Bcl-2 inhibits retinoic acid-induced apoptosis during the neural differentiation of embryonal stem cells

Growth Factors as Tools in Photoreceptor Cell Regeneration and Vision Recovery

Photoreceptor loss is a major cause of blindness around the world. Stem cell therapy offers a new strategy in retina degenerative disease. Retinal progenitors can be derived from embryonic stem cells (ESC) in vitro, but cannot be processed to a mature state. In addition, the adult recipient retina presents a very different environment than the photoreceptor precursor donor. It seems that modulation of the recipient environment by ectopic development regulated growth factors for transplanted cells could generate efficient putative photoreceptors. The purpose of this review article was to investigate the signaling pathway of growth factors including: insulin-like growth factors (IGFs), fibroblast growth factors (FGF), Nerve growth factor (NGF), Brain-derived neurotrophic factor (BDNF), Taurin and Retinoic acid (RA) involved in the differentiation of neuroretina cell, like; photoreceptor and retinal progenitor cells. Given the results available in the related literature, the differentiation efficacy of ESCs toward the photoreceptor and retinal neurons and the important role of growth factors in activating signaling pathways such as Akt, Ras/Raf1/ and ERKs also inhibit the ASK1/JNK apoptosis pathway. Manipulating differentiated culture, growth factors can influence photoreceptor transplantation efficiency in retinal degenerative disease.

Retinoic acid and TGF-β signalling cooperate to overcome MYCN-induced retinoid resistance

BACKGROUND

Retinoid therapy is widely employed in clinical oncology to differentiate malignant cells into their more benign counterparts. However, certain high-risk cohorts, such as patients with MYCN-amplified neuroblastoma, are innately resistant to retinoid therapy. Therefore, we employed a precision medicine approach to globally profile the retinoid signalling response and to determine how an excess of cellular MYCN antagonises these signalling events to prevent differentiation and confer resistance.

METHODS

We applied RNA sequencing (RNA-seq) and interaction proteomics coupled with network-based systems level analysis to identify targetable vulnerabilities of MYCN-mediated retinoid resistance. We altered MYCN expression levels in a MYCN-inducible neuroblastoma cell line to facilitate or block retinoic acid (RA)-mediated neuronal differentiation. The relevance of differentially expressed genes and transcriptional regulators for neuroblastoma outcome were then confirmed using existing patient microarray datasets.

RESULTS

We determined the signalling networks through which RA mediates neuroblastoma differentiation and the inhibitory perturbations to these networks upon MYCN overexpression. We revealed opposing regulation of RA and MYCN on a number of differentiation-relevant genes, including LMO4, CYP26A1, ASCL1, RET, FZD7 and DKK1. Furthermore, we revealed a broad network of transcriptional regulators involved in regulating retinoid responsiveness, such as Neurotrophin, PI3K, Wnt and MAPK, and epigenetic signalling. Of these regulators, we functionally confirmed that MYCN-driven inhibition of transforming growth factor beta (TGF-β) signalling is a vulnerable node of the MYCN network and that multiple levels of cross-talk exist between MYCN and TGF-β. Co-targeting of the retinoic acid and TGF-β pathways, through RA and kartogenin (KGN; a TGF-β signalling activating small molecule) combination treatment, induced the loss of viability of MYCN-amplified retinoid-resistant neuroblastoma cells.

CONCLUSIONS

Our approach provides a powerful precision oncology tool for identifying the driving signalling networks for malignancies not primarily driven by somatic mutations, such as paediatric cancers. By applying global omics approaches to the signalling networks regulating neuroblastoma differentiation and stemness, we have determined the pathways involved in the MYCN-mediated retinoid resistance, with TGF-β signalling being a key regulator. These findings revealed a number of combination treatments likely to improve clinical response to retinoid therapy, including co-treatment with retinoids and KGN, which may prove valuable in the treatment of high-risk MYCN-amplified neuroblastoma.

MiR-512-5p induces apoptosis and inhibits glycolysis by targeting p21 in non-small cell lung cancer cells

MicroRNAs are a family of small non-coding RNAs that constitute a prevalent gene regulation. In this study, we showed the expression of miR-512-5p is downregulated in non-small cell lung cancer (NSCLC) patient tumor samples compared to its paired normal lung tissues. Moreover, expression of miR-512-5p was increased by retinoic acid treatment. Overexpression of miR-512-5p induced apoptosis of NSCLC cell lines A549 and H1299, and miR-512-5p inhibitor reversed this effect in H1299 cells stably expressing miR-512. miR-512-5p inhibited glycolysis and migration in NSCLC cells, but shows no effect on cell proliferation. We identified p21 as a target gene of miR-512-5p. Overexpression of miR-512-5p led to the decrease of p21 protein and mRNA level. Knockdown of p21 resulted in similar effects on apoptosis and glycolysis as that observed of miR-512-5p overexpression, as well as rescued the effect of miR-512-5p inhibitor on cell apoptosis in H1299 cells stably expressing miR-512. In conclusion, our present study revealed miR-512-5p was able to target p21 to induce apoptosis and inhibit glycolysis in A549 and H1299 cell lines.

Beclin 1, an autophagy-related gene, augments apoptosis in U87 glioblastoma cells

Beclin 1 acts as a tumor suppressor and is an essential mediator of autophagy. Beclin 1 also interacts with Bcl-2 and can induce apoptosis by activating the mitochondrion permeabilizing function of proapoptotic multidomain proteins from the Bcl-2 family. Moreover, these Bcl-2 family members can activate autophagy by liberating Beclin 1 from its inhibition by Bcl-2/Bcl-XL at the level of the endoplasmic reticulum. We found that overexpression of Beclin 1 in U87 glioblastoma cells enhanced the capacity for cellular autophagy and induced apoptosis. Silencing of Beclin 1 decreased autophagic capacity but had little effect on apoptosis and cell proliferation. Beclin 1-Bcl-2 and Beclin 1-Bcl-xL complexes were detected by immunoprecipitation in cells that overexpressed Beclin 1. Furthermore, the levels of cytochrome c in the cytosol and the activity of caspases-3/-9 in the cytosol increased after overexpression of Beclin 1. Our results suggest that Beclin 1 induces apoptosis via binding to Bcl-2 and Bcl-xL, followed by the release of cytochrome c into the cytosol and activation of caspases-3/-9.

Growth and differentiation factor 3 induces expression of genes related to differentiation in a model of cancer stem cells and protects them from retinoic acid-induced apoptosis

Misexpression of growth factors, particularly those related to stem cell-like phenotype, is often observed in several cancer types. It has been found to influence parameters of disease progression like cell proliferation, differentiation, maintenance of undifferentiated phenotype and modulation of the immune system. GDF3 is a TGFB family member associated with pluripotency and differentiation during embryonic development that has been previously reported to be re-expressed in a number of cancer types. However, its role in tumor development and progression has not been clarified yet. In this study we decipher the role of GDF3 in an in vitro model of cancer stem cells, NCCIT cells. By classical approach to study protein function combined with high-throughput technique for transcriptome analysis and differentiation assays we evaluated GDF3 as a potential therapeutic target. We observed that GDF3 robustly induces a panel of genes related to differentiation, including several potent tumor suppressors, without impacting the proliferative capacity. Moreover, we report for the first time the protective effect of GDF3 against retinoic acid-induced apoptosis in cells with stem cell-like properties. Our study implies that blocking of GDF3 combined with retinoic acid-treatment of solid cancers is a compelling direction for further investigations, which can lead to re-design of cancer differentiation therapies.

Retinoid signaling alterations in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neuromuscular disease for which effective therapeutic interventions and an understanding of underlying disease mechanism are lacking. A variety of biochemical pathways are believed to contribute to the pathophysiology of ALS that are common to both sporadic and familial forms of the disease. Evidence from both human and animal studies indicates that expression of retinoid signaling genes is altered in ALS and may contribute to motor neuron loss. Our goals were to examine the expression and distribution of proteins of the retinoid signaling pathway in spinal cord samples from patients with sporadic and familial ALS and to evaluate the role of these proteins in motor neuron cell survival. In sporadic ALS, the cytoplasmic binding protein that facilitates nuclear translocation of retinoic acid, cellular retinoic acid binding protein-II (CRABP-II), was localized to the nucleus and retinoic acid receptor β (RARβ) was significantly increased in motor neuron nuclei when compared to either familial ALS patients or non-neurologic disease controls. Motor neurons with increased nuclear RARβ were negative for markers of apoptosis. Pre-treatment of primary motor neuron-enriched cultures with a pan-RAR or RARβ-specific agonist decreased motor neuron cell death associated with oxidative injury/stress while a RARβ-specific antagonist enhanced cell death. Our data suggest retinoid signaling is altered in ALS and increased nuclear RARβ occurs in motor neurons of sporadic ALS patients. Activation of RARβ protects motor neurons from oxidative-induced cell death.

Cdk2ap2 is a novel regulator for self-renewal of murine embryonic stem cells

In this study we present data to support the role for Cdk2ap2 in regulating self-renewal of mouse embryonic stem cells (mESCs) under permissive conditions, and cell survival during differentiation of the mESCs into terminally differentiated cell types. To understand the function of Cdk2ap2 during early development, we generated mESCs with homozygous disruption of the endogenous Cdk2ap2 locus (Cdk2ap2(tr/tr)). The Cdk2ap2(tr/tr) mESCs, when grown in a complete growth medium containing leukemia inhibitory factor (LIF), showed an early differentiation phenotype characterized by flattened colonies and a distinct intercellular boundary. We also observed downregulation of Nanog and upregulation in markers of mesoderm and endoderm differentiation, including Brachyury (T), Afp, and S100a, when compared to Wt mESCs. Cdk2ap2(tr/tr) mESCs were able to form embryoid bodies (EBs); however, those EBs were unhealthy and had an increased level of apoptosis. Furthermore, Cdk2ap2(tr/tr) mESCs were unable to form teratomas in severe combined immunodeficiency (SCID) mice. Cdk2ap2 under normal conditions has a biphasic expression, suggesting regulatory roles in early-versus-late stem cell differentiation. These data begin to add to our understanding of how Cdk2ap2 may be involved in the regulation of self-renewal of stem cells during early embryogenesis.

Comparison of chemical-induced changes in proliferation and apoptosis in human and mouse neuroprogenitor cells

There is a need to develop rapid and efficient models to screen chemicals for their potential to cause developmental neurotoxicity. Use of in vitro neuronal models, including human cells, is one approach that allows for timely, cost-effective toxicity screening. The present study compares the sensitivity of human (ReN CX) and mouse (mCNS) neuroprogenitor cell lines to chemicals using a multiplex assay for proliferation and apoptosis, endpoints that are critical for neural development. Cells were exposed to 0.001-100 μM concentrations of 11 chemicals (cadmium, chlorpyrifos oxon, dexamethasone, dieldrin, ketamine, lead, maneb, methylmercury, nicotine, trans-retinoic acid, and trimethyltin) reported in the literature to affect proliferation and/or apoptosis, and 5 chemicals (dimethyl pthalate, glyphosate, omeprazole, saccharin, and d-sorbitol) with no reports of effects on either endpoint. High-content screening of markers for proliferation (BrdU incorporation) and apoptosis (activated caspase 3 and p53) was used to assess the effect of chemicals in both cell lines. Of the chemicals tested, methylmercury, cadmium, dieldrin, chlorpyrifos oxon, trans-retinoic acid, and trimethyltin decreased proliferation by at least 50% of control in either the ReN CX or mCNS cells. None of the chemicals tested activated caspase 3 or p53 in the ReN CX cells, while methylmercury, cadmium, dieldrin, chlorpyrifos oxon, trimethyltin, and glyphosate all induced at least a doubling in these apoptotic markers in the mCNS cells. Compared to control, cadmium, trans-retinoic acid, and trimethyltin decreased cell viability (ATP levels) by at least 50% in the ReN CX cells, while cadmium, dieldrin, and methylmercury decreased viability by at least 50% in the mCNS cells. Based on these results, BrdU is an appropriate marker for assessing chemical effects on proliferation, and human cells are more sensitive than mouse cells for this endpoint. By contrast, caspase 3 and p53 were altered by environmental chemicals in mouse, but not in human cells. Therefore, these markers are not appropriate to assess the ability of environmental chemicals to induce apoptosis in the ReN CX cells.

Retinoic acid-treated pluripotent stem cells undergoing neurogenesis present increased aneuploidy and micronuclei formation

The existence of loss and gain of chromosomes, known as aneuploidy, has been previously described within the central nervous system. During development, at least one-third of neural progenitor cells (NPCs) are aneuploid. Notably, aneuploid NPCs may survive and functionally integrate into the mature neural circuitry. Given the unanswered significance of this phenomenon, we tested the hypothesis that neural differentiation induced by all-trans retinoic acid (RA) in pluripotent stem cells is accompanied by increased levels of aneuploidy, as previously described for cortical NPCs in vivo. In this work we used embryonal carcinoma (EC) cells, embryonic stem (ES) cells and induced pluripotent stem (iPS) cells undergoing differentiation into NPCs. Ploidy analysis revealed a 2-fold increase in the rate of aneuploidy, with the prevalence of chromosome loss in RA primed stem cells when compared to naïve cells. In an attempt to understand the basis of neurogenic aneuploidy, micronuclei formation and survivin expression was assessed in pluripotent stem cells exposed to RA. RA increased micronuclei occurrence by almost 2-fold while decreased survivin expression by 50%, indicating possible mechanisms by which stem cells lose their chromosomes during neural differentiation. DNA fragmentation analysis demonstrated no increase in apoptosis on embryoid bodies treated with RA, indicating that cell death is not the mandatory fate of aneuploid NPCs derived from pluripotent cells. In order to exclude that the increase in aneuploidy was a spurious consequence of RA treatment, not related to neurogenesis, mouse embryonic fibroblasts were treated with RA under the same conditions and no alterations in chromosome gain or loss were observed. These findings indicate a correlation amongst neural differentiation, aneuploidy, micronuclei formation and survivin downregulation in pluripotent stem cells exposed to RA, providing evidence that somatically generated chromosomal variation accompanies neurogenesis in vitro.

The retinoid signaling pathway inhibits hematopoiesis and uncouples from the Hox genes during hematopoietic development

Retinoic acid (RA) is a well-established inducer of Hox genes during development of neurectoderm, however effects of RA on Hox expression are poorly defined in mesoderm and not defined in the hematopoietic compartment. Both Hox genes and retinoid signaling have been suggested to modulate hematopoietic stem cell (HSC) self-renewal, supporting the notion that RA signaling might drive HSC self-renewal through Hox gene induction. Here, we investigate this possibility by comprehensively evaluating Hox gene expression using mouse embryonic stem cells differentiated in vitro. In unspecified mesoderm, we find that RA coordinately upregulates anterior 3' Hox genes from clusters A, B, and C, and downregulates posterior 5' Hox genes from clusters A-D. However, hematopoietic development of mesoderm was inhibited by RA, and we find further that retinoids are entirely dispensable for hematopoiesis in vitro. More surprisingly, in fully specified hematopoietic progenitors, Hox genes are refractory to regulation by RA, although other RA targets are normally regulated. Pulses of RA exposure demonstrate that the Hox complexes are decoupled from RA regulation progressively in lateral plate mesoderm as it undergoes hematopoietic specification. Thus, Hox genes are targets of the RA pathway only in selected cell types, and are clearly not regulated by RA in the earliest hematopoietic progenitors. We propose that the developmental uncoupling of the Hox complexes protects the Hox code from potential RA signaling centers as HSCs migrate or circulate during development.

Differential antiapoptotic effect of erythropoietin on undifferentiated and retinoic acid-differentiated SH-SY5Y cells

Erythropoietin (Epo) is known to have a significant role in tissues outside the hematopoietic system. In this work, we investigated the function of Epo in cells of neuronal origin subjected to differentiation. Treatment of SH-SY5Y cells with all-trans-retinoic acid (atRA) generated differentiated neuron-like cells, observed by increased expression of neuronal markers and morphological changes. Exposure of undifferentiated cells to proapoptotic stimuli such as staurosporine, TNF-alpha, or hypoxia, significantly increased programmed cell death, which was prevented by previous treatment with Epo. In contrast, atRA-differentiated cultures showed cell resistance to apoptosis. No additional effect of Epo was detected in previously differentiated cells. The inhibition of the PI3K/Akt pathway by Ly294002 abrogated the protective effects induced by either Epo or atRA. The effect of atRA was mediated by an increased expression of Bcl-2 whereas the Epo treatment upregulated not only Bcl-2 but also Bcl-xL. This upregulation by Epo was not detected in atRA-differentiated cells, thus confirming the lack of the protective effect of Epo. As expected, assays with AG490, an inhibitor of Jak2, blocked the Epo action only in undifferentiated cells. This reduced neuroprotective function of Epo on SH-SY5Y differentiated cells could be explained at least in part by downregulation of the Epo receptor expression, which was observed in atRA-differentiated cells. This study shows differential cellular protection induced by Epo at two stages of SH-SY5Y differentiation. The results allow us to suggest that this differential cell behavior can be ascribed to the interaction between atRA and the signaling pathways mediated by Epo.

Selective proapoptotic activity of polyphenols from red wine on teratocarcinoma cell, a model of cancer stem-like cell

Cancer stem cells are expected to be responsible for tumor initiation and metastasis. These cells are therefore potential targets for innovative anticancer therapies. However, the absence of bona fide cancer stem cell lines is a real problem for the development of such approaches. Since teratocarcinoma cells are totipotent stem cells with a high degree of malignancy, we used them as a model of cancer stem cells in order to evaluate the anticancer chemopreventive activity of red wine polyphenols (RWPs) and to determine the underlying cellular and molecular mechanisms. We therefore investigated the effects of RWPs on the embryonal carcinoma (EC) cell line P19 which was grown in the same culture conditions as the most appropriate normal cell line counterpart, the pluripotent embryonic fibroblast cell line NIH/3T3. The present study indicates that RWPs selectively inhibited the proliferation of P19 EC cells and induced G1 cell cycle arrest in a dose-dependent manner. Moreover, RWPs treatment specifically triggered apoptosis of P19 EC cells in association with a dramatic upregulation of the tumor suppressor gene p53 and caspase-3 activation. Our findings suggest that the chemopreventive activity of RWPs on tumor initiation and development is related to a growth inhibition and a p53-dependent induction of apoptosis in teratocarcinoma cells. In addition, this study also shows that the EC cell line is a convenient source for studying the responses of cancer stem cells to new potential anticancer agents.

Reelin signals survival through Src-family kinases that inactivate BAD activity

Reelin plays an important role in the migration of embryonic neurons, but its continuing presence suggests additional functions in the brain. We now report a novel function where reelin protects P19 embryonal cells from apoptosis during retinoic acid-induced neuronal differentiation. This increased survival is associated with reelin activation of the phosphatidyl-inositol-3-kinase (PI3 K)/Akt pathway. When PI3 K was inhibited with LY294002, reelin failed to protect against this retinoic acid-induced apoptosis. The protective effect of reelin includes activating the Src-family kinases/PI3 K/Akt pathway which then led to selective phosphorylation of Bcl-2/Bcl-XL associated death promoter (BAD) at serine-136, while the phosphorylation-incompetent mutation of BAD (S136A) suppressed this protection. These and additional studies define a novel pathway where reelin binds apoE receptors, significantly activates the PI3 K/Akt pathway causing phosphorylation of BAD which helps to protect cells from apoptosing, thus serving an important role in promoting the survival of maturing neurons in the brain.

Suppression of PTEN expression during aggregation with retinoic acid in P19 mouse embryonal carcinoma cells

Apoptosis is thought to be involved in the maintenance of cellular homeostasis, as well as various pathological processes. However, little information is available about the regulation of apoptosis during the aggregation stage of P19 embryonal carcinoma (EC) cells. Here we report that aggregation-induced apoptosis is markedly attenuated by treatment with retinoic acid (RA). PTEN (phosphatase and tensin homolog deleted on chromosome 10) expression was down-regulated during the aggregation phase of P19 EC cells in the presence, but not in the absence, of RA. Suppression of PTEN expression during the aggregation was accompanied by increased phosphorylation of serine/threonine kinase Akt and glycogen synthase kinase-3beta (GSK-3beta). Our results suggest that RA attenuates the induction of apoptosis during the aggregation phase of P19 EC cells, probably by suppressing PTEN expression.

Increase in apoptosis with neural differentiation and shortening of the lifespan of P19 cells overexpressing tau

Apoptosis or programmed cell death is considered to be involved in neurodegenerative disorders including Alzheimer's disease (AD). AD is characterized by intracellular aggregates of hyperphosphorylated tau, a microtubule-associated protein. To investigate the effect of the overexpression of tau in P19 cells, we engineered P19 wild-type cells (P19wt) stably expressing human tau441 (P19tau). When P19tau cells were induced to undergo neural differentiation by treatment with retinoic acid (RA), a remarkable increase in apoptosis was observed. However, in the undifferentiated state, there was no notable difference of phenotype between P19wt and P19tau cells. Additionally, we found that tau dissociated from microtubules, and co-localized with the RA receptor (RAR) at nucleoli. Further, the lifespan of the differentiated P19tau cells was shorter than that of P19wt cells, and the re-treatment of differentiated P19wt cells with RA resulted in a reduction of lifespan. These observations suggested that tau affects RA signaling in apoptosis and lifespan during the neural differentiation induced by RA treatment.

Transcriptional repression induces a slowly progressive atypical neuronal death associated with changes of YAP isoforms and p73

Transcriptional disturbance is implicated in the pathology of polyglutamine diseases, including Huntington's disease (HD). However, it is unknown whether transcriptional repression leads to neuronal death or what forms that death might take. We found transcriptional repression-induced atypical death (TRIAD) of neurons to be distinct from apoptosis, necrosis, or autophagy. The progression of TRIAD was extremely slow in comparison with other types of cell death. Gene expression profiling revealed the reduction of full-length yes-associated protein (YAP), a p73 cofactor to promote apoptosis, as specific to TRIAD. Furthermore, novel neuron-specific YAP isoforms (YAPΔCs) were sustained during TRIAD to suppress neuronal death in a dominant-negative fashion. YAPΔCs and activated p73 were colocalized in the striatal neurons of HD patients and mutant huntingtin (htt) transgenic mice. YAPΔCs also markedly attenuated Htt-induced neuronal death in primary neuron and Drosophila melanogaster models. Collectively, transcriptional repression induces a novel prototype of neuronal death associated with the changes of YAP isoforms and p73, which might be relevant to the HD pathology.

In vitro differentiation of mouse embryonic stem cells: enrichment of endodermal cells in the embryoid body

Embryonic stem (ES) cells have the potential to differentiate into all three germ layers, providing new perspectives not only for embryonic development but also for the application in cell replacement therapies. Even though the formation of an embryoid body (EB) in a suspension culture has been the most popular method to differentiate ES cells into a wide range of cells, not much is known about the characteristics of EB cells. To this end, we investigated the process of EB formation in the suspension culture of ES cells at weekly intervals for up to 6 weeks. We observed that the central apoptotic area is most active in the first week of EB formation and that the cell adhesion molecules, except beta-catenin, are highly expressed throughout the examination period. The sequential expression of endodermal genes in EBs during the 6-week culture correlated closely with that of normal embryo development. The outer surface of EBs stained positive for alpha-fetoprotein and GATA-4. When isolated from the 2-week-old EB by trypsin treatment, these endodermal lineage cells matured in vitro into hepatocytes upon stimulation with various hepatotrophic factors. In conclusion, our results demonstrate that endodermal cells can be retrieved from EBs and matured into specific cell types, opening new therapeutic usage of these in vitro differentiated cells in the cell replacement therapy of various diseases.

In vitro model of normal, immortalized ovarian surface epithelial and ovarian cancer cells for chemoprevention of ovarian cancer

BACKGROUND

Epithelial ovarian cancer has the highest mortality rate among the gynecologic cancers. The synthetic retinoid, N-(4-hydroxyphenyl) retinamide (4-HPR), has been used in the chemoprevention of ovarian cancer. However, the effectiveness of its application for different populations has been questioned because of the genetic differences among normal, high risk, and women with cancer.

OBJECTIVE

To explore the similarities and the differences in 4-HPR effects on different ovarian epithelial cells which mimic different populations of women, normal ovarian surface epithelium to represent the normal population of women, immortalized ovarian surface epithelium to represent premalignant changes, and cells derived from ovarian cancer cells to represent malignant changes were used as in vitro models.

METHODS

Normal ovarian surface epithelial cells, immortalized ovarian surface epithelial cells, and ovarian cancer cells were incubated for different intervals with increasing concentrations of 4-HPR. Growth inhibition, the fraction of apoptotic cells, the expression of apoptosis-related genes, including p53, p16, p21, and caspase-3, and mitochondrial permeability transition were measured before and after 4-HPR treatment.

RESULTS

Treatment with 4-HPR produced growth inhibition and apoptosis in a dose-dependent manner for all 3 cell types. 4-HPR produced the strongest activation of the p53 pathway in normal ovarian epithelial (NOE) cells, while it caused the largest increase in MPT in the cancer cells, suggesting a different mechanism for growth inhibition and/or apoptosis in these cell lines. 4-HPR, at a concentration of 10 muM, had a maximal effect on caspase-3 activity at 72 h in normal cells and at 48 h in immortalized and cancer cells, although the effects were modest.

CONCLUSIONS

Normal ovarian surface epithelial cells, immortalized ovarian surface epithelial cells, and ovarian cancer cells showed a differential response to 4-HPR. Although the same endpoints of growth inhibition and apoptosis induction were present in response to 4-HPR, these endpoints may be regulated through different pathways.

IMPLICATIONS

Clinical trials with higher concentrations of 4-HPR should prove beneficial.

Beclin 1 augmented cis-diamminedichloroplatinum induced apoptosis via enhancing caspase-9 activity

Beclin 1, identified as a Bcl-2-interacting protein, is known to enhance autophagy. However, the effect of Beclin 1 on apoptotic signaling has remained unclear. Here, we show that overexpression of Beclin 1 in MKN28 human gastric cancer cells augmented cis-diamminedichloroplatinum (CDDP)-induced apoptosis. Conversely, "knockdown" of Beclin 1 by a small inhibitory RNA in MKN 1 cells attenuated this cytotoxicity. Furthermore, not only caspase-3/7 activities, but also caspase-9 activity was increased in Beclin 1 gene transfectants treated with CDDP, and caspase-9 inhibitor completely abolished augmentation of CDDP-induced apoptosis by Beclin 1 as did a caspase-3 inhibitor. Thus, Beclin 1 augments CDDP-induced apoptosis through enhancing caspase-9 activity and functions as a pro-apoptotic molecule.

Fas, FasL, Bcl-2, and Bax in the endometrium of rhesus monkey during the menstrual cycle

To study possible role and regulation of apoptosis occurred in primate endometrium, the expression of apoptosis-related molecules, Fas, FasL, B cell lymphoma/leukaemia-2 (Bcl-2), and Bax were analyzed in relation to occurrence of apoptosis and proliferation in the cycling endometrium of the rhesus monkey using immunohistochemistry and Western blot. The cell apoptosis and proliferation were evaluated by means of in situ 3'-end labeling and Ki67 immunostaining, respectively. The results showed that the expressions of Fas, Fas ligand (FasL), Bcl-2, and Bax were co-localized predominantly in the epithelial cells of the endometrium. Modest Fas staining with no obvious change was detected throughout the menstrual cycle, while the levels of FasL and Bax protein in the epithelial cells increased in the secretory phase when apoptosis was most prevalent. In contrast, epithelial immunostaining for Bcl-2 was maximal during the proliferative phase and decreased in the secretory phase. Bcl-2 immunoreactivity was also detected in some immunocytes. The coordinated expression of Fas, FasL, Bcl-2, and Bax in the cycling endometrium of the rhesus monkey suggests that the cyclic changes in endometrial growth and regression may be regulated by the balance of these factors under the action of ovary steroids.

Chronic neonatal hypoxia leads to long term decreases in the volume and cell number of the rat cerebral cortex

Preterm birth results in significant neurodevelopmental disability. The neonatal rodent model of chronic sublethal hypoxia faithfully mimics the effect of preterm birth on the developing brain. We employed this model to test the hypothesis that the hypoxia that accompanies preterm birth results in inappropriate signaling of apoptotic mechanisms in developing brain. We performed cortical cell counts, determinations of neuronal size and Western analyses of the apoptosis related proteins, Bcl-2 and Bax, in rat pups who were raised in chronic hypoxia (FiO2 9.5%) beginning on postnatal day 3 (P3) and extending for either 10 (P13) or 30 (P33) days. A third group of animals was exposed to 30 days of hypoxia followed by an additional 30 days in a normoxic environment (P63) to assess the potential for recovery from the initial effects of hypoxia. Age matched control pups were raised in room air throughout the experimental time period. Assessment of cortical cell number revealed a 25% reduction (P < 0.01) in total cell number following 30 days of hypoxic rearing. Glia were significantly reduced by 34% and 41% after 10 and 30 days of hypoxia, respectively, while neuron numbers were only significantly reduced (14%) after 30 days of hypoxia. Animals exposed to a hypoxic environment for 30 days followed by 30 days in a normoxic environment revealed some recovery of glial cell numbers, but no significant recovery of neuronal cell numbers. Measurement of cell size at both P13 and P33 revealed that neurons of layer III were significantly smaller in cross-sectional area in hypoxic compared with control rats (P < 0.01). However, no significant difference was noted in neuronal size following 30 days of normoxic recovery. Western blot analyses of Bcl-2 and Bax protein levels demonstrated a ratio favorable to Bax at multiple time points during the period of hypoxic exposure. These data suggest that chronic exposure to hypoxia during the perinatal period alters the production and maintenance of glial and neuronal cells and that glia and neurons demonstrate differential patterns of vulnerability and recovery following subsequent periods of normoxic exposure. It is hypothesized that the mechanisms responsible for these alterations in cortical cell number may depend on the state of differentiation of the different cell types at the time of hypoxic exposure.

Modulation of the retinoic acid-induced cell apoptosis and differentiation by the human TR4 orphan nuclear receptor

In our previous studies, the TR4 orphan nuclear receptor (TR4) has been demonstrated to suppress retinoic acid (RA)-induced transactivation via a negative feedback control mechanism and in situ analysis showed that TR4 is extensively expressed in mouse brain, especially in regions where the cells are proliferating. To further study the potential roles of TR4 during cell differentiation, a tetracycline-inducible system with anti-sense TR4 in teratocarcinoma P19 cell lines was generated to analyze the retinoic acid-induced differentiation of these cells. The results indicated that the expression of TR4 reduced by doxycycline anti-sense TR4 would alter the retinoic acid-induced differentiation pathway that results in the changes of cell morphology and cell cycle profile. Unexpectedly, our data further indicated that the RA-induced apoptosis, judging by DNA fragmentation, could also be altered by the induction of anti-sense TR4. Together, these findings provide the first in vivo evidence that an orphan nuclear receptor, such as TR4, may play major roles in the RA-mediated apoptosis or differentiation in P19 cells.

Glutamate mediates cell death and increases the Bax to Bcl-2 ratio in a differentiated neuronal cell line

Excessive stimulation of the NMDA receptor by glutamate induces cell death and has been implicated in the development of several neurodegenerative diseases. While apoptosis plays a role in glutamate-mediated toxicity, the mechanisms underlying this process have yet to be completely determined. Recent evidence has shown that exposure to excitatory amino acids regulates the expression of the antiapoptotic protein, Bcl-2, and the proapoptotic protein, Bax, in neurons. Since it has been suggested that the ratio of Bax to Bcl-2 is an important determinant of neuronal survival, the reciprocal regulation of these Bcl-2 family proteins may play a role in the neurotoxicity mediated by glutamate. Here, we have used a differentiable neuronal cell line, N1E-115, to investigate the molecular properties of glutamate-induced cell death. Annexin V staining was used to determine apoptotic cell death between 0 and 5 days differentiation with DMSO/low serum. Immunoblot analysis was used to determine whether the expression of Bcl-2 or Bax was modulated during the differentiation process. Bcl-2 protein levels were increased during maturation while Bax expression remained unchanged. Maximum Bcl-2 expression was observed following 5 days of differentiation. Examination of Bcl-2 and Bax following glutamate treatment revealed that the expression of these proteins was inversely regulated. Exposure to glutamate (0.001-10 mM) for 20+/-2 h resulted in a dose-dependent decrease in cell survival (as measured by MTT analysis) that was maximal at 10 mM. These results further support the role of apoptosis in glutamate-mediated cell death. Furthermore, a significant decrease in Bcl-2 levels was observed at 1 mM and 10 mM glutamate (32.1%+/-4.8 and 33.7+/-12.8%, respectively) while a significant upregulation of Bax expression (88.2+/-17.9%) was observed at 10 mM glutamate. Interestingly, Bcl-2 and Bax levels in cells treated with glutamate from 12-24 h were not significantly different from those of control. Taken together, these findings provide additional evidence for the reciprocal regulation of Bcl-2 and Bax expression by glutamate and suggest that neuronal excitotoxicity may, in part, result from the inverse regulation of these proteins.

Enhanced in vitro midbrain dopamine neuron differentiation, dopaminergic function, neurite outgrowth, and 1-methyl-4-phenylpyridium resistance in mouse embryonic stem cells overexpressing Bcl-XL

Embryonic stem (ES) cells provide a potentially unlimited source of specialized cells for regenerative medicine. The ease of inducing stable genetic modifications in ES cells allows for in vitro manipulations to enhance differentiation into specific cell types and to optimize in vivo function of differentiated progeny in animal models of disease. We have generated mouse ES cells that constitutively express Bcl-XL, an antiapoptotic protein of Bcl-2 family. In vitro differentiation of Bcl-XL overexpressing ES (Bcl-ES) cells resulted in higher expression of genes related to midbrain dopamine (DA) neuron development and increased the number of ES-derived neurons expressing midbrain DA markers compared with differentiation of wild-type ES cells. Moreover, DA neurons derived from Bcl-ES cells were less susceptible to 1-methyl-4-phenylpyridium, a neurotoxin for DA neurons. On transplantation into parkinsonian rats, the Bcl-ES-derived DA neurons exhibited more extensive fiber outgrowth and led to a more pronounced reversal of behavioral symptoms than wild-type ES-derived DA neurons. These data suggest a role for Bcl-XL during in vitro midbrain DA neuron differentiation and provide an improved system for cell transplantation in a preclinical animal model of Parkinson's disease.

Retinoids as a potential treatment for experimental puromycin-induced nephrosis

1 Puromycin aminonucleoside (PAN)-induced nephrosis is a model of human minimal change disease. In rats, PAN induces nephrotic-range proteinuria, renal epithelial cell (podocyte) damage, infiltration of mononuclear leukocytes, and apoptosis of several renal cell types. 2 Retinoic acid (RA) modulates a wide range of biological processes, such as inflammation and apoptosis. Since renal damage by PAN is characterized by inflammatory infiltration and epithelial cell death, the effect of treatment with all-trans RA (tRA) was examined in the PAN nephrosis model and in the cultured differentiated podocyte. 3 Treatment with tRA 4 days after PAN injection did not inhibit the proteinuria peak but reversed it significantly. However, treatment with tRA both before and 2 days after the injection of PAN protected the glomerular epithelial cells, diminishing the cellular edema and diffuseness of the foot process effacement. Preservation of the podocyte architecture correlated with the inhibition of proteinuria. The anti-inflammatory effect of tRA was evidenced by the inhibition of PAN-induced interstitial mononuclear cell infiltration and the decreased renal expression of two molecules involved in monocyte infiltration: fibronectin and monocyte chemoattractant protein-1. TUNEL assays showed that tRA inhibited the PAN-induced apoptosis of cultured differentiated mouse podocytes. 4 We conclude that tRA treatment may prevent proteinuria by protecting the podocytes from injury and diminishing the interstitial mononuclear infiltrate in the model of PAN nephrosis. Retinoids are a potential new treatment for kidney diseases characterized by proteinuria and mononuclear cell infiltration.

Early programmed cell death in human NT2 cell cultures during differentiation induced by all-trans-retinoic acid

Previous studies have demonstrated that programmed cell death takes place at different stages during the development of the CNS in vivo. Our purpose in this study was to detect early programmed cell death associated with the induction of differentiation by retinoic acid (RA) in the NT2 cell line. By using the annexin V labeling as a marker of apoptosis, a significant apoptotic cell death was quantified during the third and the fourth days of the RA treatment. Double-labeling studies using the staining of the genomic DNA strand breaks with the terminal deoxyribosyl-transferase-mediated dUTP nick end-labeling (TUNEL) assay and either nestin or microtubule-associated protein 2 (MAP2) showed that 1) the early apoptotic cell death affected mostly nestin-positive cells and 2) after 8 days of differentiation, although cells with neuronal phenotypes are present, no colabeled TUNEL/MAP2 cells were detected. With regard to the neuronal protein MAP2, we observed discrete immunolabeling of a few NT2 cells as early as day 3 of the differentiation and a significant emergence of MAP2-immunopositive cells at days 6-8. Thus, our results show that, when as a whole the differentiating NT2 cell population is considered, 1) the apoptotic cell death observed during the third day of differentiation occurs mostly in undifferentiated cells, 2) this process coincides with the first detection of the neuronal phenotype in NT2 cell cultures, and 3) the end of the cell death period in NT2 cell cultures is marked by both the accumulation of MAP2-positive cells and the beginning of expression of the Bcl-2 protein in the cultures.

Retinoic acid decreases the viability of mouse blastocysts in vitro

BACKGROUND

This study was designed to examine the cytotoxic effect of retinoic acid on the blastocyst stage of mouse embryos and on subsequent early postimplantation embryo development in vitro.

METHODS AND RESULTS

Mouse blastocysts were exposed for 24 h to doses of 0, 0.1 micromol/l and 10 micromol/l all-trans retinoic acid and observed for their capacity to implant and develop during the early postimplantation period in vitro. When retinoic acid-pretreated blastocysts were allowed to implant in vitro, significantly fewer embryos were able to reach a later stage of embryo development. Compared with the findings for the control blastocysts, exposure to retinoic acid resulted in a significant reduction in the average number of total cells in blastocysts and the trophectoderm/inner cell mass lineage. The effect was associated with a significant increase in the frequency of cells identified as being engaged in apoptosis by means of the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling and Annexin V techniques.

CONCLUSIONS

This is the first evidence that retinoic acid induces cell death (apoptosis) and inhibits cell proliferation in mouse blastocysts. This results in the retardation of early postimplantation blastocyst development and subsequent blastocyst death.

Phase I/II trial of accutane as a potentiator of carboplatin and paclitaxel in squamous cell carcinomas

This study investigated the toxicity and efficacy of a 13-cis retinoic acid, carboplatin, and paclitaxel (Taxol) regimen in 18 patients with recurrent or metastatic squamous cell carcinomas (12 head and neck, 4 cervix, 1 esophagus, and 1 anus). Three patients were treated at each dose level with fenretamide (Accutane) 1 mg/kg/d orally for 14 days, carboplatin AUC of 5 mg/ml.min intravenously (IV) and paclitaxel at a dose of 135, 155, 175, 195, 205, or 225 mg/m(2) IV on day 8 every 4 weeks for 6 cycles. Fifteen evaluable patients had a total of 72 treatment cycles. There were 21 grade III or IV toxicities distributed among all the dose levels, including neutropenia, anemia, thrombocytopenia, elevated prothrombin time/partial thromboplastin time, elevated alkaline phosphatase, weight loss, alopecia, and three deaths from aspiration pneumonia and septic shock. The maximum tolerated dosage included 205 mg/m(2) paclitaxel. There was one complete response, three partial responses, and 2 stable diseases. The three partial responses were in the four patients with cervical cancer. Responses did not correlate with expression of retinoic acid receptor subtypes. Toxicity profiles and overall response rates were comparable to prior studies with similar chemotherapy regimens alone. The data support further study in a phase II trial.

Interaction between mutant ataxin-1 and PQBP-1 affects transcription and cell death

PQBP-1 was isolated on the basis of its interaction with polyglutamine tracts. In this study, using in vitro and in vivo assays, we show that the association between ataxin-1 and PQBP-1 is positively influenced by expanded polyglutamine sequences. In cell lines, interaction between the two molecules induces apoptotic cell death. As a possible mechanism underlying this phenomenon, we found that mutant ataxin-1 enhances binding of PQBP-1 to the C-terminal domain of RNA polymerase II large subunit (Pol II). This reduces the level of phosphorylated Pol II and transcription. Our results suggest the involvement of PQBP-1 in the pathology of spinocerebellar ataxia type 1 (SCA1) and support the idea that modified transcription underlies polyglutamine-mediated pathology.

Expression of selected apoptosis related genes, MIF, IGIF and TNF alpha, during retinoic acid-induced neural differentiation in murine embryonic stem cells

Apoptosis plays an important role during embryonic development. Apoptotic cell death is executed by caspases and can be regulated by the Bcl-2 family of genes. Ribonuclease protection assay was used to investigate the expression of selected apoptosis-related genes of the Bcl-2 family, pro-apoptotic Bax, Bad and anti-apoptotic Bcl-2, during differentiation of murine embryonic stem cells (ES) mediated by all-trans-retinoic acid. The mRNA expression of caspase 3, caspase 6 and certain pro-inflammatory cytokines was also investigated simultaneously. ES cells exposed to 1 microM all-trans-retinoic acid on day 8, 9 and 10 of differentiation revealed increased expression of Bax and Bad compared to the vehicle-treated cells. No effect on Bcl-2 mRNA was noted after all-trans-retinoic acid treatment. Increased mRNA expression of caspase 3 and caspase 6 in all-trans-retinoic acid-exposed ES cells suggested that caspases play an important role in retinoic acid-mediated apoptosis during ES differentiation. Increase in the expression of TNF alpha and macrophage migration inhibitory factor (MIF) was noted in retinoic acid-treated cells on day 14. Significant increase observed in interferon gamma inducing factor (IGIF/IL-18) mRNA expression in all-trans-retinoic acid-treated cells on day 14 and 17 did not translate to increased INF gamma expression. No change in the expression of other pro-inflammatory cytokines was noted with all-trans-retinoic acid treatment. The function of TNF alpha, IGIF/IL-18 and MIF in all-trans-retinoic acid-treated cells during ES differentiation and apoptosis is still speculatory. Results suggested that RA-mediated apoptosis during neural differentiation of ES cells involves up-regulation of caspase 3, caspase 6, Bad, and Bax.

Role and distribution of retinoic acid during CNS development

Retinoic acid (RA), the biologically active derivative of vitamin A, induces a variety of embryonal carcinoma and neuroblastoma cell lines to differentiate into neurons. The molecular events underlying this process are reviewed with a view to determining whether these data can lead to a better understanding of the normal process of neuronal differentiation during development. Several transcription factors, intracellular signaling molecules, cytoplasmic proteins, and extracellular molecules are shown to be necessary and sufficient for RA-induced differentiation. The evidence that RA is an endogenous component of the developing central nervous system (CNS) is then reviewed, data which include high-pressure liquid chromotography (HPLC) measurements, reporter systems and the distribution of the enzymes that synthesize RA. The latter is particularly relevant to whether RA signals in a paracrine fashion on adjacent tissues or whether it acts in an autocrine manner on cells that synthesize it. It seems that a paracrine system may operate to begin early patterning events within the developing CNS from adjacent somites and later within the CNS itself to induce subsets of neurons. The distribution of retinoid-binding proteins, retinoid receptors, and RA-synthesizing enzymes is described as well as the effects of knockouts of these genes. Finally, the effects of a deficiency and an excess of RA on the developing CNS are described from the point of view of patterning the CNS, where it seems that the hindbrain is the most susceptible part of the CNS to altered levels of RA or RA receptors and also from the point of view of neuronal differentiation where, as in the case of embryonal carcinoma (EC) cells, RA promotes neuronal differentiation. The crucial roles played by certain genes, particularly the Hox genes in RA-induced patterning processes, are also emphasized.

Differentiation-associated apoptosis of neural stem cells is effected by Bcl-2 overexpression: impact on cell lineage determination

Apoptosis is an integral part of neural development. To elucidate the importance of programmed cell death on cell lineage determination we utilized murine PCC7-Mzl cells, a model system for neural differentiation. Treatment of pluripotent PCC7-Mzl stem cells with 0.1 microM all-trans retinoic acid (RA) causes a cease of proliferation and an initiation of differentiation into neurons, glial cells and fibroblasts. Simultaneously, a fraction of the cell culture (ca. 25%) dies within 24 h by apoptosis. We transfected PCC7-Mzl cells with the human bcl-2 cDNA and generated PCC7-Mz-Bcl-2 cell lines expressing two- to tenfold higher levels of Bcl-2 than parental cells. Overexpression of Bcl-2 resulted in hypophosphorylation of the retinoblastoma (Rb) protein and consequently prolonged the doubling time of the culture from 18 h to 23 h. RA-induced apoptosis was drastically reduced to 3 to 15% depending on the level of Bcl-2 expression. RA-induced caspase activation, cytochrome c release from the mitochondria to the cytosol and DNA fragmentation was completely blocked. Furthermore, treating Bcl-2 cultures with ceramide (10 microM), a second messenger mediating the RA-initiated death signal in parental cells, no longer caused DNA laddering. Bcl-2 overexpression did not interfere with the potential of PCC7-Mz cells to develop into neurons, glial cells and fibroblasts. However, the relative distribution of cell types in the culture was shifted such that the fraction of neurons was reduced to half (from 60 to 30%) with a concomitant increase in the number of glial and fibroblastoid cells. Furthermore, Bcl-2-overexpressing neurons, but not neurons of parental or mock-transfected PCC7-Mzl cultures, were able to grow as single cells.

Proteomic characterization of early-stage differentiation of mouse embryonic stem cells into neural cells induced by all-trans retinoic acid in vitro

Embryonic stem (ES) cells are totipotent stem cells, which can differentiate into various kinds of cell types, including neurons. They are widely used as a model system for investigating mechanisms of differentiation events during early mouse development. In this study, proteomic techniques were used to approach the protein profile associated with the early-stage differentiation of ES cells into neuronal cells induced by all-trans retinoic acid (ATRA) in vitro. In comparison of the protein profile of parent ES cells with that of ES-derived neural-committed cells, which was induced by ATRA for four days, 24 differentially displayed protein spots were selected from two-dimensional electrophoresis (2-DE) gels for further protein identification by pepide mass fingerprinting (PMF). Nine proteins were known to being involved in the process of neural differentiation and/or neural survival. Of those, alpha-3/alpha-7 tubulin and vimentin were down-regulated, while cytokeratin 8, cytokeratin 18, G1/S-special cyclin D2, follistatin-related protein, NEL protein, platelet-activating factor acetylhydrolase IB alpha-subunit, and thioredoxin peroxidase 2 were upregulated during differentiation of ES cells to neural cells. Additionally, other 12 protein (five upregulated and seven downregulated) spots associated with ES cell differentiation into neuronal cells were not matched to known proteins so far, implicating that they might be novel proteins. The results above indicated that the molecular mechanisms of differentiation of ES cells to neural cells in vitro might be similar to those of other neural systems in vitro and identified that proteomic analysis is an effective strategy to comprehensively unravel the regulatory network of differentiation.

EAT/mcl-1 expression in the human embryonal carcinoma cells undergoing differentiation or apoptosis

Differentiation and apoptosis are precisely regulated events in early embryogenesis. Retinoic acid-induced differentiation in the embryonal carcinoma (EC) cell line NCR-G3 triggers concurrent induction of apoptosis. Using this system, which serves as a model of early embryogenesis, the expression of various bcl-2-related genes was analyzed as these genes display either positive or negative regulatory effects on apoptosis. EAT/mcl-1, an antiapoptotic bcl-2-related gene and immediate early gene, was dramatically expressed at an early stage of NCR-G3 differentiation. Bcl-xL, another antiapoptotic gene, was induced at a middle stage of differentiation and then gradually decreased to basal level. Expression of Bax, a proapoptotic molecule, was detected at a high level and remained relatively constant. Meanwhile, Bcl-2 and Bcl-xS were below detectable levels throughout the various stages of differentiation. As the balance of bcl-2 genes is a crucial regulatory step in apoptosis, the results suggest that EAT and Bax likely regulate apoptosis in the early stages of differentiation. In later stages of differentiation, down-regulation of EAT was found to coincide with a gradual increase in apoptosis of NCR-G3 cells. Furthermore, use of the monoclonal antibody (3A2) specific to EAT revealed that EAT is localized to the outer mitochondrial membrane in human EC cells. In addition, EAT immunoreactivity was not detected in apoptotic NCR-G3 cells while it was observed in nearly all viable cells. The findings suggest that rapid induction of EAT may prevent NCR-G3 cells from undergoing apoptosis, thereby supporting viability at the early stage of differentiation.

Retinoic acid reduces apoptosis and oxidative stress by preservation of SOD protein level

Retinoic acid (RA) has already been shown to exert antiapoptotic and antioxidative activity in various cells. In this study, we determined the effect of RA on the mRNA and protein levels of the Cu-,Zn-superoxide dismutase (SOD-1) and Mn-superoxide dismutase (SOD-2) during staurosporine-induced apoptosis in primary cultures from neonatal rat hippocampus. Exposure to staurosporine (300 nM, 24 h) increased the percentage of apoptotic neurons to 62% compared with 18% in controls. We determined an increase in the reactive oxygen species (ROS) content from 4 up to 48 h after the induction of the injury. Treatment with staurosporine did not significantly change the mRNA levels of SOD-1 and SOD-2. However, the SOD-1 and SOD-2 protein levels markedly decreased 24 and 48 h after the addition of staurosporine. Compared with staurosporine-exposed controls, RA (10 nM)-treated cultures showed a significant increase in neuronal survival, a reduced neuronal ROS content, and enhanced protein levels of SOD-1 and SOD-2 24 and 48 h after the start of the exposure to staurosporine. The results suggest that RA reduced staurosporine-induced oxidative stress and apoptosis by preventing the decrease in the protein levels of SOD-1 and SOD-2, and thus supported the antioxidant defense system.

Antisense inhibition of BCL-2 expression induces retinoic acid-mediated cell death during differentiation of human NT2N neurons

Changes in expression of the proto-oncogene Bcl-2 are well known in the developing brain, with a high expression level in young post-mitotic neurons that are beginning the outgrowth of processes. The physiological significance of the Bcl-2 up-regulation in these neurons is not fully understood. We used a differentiation model for human CNS neurons to study the expression and function of Bcl-2. NT2/D1 human neuronal precursor cells differentiated into a neuronal phenotype in the presence of 10 microM retinoic acid for 3-5 weeks. This concentration of retinoic acid was not toxic to undifferentiated NT2/D1 cells but was sufficient to up-regulate the BCL-2 protein in 6 days. The BCL-2 levels increased further after 3 weeks, i.e. when the cells started to show neuronal morphology. Inhibition of the accumulation of endogenous BCL-2 with vectors expressing the antisense mRNA of Bcl-2 caused extensive apoptosis after 3 weeks of the retinoic acid treatment. The loss of neuron-like cells from differentiating cultures indicated that the dead cells were those committed to neuronal differentiation. Death was related to the presence of retinoic acid since withdrawal of retinoic acid after 16 days of treatment dramatically increased cell surviving. The ability of BCL-2 to prevent retinoic acid-induced cell death was also confirmed in undifferentiated NT2/D1 cells that were transfected with a vector containing Bcl-2 cDNA in sense orientation and exposed to toxic doses (40-80 microM) of retinoic acid. Furthermore, down-regulation of BCL-2 levels by an antisense oligonucleotide in neuronally differentiated NT2/D1 cells increased their susceptibility to retinoic acid-induced apoptosis. These results indicate that one function of the up-regulation of endogenous BCL-2 during neuronal differentiation is to regulate the sensitivity of young post-mitotic neurons to retinoic acid-mediated apoptosis.

Effects of protease inhibitors and antioxidants on In vitro survival of porcine primordial germ cells

One of the problems associated with in vitro culture of primordial germ cells (PGCs) is the large loss of cells during the initial period of culture. This study characterized the initial loss and determined the effectiveness of two classes of apoptosis inhibitors, protease inhibitors, and antioxidants on the ability of porcine PGCs to survive in culture. Results from electron microscopic analysis and in situ DNA fragmentation assay indicated that porcine PGCs rapidly undergo apoptosis when placed in culture. Additionally, alpha(2)-macroglobulin, a protease inhibitor and cytokine carrier, and N:-acetylcysteine, an antioxidant, increased the survival of PGCs in vitro. While other protease inhibitors tested did not affect survival of PGCs, all antioxidants tested improved survival of PGCs (P: < 0.05). Further results indicated that the beneficial effect of the antioxidants was critical only during the initial period of culture. Finally, it was determined that in short-term culture, in the absence of feeder layers, antioxidants could partially replace the effect(s) of growth factors and reduce apoptosis. Collectively, these results indicate that the addition of alpha(2)-macroglobulin and antioxidants can increase the number of PGCs in vitro by suppressing apoptosis.

Characterization of the mouse nuclear orphan receptor TR2-11 gene promoter and its potential role in retinoic acid-induced P19 apoptosis

The complete mouse orphan nuclear receptor TR2-11 gene structure and its 5'-untranscribed region were characterized. This gene contains 14 exons, with the first exon encoding only the 5'-untranslated sequence. The regulatory region of this gene was characterized by using reporter assays that define the minimal promoter activity in a sequence 212 nucleotides upstream from the translation initiation site. Furthermore, it was concluded that splicing of intron 1 is required for efficient promoter activity. Reporters driven by this promoter were induced by retinoic acid (RA) in COS-1 cells supplied with exogenous retinoic acid receptor-alpha (RAR(alpha)) and retinoid receptor X-beta (RXR(beta)). Binding of RAR(alpha)/RXR(beta) to the minimal promoter region was demonstrated in gel retardation assays. In P19 cells, both the endogenous TR2-11 gene and the reporters driven by this promoter were induced by RA in a protein synthesis-independent manner, and overexpression of TR2-11 protein resulted in cellular apoptosis in the absence of RA. The regulation of TR2-11 by RA and the implication of TR2 up-regulation in P19 cellular apoptosis are discussed.

Retinoic acid-mediated enhancement of the cholinergic/neuronal nitric oxide synthase phenotype of the medial septal SN56 clone: establishment of a nitric oxide-sensitive proapoptotic state

It is unclear what mechanisms lead to the degeneration of basal forebrain cholinergic neurons in Alzheimer's or other human brain diseases. Some brain cholinergic neurons express neuronal nitric oxide (NO) synthase (nNOS), which produces a free radical that has been implicated in some forms of neurodegeneration. We investigated nNOS expression and NO toxicity in SN56 cells, a clonal cholinergic model derived from the medial septum of the mouse basal forebrain. We show here that, in addition to expressing choline acetyltransferase (ChAT), SN56 cells express nNOS. Treatment of SN56 cells with retinoic acid (RA; 1 microM) for 48 h increased ChAT mRNA (+126%), protein (+88%), and activity (+215%) and increased nNOS mRNA (+98%), protein (+400%), and activity (+15%). After RA treatment, SN56 cells became vulnerable to NO excess generated with S-nitro-N-acetyl-DL-penicillamine (SNAP) and exhibited increased nuclear DNA fragmentation that was blocked with a caspase-3 inhibitor. Treatment with dexamethasone, which largely blocked the RA-mediated increase in nNOS expression, or inhibition of nNOS activity with methylthiocitrulline strongly potentiated the apoptotic response to SNAP in RA-treated SN56 cells. Caspase-3 activity was reduced when SNAP was incubated with cells or cell lysates, suggesting that NO can directly inhibit the protease. Thus, whereas RA treatment converts SN56 cells to a proapoptotic state sensitive to NO excess, endogenously produced NO appears to be anti-apoptotic, possibly by tonically inhibiting caspase-3.

Cell cycle regulators in neural stem cells and postmitotic neurons

In the mammalian central nervous system, neurons withdraw from the cell cycle immediately after their differentiation from proliferative neuroepithelial cells. Even while postmitotic neurons remain in permanent mitotic quiescence, they express a number of cell cycle regulators required for cell cycle progression. This review focuses on the expression and functions of members of the retinoblastoma protein (Rb) family (Rb, p107, p130) and necdin, all of which are growth suppressors that interact with the viral oncoproteins and the E2F family proteins. These molecules are differentially expressed in proliferative neural progenitors and postmitotic neurons in the developing neuroepithelium in vivo and differentiating embryonal carcinoma cells in vitro. During neurogenesis, dysfunction of the Rb family proteins causes impaired neuronal differentiation accompanied by cell death (apoptosis). Thus, the Rb family proteins are essential for both terminal mitosis of neuronal progenitors and survival of nascent neurons. However, the Rb family proteins seem to be dispensable for the maintenance of the postmitotic state of terminally differentiated neurons. Necdin is expressed exclusively in postmitotic cells and may contribute to their permanent mitotic arrest. These cell cycle regulators coordinately act in the generation, survival and demise of postmitotic neurons.

All-trans-retinoic acid effects the growth, differentiation and apoptosis of normal human myeloid progenitors derived from purified CD34+ bone marrow cells

We have previously shown that all-trans retinoic acid (ATRA) increases the number of CFU-GM colonies grown from unseparated human bone marrow cells with crude sources of colony stimulating factors. In this study, we further characterized the effect of ATRA on the growth of CFU-GM stimulated by individual cytokines from multiple samples of CD34+ enriched or purified human bone marrow cells. The number of IL-3- or GM-CSF-induced CFU-GM with 3 x 10(-7) M ATRA was 3.25+/-1.13, and 2.17+/-0.8-fold greater respectively, compared to controls without ATRA, while G-CSF had no effect and the ratio of colony-induced with or without ATRA was 1.06+/-0.17 (P = 0.00012). No colonies grew with ATRA + IL-6 or ATRA without a cytokine. Maximum enhancing effect on IL-3-induced CFU-GM occurred when ATRA was added on day 2, gradually diminished when delaying ATRA, and in cultures of day 9 or older adding ATRA had no effect. In 14 days liquid cultures of purified CD34+ cells with IL-3, ATRA increased the number of myeloid differentiated cells to 91-95%, compared to 37-70% with IL-3 alone. In addition, the number of apoptotic cells using the annexin V method increased after 14 days from 5.1% with IL-3 to 17.1% with IL-3 + ATRA and by the TUNEL in situ method from 10-26% to 60-95%, respectively. This study demonstrates that ATRA consistently enhances the growth of myeloid progenitors from CD34+ cells. This effect is dependent on the stimulating cytokine, suggesting the myeloid cells responding to ATRA are the less mature CFU-GMs that are targets of IL-3 and GM-CSF and not the G-CSF-responding mature progenitors. The growth stimulation by ATRA and IL-3 is also associated with granulocyte differentiation and increased apoptosis. These studies further suggest a potential role of pharmacological doses of ATRA on the development of normal human hematopoietic cells.

Effect of 9-cis-retinoic acid on oral squamous cell carcinoma cell lines

Retinoic acid (RA) has been shown to be effective in suppressing premalignant lesions and preventing second primary malignancies in patients cured of squamous cell carcinoma of the head and neck. However, the precise mechanisms of these effects are still uncertain. In the present study, we examined the effect of 9-cis-RA on the growth of six oral cancer cell lines (HSC-2, HSC-3, HSC-4, Ca9-22, Ho-1-N-1 and Ho-1-u-1). In addition, the relationship among growth and differentiation of tumor cells, RA responsiveness and the expression of nuclear retinoic acid receptors were also investigated. Among the six cell lines examined, five (HSC-2, HSC-3, HSC-4, Ca9-22 and Ho-1-u-1) displayed growth inhibition after treatment with 1x10(-6) M 9-cis-RA, while Ho-1-N-1 cells were resistant to 9-cis-RA. The expression level of RARbeta in 9-cis-RA resistant Ho-1-N-1 cells was very low in comparison with the sensitive cell lines. On the other hand, all of the six the cell lines expressed RARalpha, RARgamma, and RXRalpha at various levels. 9-cis-RA induced accumulation of cell population in G1 phase in HSC-3 cells on the 6th day of the treatment, followed by a marked reduction in the levels of hyperphosphorylated pRB, whereas p53 level was not altered. Interestingly, 9-cis-RA induced transiently the expression of p21(Waf1/Cip1), p27(Kip1), p300, CBP, BAX, Bak and bcl-2 proteins, respectively. This effect was associated with reduction of cyclin D1, cdk4 and CDK-activating kinase (cyclin H and cdk7) protein in HSC-3 cells. These results suggest that the growth inhibitory effect of 9-cis-RA on oral squamous cell carcinoma may depend on the expression levels of RARs, especially RARbeta proteins and RXRalpha proteins, and that 9-cis-RA may provide a powerful therapeutic agent for head and neck cancers.

Apoptosis and regulation of Bax and Bcl-X proteins during human neonatal vascular remodeling

To verify that apoptosis is one of the possible mechanisms of neonatal vascular remodeling during the transition from fetal to neonatal circulation, we assayed for apoptosis and evaluated the expression of apoptosis-regulatory proteins in umbilical vessel versus ascending aorta, ductus arteriosus (DA) versus adjacent pulmonary artery and aorta, or aorta versus its branching arteries. Twenty-two umbilical cords (UCs), 6 DAs with adjacent aortas and pulmonary arteries, and 4 aortic arches with their branching great arteries were obtained from neonates. Smooth muscle cell (SMC) apoptosis in umbilical vessels was identified in all UCs. The expressions of Bax and Bcl-X were stronger in umbilical artery than in the neonatal aorta, but Bcl-2 was weak in both arteries in immunohistochemistry. In the immunoblot analysis of UCs, the expression of the proapoptotic short isoform of Bcl-X was stronger than in other tissue, and caspase-3 was selectively activated, whereas it was not in the other components of the cardiovascular system. In contrast, the expression patterns of the FasAg and Fas ligand were similar in umbilical artery and aorta. Regulation of Bcl-2 family proteins was also observed in other vascular sites at which SMCs undergo apoptosis on hemodynamic changes during birth, such as the DA and the branching points of the great arteries from the aortic arch. Apoptosis is involved in the regression of human umbilical vessels and the DA and in the remodeling of the branching great arteries during the neonatal period, when Bcl-2 family proteins are likely to play a key role.