Identification of transcriptional regulatory cascades in retinoic acid-induced growth arrest of HepG2 cells

Retinoids in the Pathogenesis and Treatment of Liver Diseases

Vitamin A (VA), all-trans-retinol (ROL), and its analogs are collectively called retinoids. Acting through the retinoic acid receptors RARα, RARβ, and RARγ, all-trans-retinoic acid, an active metabolite of VA, is a potent regulator of numerous biological pathways, including embryonic and somatic cellular differentiation, immune functions, and energy metabolism. The liver is the primary organ for retinoid storage and metabolism in humans. For reasons that remain incompletely understood, a body of evidence shows that reductions in liver retinoids, aberrant retinoid metabolism, and reductions in RAR signaling are implicated in numerous diseases of the liver, including hepatocellular carcinoma, non-alcohol-associated fatty liver diseases, and alcohol-associated liver diseases. Conversely, restoration of retinoid signaling, pharmacological treatments with natural and synthetic retinoids, and newer agonists for specific RARs show promising benefits for treatment of a number of these liver diseases. Here we provide a comprehensive review of the literature demonstrating a role for retinoids in limiting the pathogenesis of these diseases and in the treatment of liver diseases.

Peretinoin, an Acyclic Retinoid, for the Secondary Prevention of Hepatocellular Carcinoma

The high rates of hepatocellular carcinoma (HCC) recurrence after initially successful curative therapy emphasize ongoing unmet needs to prevent or reduce HCC recurrence. Retinoid acid (RA), a metabolite of vitamin A and its related analogues (termed retinoids) has been suggested as a promising chemotherapeutic agent in cancer treatment. The synthetic oral retinoid peretinoin is the only agent for the secondary chemoprevention of HCC after curative therapy that is currently well applied into clinical development. Here we present an updated summary of the molecular pathogenesis of HCC and of preclinical and clinical findings with peretinoin, including its clinical characteristics, safety and tolerability profile and future perspectives for clinical use.

Retinoic Acids in the Treatment of Most Lethal Solid Cancers

Although the use of oral administration of pharmacological all-trans retinoic acid (ATRA) concentration in acute promyelocytic leukaemia (APL) patients was approved for over 20 years and used as standard therapy still to date, the same use in solid cancers is still controversial. In the present review the literature about the top five lethal solid cancers (lung, stomach, liver, breast, and colon cancer), as defined by The Global Cancer Observatory of World Health Organization, and retinoic acids (ATRA, 9-cis retinoic acid, and 13-cis retinoic acid, RA) was compared. The action of retinoic acids in inhibiting the cell proliferation was found in several cell pathways and compartments: from membrane and cytoplasmic signaling, to metabolic enzymes, to gene expression. However, in parallel in the most aggressive phenotypes several escape routes have evolved conferring retinoic acids-resistance. The comparison between different solid cancer types pointed out that for some cancer types several information are still lacking. Moreover, even though some pathways and escape routes are the same between the cancer types, sometimes they can differently respond to retinoic acid therapy, so that generalization cannot be made. Further studies on molecular pathways are needed to perform combinatorial trials that allow overcoming retinoic acids resistance.

Translational Potential of Therapeutics Targeting Regulatory Myeloid Cells in Tuberculosis

Despite recent advances in tuberculosis (TB) drug development and availability, successful antibiotic treatment is challenged by the parallel development of antimicrobial resistance. As a result, new approaches toward improving TB treatment have been proposed in an attempt to reduce the high TB morbidity and mortality rates. Host-directed therapies (HDTs), designed to modulate host immune components, provide an alternative approach for improving treatment outcome in both non-communicable and infectious diseases. Many candidate immunotherapeutics, designed to target regulatory myeloid immune components in cancer, have so far proven to be of value as repurposed HDT in TB. Several of these studies do however lack detailed description of the mechanism or host pathway affected by TB HDT treatment. In this review, we present an argument for greater appreciation of the role of regulatory myeloid cells, such as myeloid-derived suppressor cells (MDSC), as potential targets for the development of candidate TB HDT compounds. We discuss the role of MDSC in the context of Mycobacterium tuberculosis infection and disease, focussing primarily on their specific cellular functions and highlight the impact of HDTs on MDSC frequency and function.

Modulating the cellular microenvironment with disulfide-containing nanoparticles as an auxiliary cancer treatment strategy

Disulfide-containing nanoparticles modulate cellular redox microenvironment when deliver drug into cells, and have significant influence on therapeutic response and efficacy.

Retinoid roles in blocking hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major health issue in many countries. The prognosis of HCC is still poor due to its high recurrence rate and its resistance to chemotherapy. Retinoids have long been known to have a connection with liver diseases, including HCC. Many experimental and clinical investigations have demonstrated associations between retinoids and hepatic disease, including the loss of retinoid activity in HCC cell lines and decreased hepatic retinoid stores and altered retinoid signaling in patients with cirrhosis and HCC. Based on these findings, preclinical and clinical investigations of retinoid effects on HCC have been undertaken. Recently, clinical trial results for the use of a synthetic retinoid, acyclic retinoid (ACR), to prevent HCC recurrence were published. In addition, extensive experimental studies on the action of retinoids in liver disease, including chronic viral hepatitis and non-alcoholic fatty liver disease (NAFLD), which lead to HCC have been performed. In the first section of this review, we will summarize the effectiveness and roles of retinoid for treating liver disease and blocking HCC. Subsequently, we will focus on ACR actions in blocking HCC.

Biological and clinical implications of retinoic acid-responsive genes in human hepatocellular carcinoma cells

BACKGROUND & AIMS

Accumulating data from epidemiological and experimental studies have suggested that retinoids, which are vitamin A derivatives, exert antitumor activity in various organs. We performed a gene screening based on in silico analysis of retinoic acid response elements (RAREs) to identify the genes facilitating the antitumor activity of retinoic acid (RA) and investigated their clinical significance in hepatocellular carcinoma (HCC).

METHODS

In silico analysis of RAREs was performed in the 5-kb upstream region of EST clusters. Chromatin immunoprecipitation analysis of the retinoic acid receptors and gene expression analysis were performed in HuH7, HepG2, and MCF7 cells treated with all-trans RA (ATRA). mRNA expression of RA-responsive genes was investigated using tumor and non-tumor tissues of clinical HCC samples from 171 patients. The association between gene expression and survival of patients was examined by Cox regression analysis.

RESULTS

We identified 201 candidate genes with promoter regions containing consensus RARE and finally selected 26 RA-responsive genes. Of these, downregulation of OTU domain-containing 7B (OTUD7B) gene, which was upregulated by ATRA, in tumor tissue was associated with a low cancer-specific survival of HCC patients. Functional analyses revealed that OTUD7B negatively regulates nuclear factor κB (NF-κB) signaling and decreases the survival of HCC cells.

CONCLUSIONS

We identified RA-responsive genes which are regulated by retinoid signal and found that low-OTUD7B mRNA expression is associated with a poor prognosis for HCC patients. OTUD7B-mediated inhibition of NF-κB signaling may be an effective target for antitumor therapy for HCC.

Enhancement of all-trans retinoic acid-induced differentiation by pH-sensitive nanoparticles for solid tumor cells

Cancer differentiation therapy is an attractive concept and has been clinically used to treat leukemia. However, it is limited to date for solid tumors. In this study, the pH-sensitive nanoparticles based on poly(amidoamine) (PAMAM) dendrimers are synthesized by coupling 3,4,5,6-tetrahydrophthalic anhydride with the first generation PAMAM. The modified dendrimers can self-assemble in aqueous solution to form nanoparticles with a diameter of 125-435 nm. The nanoparticles are relatively stable at physiological pH (pH 7.4) but dissociated in acidic environments (pH 5.0 or 6.0). The present studies show that the proliferation inhibition and albumin secretion of hepatoma carcinoma cells are enhanced with all-trans retinoic acid (ATRA) encapsulated in the nanoparticles. The enhancement of induced differentiation is due to the high internalization of ATRA in the cells by the nanoparticles. These experimental results demonstrate that pH-sensitive nanoparticles may be efficient for improving the differentiation therapy for solid tumor.

Peretinoin, an acyclic retinoid, improves the hepatic gene signature of chronic hepatitis C following curative therapy of hepatocellular carcinoma

Background

The acyclic retinoid, peretinoin, has been shown to be effective for suppressing hepatocellular carcinoma (HCC) recurrence after definitive treatment in a small-scale randomized clinical trial. However, little has been documented about the mechanism by which peretinoin exerts its inhibitory effects against recurrent HCC in humans in vivo.

Methods

Twelve hepatitis C virus-positive patients whose HCC had been eradicated through curative resection or ablation underwent liver biopsy at baseline and week 8 of treatment with either a daily dose of 300 or 600 mg peretinoin. RNA isolated from biopsy samples was subjected to gene expression profile analysis.

Results

Peretinoin treatment elevated the expression levels of IGFBP6, RBP1, PRB4, CEBPA, G0S2, TGM2, GPRC5A, CYP26B1, and many other retinoid target genes. Elevated expression was also observed for interferon-, Wnt-, and tumor suppressor-related genes. By contrast, decreased expression levels were found for mTOR- and tumor progression-related genes. Interestingly, gene expression profiles for week 8 of peretinoin treatment could be classified into two groups of recurrence and non-recurrence with a prediction accuracy rate of 79.6% (P<0.05). In the liver of patients with non-recurrence, expression of PDGFC and other angiogenesis genes, cancer stem cell marker genes, and genes related to tumor progression was down-regulated, while expression of genes related to hepatocyte differentiation, tumor suppression genes, and other genes related to apoptosis induction was up-regulated.

Conclusions

Gene expression profiling at week 8 of peretinoin treatment could successfully predict HCC recurrence within 2 years. This study is the first to show the effect of peretinoin in suppressing HCC recurrence in vivo based on gene expression profiles and provides a molecular basis for understanding the efficacy of peretinoin.

Impact of intracellular alpha fetoprotein on retinoic acid receptors-mediated expression of GADD153 in human hepatoma cell lines

The aim of our study was to gain a better understanding of the molecular mechanism underlying the previously unrecognized role of cytoplasmic alpha fetoprotein (AFP) in retinoic acid receptors (RAR) mediated expression and biological effects of GADD153. Using microarray analysis, the expression of the GADD153 gene showed the greatest fold change among apoptosis/growth related genes in response to ATRA. AFP was able to interact with RAR in HepG2 cells, which was undetectable in HLE cells owing to absence of AFP. ATRA promoted nuclei entrance of RAR, expression of GADD153 and apoptosis, and these changes were reversed after transfection with the afp gene or addition of AGN193109. The level of GADD153 was gradually elevated as the effect of AFP was counteracted by increasing dose or prolonging treatment time with ATRA in HepG2 cells. Knockdown of AFP in siRNA-transfected HepG2 cells or over-expression of AFP in afp gene-transfected HLE cells was synchronously associated with up-regulation or down-regulation, respectively, of GADD153 expression. Both ATRA administration and AFP knockdown were each able to promote greater binding of RAR to its response element with consequent elevation of the proportion of apoptotic cells. Conversely, transfection of HLE cells with pcDNA3.1-afp resulted in apparent reduction of RAR binding to DNA and change of biological effect. These data taken together demonstrate the involvement of AFP in RAR-mediated expression and biological effects of GADD153. These findings provide a novel insight into the mechanism underlying the impact of AFP on the RAR signal network.

All-trans retinoic acid induces cellular senescence via upregulation of p16, p21, and p27

We here present a new anti-tumor mechanism of all-trans retinoic acid (ATRA). ATRA induced several biomarkers of cellular senescence including irreversible G1 arrest, morphological changes, senescence-associated β-galactosidase, and heterochromatin foci in HepG2 cells. ATRA also upregulated levels of p16, p21, and p27 which lead to activation of Rb and subsequent inactivation of E2F1. These effects were abolished by the RNA interference-mediated silencing of p16, p21, and p27. Moreover, ATRA failed to induce cellular senescence in Huh7 and HCT116, in which p16, p21, and p27 were not upregulated by ATRA, confirming that ATRA induces cellular senescence via upregulation of p16, p21, and p27.

Early growth response 1 (Egr1) regulates cholesterol biosynthetic gene expression

The early growth response (EGR) family of transcription factors has been implicated in control of lipid biosynthetic genes. Egr1 is induced by insulin both in vitro and in vivo and is the most highly expressed family member in liver. In this study, we investigated whether Egr1 regulates cholesterol biosynthetic genes in liver. Using an insulin-sensitive liver cell line, we show that localization of Egr1 to cholesterol biosynthetic genes is induced by insulin treatment and that this localization precedes the induction of the genes. Reduction in Egr1 expression using targeted siRNA blunted the insulin-dependent induction of cholesterol genes. A similar reduction in squalene epoxidase expression was also observed in Egr1 null mice. In addition, application of chromatin immunoprecipitation (ChIP) samples to tiled gene microarrays revealed localization of Egr1 in promoter regions of many cholesterol gene loci. In vivo ChIP assays using liver tissue show that Egr1 localization to several cholesterol biosynthetic gene promoters is induced by feeding. Finally, analysis of plasma cholesterol in Egr1(-/-) mice indicated a significant decrease in serum cholesterol when compared with wild-type mice. Together these data point to Egr1 as a modulator of the cholesterol biosynthetic gene family in liver.

ATRA in combination with nedaplatin inhibits cell proliferation but promotes apoptosis in human hepatoma cell line Huh-7

AIM: To observe the effects of all-trans retinoic acid (ATRA) and nedaplatin, alone or in combination, on cell proliferation and apoptosis in human hepatoma cell line Huh-7, and to determine whether the two drugs in combination have a synergistic effect in treating hepatocarcinoma.

METHODS: After Huh-7 cells were incubated with different concentrations of ATRA (10^-4, 10^-5 and 10^-6 mol/L) and nedaplatin (1, 2 and 5 mg/L), alone or in combination, for 24, 48 and 72 h, cell morphology changes were observed using an inverted microscope; cell proliferation was evaluated by MTT assay; and apoptosis was evaluated by flow cytometry.

RESULTS: Both ATRA and nedaplatin could markedly inhibit cell proliferation in a time- and concentration-dependent manner (all P < 0.01). ATRA and nedaplatin in combination had a significant synergistic effect on cell proliferation compared with ATRA or nedaplatin alone (both P < 0.01). Both ATRA and nedaplatin promoted the apoptosis of Huh-7 cells. The apoptosis rate was significantly lower in Huh-7 cells treated with ATRA and nedaplatin alone for 48 h than in those treated with the two drugs in combination (28.49% ± 0.6%, 42.57% ± 1.03% vs 55.35% ± 1.30%, both P < 0.01), suggesting a synergistic effect of combined nedaplatin and ATRA on the apoptosis of Huh-7 cells.

CONCLUSION: Both ATRA and nedaplatin can inhibit cell proliferation and promote apoptosis in human hepatoma cell line Huh-7. ATRA combined with nedaplatin has a significant synergistic effect on the proliferation and apoptosis of Huh-7 cells.

Regulatory interdependence of myeloid transcription factors revealed by Matrix RNAi analysis

The knockdown of 78 transcription factors in differentiating human THP-1 cells using matrix RNAi reveals their interdependence

Background

With the move towards systems biology, we need sensitive and reliable ways to determine the relationships between transcription factors and their target genes. In this paper we analyze the regulatory relationships between 78 myeloid transcription factors and their coding genes by using the matrix RNAi system in which a set of transcription factor genes are individually knocked down and the resultant expression perturbation is quantified.

Results

Using small interfering RNAs we knocked down the 78 transcription factor genes in monocytic THP-1 cells and monitored the perturbation of the expression of the same 78 transcription factors and 13 other transcription factor genes as well as 5 non-transcription factor genes by quantitative real-time RT-PCR, thereby building a 78 × 96 matrix of perturbation and measurement. This approach identified 876 cases where knockdown of one transcription factor significantly affected the expression of another (from a potential 7,488 combinations). Our study also revealed cell-type-specific transcriptional regulatory networks in two different cell types.

Conclusions

By considering whether the targets of a given transcription factor are naturally up- or downregulated during phorbol 12-myristate 13-acetate-induced differentiation, we could classify these edges as pro-differentiative (229), anti-differentiative (76) or neither (571) using expression profiling data obtained in the FANTOM4 study. This classification analysis suggested that several factors could be involved in monocytic differentiation, while others such as MYB and the leukemogenic fusion MLL-MLLT3 could help to maintain the initial undifferentiated state by repressing the expression of pro-differentiative factors or maintaining expression of anti-differentiative factors.

Identification of an inter-transcription factor regulatory network in human hepatoma cells by Matrix RNAi

Transcriptional regulation by transcriptional regulatory factors (TRFs) of their target TRF genes is central to the control of gene expression. To study a static multi-tiered inter-TRF regulatory network in the human hepatoma cells, we have applied a Matrix RNAi approach in which siRNA knockdown and quantitative RT-PCR are used in combination on the same set of TRFs to determine their interdependencies. This approach focusing on several liver-enriched TRF families, each of which consists of structurally homologous members, revealed many significant regulatory relationships. These include the cross-talks between hepatocyte nuclear factors (HNFs) and the other TRF groups such as CCAAT/enhancer-binding proteins (CEBPs), retinoic acid receptors (RARs), retinoid receptors (RXRs) and RAR-related orphan receptors (RORs), which play key regulatory functions in human hepatocytes and liver. In addition, various multi-component regulatory motifs, which make up the complex inter-TRF regulatory network, were identified. A large part of the regulatory edges identified by the Matrix RNAi approach could be confirmed by chromatin immunoprecipitation. The resultant significant edges enabled us to depict the inter-TRF TRN forming an apparent regulatory hierarchy of (FOXA1, RXRA) → TCF1 → (HNF4A, ONECUT1) → (RORC, CEBPA) as the main streamline.

Identification of DNA regions and a set of transcriptional regulatory factors involved in transcriptional regulation of several human liver-enriched transcription factor genes

Mammalian tissue- and/or time-specific transcription is primarily regulated in a combinatorial fashion through interactions between a specific set of transcriptional regulatory factors (TRFs) and their cognate cis-regulatory elements located in the regulatory regions. In exploring the DNA regions and TRFs involved in combinatorial transcriptional regulation, we noted that individual knockdown of a set of human liver-enriched TRFs such as HNF1A, HNF3A, HNF3B, HNF3G and HNF4A resulted in perturbation of the expression of several single TRF genes, such as HNF1A, HNF3G and CEBPA genes. We thus searched the potential binding sites for these five TRFs in the highly conserved genomic regions around these three TRF genes and found several putative combinatorial regulatory regions. Chromatin immunoprecipitation analysis revealed that almost all of the putative regulatory DNA regions were bound by the TRFs as well as two coactivators (CBP and p300). The strong transcription-enhancing activity of the putative combinatorial regulatory region located downstream of the CEBPA gene was confirmed. EMSA demonstrated specific bindings of these HNFs to the target DNA region. Finally, co-transfection reporter assays with various combinations of expression vectors for these HNF genes demonstrated the transcriptional activation of the CEBPA gene in a combinatorial manner by these TRFs.