All trans-retinoic acid induces apoptosis via p38 and caspase pathways in metaplastic Barrett's cells

Retinoic acid receptor alpha inhibits ferroptosis by promoting thioredoxin and protein phosphatase 1F in lung adenocarcinoma

Ferroptosis is a recently discovered form of cell death that plays an important role in tumor growth and holds promise as a target for antitumor therapy. However, evidence in the regulation of ferroptosis in lung adenocarcinoma (LUAD) remains elusive. Here, we show that retinoic acid receptor alpha (RARA) is upregulated with the treatment of ferroptosis inducers (FINs). Pharmacological activation of RARA increases the resistance of LUAD to ferroptosis according to cell viability and lipid peroxidation assays, while RARA inhibitor or knockdown (KD) does the opposite. Through transcriptome sequencing in RARA-KD cells and chromatin immunoprecipitation (CHIP)-Seq data, we identify thioredoxin (TXN) and protein phosphatase 1 F (PPM1F) as downstream targets of RARA, both of which inhibit ferroptosis. We confirm that RARA binds to the promotor region of TXN and PPM1F and promotes their transcription by CHIP-qPCR and dual-luciferase assays. Overexpression of TXN and PPM1F reverses the effects of RARA knockdown on ferroptosis in vitro and vivo. Clinically, RARA knockdown or inhibitor increases cells' sensitivity to pemetrexed and cisplatin (CDDP). Immunohistochemistry (IHC) of LUAD from our cohort shows the same expression tendency of RARA and the downstream targets. Our study uncovers that RARA inhibits ferroptosis in LUAD by promoting TXN and PPM1F, and inhibiting RARA-TXN/PPM1F axis represents a promising strategy for improving the efficacy of FINs or chemotherapy in the treatment of LUAD patients.

Chemoprevention of esophageal adenocarcinoma in a rat surgical model by a cysteinyl leukotriene receptor‑1 antagonist

Reflux of gastroduodenal contents into the esophagus leads to the development of esophagitis and inflammation-associated pathologies, such as Barrett's esophagus (BE) and esophageal adenocarcinoma (EAC). The role of the lipoxygenase (LOX) pathway in carcinogenesis has been recently reported; however, its involvement in esophageal carcinogenesis remains unclear. To address this, the present study investigated the potential of pranlukast, a cysteinyl leukotriene receptor-1 antagonist, to suppress the progression of BE and EAC in a rat duodenogastroesophageal reflux (DGER) model. Male Wistar rats that underwent DGER were divided into two groups. One group was fed commercial chow (control group), and the other was fed experimental chow containing pranlukast (pranlukast group). The rats were sacrificed at 10, 20, 30 and 40 weeks after surgery, and their esophagi were examined. Expression levels of 5-LOX, CD68, IL-8, VEGF and Ki-67 were investigated using immunohistochemistry, and apoptosis was analyzed using the TUNEL method. In the pranlukast group, esophagitis was milder, and the incidence of BE and EAC was significantly lower (P<0.05) compared with that in the control group at 40 weeks after surgery. The number of cells positive for IL-8 and VEGF were significantly lower in the pranlukast group compared with the control group. Proliferative activity was also lower in the pranlukast group compared with the control group (P<0.05). Pranlukast treatment increased apoptosis (P<0.05). Overall, Pranlukast suppressed esophageal carcinogenesis in a rat DGER model, decreasing inflammatory cytokines such as IL-8 and VEGF.

Serum Metabolomic Profiling Reveals Biomarkers for Early Detection and Prognosis of Esophageal Squamous Cell Carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most common aggressive malignancies worldwide, particularly in northern China. The absence of specific early symptoms and biomarkers leads to late-stage diagnosis, while early diagnosis and risk stratification are crucial for improving overall prognosis. We performed UPLC-MS/MS on 450 ESCC patients and 588 controls consisting of a discovery group and two validation groups to identify biomarkers for early detection and prognosis. Bioinformatics and clinical statistical methods were used for profiling metabolites and evaluating potential biomarkers. A total of 105 differential metabolites were identified as reliable biomarker candidates for ESCC with the same tendency in three cohorts, mainly including amino acids and fatty acyls. A predictive model of 15 metabolites [all-trans-13,14-dihydroretinol, (±)-myristylcarnitine, (2S,3S)-3-methylphenylalanine, 3-(pyrazol-1-yl)-L-alanine, carnitine C10:1, carnitine C10:1 isomer1, carnitine C14-OH, carnitine C16:2-OH, carnitine C9:1, formononetin, hyodeoxycholic acid, indole-3-carboxylic acid, PysoPE 20:3, PysoPE 20:3(2n isomer1), and resolvin E1] was developed by logistic regression after LASSO and random forest analysis. This model held high predictive accuracies on distinguishing ESCC from controls in the discovery and validation groups (accuracies > 89%). In addition, the levels of four downregulated metabolites [hyodeoxycholic acid, (2S,3S)-3-methylphenylalanine, carnitine C9:1, and indole-3-carboxylic acid] were significantly higher in early cancer than advanced cancer. Furthermore, three independent prognostic markers were identified by multivariate Cox regression analyses with and without clinical indicators: a high level of MG(20:4)isomer and low levels of 9,12-octadecadienoic acid and L-isoleucine correlated with an unfavorable prognosis; the risk score based on these three metabolites was able to stratify patients into low or high risk. Moreover, pathway analysis indicated that retinol metabolism and linoleic acid metabolism were prominent perturbed pathways in ESCC. In conclusion, metabolic profiling revealed that perturbed amino acids and lipid metabolism were crucial metabolic signatures of ESCC. Both panels of diagnostic and prognostic markers showed excellent predictive performances. Targeting retinol and linoleic acid metabolism pathways may be new promising mechanism-based therapeutic approaches. Thus, this study would provide novel insights for the early detection and risk stratification for the clinical management of ESCC and potentially improve the outcomes of ESCC.

Topical Gel of Vitamin A Solid Lipid Nanoparticles: A Hopeful Promise as a Dermal Delivery System

Purpose: The Objective of the present investigation was to enhance the skin delivery of vitamin A (Vit A) via producing solid lipid nanoparticles (SLNs) through ultrasonication technique.

Methods: For achieving optimal skin delivery, impacts of two surfactants ratio of Tween80:Span80 on nanoparticles (NPs) features and the respective functions were examined. Powder X-ray diffractometer (PXRD), photon correlation spectroscopy, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) were applied for characterizing the solid state of Vit A in the SLN.

Results: Results showed that size of the NPs is usually enhanced by adding co-emulsifier (Span80). Notably, minimum NPs size (64.85±4.259 nm) was achieved while the hydrophilic-lipophilic balance (HLB) of the binary surfactants was 12.08, close to HLB of beeswax (HLB=12) as lipid matrix. Also, maximum entrapment efficiency (66.01±8.670%) was observed in the formulation. DSC thermogram indicated an amorphous form of Vit A in SLN. ATR-FTIR spectra of Vit A-SLN illustrated that prominent functional groups are found in the formulations that might be a sign of acceptable entrapment of Vit A in a lipid matrix. Moreover, ATR-FTIR studies showed no chemical interactions between Vit A and excipients. Skin irritation test proved the non-irritancy of Vit A-SLN2, when applied to the dorsal region of Wistar rats. Finally, any cellular toxicity was not seen for NPs.

Conclusion: It was found that the procured Vit A-SLNs could be utilized as potent carriers for the dermal delivery of Vit A.

Expression of programmed death ligand 1 (PD-L1) is associated with metastasis and differentiation in gastric cancer

AIMS

Programmed death ligand 1 (PD-L1, CD274) has been reported to be expressed abnormally in many cancers, nevertheless, effect of PD-L1 on tumor cells remains unclear, especially in gastric cancer (GC). This study aimed to investigate the role of PD-L1 in metastasis and differentiation in GC.

MAIN METHODS

Immunohistochemistry was performed on 237 paired GC tissues. shPD-L1 cells were generated by lentivirus shRNA solution and PD-L1-overexpressing cells were constructed by pcDNA3.1. Expression of PD-L1 and E-cadherin in GC cells were detected by western blot.

KEY FINDINGS

PD-L1 expression was significantly lower in GC than that in adjacent normal tissues, especially in poorly differentiated and metastatic GC, but was positively correlated to survival time of patients. Moreover, PD-L1 ablation could decrease E-cadherin expression, promote cell migration and wound repair ability. In turn, overexpression of PD-L1 increased E-cadherin expression and inhibited wound repair ability. At the same time, All-trans retinoic acid (ATRA), which has the properties of pro-differentiation and inhibition of invasion and metastasis, upregulated the expression of PD-L1 and E-cadherin.

SIGNIFICANCE

These findings not only identify PD-L1 may have a positive role for the treatment of GC, but also implicate that ATRA combined PD-L1 antibody drugs may enhance anti-tumor Immunity in GC.

The Pleiotropic Role of Retinoic Acid/Retinoic Acid Receptors Signaling: From Vitamin A Metabolism to Gene Rearrangements in Acute Promyelocytic Leukemia

The family of retinoic acid receptors (RARs: RARα, -β, and -γ) has remarkable pleiotropy characteristics, since the retinoic acid/RARs pathway is involved in numerous biological processes not only during embryonic development, but also in the postnatal phase and during adulthood. In this review, we trace the roles of RA/RARs signaling in the immune system (where this pathway has both an immunosuppressive role or is involved in the inflammatory response), in hematopoiesis (enhancing hematopoietic stem cell self-renewal, progenitor cells differentiation or maintaining the bone marrow microenvironment homeostasis), and in bone remodeling (where this pathway seems to have controversial effects on bone formation or osteoclast activation). Moreover, in this review is shown the involvement of RAR genes in multiple chromosomal rearrangements generating different fusion genes in hematological neoplasms, with a particular focus on acute promyelocytic leukemia and its variant subtypes. The effect of different RARs fusion proteins on leukemic transformation, on patients’ outcome, and on therapy response is also discussed.

Chemoprevention in Barrett's Esophagus: Current Status

Chemoprevention in Barrett's esophagus is currently applied only in research settings. Identifying pathways that can be targeted by safe, pharmaceutical or natural compounds is key to expanding the scope of chemoprevention. Defining meaningful surrogate markers of cancer progression is critical to test the efficacy of chemopreventive approaches. Combinatorial chemoprevention that targets multiple components of the same pathway or parallel pathways could reduce the risk and improve the efficacy of chemoprevention. Here we discuss the role of chemoprevention as an independent or an adjuvant management option in BE-associated esophageal adenocarcinoma.

Embryological signaling pathways in Barrett's metaplasia development and malignant transformation; mechanisms and therapeutic opportunities

Barrett's metaplasia of the esophagus (BE) is the precursor lesion of esophageal adenocarcinoma (EAC), a deadly disease with a 5-year overall survival of less than 20%. The molecular mechanisms of BE development and its transformation to EAC are poorly understood and current surveillance and treatment strategies are of limited efficacy. Increasing evidence suggests that aberrant signaling through pathways active in the embryological development of the esophagus contributes to BE development and progression to EAC. We discuss the role that the Bone morphogenetic protein, Hedgehog, Wingless-Type MMTV Integration Site Family (WNT) and Retinoic acid signaling pathways play during embryological development of the esophagus and their contribution to BE development and malignant transformation. Modulation of these pathways provides new therapeutic opportunities. By integrating findings in developmental biology with those from translational research and clinical trials, this review provides a platform for future studies aimed at improving current management of BE and EAC.

Deficient expression of aldehyde dehydrogenase 1A1 is consistent with increased sensitivity of Gorlin syndrome patients to radiation carcinogenesis

Human phenotypes that are highly susceptible to radiation carcinogenesis have been identified. Sensitive phenotypes often display robust regulation of molecular features that modify biological response, which can facilitate identification of the pathways/networks that contribute to pathophysiological outcomes. Here we interrogate primary dermal fibroblasts isolated from Gorlin syndrome patients (GDFs), who display a pronounced inducible tumorigenic response to radiation, in comparison to normal human dermal fibroblasts (NHDFs). Our approach exploits newly developed thiol reactive probes to define changes in protein thiol profiles in live cell studies, which minimizes artifacts associated with cell lysis. Redox probes revealed deficient expression of an apparent 55 kDa protein thiol in GDFs from independent Gorlin syndrome patients, compared with NHDFs. Proteomics tentatively identified this protein as aldehyde dehydrogenase 1A1 (ALDH1A1), a key enzyme regulating retinoic acid synthesis, and ALDH1A1 protein deficiency in GDFs was confirmed by Western blot. A number of additional protein thiol differences in GDFs were identified, including radiation responsive annexin family members and lamin A/C. Collectively, candidates identified in our study have plausible implications for radiation health effects and cancer susceptibility.

Retinoic acid alters the proliferation and survival of the epithelium and mesenchyme and suppresses Wnt/β-catenin signaling in developing cleft palate

Retinoic acid (RA) contributes to cleft palate; however, the cellular and molecular mechanisms responsible for the deleterious effects on the developing palate are unclear. Wnt signaling is a candidate pathway in the cleft palate and is associated with RA in organ development; thus, we aim to investigate whether RA-induced cleft palate also results from altered Wnt signaling. Administration of RA to mice altered cell proliferation and apoptosis in craniofacial tissues by regulating molecules controlling cell cycle and p38 MAPK signaling, respectively. This altered cell fate by RA is a crucial mechanism contributing to 100% incidence of cleft palate. Moreover, Wnt/β-catenin signaling was completely inhibited by RA in the early developing palate via its binding and activation with RA receptor (RAR) and is responsible for RA-induced cleft palate. Furthermore, PI3K/Akt signaling was also involved in actions of RA. Our findings help in elucidating the mechanisms of RA-induced cleft palate.

Activation of Akt pathway by transcription-independent mechanisms of retinoic acid promotes survival and invasion in lung cancer cells

Background

All-trans retinoic acid (ATRA) is currently being used in clinical trials for cancer treatment. The use of ATRA is limited because some cancers, such as lung cancer, show resistance to treatment. However, little is known about the molecular mechanisms that regulate resistance to ATRA treatment. Akt is a kinase that plays a key role in cell survival and cell invasion. Akt is often activated in lung cancer, suggesting its participation in resistance to chemotherapy. In this study, we explored the hypothesis that activation of the Akt pathway promotes resistance to ATRA treatment at the inhibition of cell survival and invasion in lung cancer. We aimed to provide guidelines for the proper use of ATRA in clinical trials and to elucidate basic biological mechanisms of resistance.

Results

We performed experiments using the A549 human lung adenocarcinoma cell line. We found that ATRA treatment promotes PI3k-Akt pathway activation through transcription-independent mechanisms. Interestingly, ATRA treatment induces the translocation of RARα to the plasma membrane, where it colocalizes with Akt. Immunoprecipitation assays showed that ATRA promotes Akt activation mediated by RARα-Akt interaction. Activation of the PI3k-Akt pathway by ATRA promotes invasion through Rac-GTPase, whereas pretreatment with 15e (PI3k inhibitor) or over-expression of the inactive form of Akt blocks ATRA-induced invasion. We also found that treatment with ATRA induces cell survival, which is inhibited by 15e or over-expression of an inactive form of Akt, through a subsequent increase in the levels of the active form of caspase-3. Finally, we showed that over-expression of the active form of Akt significantly decreases expression levels of the tumor suppressors RARβ2 and p53. In contrast, over-expression of the inactive form of Akt restores RARβ2 expression in cells treated with ATRA, indicating that activation of the PI3k-Akt pathway inhibits the expression of ATRA target genes.

Conclusion

Our results demonstrate that rapid activation of Akt blocks transcription-dependent mechanism of ATRA, promotes invasion and cell survival and confers resistance to retinoic acid treatment in lung cancer cells. These findings provide an incentive for the design and clinical testing of treatment regimens that combine ATRA and PI3k inhibitors for lung cancer treatment.

A novel all-trans retinoid acid derivatives inhibits the migration of breast cancer cell lines MDA-MB-231 via myosin light chain kinase involving p38-MAPK pathway

OBJECTIVE

To explore the effect and its probable mechanism of a synthetic retinoid 4-amino-2-tri-fluoromethyl-phenyl ester (ATPR) on the migration of human breast cancer MDA-MB-231 cells.

METHODS

MTT assay was performed to measure the proliferation of MDA-MB-231 cells treated with different concentrations of all-trans retinoic acid (ATRA) and ATPR. The effect of ATPR and ML-7, a selective inhibitor of myosin light chain kinase (MLCK), and SB203580, an inhibitor of p38, on the migration of MDA-MB-231 cells were analyzed by wound healing assay. The expression of MLCK and phosphorylation of myosin light chain (MLC), ERK, JNK, p38 proteins were detected by western blot

RESULTS

After the cells were treated by ATRA and ATPR, the proliferation and migration of breast cancer MDA-MB-231 cells were inhibited significantly. The IC 50 of ATRA and ATPR is 34.08 μmol/l and 18.06 μmol/l respectively. The relative migration rate of MDA-MB-231 cells treated with ATPR reached 50% at 48 h while the ATRA group is over 90%. The relative migration rate of ML-7 group and SB group had significant decrease compared with control group. The expression level of MLCK and phosphorylation of MLC of breast cancer cells was reduced when the cells were treated by ATPR with 48 h, the phosphorylation of ERK, JNK and p38 in breast cancer also reduced when cells were treated by ATPR with 2 h. In addition, ML-7 (50 μmol/l) could inhibit the phosphorylation of p38 and SB (50 μmol/l) could inhibit the expression of MLCK and phosphorylation of MLC.

CONCLUSIONS

ATPR had a better inhibition on the proliferation and the migration of breast cancer MDA-MB-231 cells than ATRA, and its probable mechanism was associated with the down regulation of expression of MLCK and phosphorylation of MLC protein involving p38-MAPK pathway.

Molecular mechanisms of Barrett's esophagus

Barrett's esophagus (BE) is defined as the metaplastic conversion of esophageal squamous epithelium to intestinalized columnar epithelium. As a premalignant lesion of esophageal adenocarcinoma (EAC), BE develops as a result of chronic gastroesophageal reflux disease (GERD). Many studies have been conducted to understand the molecular mechanisms of this disease. This review summarizes recent results involving squamous and intestinal transcription factors, signaling pathways, stromal factors, microRNAs, and other factors in the development of BE. A conceptual framework is proposed to guide future studies. We expect elucidation of the molecular mechanisms of BE to help in the development of improved management of GERD, BE, and EAC.

Chemoprevention of esophageal adenocarcinoma

The incidence of esophageal adenocarcinoma (EAC) is rising rapidly in Western countries, and effective chemoprevention for this malignancy is lacking. Endoscopic surveillance of patients with Barrett's esophagus is currently employed to diagnose EAC at earlier stages, but this strategy has several limitations. Non-steroidal anti-inflammatory drugs and proton pump inhibitors are the most promising agents for prevention of EAC, and a randomized controlled trial of aspirin and esomeprazole is ongoing. Other agents under investigation include green tea, berries, and antioxidants. Cost-effectiveness analyses have shown that chemopreventive agents need to be highly effective at preventing EAC in order to have benefit beyond endoscopic surveillance.

Chemoprevention in Barrett's esophagus: A pill a day?

Esophageal adenocarcinoma is increasing in incidence. The main risk factor is the premalignant condition of Barrett's esophagus. There is great interest in chemoprevention to prevent or slow malignant transformation. There are many agents proposed as playing a role in chemoprevention; however, none is licensed for this role as yet. Aspirin possesses many favorable qualities for chemoprevention and is the focus of the largest randomized control trial in this field.

Malignant transformation of non-neoplastic Barrett's epithelial cells through well-defined genetic manipulations

Background

Human Barrett's cancer cell lines have numerous, poorly-characterized genetic abnormalities and, consequently, those lines have limited utility as models for studying the early molecular events in carcinogenesis. Cell lines with well-defined genetic lesions that recapitulate various stages of neoplastic progression in Barrett's esophagus would be most useful for such studies.

Methodology/Principal Findings

To develop such model cell lines, we started with telomerase-immortalized, non-neoplastic Barrett's epithelial (BAR-T) cells, which are spontaneously deficient in p16, and proceeded to knock down p53 using RNAi, to activate Ras by introducing oncogenic H-Ras^G12V, or both. BAR-T cells infected with either p53 RNAi or oncogenic H-Ras^G12V alone maintained cell-to-cell contact inhibition and did not exhibit anchorage-independent growth in soft agar. In contrast, the combination of p53 RNAi knockdown with expression of oncogenic H-Ras^G12V transformed the p16-deficient BAR-T cells, as evidenced by their loss of contact inhibition, by their formation of colonies in soft agar, and by their generation of tumors in immunodeficient mice.

Conclusions/Significance

Through these experiments, we have generated a number of transformed and non-transformed cell lines with well-characterized genetic abnormalities recapitulating various stages of carcinogenesis in Barrett's esophagus. These lines should be useful models for the study of carcinogenesis in Barrett's esophagus, and for testing the efficacy of chemopreventive and chemotherapeutic agents.

Between death and survival: retinoic acid in regulation of apoptosis

The vitamin A metabolite all-trans-retinoic acid (RA) regulates multiple biological processes by virtue of its ability to regulate gene expression. It thus plays critical roles in embryonic development and is involved in regulating growth, remodeling, and metabolic responses in adult tissues. RA can also suppress carcinoma cell growth and is currently used in treatment of some cancers. Growth inhibition by RA may be exerted by induction of differentiation, cell cycle arrest, or apoptosis, or by a combination of these activities. Paradoxically, in the context of some cells, RA not only fails to inhibit growth but, instead, enhances proliferation and survival. This review focuses on the involvement of RA in regulating apoptotic responses. It includes brief overviews of transcriptional signaling by RA and of apoptotic pathways, and then addresses available information on the mechanisms by which RA induces apoptosis or, conversely, inhibits cell death and enhances survival.

In benign Barrett's epithelial cells, acid exposure generates reactive oxygen species that cause DNA double-strand breaks

Cells that sustain double-strand breaks (DSB) can develop genomic instability, which contributes to carcinogenesis, and agents that cause DSBs are considered potential carcinogens. We looked for evidence of acid-induced DNA damage, including DSBs, in benign Barrett's epithelial (BAR-T) cell lines in vitro and in patients with Barrett's esophagus in vivo. In BAR-T cells, we also explored the mechanisms underlying acid-induced DNA damage. We exposed BAR-T cells to acid in the presence of a fluorescent probe for reactive oxygen species (ROS) and in the presence or absence of disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (which prevents intracellular acidification) and N-acety-l-cysteine (a scavenger of ROS). DSBs were detected by Western blotting and immunofluorescence for histone H2AX phosphorylation and by CometAssay. During endoscopy in patients with Barrett's esophagus, we took biopsy specimens from the metaplastic mucosa before and after esophageal perfusion with 0.1 N HCl for 3 min and sought DSBs by Western blotting for histone H2AX phosphorylation. In BAR-T cells, acid exposure resulted in ROS production and caused a time-dependent increase in levels of phospho-H2AX that continued for at least 48 h. Pretreatment with disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate or N-acety-l-cysteine prevented the acid-induced increase in phospho-H2AX levels. DSBs also were detected in biopsy specimens of Barrett's metaplasia following esophageal acid perfusion in all of 6 patients with Barrett's esophagus. Acid exposure causes DSBs in Barrett's epithelial cells through ROS produced as a consequence of intracellular acidification. These findings suggest that acid can be considered a carcinogen in Barrett's esophagus.

Ion transport and barrier function in a telomerase-immortalized human nondysplastic, Barrett's cell line (BAR-T)

Barrett's specialized columnar epithelium (SCE) replaces reflux-damaged squamous epithelium. The benefits of SCE lie in its superior protection of the esophagus against further reflux damage. It was shown that this protection is dependent on ion transport and barrier function of SCE. The risks of SCE lie in its higher predisposition to malignant transformation. An understanding of underlying mechanisms of both processes would benefit considerably from greater knowledge of the structure and function of native SCE - the latter recently advanced by the availability of a telomerase-immortalized, nonneoplastic, human Barrett's cell line (BAR-T). Some of BAR-T characteristics for growth and differentiation have been described recently, but not its capacity to serve as a model for ion transport and barrier function of SCE. To determine the latter, BAR-T cells were grown in enriched media, seeded on permeable supports, and subjected to electrical, biochemical, and morphologic study. HET-1A (esophageal epithelial cell line), a nonneoplastic, human esophageal squamous cell line, was also studied for comparison. BAR-T, but not HET-1A cells in HEPES Ringer solution behaved as polarized monolayers with the capacity for ion transport and barrier function. This was evident electrically with a volt-ohm meter (EVOM),which recorded in BAR-T a resting potential difference of 2.0 +/- 0.2 mV, Isc of 17.4 +/- 3.3 microAmps/cm2 and resistance of 103 +/- 12 ohms x cm2. Further, Isc in BAR-T was inhibitable by exposure to Na-free solution, serosal ouabain, and luminal 4-acetamido4'-isothiocyano-2,2'-stilbenedisulfonic acid. Expression of tight junction genes were determined in BAR-T and HET-1A cells using quantitative reverse transcriptase-polymerase chain reaction, with expression of zonula occludens-1 (ZO-1) set at 1 as reference. Claudins 1, 4, and 12 were prominently expressed in BAR-T (0.2-0.6 of ZO-1), while claudins 1, 11, and 12 were prominently expressed in HET-1A(0.1-0.8 of ZO-1). BAR-T, but not HET-1A, expressed claudins 4, 8, 16, 18, and 23, and HET-1A, but not BAR-T, expressed claudins 11, 15, and 20. Protein expression of prominently expressed claudins in BAR-T correlated with mRNA expression. Immunofluorescence and confocal microscopy localized claudins 1 and 4 in BAR-T to cell membranes and claudin 18, specifically to the tight junction. Membrane polarization was also documented in BAR-T by immunolocalization of NaK,ATPase to the basolateral membrane. BAR-T, but not HET-1A cells grown on permeable supports form a polarized monolayer with both ion transport and barrier function. Since a number of features of BAR-T are similar to Barrett's SCE and distinct from HET-1A, the BAR-T cell line represents a valuable resource for the study of ion transport and barrier function of nondysplastic SCE.

Unlike esophageal squamous cells, Barrett's epithelial cells resist apoptosis by activating the nuclear factor-kappaB pathway

Apoptosis is an important mechanism for maintaining tissue homeostasis and for preventing the proliferation of cells with mutations that could result in malignancy. Barrett's epithelium has been reported to be more resistant to apoptosis than normal esophageal squamous epithelium. We have explored the contribution of the nuclear factor-kappaB (NF-kappaB) pathway to apoptotic resistance in non-neoplastic, telomerase-immortalized esophageal squamous (NES) and Barrett's (BAR-T) epithelial cell lines. We exposed these cells to UV-B irradiation in doses known to cause DNA damage and to induce apoptosis in normal cells, and studied apoptosis as well as the expression of phospho-H2AX, NF-kappaB, Bcl-2, XIAP, cIAP-1, and survivin proteins. We also used Bay 11-7085 and siRNAs to NF-kappaB and Bcl-2 to assess the effects of NF-kappaB and Bcl2 inhibition on apoptosis. UV-B irradiation at low doses (50 and 100 J/m(2)) caused DNA damage in both NES and BAR-T cells but significantly increased apoptosis only in NES cells. UV-B irradiation caused a decrease in the levels of NF-kappaB, Bcl-2, cIAP-1, XIAP, and survivin in NES cells but increased the levels of those proteins in BAR-T cells. The resistance of BAR-T cells to apoptosis induced by low-dose UV-B irradiation was abolished by Bay 11-7085 and by siRNA for NF-kappaB and was decreased significantly by siRNA for Bcl-2. We conclude that the ability of Barrett's epithelial cells to activate the NF-kappaB pathway when they have sustained DNA damage allows them to resist apoptosis. This capacity to avoid apoptosis despite genotoxic damage may underlie the persistence and malignant predisposition of Barrett's metaplasia.

Combination of all-trans retinoic acid and paclitaxel-induced differentiation and apoptosis in human glioblastoma U87MG xenografts in nude mice

BACKGROUND

Glioblastoma, which is the most malignant brain tumor, remains incurable and almost always causes death. As a new treatment strategy, the combination of all-trans retinoic acid (ATRA) and paclitaxel was explored for controlling the growth of glioblastoma U87MG xenografts.

METHODS

Human glioblastoma U87MG xenografts were developed in athymic nude mice for treatments with ATRA, paclitaxel, and ATRA plus paclitaxel. The efficacy of treatments in controlling tumor growth was assessed by histologic examination, Western blot analysis, and immunofluorescent labelings.

RESULTS

Astrocytic differentiation in U87MG xenografts was associated with increased GFAP expression and decreased telomerase expression. The combination of ATRA and paclitaxel was found to cause more apoptosis than paclitaxel alone. Apoptosis occurred with down-regulation of MEK-2 and overexpression of p-ERK, p-JNK, and p-p38 MAPK. Down-regulation of both Akt and p-Akt also favored the apoptotic process. Combination therapy activated the receptor-mediated pathway of apoptosis with induction of TNF-alpha, activation of caspase-8, and cleavage of Bid to tBid. Combination therapy also induced the mitochondria-mediated pathway of apoptosis with an increase in the Bax:Bcl-2 ratio and mitochondrial release of cytochrome c and Smac/Diablo into the cytosol. In addition, combination therapy promoted phosphorylation of Bcl-2 for its inactivation and down-regulated NF-kappaB and BIRC proteins, indicating suppression of several cell survival factors. Western blot analysis demonstrated that activation of cysteine proteases such as calpain, caspase-12, caspase-9, and caspase-3 contributed to apoptosis. Immunofluorescent labelings confirmed overexpression of cysteine proteases in apoptosis.

CONCLUSIONS

Treatment of U87MG xenografts with a combination of ATRA and paclitaxel induced differentiation and also multiple molecular mechanisms for apoptosis.

A novel role for the retinoic acid-catabolizing enzyme CYP26A1 in Barrett's associated adenocarcinoma

Vitamin A deficiency is associated with carcinogenesis, and upregulation of CYP26A1, a major retinoic acid (RA)-catabolizing enzyme, has recently been shown in cancer. We have previously demonstrated alterations of RA biosynthesis in Barrett's oesophagus, the precursor lesion to oesophageal adenocarcinoma. The aims of this study were to determine CYP26A1 expression levels and functional effects in Barrett's associated carcinogenesis. Retinoic acid response element reporter cells were used to determine RA levels in non-dysplastic and dysplastic Barrett's cell lines and endoscopic biopsies. CYP26A1 expression levels, with or without induction by RA and lithocholic acid, were determined by quantitative reverse transcriptase-PCR (RT-PCR) and immunohistochemistry. CYP26A1 promoter activity was determined by a luciferase reporter construct. CYP26A1 was stably overexpressed in GihTERT cells, which were evaluated for gene-expression changes (pathway array and quantitative RT-PCR), cellular proliferation (cytometric DNA profile and colorimetric assay) and invasion (in vitro matrigel assay) with or without the CYP inhibitor ketaconazole. RA levels decreased progressively with the degree of dysplasia (P<0.05) and were inversely correlated with CYP26A1 gene levels and activity (P<0.01). CYP26A1 expression was increased synergistically by RA and lithocholic acid (P<0.05). Overexpression of CYP26A1 led to induction of c-Myc, epidermal growth factor receptor and matrix metalloproteinase 3 as well as downregulation of tissue inhibitor metalloproteinase 1 and 3. Functional effects of CYP26A1 overexpression were increased proliferation (P<0.01) and invasion in vitro (P<0.01), which were inhibited by ketaconazole. Overexpression of CYP26A1 causes intracellular RA depletion and drives the cell into a highly proliferative and invasive state with induction of other known oncogenes.

In non-neoplastic Barrett's epithelial cells, acid exerts early antiproliferative effects through activation of the Chk2 pathway

Acid exerts pro-proliferative effects in Barrett's-associated esophageal adenocarcinoma cells. In non-neoplastic Barrett's epithelial (BAR-T) cells, in contrast, we have shown that acid exposure has antiproliferative effects. To explore our hypothesis that the acid-induced, antiproliferative effects are mediated by alterations in the proteins that regulate the G(1)-S cell cycle checkpoint, we exposed non-neoplastic Barrett's cells to acidic media (pH 4.0) and analyzed G(1)-S checkpoint proteins' expression, phosphorylation, and activity levels by Western blot. We studied acid effects on growth (by cell counts), proliferation (by flow cytometry and bromodeoxyuridine incorporation), cell viability (by trypan blue staining), and apoptosis (by annexin V staining), and we used caffeine and small interfering RNA to assess the effects of checkpoint kinase 2 (Chk2) inhibition on G(1)-S progression. Acid exposure significantly decreased cell numbers without affecting cell viability and with only a slight increase in apoptosis. Within 2 h of acid exposure, there was a delay in progression through the G(1)-S checkpoint that was associated with increased phosphorylation of Chk2, decreased levels of Cdc25A, and decreased activity of cyclin E-cyclin-dependent kinase 2; by 4 h, a continued delay at G(1)-S was associated with increased expression of p53 and p21. Caffeine and Chk2 siRNA abolished the acid-induced G(1)-S delay at 2 but not at 4 h. We conclude that acid exposure in non-neoplastic BAR-T cells causes early antiproliferative effects that are mediated by the activation of Chk2. Thus, we have elucidated a mechanism whereby acid can exert disparate effects on proliferation in neoplastic and non-neoplastic BAR-T cells.