a expression were not associated with overall or disease-free survival in squamous cell carcinoma patients. Our data indicate that further evaluation of miR-30e and miR-16-2 as prognostic biomarkers is warranted in patients with esophageal adenocarcinoma. In addition, the role of miR-34a in esophageal cancer also warrants further study.

Hypermethylation of RARβ2 correlates with high COX-2 expression and poor prognosis in patients with colorectal carcinoma

Silencing of gene expression by aberrant methylation at the CpG islands is common in human tumors, including colorectal cancer. This epigenetic alteration affects promoter of genes having crucial cellular functions such as tumor suppressor, DNA repair, apoptosis, cell adhesion, etc. We investigated the methylation status in the promoter regions of the RARβ2, RASSF1A, DAPKinase, and CDH1 genes in 73 colorectal carcinoma and 43 paired normal tissues of Tunisian patients using methylation-specific PCR assays. The association between methylation status and the clinicopathological features was evaluated. To determine whether aberrant methylation affects gene expression, we performed immunohistochemistry analysis for E-cadherin and COX-2, a target gene of RARβ2. The methylation frequencies vary from 80.8% for RARβ2 to 35.6% for RASSF1A while in non-tumor-paired samples; the frequencies of methylation are significantly lower for all the fourth genes tested. The methylation status did not correlate with any of the clinical features considered; however, aberrant methylation of RARβ2 was associated with a shortened overall patients' survival (p log rank = 0.026); nevertheless, it needs to be confirmed on larger sample size. Moreover, a significant inverse association was observed between methylation status of RARβ2 and COX-2 protein expression in tumor specimen (p = 0.014). On the other hand, we found that loss of E-cadherin expression was significantly associated with aberrant methylation of the CDH1 promoter (p = 0.005). Our findings showed that RARβ2 was frequently methylated in colorectal cancer and correlated with a worse prognosis and high expression of COX-2 suggesting a link between these two proteins in colorectal carcinogenesis. We also showed that epigenetic alteration of CDH1 is a major mechanism of the loss of E-cadherin protein expression in primary colorectal tumors.

Celecoxib increases retinoid sensitivity in human colon cancer cell lines

Retinoid resistance has limited the clinical application of retinoids as differentiation-inducing and apoptosis-inducing drugs. This study was designed to investigate whether celecoxib, a selective COX-2 inhibitor, has effects on retinoid sensitivity in human colon cancer cell lines, and to determine the possible mechanism of said effects. Cell viability was measured using the MTT assay. Apoptosis was detected via Annexin-V/PI staining and the flow cytometry assay. PGE₂ production was measured with the ELISA assay. The expression of RARβ was assayed via western blotting. The results showed that celecoxib enhanced the inhibitory effect of ATRA in both COX-2 high-expressing HT-29 and COX-2 low-expressing SW480 cell lines. Further study showed the ATRA and celecoxib combination induced greater apoptosis, but that the addition of PGE₂ did not affect the enhanced growth-inhibitory and apoptosis-inducing effects of the combination. Moreover, NS398 (another selective COX-2 inhibitor) did not affect the inhibitory effects of ATRA in the two cell lines. Western blotting showed that the expression of RARβ in HT-29 cell lines was increased by celecoxib, but not by NS398, and that the addition of PGE₂ did not affect the celecoxib-induced expression of the retinoic acid receptor beta. In conclusion, celecoxib increased the expression of RARβ and the level of cellular ATRA sensitivity through COX-2-independent mechanisms. This finding may provide a potential strategy for combination therapy.

Benzo[a]pyrene diol epoxide suppresses retinoic acid receptor-beta2 expression by recruiting DNA (cytosine-5-)-methyltransferase 3A

Tobacco smoke is an important risk factor for various human cancers, including esophageal cancer. How benzo [a]pyrene diol epoxide (BPDE), a carcinogen present in tobacco smoke as well as in environmental pollution, induces esophageal carcinogenesis has yet to be defined. In this study, we investigated the molecular mechanism responsible for BPDE-suppressed expression of retinoic acid receptor-beta2 (RAR-beta2) in esophageal cancer cells. We treated esophageal cancer cells with BPDE before performing methylation-specific polymerase chain reaction (MSP) to find that BPDE induced methylation of the RAR-beta2 gene promoter. We then performed chromatin immunoprecipitation (ChIP) assays to find that BPDE recruited genes of the methylation machinery into the RAR-beta2 gene promoter. We found that BPDE recruited DNA (cytosine-5-)-methyltransferase 3 alpha (DNMT3A), but not beta (DNMT3B), in a time-dependent manner to methylate the RAR-beta2 gene promoter, which we confirmed by reverse transcription-polymerase chain reaction (RT-PCR) analysis of the reduced RAR-beta2 expression in these BPDE-treated esophageal cancer cell lines. However, BPDE did not significantly change DNMT3A expression, but it slightly reduced DNMT3B expression. DNA methylase inhibitor 5-aza-2'-deoxycytidine (5-Aza) and DNMT3A small hairpin RNA (shRNA) vector antagonized the effects of BPDE on RAR-beta2 expressions. Transient transfection of the DNMT3A shRNA vector also antagonized BPDE's effects on expression of RAR-beta2, c-Jun, phosphorylated extracellular signal-regulated protein kinases 1/2 (ERK1/2), and cyclooxygenase-2 (COX-2), suggesting a possible therapeutic effect. The results of this study form the link between the esophageal cancer risk factor BPDE and the reduced RAR-beta2 expression.

Antitumor effect of retinoic acid receptor-beta2 associated with suppression of cyclooxygenase-2

Retinoic acid receptor-beta2 (RAR-beta2) is a putative tumor suppressor gene in various cancers. To determine the underlying molecular mechanisms, we transfected RAR-beta2 cDNA into esophageal cancer TE-1 and TE-8 cells and found that RAR-beta2 suppressed tumor cell growth in vitro and tumor formation in nude mice in TE-8 cells, whereas the stable transfection of RAR-beta2 did not restore retinoid sensitivity or inhibit tumor formation in nude mouse in TE-1 cells. Molecularly, we revealed that RAR-beta2 antitumor activity was associated with expression and suppression of cyclooxygenase-2 (COX-2) in these tumor cell lines. Moreover, antisense RAR-beta2 cDNA induced COX-2 expression in TE-3 cells. Furthermore, when COX-2 expression is first blocked by using antisense COX-2 expression vector, the effect of RAR-beta2 is diminished in these tumor cells. In addition, we analyzed expression of RAR-beta2 and COX-2 mRNA in tissue specimens and found that RAR-beta2 expression is associated with low levels of COX-2 expression in esophageal cancer tissues. Induction of RAR-beta2 expression in oral leukoplakia tissues after the patients treated with 13-cis RA correlated with a reduction in COX-2 expression and clinical response. Our findings indicate that some of RAR-beta2 antitumor activities are mediated by suppression of COX-2 expression in some of these esophageal cancer cells. After correlating antitumor effect of RAR-beta2 with COX-2 expression in the published studies, we also found the association. Thus, further studies will determine whether manipulation of COX-2 expression in different cancers can antagonize RAR-beta2 activity.

Risk factors and gene expression in esophageal cancer

Esophageal cancer is a significant worldwide health problem because of its poor prognosis and high incidence in certain parts of the world. Tobacco smoke and alcohol consumption are significant risk factors for esophageal squamous cell carcinoma, whereas frequent gastroesophageal reflux and subsequent inflammatory reactions play a role in causing the adenocarcinoma. Esophageal carcinogenesis involves multiple genetic alterations. A large body of knowledge has been generated regarding molecular alterations associated with esophageal carcinogenesis. These alterations include aberrant cell cycle control, DNA repair, cellular enzymes, growth factor receptors, and nuclear receptors. This chapter reviews the most frequent gene alterations and their correlation with risk factors as well as the prevention strategies in esophageal cancer.

Anti-inflammatory effect of retinoic acid on prostaglandin synthesis in cultured cortical astrocytes

Prostanoids are important mediators of inflammation and pain signaling. Although it is now well accepted that astrocytes participate in inflammatory reactions in the CNS, the molecular regulation of this activity is still largely unknown. Specifically, the regulation of prostanoid synthesis by this type of glia remains to be resolved. Recent evidence suggests that the transcriptional regulator retinoic acid (RA) is involved in regulation of the immune response. We have investigated the expression pattern of the enzymes that catalyze prostanoid and leukotriene synthesis in cultured cortical astrocytes, their stimulation by lipopolysaccharides (LPS) and their regulation by RA. The data indicate that astrocytes are an important source of prostaglandins (PGs) and that RA reduces their inflammatory biosynthesis. LPS treatment induced the expression of enzymes for the production of arachidonic acid and PGs but caused down-regulation of a PG degrading enzyme and of leukotriene synthesizing enzymes that compete with PG synthesis. Consequently, the secretion of the PGE(2) was highly increased after LPS exposure. RA counteracted the inflammatory regulation of cyclooxygenase (COX)-2 mRNA and protein in astrocytes and thereby reduced the synthesis of PGE(2) by approximately 60%. In the absence of LPS, RA enhanced the expression of COX-1 mRNA. In conclusion, RA might be effective in suppressing inflammatory processes in the brain by inhibiting PG synthesis.

Tumor-suppressive activity of retinoic acid receptor-beta in cancer

Retinoids, a group of structural and functional analogs of vitamin A, are known to regulate a large number of essential biological processes and to suppress carcinogenesis. The effects of retinoids are mainly mediated by nuclear retinoid receptors, which include retinoic acid receptors (RARs) and retinoid X receptors (RXRs). Each receptor has three subtypes (alpha, beta, and gamma) and each subtype has different isoforms. Retinoic acid receptor-beta (RAR-beta) has four isoforms that have different affinities to retinoids and different biological functions. Loss of expression of RAR-beta(2) during cancer development is associated with tumorigenesis and retinoid resistance; induction of its expression, on the other hand, can suppress carcinogenesis. Expression of another isoform, RAR-beta(4), is increased in various types of cancer. RAR-beta(4) transgenic mice develop hyperplasia and neoplasia in various tissues, and induction of RAR-beta(4) expression increases the growth of tumor cells that do not express RAR-beta(2). Future studies will focus on molecular pathways involving RAR-beta(2) and the role of RAR-beta(4) in cancer development.

RRIG1 mediates effects of retinoic acid receptor beta2 on tumor cell growth and gene expression through binding to and inhibition of RhoA

The expression of retinoic acid receptor beta2 (RAR-beta2) is frequently lost in various cancers and their premalignant lesions. However, the restoration of RAR-beta2 expression inhibits tumor cell growth and suppresses cancer development. To understand the molecular mechanisms responsible for this RAR-beta2-mediated antitumor activity, we did restriction fragment differential display-PCR and cloned a novel retinoid receptor-induced gene 1 (RRIG1), which is differentially expressed in RAR-beta2-positive and RAR-beta2-negative tumor cells. RRIG1 cDNA contains 2,851 bp and encodes a protein with 276 amino acids; the gene is localized at chromosome 9q34. Expressed in a broad range of normal tissues, RRIG1 is also lost in various cancer specimens. RRIG1 mediates the effect of RAR-beta2 on cell growth and gene expression (e.g., extracellular signal-regulated kinase 1/2 and cyclooxygenase-2). The RRIG1 protein is expressed in the cell membrane and binds to and inhibits the activity of a small GTPase RhoA. Whereas induction of RRIG1 expression inhibits RhoA activation and f-actin formation and consequently reduces colony formation, invasion, and proliferation of esophageal cancer cells, antisense RRIG1 increases RhoA activity and f-actin formation and thus induces the colony formation, invasion, and proliferation of these cells. Our findings therefore show a novel molecular pathway involving RAR-beta2 regulation of RRIG1 expression and RRIG1-RhoA interaction. An understanding of this pathway may translate into better control of human cancer.

Vitamin A active metabolite, all-trans retinoic acid, induces spinal cord sensitization. I. Effects after oral administration

BACKGROUND AND PURPOSE

Retinoic acid is an active metabolite of vitamin A involved in the modulation of the inflammatory and nociceptive responses. The aim of the present study was to analyze the properties of spinal cord neuronal responses of male Wistar rats treated with all-trans retinoic acid (ATRA) p.o. in the normal situation and under carrageenan-induced inflammation. We also studied the expression and distribution of cyclooxygenases (COX) in the spinal cord.

EXPERIMENTAL APPROACH

Properties of spinal cord neurons were studied by means of the single motor unit technique. The expression of COX enzymes in the spinal cord was assessed by Western blot analysis and immunohistochemistry.

KEY RESULTS

Intensity thresholds for mechanical and electrical stimulation (C-fibers) were significantly lower in animals treated with ATRA than vehicle, either in normal rats or in rats with inflammation. The size of cutaneous receptive fields was also larger in animals treated with ATRA in the normal and inflammatory conditions. The expression of COX-2 enzyme, but not COX-1, was significantly higher in animals treated with ATRA. COX-2 labeling was observed in dorsal horn cells and in ventral horn motoneurons.

CONCLUSIONS AND IMPLICATIONS

In conclusion, the oral treatment with ATRA in rats induces a sensitization-like effect on spinal cord neuronal responses similar to that observed in animals with inflammation and might explain the enhancement of allodynia and hyperalgesia observed in previously published behavioral experiments. The mechanism of action involves an over-expression of COX-2, but not COX-1, in dorsal and ventral horn areas of the lumbar spinal cord.

Vitamin A active metabolite, all-trans retinoic acid, induces spinal cord sensitization. II. Effects after intrathecal administration

BACKGROUND AND PURPOSE

In our previous study (see accompanying paper) we observed that all-trans retinoic acid (ATRA) p.o. induces changes in spinal cord neuronal responses similar to those observed in inflammation-induced sensitization. In the present study we assessed the it. effects of ATRA, and its mechanisms of action.

EXPERIMENTAL APPROACH

The effects of all drugs were studied after it. administration in nociceptive withdrawal reflexes using behavioural tests in awake male Wistar rats.

KEY RESULTS

The administration of ATRA in normal rats induced a dose-dependent enhancement of nociceptive responses to noxious mechanical and thermal stimulation, as well as responses to innocuous stimulation. The intensity of the responses was similar to that observed in non-treated animals after carrageenan-induced inflammation. The effect induced by ATRA was fully prevented by the previous administration of the retinoic acid receptor (RAR) pan-antagonist LE540 but not by the retinoid X receptor (RXR) pan-antagonist HX531, suggesting a selective action on spinal cord RARs. The COX inhibitor dexketoprofen and the interleukin-1 receptor antagonist IL-1ra inhibited ATRA effect. The results indicate that COX and interleukin-1 are involved in the effects of ATRA in the spinal cord, similar to that seen in inflammation.

CONCLUSIONS AND IMPLICATIONS

In conclusion, ATRA induces changes in the spinal cord similar to those observed in inflammation. The sensitization-like effect induced by ATRA was mediated by RARs and associated with a modulation of COX-2 and interleukin-1 activities. ATRA might be involved in the mechanisms underlying the initiation and/or maintenance of sensitization in the spinal cord.

The adenomatous polyposis coli tumor suppressor gene regulates expression of cyclooxygenase-2 by a mechanism that involves retinoic acid

Mutations in the adenomatous polyposis coli (APC) gene result in uncontrolled proliferation of intestinal epithelial cells and are associated with the earliest stages of colorectal carcinogenesis. Cyclooxygenase-2 (COX-2) is elevated in human colorectal cancers and plays an important role in colorectal tumorigenesis; however, the mechanisms by which APC mutations result in increased COX-2 expression remain unclear. We utilized APC mutant zebrafish and human cancer cells to investigate how APC modulates COX-2 expression. We report that COX-2 is up-regulated in APC mutant zebrafish because of a deficiency in retinoic acid biosynthesis. Treatment of both APC mutant zebrafish and human carcinoma cell lines with retinoic acid significantly reduces COX-2 expression. Retinoic acid regulates COX-2 levels by a mechanism that involves participation of the transcription factor C/EBP-beta. APC mutant zebrafish express higher levels of C/EBP-beta than wild-type animals, and retinoic acid supplementation reduces C/EBP-beta expression to basal levels. Both morpholino knockdown of C/EBP-beta in APC mutant zebrafish and silencing of C/EBP-beta using small interfering RNA in HT29 colon cancer cells robustly decrease COX-2 expression. Our findings support a sequence of events in which mutations in APC result in impaired retinoic acid biosynthesis, elevated levels of C/EBP-beta, up-regulation of COX-2, increased prostaglandin E(2) accumulation, and activation of Wnt target genes.

9-cis-Retinoic acid inhibition of lung carcinogenesis in the A/J mouse model is accompanied by increased expression of RAR-beta but no change in cyclooxygenase-2

9-cis-Retinoic acid (9cRA) binds both retinoic acid receptors (RARs) and retinoid X receptors (RXRs) and has been shown to be a potential chemopreventive agent both in lung cancer cell culture studies and in clinical trials studying former smokers. However, direct evidence of the efficacy of 9cRA against lung tumor development in vivo is lacking. In the present study, we determined whether treatment with 9cRA has the potential to inhibit lung carcinogenesis by upregulating RAR-beta and down-regulating COX-2 expression in the A/J mouse lung cancer model. A/J mice (n=14-15/group) were treated as follows: (1) Control (Sham treated); (2) NNK (100mg NNK/kg body weight); (3) NNK+9cRA (15mg/kg diet); and (4) NNK+celecoxib (a COX-2-specific inhibitor, 500mg/kg diet). Tumor incidence, tumor multiplicity, RAR-beta mRNA, COX-2 mRNA, and COX-2 protein levels in lung samples of mice were determined 4 months after carcinogen injection. The results showed that mice receiving 9cRA supplementation had significantly lower tumor multiplicity (48% reduction, P<0.05) and showed a trend toward lower tumor incidence (40% reduction, P=0.078), as compared with the mice given NNK alone. Although, celecoxib treatment resulted in greater declines in tumor incidence and tumor multiplicity (75 and 88%, respectively, P<0.05), the chemoprotective effects of celecoxib were accompanied by increased mortality while 9cRA treatment resulted in no weight-loss associated toxicity or mortality. Supplementation with 9cRA was effective in increasing RAR-beta mRNA, but this increase was not accompanied by decreased levels of COX-2 mRNA or protein. These results suggest that 9cRA supplementation may provide protection against lung carcinogenesis and this effect may be mediated in part by 9cRA induction of RAR-beta, but not inhibition of COX-2 transcription.

Induction of cyclooxygenase-2 by benzo[a]pyrene diol epoxide through inhibition of retinoic acid receptor-beta 2 expression

Benzo[a]pyrene diol epoxide (BPDE, a carcinogen present in tobacco smoke and environmental pollution) has been shown to suppress retinoic acid receptor-beta2 (RAR-beta(2)) and induce cyclooxygenase-2 (COX-2) expression. Restoration of RAR-beta(2) inhibited growth and colony formation of esophageal cancer cells, which was correlated with COX-2 suppression. In this study, we investigated the molecular mechanisms for RAR-beta(2)-mediated suppression of COX-2 expression using BPDE as a tool. We found that BPDE-induced COX-2 expression was through inhibition of RAR-beta(2) and consequently, induction of epidermal growth factor receptor (EGFR), extracellular signal-regulated protein kinases 1/2 (Erk1/2) phosphorylation, and c-Jun expression. Esophageal cancer cells that do not express RAR-beta(2) did not respond to BPDE for induction of COX-2. BPDE was also unable to induce COX-2 expression after RAR-beta(2) expression was manipulated in these esophageal cancer cells. Furthermore, BPDE induced time-dependent methylation of RAR-beta(2) gene promoter in esophageal cancer cells. Transfection of RAR-beta(2) expression vector into esophageal cancer cells suppressed expression of EGFR, Erk1/2 phosphorylation, c-Jun, and COX-2. In addition, co-treatment of RAR-beta(2)-positive cells with BPDE and the MEK1/2 inhibitor U0126 caused little change in c-Jun and COX-2 expression. This study demonstrated that BPDE-suppressed expression of RAR-beta(2) results in COX-2 induction and restoration of RAR-beta(2) expression reduces COX-2 protein in esophageal cancer cells, thereby further supporting our previous finding that RAR-beta(2) plays an important role in suppressing esophageal carcinogenesis.

Multiple genetic and epigenetic interacting mechanisms contribute to clonally selection of drug-resistant tumors: Current views and new therapeutic prospective

Successful treatment of cancer requires a clear understanding of drug-resistance mechanism. Cancer patient are often treated with standard protocols without considering individual difference in chemosensitivity, whereas the efficacy of anticancer drug varies widely among individual patients. Since chemosensitivity involves multiple interacting factors, it is not sufficient to investigate a single gene or factor to fix chemoresistance. Along with affecting disease progression, the synergism between genetic and epigenetic abnormalities can contribute to convert a sensible tumor cell in a resistant one. Unlike genetic changes, epigenetic changes are potentially reversible. Therefore, treatment with DNA methylation inhibitors can reactivate the expression of genes improperly methylated and can reverse many aspect of cancer phenotype such as drug resistance. The demethylating agents are used in the treatment of several kind of tumor, but toxicity and the potential outcome on the normal methylation patterns have always been concern of researchers and clinicals. It is necessary to create individual chemosensitivity-chemoresistance maps in order to identify the combination of drugs for optimized treatments. An overview on genetic and epigenetic events contributing to clonally selection of chemotherapeutic-resistant tumors is discussed.

A high-fat diet generates alterations in nuclear receptor expression: prevention by vitamin A and links with cyclooxygenase-2 and beta-catenin

Epidemiologic studies suggest that intake of high energy from fat, inducing overweight, increases the risk of cancer development and promotes colon carcinogenesis. It is therefore important to understand which parameters are affected early on by a high-fat diet in order to devise and improve protective nutritional strategies. We investigated the effect of high energy/fat intake on colon mucosa of male Wistar rats induced by a single 1,2-dimethylhydrazine (DMH) injection. Aberrant crypt foci (ACF) were numbered and modifications in cyclooxygenase-2 (COX-2) and beta-catenin levels assessed. Peroxisome proliferator- and retinoic acid-activated receptors (PPAR and RAR, RXR) are key transcription factors regulating gene expression in response to nutrient-activated signals. A short-term study was designed to evaluate whether alterations in mRNA expression of nuclear receptors can be detected at the beginning of the weight gain phase induced by an appetizing hyperlipidic diet (HLD). HLD consumption induced early downregulation of PPARgamma (-33.1%) and RARbeta (-53.1%) mRNA expression concomitant with an increase in levels of COX-2 (+45.5%) and beta-catenin (+84.56%) and in the number of ACF (191.56 +/- 88.60 vs. 21.14 +/- 11.64, p < 0.05). These findings suggest that HLD increases ACF occurrence, possibly through alterations in the mRNA expression profile of nuclear receptors. Moreover, the use HLD rich in retinyl esters or supplemented with all-trans retinoic acid led to a reduction in the number of ACF. Vitamin A also prevented HLD-induced alterations and the increase in levels of COX-2 and beta-catenin. The present observations show a protective role for vitamin A against disturbances associated with HLD exposure in induced colon carcinogenesis.

Identifying and defusing weapons of mass inflammation in carcinogenesis

The continued cancer risks associated with chronic inflammation necessitate the identification of inflammatory molecules and the cancer pathways they affect. Evidence indicates that there are multiple mechanisms linking inflammation to cancer and that there are multiple targets for chemoprevention. Here, we review some of the key factors and the cancer pathways they disturb as a necessary prerequisite to the identification of targets for chemoprevention.

Increased retinoic acid receptor-beta4 correlates in vivo with reduced retinoic acid receptor-beta2 in esophageal squamous cell carcinoma

Different retinoic acid receptor-beta (RAR-beta) isoforms seem to have contrasting biological effects in human carcinogenesis. Both in vitro and in vivo data indicate that RAR-beta2 expression is frequently lost or reduced (and transfecting RAR-beta2 suppresses growth and promotes apoptosis) in various cancer cells and tissues, whereas RAR-beta4 expression is increased in several cancer cell lines. To clarify the effects of different RAR-beta isoforms in esophageal carcinogenesis, we used real-time quantitative reverse transcription-PCR to assess in vivo RAR-beta mRNA levels in specimens of normal and malignant human esophageal tissue, comparing these levels with each other and the expressions of other genes. RAR-beta2 mRNA expression was significantly reduced (i.e., lower in cancer than normal tissue) in 67% (18 of 27, P = 0.001) and RAR-beta(4) mRNA was increased in 52% (14 of 27, P = 0.054) of our esophageal cancer cases. The expressions of RAR-beta1, chicken ovalbumin upstream promoter-transcription factor-I (COUP-TFI), COUP-TFII, and peroxisome proliferator-activated receptor-gamma (PPAR-gamma) mRNA were reduced, whereas epidermal growth factor receptor and cyclin D1 expressions were increased in tumor compared with in normal tissues. Reduced RAR-beta2 expression correlated with increased RAR-beta4 expression (P = 0.002) and with the suppression of COUP-TFI and COUP-TFII (P = 0.050 and 0.023, respectively) in tumor samples. These are the first in vivo expression patterns of RAR-beta2 and RAR-beta4 reported in humans or animals and support the in vitro data on these isoforms and their contrasting biological effects in human carcinogenesis.

Oral cancer prevention and the evolution of molecular-targeted drug development

The multifaceted rationale for molecular-targeted prevention of oral cancer is strong. Oral cancer is a major global threat to public health, causing great morbidity and mortality rates that have not improved in decades. Oral cancer development is a tobacco-related multistep and multifocal process involving field carcinogenesis and intraepithelial clonal spread. Biomarkers of genomic instability, such as aneuploidy and allelic imbalance, can accurately measure the cancer risk of oral premalignant lesions, or intraepithelial neoplasia (IEN). Retinoid-oral IEN studies (eg, of retinoic acid receptor-beta, p53, genetic instability, loss of heterozygosity, and cyclin D1) have advanced the overall understanding of the biology of intraepithelial carcinogenesis and of preventive agent molecular mechanisms and targets-important advances for monitoring preventive interventions and assessing cancer risk and pharmacogenomics. Clinical management of oral IEN varies from watchful waiting to complete resection, although complete resection does not prevent oral cancer in high-risk patients. New approaches, such as interventions with molecular-targeted agents and agent combinations in molecularly defined high-risk oral IEN patients, are urgently needed to reduce the devastating worldwide consequences of oral cancer.

A retinoic acid receptor beta/gamma-selective prodrug (tazarotene) plus a retinoid X receptor ligand induces extracellular signal-regulated kinase activation, retinoblastoma hypophosphorylation, G0 arrest, and cell differentiation

Retinoic acid receptor (RAR)beta is perceived to function as a tumor suppressor gene in various contexts where its absence is associated with tumorigenicity and its presence causes cell cycle arrest. Tazarotene is a prodrug selective for RARbeta/gamma, thereby motivating interest in determining whether tazarotene might activate putative tumor suppressor activity. Using HL-60 human myeloblastic leukemia cells, a cell line that undergoes G0 cell cycle arrest and myeloid differentiation in response to retinoic acid (RA), tazarotene failed to cause extracellular signal-regulated kinase (ERK) activation, a requirement for retinoic acid (RA)-induced G0 arrest and differentiation; retinoblastoma (RB) hypophosphorylation, another characteristic of RA-induced G0 arrest and cell differentiation; G0 arrest; or differentiation into mature myeloid cells. However, when used in combination with a retinoid X receptor (RXR)-selective ligand, tazarotene caused ERK activation, RB tumor suppressor protein hypophosphorylation, G0 arrest, and myeloid differentiation. The kinetics of G0 arrest and differentiation was similar to that of RA. Dose-response studies showed that diminishing tazarotene progressively diminished both induced cell differentiation and G0 arrest, where the doses for cellular effects were consistent with the transcriptional transactivation data. For either tazarotene or an RARalpha-selective ligand, diminishing the coadministered RXR-selective ligand diminished both induced differentiation and G0 arrest. Tazarotene could propel either early or late portions of the period leading to differentiation and G0 arrest and was interchangeable with an RARalpha-selective ligand. Tazarotene used with RXR-selective ligand may thus be a useful antineoplastic agent in differentiation induction therapy as exemplified by the prototypical RA treatment of acute promyelocytic leukemia.

Prognostic Factors in Resected Stage I Non–Small-Cell Lung Cancer: A Multivariate Analysis of Six Molecular Markers

Purpose

To analyze the prognostic significance of six molecular biomarkers (death-associated protein kinase [DAPK] promoter methylation, interleukin-10 [IL-10] protein expression, cyclooxygenase-2 [COX-2] mRNA expression, human telomerase reverse transcriptase catalytic subunit [hTERT] mRNA expression, retinoic acid receptor-beta [RAR-β] mRNA expression, and K-ras mutational status) in stage I non–small-cell lung cancer (NSCLC) patients.

Patients and Methods

Biomarker analyses were performed on tumors from 94 patients with stage I NSCLC who underwent surgical resection at our institution. A minimum follow-up period of 5 years was required. DAPK methylation was assessed by methylation-specific polymerase chain reaction (PCR). RAR-β, COX-2, and hTERT mRNA levels were determined by in situ hybridization with digoxigenin-labeled antisense riboprobes. K-ras mutation status was determined by the PCR–primer introduced restriction with enrichment for mutant alleles method. IL-10 protein expression was analyzed by immunohistochemistry using a polyclonal antihuman IL-10 antibody. Cancer-specific survival was analyzed with a Cox proportional hazards model. To identify independent prognostic factors, a stepwise selection method was used.

Results

DAPK methylation, IL-10 lack of expression, COX-2 expression, hTERT expression, RAR-β expression, and K-ras mutations were observed in 46.8%, 29.8%, 59.6%, 34.0%, 23.4%, and 34.0% of patients, respectively. In the final model, DAPK methylation and IL-10 lack of expression were significant negative prognostic factors for cancer-specific survival, whereas COX-2 expression was of borderline significance.

Conclusion

In this cohort of resected stage I NSCLC patients, molecular markers that independently predict cancer-specific survival have been identified. The prognostic roles of DAPK methylation, IL-10, and other biomarkers in NSCLC merit further investigation.

Peroxisome Proliferator-Activated Receptor-γ Suppresses Cyclooxygenase-2 Expression in Human Prostate Cells

Recent studies have found that cyclooxygenase-2 (COX-2) protein expression was low and inducible with cytokines in prostate cancer cells (in the absence of serum) and that, in contrast, COX-2 expression was high in normal prostate epithelial cells (EC). Peroxisome proliferator-activated receptor-γ (PPAR-γ) was expressed at high levels in the prostate cancer cell line PC-3 but not in ECs. In contrast to previous findings by others, PPAR-γ ligands did not induce PPAR-γ expression in EC or PC-3. The present study examined the relationship between PPAR-γ and COX-2 expression patterns in EC and PC-3 in the presence and absence of serum and/or the PPAR-γ agonist 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2). We also evaluated the effects that the forced expression of PPAR-γ1 and PPAR-γ2 had on COX-2 in ECs. We found that expression of PPAR-γ and COX-2 protein was inversely correlated in ECs and PC-3. Low COX-2 expression in PC-3 was up-regulated by serum, and 15d-PGJ2 blocked serum-induced COX-2 expression and activity in a dose-dependent manner. 15d-PGJ2 had no effect on COX-2 expression in ECs or PPAR-γ expression in either cell type. However, forced expression of PPAR-γ1 or PPAR-γ2 in ECs suppressed the high level of endogenous COX-2. This effect was not isoform specific and was augmented by 15d-PGJ2. The present study showed that PPAR-γ activation can be an important regulator of COX-2 in prostate cells and may be an important target for prostate cancer chemoprevention.

Retinoic acid receptors and cancers

Studies utilizing experimental animals, epidemiological approaches, cellular models, and clinical trials all provide evidence that retinoic acid and some of its synthetic derivatives (retinoids) are useful pharmacological agents in cancer therapy and prevention. In this chapter, we first review the current knowledge of retinoic acid receptors (RARs) and their role in mediating the actions of retinoic acid. We then focus on a discussion of RARalpha and acute promyelocytic leukemia followed by a discussion of the role of RARs, in particular RARbeta expression, in other cancer types. Loss of normal RAR function in the presence of physiological levels of RA (either due to alterations in the protein structure or level of expression) is associated with a variety of different cancers. In some cases treatment with pharmacological doses of RA can be effective.

Retinoic acid causes cell growth arrest and an increase in p27 in F9 wild type but not in F9 retinoic acid receptor β2 knockout cells

We have previously shown that an F9 teratocarcinoma retinoic acid receptor beta(2) (RARbeta(2)) knockout cell line exhibits no growth arrest in response to all-trans-retinoic acid (RA), whereas F9 wild type (Wt), F9 RARalpha(-/-), and F9 RARgamma(-/-) cell lines do growth arrest in response to RA. To examine the role of RARbeta(2) in growth inhibition, we analyzed the cell cycle regulatory proteins affected by RA in F9 Wt and F9 RARbeta(2)(-/-) cells. Flow microfluorimetry analyses revealed that RA treatment of F9 Wt cells greatly increased the percentage of cells in the G1/G0 phase of the cell cycle. In contrast, RA did not alter the cell cycle distribution profile of RARbeta(2)(-/-) cells. In F9 Wt cells, cyclin D1, D3, and cyclin E protein levels decreased, while cyclin D2 and p27 levels increased after RA treatment. Compared to the F9 Wt cells, the F9 RARbeta(2)(-/-) cells exhibited lower levels of cyclins D1, D2, D3, and E in the absence of RA, but did not exhibit further changes in the levels of these cell cycle regulators after RA addition. Since RA significantly increased the level of p27 protein (approximately 24-fold) in F9 Wt as compared to the F9 RARbeta(2)(-/-) cells, we chose to study p27 in greater detail. The p27 mRNA level and the rate of p27 protein synthesis were increased in RA-treated F9 Wt cells, but not in F9 RARbeta(2)(-/-) cells. Moreover, RA increased the half-life of p27 protein in F9 Wt cells. Reduced expression of RARbeta(2) is associated with the process of carcinogenesis and RARbeta(2) can mediate the growth arrest induced by RA in a variety of cancer cells. Using both genetic and molecular approaches, we have identified some of the molecular mechanisms, such as the large elevation of p27, through which RARbeta(2) mediates these growth inhibitory effects of RA in F9 cells.

Effects of Acyclic Retinoid on Growth, Cell Cycle Control, Epidermal Growth Factor Receptor Signaling, and Gene Expression in Human Squamous Cell Carcinoma Cells

We described recently the growth inhibitory effects of the novel compound acyclic retinoid (ACR) in human hepatoma cell lines (M. Suzui et al., Cancer Res., 62: 3997-4006, 2002). In this study we examined the cellular and molecular effects of ACR on human squamous cell carcinoma (SCC) cells. ACR inhibited growth of the esophageal SCC cell line HCE7, and the head and neck SCC cell lines YCU-N861 and YCU-H891, with IC(50) values of approximately 10, 25, and 40 microM, respectively. Detailed studies were then done with HCE7 cells. Treatment of these cells with 10 microM ACR caused an increase of cells in G(0)-G(1) and induced apoptosis. This was associated with two phases of molecular events. During phase 1, which occurred within 6-12 h, there was an increase in the retinoic acid receptor beta (RARbeta) and p21(CIP1) proteins, and their corresponding mRNAs, and a decrease in the hyperphosphorylated form of the retinoblastoma protein. During phase 2, which occurred at approximately 24 h, there was a decrease in the cellular level of transforming growth factor alpha, and the phosphorylated (i.e., activated) forms of the epidermal growth factor receptor, Stat3, and extracellular signal-regulated kinase proteins, and a decrease in both cyclin D1 protein and mRNA. Reporter assays indicated that ACR inhibited the transcriptional activity of the cyclin D1, c-fos, and activator protein promoters. On the other hand, ACR markedly stimulated the activity of a retinoic acid response element-CAT reporter when the cells were cotransfected with a RARbeta expression vector. A hypothetical model explaining these two phases is presented. The diverse effects that we obtained with ACR suggest that this agent might be useful in the chemoprevention and/or therapy of human SCCs.

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Rethinking nutritional support for persons with cancer cachexia

Cancer cachexia is a poorly understood syndrome of anorexia, weight loss, and muscle wasting that negatively impacts quality of life and survival in cancer patients. Research has clearly implicated pro-inflammatory cytokines in the biology of cancer cachexia. More recent research implicates products of arachidonic acid and suggests that cachexia may be a chronic inflammatory condition rather than a nutritional aberration. To date, nutritional support to slow weight loss has focused primarily on increasing calorie intake. Alternatively, many foods contain factors that can modulate the synthesis or activity of pro-inflammatory mediators, especially the synthesis of prostaglandin E2 from arachidonic acid. These factors and foods are sometimes called nutraceuticals, and research is needed to evaluate their efficacy in combating cancer cachexia.

Reduced 15S-lipoxygenase-2 expression in esophageal cancer specimens and cells and upregulation in vitro by the cyclooxygenase-2 inhibitor, NS398

Alterations in arachidonic acid metabolism are involved in human carcinogenesis. Cyclooxygenase (COX) and lipoxygenase (LOX) are key enzymes in this metabolism. We analyzed the expression of 15S-lipoxygenase-2 (15-LOX-2) mRNA and protein in surgical specimens from normal (N=37) and malignant (63) esophageal tissues using in situ hybridization and immunohistochemistry (IHC), and in normal (1), premalignant (1), and malignant (5) esophageal cell lines using Northern and Western blotting. 15-LOX-2 was expressed in normal esophageal epithelial cells (EECs) at the highest levels, whereas an SV40-immortalized HET-1A line and three of five esophageal cancer cell lines failed to express it at detectable levels. 15-LOX-2 was detected in 76% (28/37) of the normal esophageal mucosae, but only in 46% (29/63) of the cancer specimens using IHC (P<.01). Transient transfection of 15-LOX-2 expression vectors into esophageal cancer cells significantly inhibited the proliferation of 15-LOX-2-negative cancer cells. The COX-2 inhibitor, NS398, induced 15-LOX-2 expression in esophageal cancer cells, which is associated with reduced cell viability. This study demonstrated that 15-LOX-2 expression is lost in esophageal cancers and that the induction of 15-LOX-2 can inhibit cancer cell proliferation. Further investigation of the effects of nonsteroidal anti-inflammatory drugs on 15-LOX-2 expression and apoptosis in esophageal cancer cells may be warranted.

Cyclooxygenase 2 selective inhibitors in cancer treatment and prevention

Prostaglandin synthesis by a number of enzymes is important at all stages during the genesis of cancer. The availability of prostaglandin H(2) as a substrate for prostaglandin production is a critical control point in its synthesis. Cyclooxygenase (COX) occurs in two forms (COX-1 and -2) and acts as the rate-limiting enzyme that generates prostaglandin H(2). COX-1 is produced as a steady-state enzyme, while COX-2 is heavily involved in inflammation and tumorigenesis. Differences in the catalytic sites of these enzymes are utilised to generate COX-2 selective inhibitors. Certain chemical characteristics of non-steroidal anti-inflammatory drugs and COX-2 selective inhibitors make some of these inhibitors more effective against COX-2 than others. Epidemiological, animal and preclinical data demonstrate the promise of non-steroidal anti-inflammatory drugs and COX-2 selective inhibitors as anticancer agents. Ongoing clinical trials are designed to determine the efficacy of non-steroidal anti-inflammatory drugs and COX-2 selective inhibitors in the prevention and treatment of many types of cancer.