Retinoids and retinoic acid receptors regulate growth arrest and apoptosis in human mammary epithelial cells and modulate expression of CBP/p300

Effects of the Acetyltransferase p300 on Tumour Regulation from the Novel Perspective of Posttranslational Protein Modification

p300 acts as a transcription coactivator and an acetyltransferase that plays an important role in tumourigenesis and progression. In previous studies, it has been confirmed that p300 is an important regulator in regulating the evolution of malignant tumours and it also has extensive functions. From the perspective of non-posttranslational modification, it has been proven that p300 can participate in regulating many pathophysiological processes, such as activating oncogene transcription, promoting tumour cell growth, inducing apoptosis, regulating immune function and affecting embryo development. In recent years, p300 has been found to act as an acetyltransferase that catalyses a variety of protein modification types, such as acetylation, propanylation, butyylation, 2-hydroxyisobutyration, and lactylation. Under the catalysis of this acetyltransferase, it plays its crucial tumourigenic driving role in many malignant tumours. Therefore, the function of p300 acetyltransferase has gradually become a research hotspot. From a posttranslational modification perspective, p300 is involved in the activation of multiple transcription factors and additional processes that promote malignant biological behaviours, such as tumour cell proliferation, migration, and invasion, as well as tumour cell apoptosis, drug resistance, and metabolism. Inhibitors of p300 have been developed and are expected to become novel anticancer drugs for several malignancies. We review the characteristics of the p300 protein and its functional role in tumour from the posttranslational modification perspective, as well as the current status of p300-related inhibitor research, with a view to gaining a comprehensive understanding of p300.

The synergistic effect of eucalyptus oil and retinoic acid on human esophagus cancer cell line SK-GT-4

Background

In order to improve cancer patients' chances of survival, scientists have prioritized finding alternatives to chemotherapy, focusing their efforts on natural sources. The current study investigates the anti-cancer action of retinoic acid and Eucalyptus oil in esophageal cancer and studies their combined effect as well as the cellular pathways that each trigger as part of ongoing research in this field. As a model of esophageal cancer, the SK-GT-4 cancer cell line was treated with a series of concentrations of both materials.

Results

The concentrations of Eucalyptus oil (10, 100, 1000, and 1500 g/mL) and Retinoic acid (5, 100, 150, and 200 M/mL) were used for treatment of cells. The MTT test was used to assess the anti-cancer activity of Eucalyptus oil and Retinoic acid, and qPCR was used to determine cellular pathways. Our findings show that both Eucalyptus oil and Retinoic acid inhibit cancer cell growth significantly. Our findings revealed that the IC50 values for eucalyptus oil were 63 g/mL and 111.3 M l/mL for retinoic acid. Furthermore, the impact was at the level that causes apoptosis. The findings suggested that any herbal substance could act as an inducer of the caspase-9-dependent pathway. The caspase-8-dependent pathway, on the other hand, was restricted to retinoic acid.

Conclusion

Our research discovered that the two chemicals worked together to create a synergistic effect. This synergistic effect could be attributed to a close connection between external and internal apoptotic pathways, which inhibits SK-GT-4 cell growth.

Graphical Abstract

Alteration of the Retinoid Acid-CBP Signaling Pathway in Neural Crest Induction Contributes to Enteric Nervous System Disorder

Hirschsprung Disease (HSCR) and/or hypoganglionosis are common pediatric disorders that arise from developmental deficiencies of enteric neural crest cells (ENCCs). Retinoid acid (RA) signaling has been shown to affect neural crest (NC) development. However, the mechanisms underlying RA deficiency-induced HSCR or hypoganglionosis are not well-defined. In this report, we found that in HSCR patient bowels, the RA nuclear receptor RARα and its interacting coregulator CREB-binding protein (CBP) were expressed in enteric neural plexuses in the normal ganglionic segment. However, the expression of these two genes was significantly inhibited in the pathological aganglionic segment. In a Xenopus laevis animal model, endogenous RARα interacted with CBP and was expressed in NC territory. Morpholino-mediated knockdown of RARα blocked expression of the NC marker genes Sox10 and FoxD3 and inhibited NC induction. The morphant embryos exhibited reduced nervous cells in the gastrointestinal anlage, a typical enteric nervous deficiency-associated phenotype. Injection of CBP mRNA rescued NC induction and reduced enteric nervous deficiency-associated phenotypes. Our work demonstrates that RARα regulates Sox10 expression via CBP during NC induction, and alteration of the RA-CBP signaling pathway may contribute to the development of enteric nervous system disorders.

Retinoic acid and sodium butyrate suppress the cardiac expression of hypertrophic markers and proinflammatory mediators in Npr1 gene-disrupted haplotype mice

The objective of the present study was to examine the genetically determined differences in the natriuretic peptide receptor-A (NPRA) gene (Npr1) copies affecting the expression of cardiac hypertrophic markers, proinflammatory mediators, and matrix metalloproteinases (MMPs) in a gene-dose-dependent manner. We determined whether stimulation of Npr1 by all-trans retinoic acid (RA) and histone deacetylase (HDAC) inhibitor sodium butyric acid (SB) suppress the expression of cardiac disease markers. In the present study, we utilized Npr1 gene-disrupted heterozygous (Npr1(+/-), 1-copy), wild-type (Npr1(+/+), 2-copy), gene-duplicated (Npr1(++/+), 3-copy) mice, which were treated intraperitoneally with RA, SB, and a combination of RA/SB, a hybrid drug (HB) for 2 wk. Untreated 1-copy mice showed significantly increased heart weight-body weight (HW/BW) ratio, blood pressure, hypertrophic markers, including beta-myosin heavy chain (β-MHC) and proto-oncogenes (c-fos and c-jun), proinflammatory mediator nuclear factor kappa B (NF-κB), and MMPs (MMP-2, MMP-9) compared with 2-copy and 3-copy mice. The heterozygous (haplotype) 1-copy mice treated with RA, SB, or HB, exhibited significant reduction in the expression of β-MHC, c-fos, c-jun, NF-κB, MMP-2, and MMP-9. In drug-treated animals, the activity and expression levels of HDAC were significantly reduced and histone acetyltransferase activity and expression levels were increased. The drug treatments significantly increased the fractional shortening and reduced the systolic and diastolic parameters of the Npr1(+/-) mice hearts. Together, the present results demonstrate that a decreased Npr1 copy number enhanced the expression of hypertrophic markers, proinflammatory mediators, and MMPs, whereas an increased Npr1 repressed the cardiac disease markers in a gene-dose-dependent manner.

All-trans retinoic acid and sodium butyrate enhance natriuretic peptide receptor a gene transcription: role of histone modification

The objective of the present study was to delineate the mechanisms of GC-A/natriuretic peptide receptor-A (GC-A/NPRA) gene (Npr1) expression in vivo. We used all-trans retinoic acid (ATRA) and histone deacetylase (HDAC) inhibitor, sodium butyrate (NaBu) to examine the expression and function of Npr1 using gene-disrupted heterozygous (1-copy; +/-), wild-type (2-copy; +/+), and gene-duplicated heterozygous (3-copy; ++/+) mice. Npr1(+/-) mice exhibited increased renal HDAC and reduced histone acetyltransferase (HAT) activity; on the contrary, Npr1(++/+) mice showed decreased HDAC and enhanced HAT activity compared with Npr1(+)(/+) mice. ATRA and NaBu promoted global acetylation of histones H3-K9/14 and H4-K12, reduced methylation of H3-K9 and H3-K27, and enriched accumulation of active chromatin marks at the Npr1 promoter. A combination of ATRA-NaBu promoted recruitment of activator-complex containing E26 transformation-specific 1, retinoic acid receptor α, and HATs (p300 and p300/cAMP response element-binding protein-binding protein-associated factor) at the Npr1 promoter, and significantly increased renal NPRA expression, GC activity, and cGMP levels. Untreated 1-copy mice showed significantly increased systolic blood pressure and renal expression of α-smooth muscle actin (α-SMA) and proliferating cell nuclear antigen (PCNA) compared with 2- and 3-copy mice. Treatment with ATRA and NaBu synergistically attenuated the expression of α-SMA and PCNA and reduced systolic blood pressure in Npr1(+/-) mice. Our findings demonstrate that epigenetic upregulation of Npr1 gene transcription by ATRA and NaBu leads to attenuation of renal fibrotic markers and systolic blood pressure in mice with reduced Npr1 gene copy number, which will have important implications in prevention and treatment of hypertension-related renal pathophysiological conditions.

Purification and characterization of recombinant CH3 domain fragment of the CREB-binding protein

CREB-binding protein (CBP) is an important coactivator of basal transcription machinery and a critical regulator of cellular proliferation, differentiation, and apoptosis. It is hypothesized that CBP function is regulated by post-translational modifications, such as phosphorylation and methylation. Specific kinase-mediated phosphorylation of CBP has been shown to affect not only intrinsic histone acetyl transferase activity, but also transcriptional activity of various target promoters and interaction with binding partners. While most of the identified CBP phosphorylation sites have been mapped to the N-terminus of the protein, based on previous studies of the CBP homolog (p300), protein kinase B/Akt is predicted to phosphorylate the C-terminus of CBP. However, there is no direct evidence of Akt-mediated phosphorylation of CBP. Here we report the first purification procedure of recombinant fragment of CBP, encompassing the cysteine/histidine-rich domain 3 (CH3) and glutamine-rich (Q) domain of the protein, which is suitable for structural and interaction studies. We provide the first evidence of protein-protein interaction between the full-length Akt1 and the C-terminus of CBP by fluorescence spectroscopy and the subsequent phosphorylation of CBP by in vitro phosphorylation assay. Our results suggest that Akt signaling may have important implications on the in vivo molecular interaction of CBP with various transcription factors and modulation of cellular responses.

Hepatitis B virus X protein overcomes the growth-inhibitory potential of retinoic acid by downregulating retinoic acid receptor-beta2 expression via DNA methylation

Aberrant promoter methylation of retinoic acid receptor-beta(2) (RAR-beta(2)) is frequently detected in hepatitis B virus (HBV)-positive hepatocellular carcinoma (HCC); however, the mechanism of methylation and its biological significance are unknown. This study showed that HBx, the principal oncogene product of HBV, induced promoter hypermethylation of RAR-beta(2) via upregulation of DNA methyltransferases 1 and 3a, resulting in downregulation of its expression in human HCC cells. In addition, HBx abolished the potential of retinoic acid (RA) to downregulate levels of G(1)-checkpoint regulators including p16, p21 and p27, resulting in activation of E2F1 in the presence of RA. As a consequence, HBx-expressing cells were less susceptible to RA-induced cell growth inhibition compared with control cells. These effects almost completely disappeared when levels of RAR-beta(2) in HBx-expressing cells were restored by treatment with a universal DNA methylation inhibitor, 5-aza-2'-deoxycytidine. As RAR-beta(2) is a major executor of the anti-tumour potential of RA, its epigenetic downregulation by HBx is likely to be an important step during HBV-mediated tumorigenesis.

Effects of retinoic acid isomers on apoptosis and enzymatic antioxidant system in human breast cancer cells

Retinoic acids (RAs) modulate growth, differentiation, and apoptosis in normal, pre-malignant & malignant cells. In the present study, the effects of RA isomers (all-trans RA, 13-cis RA, and 9-cis RA) on the cell signal transduction of human breast cancer cells have been studied. The relationship between RAs and an enzymatic antioxidant system was also determined. Estrogen-receptor (ER) positive MCF-7 and ER-negative MDA-MB-231 human breast cancer cells were treated with different doses of each RA isomers, all-trans RA, 13-cis RA, or 9-cis RA. Treatment of RA isomers inhibited cell viability and induced apoptosis of MCF-7 cells as a result of increased caspase activity in cytoplasm and cytochrome C released from mitochondria. All-trans RA was the most effective RA isomer in both cell growth inhibition and induction of apoptosis in MCF-7 cells. However, no significant effect of RA isomers was observed on the cell growth or apoptosis in ER-negative MDA-MB-231 cells. In addition, activities of antioxidant enzymes such as catalase and glutathione peroxidase were decreased effectively after treatment of RA in MCF-7 cells, whereas SOD activity was rarely affected. Thus, the present data suggest that all-trans RA is the most potential inducer of apoptosis and modulator of antioxidant enzymes among RA isomers in MCF-7 human breast cancer cells.

Nitration of cathepsin D enhances its proteolytic activity during mammary gland remodelling after lactation

Proteomic studies in the mammary gland of control lactating and weaned rats have shown that there is an increased pattern of nitrated proteins during weaning when compared with controls. Here we report the novel finding that cathepsin D is nitrated during weaning. The expression and protein levels of this enzyme are increased after 8 h of litter removal and this up-regulation declines 5 days after weaning. However, there is a marked delay in cathepsin D activity since it does not increase until 2 days post-weaning and remains high thereafter. In order to find out whether nitration of cathepsin D regulates its activity, iNOS (inducible nitric oxide synthase)−/− mice were used. The expression and protein levels of this enzyme were similar to WT (wild-type) animals, but the proteolytic activity was significantly reduced during weaning in knockout compared to WT mice. in vitro treatment of recombinant human cathepsin D or lactating mammary gland homogenates with relatively low concentrations of peroxynitrite enhances the nitration as well as specific activity of this enzyme. Using MS, it has been shown that the residue Tyr168 was nitrated. All of these results show that protein nitration during weaning might be a signalling pathway involved in mammary gland remodelling.

Silencing of MBD1 and MeCP2 in prostate-cancer-derived PC3 cells produces differential gene expression profiles and cellular phenotypes

Alterations in genomic CpG methylation patterns have been found to be associated with cell transformation and neoplasia. Although it is recognized that methylation of CpG residues negatively regulates gene expression, how the various MBPs (methyl-binding proteins) contribute to this process remains elusive. To determine whether the two well characterized proteins MeCP2 (methyl-CpG-binding protein 2) and MBD1 (methyl-CpG-binding domain 1) have distinct or redundant functions, we employed RNAi (RNA interference) to silence their expression in the prostate cancer-derived PC3 cell line, and subsequently compared cell growth, invasion and migration properties of these cell lines in addition to their respective mRNA-expression profiles. Cells devoid of MeCP2 proliferated more poorly compared with MBD1-deficient cells and the parental PC3 cells. Enhanced apoptosis was observed in MeCP2-deficient cells, whereas apoptosis in parental and MBD1-deficient cells appeared to be equivalent. Boyden chamber invasion and wound-healing migration assays showed that MBD1-silenced cells were both more invasive and migratory compared with MeCP2-silenced cells. Finally, gene chip microarray analyses showed striking differences in the mRNA-expression profiles obtained from MeCP2- and MBD1-depleted cells relative to each other as well as when compared with control cells. The results of the present study suggest that MeCP2 and MBD1 silencing appear to affect cellular processes independently in vivo and that discrete sets of genes involved in cellular proliferation, apoptosis, invasion and migration are targeted by each protein.

Epstein-Barr virus latent membrane protein 1 suppresses the growth-inhibitory effect of retinoic acid by inhibiting retinoic acid receptor-beta2 expression via DNA methylation

Epigenetic alteration through DNA methylation in retinoic acid receptor-beta2 (RAR-beta2) is common in human tumors including nasopharyngeal carcinoma (NPC); however, the mechanism and its biological significance are unknown. Here, we report that the Epstein-Barr virus (EBV) oncogene product, latent membrane protein 1 (LMP1), induces promoter hypermethylation of RAR-beta2 via up-regulation of DNA methyltransferases 1, 3a, and 3b, leading to decrease in RAR-beta2 expression in NPC cells. In addition, LMP1 abolished the potentials of retinoic acid (RA) to down-regulate Cdk2 and Cdk4 and to up-regulate p16, p21, and p27, resulting in activation of E2F1 in the presence of RA. As a consequence, LMP1 could abrogate the growth-inhibitory effect of RA by releasing cell cycle arrest at G1 phase. Considering that RAR-beta2 is a major executor of the anti-tumor potentials of retinoids, its down-regulation by LMP1 might play an important role during EBV-mediated tumorigenesis.

Bidirectional CLOCK/BMAL1-dependent circadian gene regulation by retinoic acid in vitro

A central circadian clock located in the suprachiasmatic nucleus (SCN) of the mammalian hypothalamus entrains peripheral clocks through both neural and humoral factors. Although candidates for entrainment factors have been described, their details remain obscure. Here, we screened ligands for nuclear receptors that affect CLOCK/BMAL1-dependent transactivation of the mouse Period1 (mPer1) gene in NIH3T3 cells. We found that retinoic acids (RAs) significantly up-regulate mPer1 expression in an E-box-dependent manner. We also found that RAs up-regulate the expression of other E-box-dependent circadian genes such as mPer2, arginine vasopressin (mAVP), and peroxisome proliferator-activated receptor alpha (mPPARalpha). Surprisingly, the effect of RAs on CLOCK/BMAL1 (E-box)-dependent mRNA expression was bidirectional and depended on the presence of exogenous retinoic acid receptor alpha (RARalpha). These results suggest that RAs regulate the CLOCK/BMAL1-dependent transcription of circadian genes in a complex manner.

A Repressive Epigenetic Domino Effect Confers Susceptibility to Breast Epithelial Cell Transformation: Implications for Predicting Breast Cancer Risk

Retinoic acid (RA) is a master epigenetic regulator that plays a pivotal role in both breast morphogenesis and development. Here, we show for the first time that RA, via the RA receptor alpha (RARalpha), epigenetically regulates in a concerted fashion the transcription of two RA-responsive genes, the RA receptor beta2 (RARbeta2) and the cellular retinol-binding protein 1 (CRBP1). Specifically, an impaired RA signal through RARalpha in human breast epithelial cells triggers a repressive epigenetic domino effect, involving first RARbeta2 and second CRBP1. The phenotype acquired by breast epithelial cells clearly implies that the resistance to RA-mediated growth inhibition precedes the acquisition of morphological epithelial transformation, thus supporting the occurrence of sequential transcriptional silencing of first RARbeta2 and second CRBP1. The identification of this epigenetic network mechanistically linking RARbeta2 and CRBP1 transcription provides the basis for devising more accurate epigenetic tests for the prediction of breast cancer risk.

Retinoic acid signaling is required for proper morphogenesis of mammary gland

Retinoic acid (RA), a bioactive chemical compound synthesized from dietary derived vitamin A, has been successfully used as a chemopreventive and chemotherapeutic agent through the regulation of cell proliferation, differentiation, and apoptosis acting via the retinoic acid receptors. Despite two decades of research on the function of retinoic acid, the physiological role of RA in mammary gland development is still not well characterized. In this report, we demonstrate that RA is required for proper morphogenesis of mouse mammary gland in a novel transgenic mouse model system. It was found that inhibition of RA signaling in vivo leads to excessive mammary ductal morphogenesis through upregulation of cyclin D1 and MMP-3 expression. Furthermore, we show that the transgene-induced excessive branching morphogenesis could be reversed by treatment with RA, demonstrating the direct physiological effect of RA signaling in vivo. In addition, we demonstrate that excessive branching morphogenesis in the transgenic mammary gland are cell-autonomous and do not require stromal signals within the transgenic mammary gland. Finally, we provide evidence suggesting that retinoic acid signaling is required for appropriate mammary gland differentiation. Collectively, our data indicate for the first time that retinoic acid signaling is required to maintain the homeostasis of mammary gland morphogenesis.

Environmental xenobiotics and nuclear receptors--interactions, effects and in vitro assessment

A group of intracellular nuclear receptors is a protein superfamily including arylhydrocarbon AhR, estrogen ER, androgen AR, thyroid TR and retinoid receptors RAR/RXR as well as molecules with unknown function known as orphan receptors. These proteins play an important role in a wide range of physiological as well as toxicological processes acting as transcription factors (ligand-dependent signalling macromolecules modulating expression of various genes in a positive or negative manner). A large number of environmental pollutants and other xenobiotics negatively affect signaling pathways, in which nuclear receptors are involved, and these modulations were related to important in vivo toxic effects such as immunosuppression, carcinogenesis, reproduction or developmental toxicity, and embryotoxicity. Presented review summarizes current knowledge on major nuclear receptors (AhR, ER, AR, RAR/RXR, TR) and their relationship to known in vivo toxic effects. Special attention is focused on priority organic environmental contaminants and experimental approaches for determination and studies of specific toxicity mechanisms.

Valproic acid, in combination with all-trans retinoic acid and 5-aza-2'-deoxycytidine, restores expression of silenced RARbeta2 in breast cancer cells

Epigenetic silencing of tumor suppressor genes has been established as an important process of carcinogenesis. The retinoic acid (RA) receptor beta2 (RARbeta2) gene is one such tumor suppressor gene often silenced during carcinogenesis. The combined use of histone deacetylase and DNA methyltransferase inhibitors has been shown to reverse the epigenetic silencing of numerous growth regulatory genes. Valproic acid (VPA), which has long been used in the treatment of epilepsy, was shown recently to be an effective histone deacetylase inhibitor that can induce differentiation of neoplastically transformed cells. In this study, we show for the first time that VPA, in combination with RA and the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (Aza-dC), can overcome the epigenetic barriers to transcription of a prototypical silenced tumor suppressor gene, RARbeta2, in human breast cancer cells. Chromatin immunoprecipitation assays show that the combination of VPA, RA, and Aza-dC increases histone acetylation at the silenced RARbeta2 promoter of MCF-7 breast cancer cells. Furthermore, reverse transcription-PCR analyses reveal cell type-specific effects in the actions of VPA on RARbeta2 expression in cultured human breast cancer cells. Finally, we show that VPA, in combination with RA and Aza-dC, inhibits the proliferation of both estrogen receptor alpha-positive (MCF-7) and estrogen receptor alpha-negative (MDA-MB-231) breast cancer cell lines. These data suggest that VPA may ultimately be useful in combination therapies in the treatment of human breast cancers.

Retinoic acid and the histone deacetylase inhibitor trichostatin a inhibit the proliferation of human renal cell carcinoma in a xenograft tumor model

PURPOSE

Therapy for advanced renal cell carcinoma (RCC) is ineffective in the majority of patients. We have previously reported that retinoid-induced up-regulation of retinoic acid receptor beta (RARbeta) correlated with antitumor effects in RCCs. Recent studies show that there is a reduction in the level of RARbeta2 expression in cancer cells due in part to histone hypoacetylation. Therefore, we tested whether combining histone deacetylase inhibitors with retinoic acid (RA) would restore RARbeta2 receptor expression, leading to increased growth inhibition in RCC cells.

EXPERIMENTAL DESIGN

Cell proliferation, Western blot, and reverse transcription-PCR analyses of two RA-resistant RCC cell lines, SK-RC-39 and SK-RC-45, were assessed in the presence of all-trans retinoic acid (ATRA), trichostatin A (TSA), or the combination of ATRA and TSA. Analysis of apoptosis was also done on SK-RC-39 cells treated with these combinations. Additionally, a xenograft tumor model (SK-RC-39) was used in this study to investigate the efficacy of a liposome-encapsulated, i.v. form of ATRA (ATRA-IV) plus TSA combination therapy.

RESULTS

Enhanced inhibition of the proliferation of RCC cell lines and of tumor growth in a xenograft model was observed with the combination of ATRA plus TSA. Reactivation of RARbeta2 mRNA expression was observed in SK-RC-39 and SK-RC-45 cells treated with TSA alone or TSA in combination with ATRA. A partial G0-G1 arrest and increased apoptosis were observed with SK-RC-39 cells on treatment with ATRA and TSA.

CONCLUSIONS

The combination of ATRA and the histone deacetylase inhibitor TSA elicits an additive inhibition of cell proliferation in RCC cell lines. These results indicate that ATRA and histone deacetylase inhibitor therapies should be explored for the treatment of advanced RCC.

Retinoic Acid Receptor- 2 Promoter Methylation in Random Periareolar Fine Needle Aspiration

Methylation of the retinoic acid receptor-beta2 (RARbeta2) P2 promoter is hypothesized to be an important mechanism for loss of RARbeta2 function during early mammary carcinogenesis. The frequency of RARbeta2 P2 methylation was tested in (a) 16 early stage breast cancers and (b) 67 random periareolar fine needle aspiration (RPFNA) samples obtained from 38 asymptomatic women who were at increased risk for breast cancer. Risk was defined as either (a) 5-year Gail risk calculation > or = 1.7%; (b) prior biopsy exhibiting atypical hyperplasia, lobular carcinoma in situ, or ductal carcinoma in situ; or (c) known BRCA1/2 mutation carrier. RARbeta2 P2 promoter methylation was assessed at two regions, M3 (-51 to 162 bp) and M4 (104-251 bp). In early stage cancers, M4 methylation was observed in 11 of 16 (69%) cases; in RPFNA samples, methylation was present at M3 and M4 in 28 of 56 (50%) and 19 of 56 (38%) cases, respectively. RPFNAs were stratified for cytologic atypia using the Masood cytology index. The distribution of RARbeta2 P2 promoter methylation was reported as a function of increased cytologic abnormality. Methylation at both M3 and M4 was observed in (a) 0 of 10 (0%) of RPFNAs with Masood scores of < or = 10 (nonproliferative), (b) 3 of 20 (15%) with Masood scores of 11 to 12 (low-grade proliferative), (c) 3 of 10 (30%) with Masood scores of 13 (high-grade proliferative), and (d) 7 of 14 (50%) with Masood scores of 14 of 15 (atypia). Results from this study indicate that the RARbeta2 P2 promoter is frequently methylated (69%) in primary breast cancers and shows a positive association with increasing cytologic abnormality in RPFNA.

Induction of PDCD4 tumor suppressor gene expression by RAR agonists, antiestrogen and HER-2/neu antagonist in breast cancer cells. Evidence for a role in apoptosis

The growth of human breast tumor cells is regulated through signaling involving cell surface growth factor receptors and nuclear receptors of the steroid/thyroid/retinoid receptor gene family. Retinoic acid receptors (RARs), members of the steroid/thyroid hormone receptor gene family, are ligand-dependent transcription factors, which have in vitro and in vivo growth inhibitory activity against breast cancer cells. RAR-agonists inhibit the proliferation of many human breast cancer cell lines, particularly those whose growth is stimulated by estradiol (E2) or growth factors. Additionally, RAR-agonists and synthetic retinoids such as Ferentinide have been shown to induce apoptosis in malignant breast cells but not normal breast cells. To better define the genes involved in RAR-mediated growth inhibition of breast cancer cells, we used oligonucleotide microarray analysis to create a database of genes that are potentially regulated by RAR-agonists in breast cancer cells. We found that PDCD4 (programmed cell death 4), a tumor suppressor gene presently being evaluated as a target for chemoprevention, was induced about three-fold by the RARalpha-selective agonist Am580, in T-47D breast cancer cells. RAR pan-agonists and Am580, but not retinoid X receptors (RXR)-agonists, stimulate the expression of PDCD4 in a wide variety of retinoid-inhibited breast cancer cell lines. RAR-agonists did not induce PDCD4 expression in breast cancer cell lines, which were not growth inhibited by retinoids. We also observed that antiestrogen and the HER-2/neu antagonist, Herceptin (Trastuzumab), also induced PDCD4 expression in T-47D cells, suggesting that PDCD4 may play a central role in growth inhibition in breast cancer cells. Transient overexpression of PDCD4 in T-47D (ER+, RAR+) and MDA-MB-231 (ER-, RAR-) cells resulted in apoptotic death, suggesting a role for PDCD4 in mediating apoptosis in breast cancer cells. PDCD4 protein expression has previously been reported in small ductal epithelium of normal breast. To date, there has been no report of induction of PDCD4 expression by RAR-agonists, antiestrogen or HER2/neu antagonist in breast cancer cells and its potential role in apoptosis in these cells.

Differential expression of retinoic acid receptor beta (RARβ) and the AP-1 transcription factor in normal, premalignant and malignant human laryngeal tissues

The anticancer effects of retinoids are mainly mediated by their nuclear receptors. Recent studies have demonstrated that retinoic acid receptor beta (RARbeta) plays a pivotal role from the early stages of laryngeal carcinogenesis; however, the exact mechanism of this detrimental effect has not yet been elucidated. One of the best-documented actions of retinoid receptors is the transrepression of activator protein-1 (AP-1) transcription factor activity, although this complex interplay has not been clarified. The present report is the first systematic morphological evaluation of the cross-talk of RARbeta and AP-1 transcription factor in a large series of human laryngeal tissues containing normal epithelium, premalignant lesions (hyperplasia and/or dysplasia) and squamous cell carcinoma. Immunohistochemical methodology was performed on formalin-fixed, paraffin-embedded sections by using a panel of monoclonal and polyclonal antibodies against RARbeta and the AP-1 components c-Jun, p-c-Jun (phosphorylated, active c-Jun) and c-Fos proteins. Their expression was screened and compared in 154 patients with various laryngeal histological entities. Nuclear expression of RARbeta, c-Jun, p-c-Jun and c-Fos was detected in 81 (89.2%), 48 (52.8%), 66 (72.6%) and 73 (80.3%), respectively, out of 91 specimens with normal-appearing laryngeal epithelium; in 86 (87.8%), 94 (95.9%), 94 (95.9%) and 94 (95.9%), respectively, out of 98 specimens with hyperplastic laryngeal epithelium; in 58 (56.8%), 92 (90.2%), 96 (94.1%) and 96 (94.1%), respectively, out of 102 specimens with dysplastic laryngeal epithelium; in 10 (22.3%), 41 (91.2%), 44 (97.8%) and 41 (91.2%), respectively, out of 45 specimens with well-differentiated squamous cell carcinoma; in 13 (30.3%), 37 (86%), 39 (90.7%) and 41 (95.3%), respectively, out of 43 specimens with moderately-differentiated squamous cell carcinoma; and in 8 (66.7%), 10 (83.3%), 12 (100%) and 12 (100%), respectively, out of 12 specimens with poorly-differentiated squamous cell laryngeal carcinoma. Statistical analysis and correlation of the intensity of nuclear immunostaining of the studied proteins among the various histological entities revealed statistically significant results. The progressive upregulation of the AP-1 transcription factor constituents and downregulation of the RARbeta protein detected from the onset of laryngeal tumorigenesis suggests an important role for the immediate-early AP-1/RARbeta on/off "switch" in the process of laryngeal carcinogenesis.

CBP/p300 induction is required for retinoic acid sensitivity in human mammary cells

The coactivators CBP and p300 are recruited by retinoic acid receptors (RARs) during retinoid mediated transcriptional regulation. To assess the role of CBP/p300 in all-trans-retinoic acid (ATRA)-mediated growth arrest in mammary epithelial cells, two systems were tested: (1) ATRA resistant MCF-7 cells were transduced with a functional RAR-beta 2; (2) normal human mammary epithelial cells (HMECs) were transduced with a pan-RAR dominant negative, RAR-alpha 403. Expression of RAR-beta 2 in MCF-7 cells resulted in increased sensitivity to ATRA-induced growth arrest and correlated with induction of CBP/p300 mRNA and protein. Inhibition of RAR function in HMECs resulted in resistance to ATRA-induced growth arrest and loss of CBP/p300 induction. Antisense suppression of CBP/p300 in HMECs resulted in decreased retinoic acid response element reporter trans-activation and decreased ATRA-mediated growth arrest. Thus, in human mammary epithelial cells, CBP/p300 were both modulated by an ATRA signaling pathway and were required for a normal response to ATRA.