Retinoic acid rapidly decreases phosphatidylinositol turnover during neuroblastoma cell differentiation

Designing Small Molecule PI3Kγ Inhibitors: A Review of Structure-Based Methods and Computational Approaches

The PI3K/AKT/mTOR pathway plays critical roles in a wide array of biological processes. Phosphatidylinositol 3-kinase gamma (PI3Kγ), a class IB PI3K family member, represents a potential therapeutic opportunity for the treatment of cancer, inflammation, and autoimmunity. In this Perspective, we provide a comprehensive overview of the structure, biological function, and regulation of PI3Kγ. We also focus on the development of PI3Kγ inhibitors over the past decade and emphasize their binding modes, structure-activity relationships, and pharmacological activities. The application of computational technologies and artificial intelligence in the discovery of novel PI3Kγ inhibitors is also introduced. This review aims to provide a timely and updated overview on the strategies for targeting PI3Kγ.

Multi-species transcriptome meta-analysis of the response to retinoic acid in vertebrates and comparative analysis of the effects of retinol and retinoic acid on gene expression in LMH cells

Background

Retinol (RO) and its active metabolite retinoic acid (RA) are major regulators of gene expression in vertebrates and influence various processes like organ development, cell differentiation, and immune response. To characterize a general transcriptomic response to RA-exposure in vertebrates, independent of species- and tissue-specific effects, four publicly available RNA-Seq datasets from Homo sapiens, Mus musculus, and Xenopus laevis were analyzed. To increase species and cell-type diversity we generated RNA-seq data with chicken hepatocellular carcinoma (LMH) cells. Additionally, we compared the response of LMH cells to RA and RO at different time points.

Results

By conducting a transcriptome meta-analysis, we identified three retinoic acid response core clusters (RARCCs) consisting of 27 interacting proteins, seven of which have not been associated with retinoids yet. Comparison of the transcriptional response of LMH cells to RO and RA exposure at different time points led to the identification of non-coding RNAs (ncRNAs) that are only differentially expressed (DE) during the early response.

Conclusions

We propose that these RARCCs stand on top of a common regulatory RA hierarchy among vertebrates. Based on the protein sets included in these clusters we were able to identify an RA-response cluster, a control center type cluster, and a cluster that directs cell proliferation. Concerning the comparison of the cellular response to RA and RO we conclude that ncRNAs play an underestimated role in retinoid-mediated gene regulation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07451-2.

Incorporating genomic, transcriptomic and clinical data: a prognostic and stem cell-like MYC and PRC imbalance in high-risk neuroblastoma

BACKGROUND

Previous studies suggested that cancer cells possess traits reminiscent of the biological mechanisms ascribed to normal embryonic stem cells (ESCs) regulated by MYC and Polycomb repressive complex 2 (PRC2). Several poorly differentiated adult tumors showed preferentially high expression levels in targets of MYC, coincident with low expression levels in targets of PRC2. This paper will reveal this ESC-like cancer signature in high-risk neuroblastoma (HR-NB), the most common extracranial solid tumor in children.

METHODS

We systematically assembled genomic variants, gene expression changes, priori knowledge of gene functions, and clinical outcomes to identify prognostic multigene signatures. First, we assigned a new, individualized prognostic index using the relative expressions between the poor- and good-outcome signature genes. We then characterized HR-NB aggressiveness beyond these prognostic multigene signatures through the imbalanced effects of MYC and PRC2 signaling. We further analyzed Retinoic acid (RA)-induced HR-NB cells to model tumor cell differentiation. Finally, we performed in vitro validation on ZFHX3, a cell differentiation marker silenced by PRC2, and compared cell morphology changes before and after blocking PRC2 in HR-NB cells.

RESULTS

A significant concurrence existed between exons with verified variants and genes showing MYCN-dependent expression in HR-NB. From these biomarker candidates, we identified two novel prognostic gene-set pairs with multi-scale oncogenic defects. Intriguingly, MYC targets over-represented an unfavorable component of the identified prognostic signatures while PRC2 targets over-represented a favorable component. The cell cycle arrest and neuronal differentiation marker ZFHX3 was identified as one of PRC2-silenced tumor suppressor candidates. Blocking PRC2 reduced tumor cell growth and increased the mRNA expression levels of ZFHX3 in an early treatment stage. This hypothesis-driven systems bioinformatics work offered novel insights into the PRC2-mediated tumor cell growth and differentiation in neuroblastoma, which may exert oncogenic effects together with MYC regulation.

CONCLUSION

Our results propose a prognostic effect of imbalanced MYC and PRC2 moderations in pediatric HR-NB for the first time. This study demonstrates an incorporation of genomic landscapes and transcriptomic profiles into the hypothesis-driven precision prognosis and biomarker discovery. The application of this approach to neuroblastoma, as well as other cancer more broadly, could contribute to reduced relapse and mortality rates in the long term.

Sulfated derivative of polysaccharide from Pinus massoniana pollen induces differentiation of human liver cancer HepG2 cells

AIM: To determine whether sulfated derivative of polysaccharide from Pinus massoniana pollen (SPPM60) can induce the differentiation of human liver cancer HepG2 cells in vitro and explore the mechanisms involved.

METHODS: The proliferation of HepG2 cells was evaluated by methyl thiazolyl tetrazolium (MTT) colorimetric assay. Cell morphology was observed using an inverted microscope and a transmission electron microscope. Cell cycle analysis was performed by flow cytometry. The concentration of cytosolic free calcium was measured by fluorescence spectrophotometry. The expression of alpha-fetoprotein (AFP) was detected by immunocytochemistry. The secretory amount of albumin (Alb) was determined using the bromocresol green method. The specific activity of gamma-glutamyltranspeptidase (γ-GT) was measured using the colorimetric method based on diazo reaction. Alkaline phosphatase (ALP) activity was measured by colorimetry.

RESULTS: SPPM60 treatment inhibited cell growth, induced the normalization of cell morphology, increased the number of cells in G0/G1 phase (76.97% ± 0.91% vs 64.62% ± 0.18%, P < 0.05), decreased the number of cells in S phase (17.21% ± 0.71% vs 24.26% ± 0.15%, P < 0.05) and G2/M phase (5.82% ± 0.20% vs 11.13% ± 0.34%, P < 0.01), reduced the concentration of cytosolic free calcium, downregulated the expression of AFP, enhanced the secretion of Alb (6.77 ± 0.33 mg/10⁶ cells vs 4.87 ± 0.30 mg/10⁶ cells, P < 0.05), lowered the activity of γ-GT and ALP (16.3 ± 0.7 U/g vs 22.3 ± 1.2 U/g and 223.3 ± 15.7 U/g vs 311.1 ± 13.4 U/g, respectively; both P < 0.05 or 0.01), and reduced the percentage of heat-resistant ALP activity (46.4% ± 1.5% vs 62.5% ± 2.3%, P < 0.05). In contrast, cells treated with polysaccharide from Pinus massoniana pollen (PPM60) showed no remarkable changes.

CONCLUSION: SPPM60 exerts anticancer activity perhaps via a mechanism associated with decreasing the concentration of cytosolic free calcium, preventing cell cycle progression, and reversing the malignant phenotype of cancer cells.

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.

Pharmacologic hemoglobin reversal: the importance of lipid intermediaries and the proposed involvement of the cAMP and phosphatidylinositol second messenger systems

Humoral and microenvironmental influences have played a major role in recent research into reversing the Hb F to Hb A switch. Early research in this area focused on hormonal influences and showed both thyroid hormone and prolactin could induce small but statistically significant reversals in hemoglobin phenotype. Recent research has focused on the effect of certain lipids in this process. The current study shows a synergy between thyroid hormone and prolactin in inducing a significant switch in adult rat hemoglobin patterns toward the neonatal pattern. Further, it is hypothesized that this synergy is due to the hormones' effect on lipid intermediaries whose effect in turn are proposed to be mediated by the cAMP and phosphatidylinositol second messenger systems.

Inducible expression of N-methyl-D-aspartate receptor, and delta and mu opioid receptor messenger RNAs and protein in the NT2-N human cell line

Retinoic acid treatment of NT-era2/cl.D1 (NT2) cells, a human teratocarcinoma cell line, yields 95% pure cultures of terminally differentiated neuronal cells. Concomitant with their terminal differentiation into neurons, NT2 cells are induced by retinoic acid to express neuronal N-methyl-D-aspartate receptor channels, which are fully functional. We determined the effects of retinoic acid-induced differentiation of NT2 cells on the levels of N-methyl-D-aspartate, delta opioid and mu opioid receptor messenger RNAs. RNA levels were measured using quantitative solution hybridization assays. The riboprobes were complementary to major portions of the coding regions of the N-methyl-D-aspartate, delta opioid and mu opioid receptor complementary DNAs. After four weeks of exposure to 10 microM retinoic acid, followed by four weeks of treatment with mitotic inhibitors (1 microM of cytosine arabinoside, 10 microM of fluorodeoxyuridine and 10 microM of uridine) the levels of N-methyl-D-aspartate receptor messenger RNA in differentiated NT2-N cells increased 10-fold, delta opioid receptor messenger RNA increased three-fold, and mu opioid receptor messenger RNA increased four-fold. Northern blot analysis revealed two transcripts for the N-methyl-D-aspartate receptor messenger RNA (4.2 and 4.4 kb) and two transcripts for delta opioid receptor messenger RNA (7.0 and 11.0 kb). To determine whether the increases in messenger RNAs were accompanied by an increased synthesis of the respective proteins, we examined the immunoperoxidase localization of N-methyl-D-aspartate receptor and delta opioid receptor antisera. N-Methyl-D-aspartate receptor-like immunoreactivity was seen within the cell bodies as well as on the processes of the retinoic acid-differentiated cells. Although delta opioid receptor-like immunoreactivity was detected within the soma of isolated cells prior to retinoic acid treatment, the apparent number of these labelled cells and their ramified processes were markedly enhanced following retinoic acid differentiation. These results demonstrate parallels between the inducible expression of the N-methyl-D-aspartate and opioid receptor messenger RNAs and proteins during the acquisition of the fully differentiated neuronal phenotype in cultured NT2 cells. Retinoic acid-differentiated NT2 cells express increased levels for the N-methyl-D-aspartate, delta opioid and mu opioid receptor messenger RNAs, providing the opportunity to study the interactions among these receptor systems in human terminally differentiated neuronal cells in culture.

Sodium butyrate decreases histamine-stimulated calcium mobilization in C6 glioma cells

The aim of this study was to investigate the effect of sodium butyrate on calcium mobilization. Histamine was found to stimulate a dose-dependent increase in intracellular calcium concentrations ([Ca2+]i) through H1 receptors, but this effect was attenuated in C6 cells pretreated with 1-5 mM sodium butyrate. Evidence is provided that release of Ca2+ from intracellular stores is decreased in a dose-dependent manner. Experiments with BAPTA that show lower levels of [Ca2+]i in cells pretreated with higher concentrations of sodium butyrate suggest that sodium butyrate also decreases Ca2+ influx. These results suggest that changes in Ca2+ mobilization are at least partially responsible for sodium butylate-induced C6 cell differentiation.

Altered phospholipid metabolism in sodium butyrate-induced differentiation of C6 glioma cells

We examined the changes in phospholipid metabolisms in sodium butyrate-treated C6 glioma cells. Treatment of 2.5 mM sodium butyrate for 24 h induced an increase in the activity of glutamine synthetase, suggesting that these cells were under differentiation. Similar treatment was associated with (i) increased arachidonic acid incorporation into phosphatidylcholine, and (ii) decreased arachidonic acid incorporation into phosphatidylinositol and (iii) phosphatidylethanolamine. These effects were subsequently investigated by examining the acylation process, de novo biosynthesis, and the agonist-stimulated phosphoinositides hydrolysis in these cells. Our results indicated that sodium butyrate stimulated the acylation of arachidonic acid into lysophosphatidylcholine, lysophosphatidylethanolamine, and lysophosphatidylinositol. The glycerol incorporation into these lipids was not affected, but the inositol incorporation into total chloroform extracts and Pl and phosphatidylinositol 4-phosphate was decreased in the sodium butyrate-treated cells. Moreover, the accumulation of the rapid histamine-stimulated phosphoinositide metabolites, i.e., inositol monophosphate, inositol diphosphate, and inositol triphosphate (IP3) was decreased in these cells. To elucidate whether the decreased inositol phosphates were due to a decrease in the phosphoinositides hydrolysis, we measured the transient IP3 production directly by a receptor-binding assay. Our results indicated that histamine-stimulated transient IP3 formations were decreased. Taken together, these results indicated that multiple changes by multiple mechanisms of phospholipid metabolisms were found in sodium butyrate-treated C6 glioma cells. The decreased IP3 formation and its subsequent action, i.e., Ca2+ mobilization, may play an early but pivotal role by which sodium butyrate induces C6 glioma cell differentiation.

Retinoic acid-induced increase in delta-opioid receptor and N-methyl-D-aspartate receptor mRNA levels in neuroblastoma x glioma (NG108-15) cells

We determined the effects of all-trans retinoic acid (RA) on the levels of delta opioid receptor (DOR) mRNA and N-Methyl-D-Aspartate receptor (NMDAR1) mRNA in neuroblastoma x glioma hybrid cells (NG108-15) by use of quantitative solution hybridization assays. The assays utilized riboprobes complementary to major portions of the coding region of the DOR and NMDAR1 cDNAs. At 10 microM RA a 3-fold increase in DOR mRNA at 48 h, and later (144 h) alterations were observed in NMDAR1 mRNA levels. Northern blot analysis revealed six transcripts for DOR mRNA ranging in size from 8.7 to 2.0 Kb, and three transcripts for NMDAR1 mRNA ranging in size from 4.1 to 3.5 Kb. Neither the size nor the fractional band intensity was affected by RA treatment. The delayed induction of DOR mRNA suggests an indirect mechanism by which RA acts on transcription of this gene. A surprising induction of DOR mRNA by the protein synthesis inhibitor cycloheximide (CHX) suggests that either a repressor molecule or degrading enzymes/proteases may regulate basal levels of this mRNA. Treatment with RA resulted in a concentration- and time-dependent morphological differentiation characterized by increased size of the cell body and the appearance of numerous short and long processes.

Caudalization by the amphibian organizer: brachyury, convergent extension and retinoic acid

Caudalization, which is proposed to be one of two functions of the amphibian organizer, initiates posterior pathways of neural development in the dorsalized ectoderm. In the absence of caudalization, dorsalized ectoderm only expresses the most anterior (archencephalic) differentiation. In the presence of caudalization, dorsalized ectorderm develops various levels of posterior neural tissues, depending on the extent of caudalization. A series of induction experiments have shown that caudalization is mediated by convergent extension: cell motility that is based on directed cell intercalation, and is essential for the morphogenesis of posterior axial tissues. During amphibian development, convergent extension is first expressed all-over the mesoderm and, after mesoderm involution, it becomes localized to the posterior mid-dorsal mesoderm, which produces notochord. This expression pattern of specific down regulation of convergent extension is also followed by the expression of the brachyury homolog. Furthermore, mouse brachyury has been implicated in the regulation of tissue elongation on the one hand, and in the control of posterior differentiation on the other. These observations suggest that protein encoded by the brachyury homolog controls the expression of convergent extension in the mesoderm. The idea is fully corroborated by a genetic study of mouse brachyury, which demonstrates that the gene product produces elongation of the posterior embryonic axis. However, there exists evidence for the induction of posterior dorsal mesodermal tissues, if brachyury homolog protein is expressed in the ectoderm. In both cases the brachyury homolog contributes to caudalization. A number of other genes appear to be involved in caudalization. The most important of these is pintavallis, which contains a fork-head DNA binding domain. It is first expressed in the marginal zone. After mesoderm involution, it is present not only in the presumptive notochord, but also in the floor plate. This is in contrast to the brachyury homolog, whose expression is restricted to mesoderm. The morphogenetic effects of exogenous RA on anteroposterior specification during amphibian embryogenesis are reviewed. The agent inhibits archencephalic differentiation and enhances differentiation of deuterencephalic and trunk levels. Thus the effect of exogenous RA on morphogenesis of CNS is very similar to that of caudalization, which is proposed to occur through the normal action of the organizer. According to a detailed analysis of the effect of lithium on morphogenesis induced by the Cynops organizer, lithium has a caudalizing effect closely comparable with that of RA. Furthermore, lithium induces convergent extension in the prechordal plate, which normally does not show cell motility.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of retinoic acid on NB 69 human neuroblastoma cells and fetal rat mid brain neurons

Retinoids are chemical compounds which play important roles in ontogenetic development and cranio-caudal differentiation in animals, but their effect on phenotypic expression of neurotransmitters are unknown. We studied the pharmacological and morphological effects of retinoic acid (RA) on two types of immature vertebrate neurons, the human derived neuroblastoma cells, NB69, and fetal rat mid brain neurons in culture. The pharmacological effects of RA on the cultures and their relation to catecholamine and acetylcholine neurotransmission were evaluated according the levels of catecholamines, tyrosine hydroxylase (TH) activity, TH immunostaining, and choline acetyltransferase (CAT) activity, respectively. RA reduces catecholamine levels and TH activity in NB69 cells and the number of dopamine neurons in cultures derived from rat fetal mid brain. The detrimental effect of RA on mid brain neurons is dose- dependent; limited to TH+ cells at low concentrations (100 to 500 nM) and toxic for all types of cells at high concentrations (1 to 2 microM). RA increases CAT activity in NB 69 cells and produces phenotypic differentiation of these to a more mature neuronal phenotype with more prolonged neurite extensions. Therefore, RA may play a trophic positive role in the differentiation of immature cells to cholinergic neurons; this contrasts with the detrimental effects of RA on catecholamine neurons.

Interferon-gamma-stimulated and GTP-binding-proteins-mediated phospholipase A2 activation in human neuroblasts

Interferon-gamma (IFN-gamma) is a potent growth-inhibitory cytokine also endowed with differentiating activity on neural cells. Binding of IFN-gamma to its high-affinity receptor induces a rapid and transient activation of phospholipase A2 (PLA2). The mechanism coupling the IFN-gamma receptor (IFN-gamma-R) to PLA2 activation is not clearly defined, and no information is available on this mechanism in neuroblast cells. We have tested the hypothesis that GTP-binding proteins (G-proteins) may couple the IFN-gamma-R to PLA2 in the human neuroblastoma (NB) cell line LAN-5. Incubation of NB cells with IFN-gamma resulted in a rapid increase in [3H]arachidonic acid (AA) release, and this effect was blocked by pretreatment with anti-IFN-gamma antibodies. IFN-gamma-stimulated AA release was still observed in permeabilized cells that were blocked by pretreatment with anti-IFN-gamma-R antibodies. Exposure of permeabilized LAN-5 cells to guanosine 5'-[gamma-thio]triphosphate (GTP[S]), a non-hydrolysable GTP analogue, induced a dose-dependent release of [3H]AA. A non-specific nucleotide effect was excluded, since similar stimulatory effects on AA mobilization were not observed by GTP, ATP, CTP, ADP and GDP. IFN-gamma-stimulated AA release was completely blocked by the guanine nucleotide analogue that inhibits G-protein function, guanosine 5'-[beta-thio]diphosphate (GDP[S]). A role for G-proteins in IFN-gamma-R coupling to PLA2 was further supported by the inhibition of IFN-gamma-induced [3H]AA release by treatment of permeabilized cells with pertussis toxin and with the antiserum against the common alpha-subunits of G-proteins. To determine a possible contribution to AA mobilization by the phospholipase C and diacyglycerol lipase pathway or by protein kinase C activation, the effects of neomycin, a phospholipase C inhibitor, and PMA (phorbol 12-myristate 13-acetate), a direct activator of protein kinase C, were investigated. Neither neomycin nor PMA affected either basal or IFN-gamma-stimulated AA release. Ca2+ concentration, which has been shown to regulate the activity of some PLA2s, does not appear to play an important role in the regulation of the IFN-gamma-stimulated PLA2 activity, since incubating permeabilized cells in different concentrations of Ca2+ induced AA release without affecting the IFN-gamma response. Altogether, these findings suggest the existence of IFN-gamma-R, which couples a Ca(2+)-independent PLA2 activation via pertussis-toxin-sensitive G-proteins.

Retinoic acid-induced differentiation of a human neuroblastoma cell line alters muscarinic receptor expression

Muscarinic receptor density increased by approximately 36% after differentiation induced by retinoic acid (Bmax, control = 126 +/- 13 fmol/mg protein; Bmax, retinoic acid-treated = 170 +/- 17 fmol/mg protein; P < 0.05), corresponding to a 170% increase in receptor content per cell. The affinity of [3H]NMS for the receptors was somewhat lower in the retinoic acid-treated cells (Kd, control = 0.14 +/- 0.04 nM; Kd, retinoic acid-treated = 0.25 +/- 0.04 nM; P < 0.05). Reverse transcriptase/polymerase chain reaction analysis using subtype-specific primers revealed that undifferentiated Sk-N-SH cells transcribed mRNA for all 5 receptor subtypes; this pattern was not affected by retinoic acid treatment. [3H]NMS displacement curves with subtype selective receptor ligands (pirenzepine, m1; AFDX-116, m2; 4-DAMP, m3) indicated the predominant expression of m3 and m1 receptor subtypes, and differentiation did not affect the pharmacological profile of the expressed receptor populations. The present results indicate that differentiation induces selective changes in the expression and activity of muscarinic receptors in a neuronal cell line.

Stimulation of receptor-coupled phospholipase A2 by interferon-gamma

The biomolecular mechanisms that mediate signal transduction by type II (gamma) interferon (IFN) are poorly understood. IFN-gamma is a potent growth inhibitory cytokine also endowed with antiviral, immunomodulatory, and differentiating activities on various cell targets, including neural cells. IFN-gamma induced a rapid and transient activation of phospholipase A2 in LAN-5, a human neuroblastoma cell line. A consequence of phospholipase A2 activation was the release of arachidonic acid and the generation of lysophospholipids from membrane phospholipids. Treatment of pre-labeled LAN-5 cells with a receptor-saturating concentration of IFN-gamma led to a time-dependent release of [3H]arachidonic acid into the culture media and generation of [32P]lysophosphatidylcholine. Pretreatment of cultures with the phospholipase A2 inhibitor, bromophenacyl bromide, markedly inhibited both [3H]arachidonic acid release and lysophosphatidylcholine production induced by IFN-gamma treatment. Pretreatment of LAN-5 cells with nordihydroguaiaretic acid, a lipoxygenase inhibitor, or with indomethacin, a cyclooxygenase inhibitor, amplified the release of [3H]arachidonic acid and production of lysophosphatidylcholine induced by non-saturating concentrations of IFN-gamma. In parallel, and with the same time-dependent effect, a significant decrease in phosphatidylcholine labeling was observed in IFN-gamma-treated cells, further indicating that a potential signal transduction mechanism of IFN-gamma is the hydrolysis of membrane phosphatidylcholine by phospholipase A2.

Muscarinic binding sites in a catecholaminergic human neuroblastoma cell line

Tyrosine hydroxylase (TH) a characteristic enzyme activity for the catecholaminergic clonal cell line LA-N-1 and choline acetyltransferase (ChAT) a characteristic enzyme activity for the cholinergic clonal cell line LA-N-2 were previously shown to be increased in these cells exposed to 10(-5) M retinoic acid (RA) as differentiating agent. An investigation of the receptor characteristics suggests a complementarity between the two cell lines. The binding of QNB, a muscarinic ligand, was undetectable with the LA-N-2 cells but was present in the LA-N-1 cells and possessed a kD of 1.8 nM and 2.2 nM and a Bmax of 0.56 and 0.68 for control and RA grown cells respectively. There was a gradual increase in QNB binding to LA-N-1 cells from 2 days in vitro (DIV) until 6 DIV in both control and RA grown cells. An IC50 of 2.5 x 10(-8) M and 0.9 x 10(-8) M for atropine inhibition was obtained for the control and RA grown cells respectively. The corresponding values for carbachol inhibition were 7 x 10(-2) M and 3 x 10(-2) M respectively. The inhibition by the agonist oxotremorine is comparable to that of carbachol and 1 mM pilocarpine inhibited the binding by 21%. QNB binding showed a low affinity for pirenzepine and for AF-DX-116 but was inhibited with a rather high affinity by 4-DAMP (IC50:110 microM) thus suggesting the presence of an M3 receptor. Acetylcholine (100 microM) plus eserine (50 microM) and BW284c55 (1 microM), an acetylcholinesterase inhibitor, reduced the binding of QNB by approximately 25%.(ABSTRACT TRUNCATED AT 250 WORDS)

Gamma-interferon, retinoic acid, and cytosine arabinoside induce neuroblastoma differentiation by different mechanisms

1. The effects of gamma-interferon (gamma-IFN), retinoic acid (RA), and cytosine arabinoside (ARA-C) on the growth, morphology, and phenotype of the human neuroblastoma (NB) cell lines, LAN-1 and GI-ME-N, have been extensively tested. 2. RA, gamma-IFN, and ARA-C induced a dose-dependent morphological differentiation and growth inhibition, without affecting cell viability. Cells exposed to 10(-6) M RA or 1000 U/ml gamma-IFN significantly decreased their growth rate within the first 24 and 48 hr of culture, respectively. Cells became smaller and polygonal and sprouted long cellular processes with varicosities along their courses. In contrast, ARA-C-differentiated cells were larger and flattened, with few elongated dendritic processes. 3. Analysis of membrane and cytoskeletal markers by immunofluorescence and Western blot showed several changes in NB-specific antigen expression after 5 days of treatment with all inducing agents. Analysis of labeled phosphatidylinositol metabolites from prelabeled cells showed, within 1 min of treatment with RA, a rapid decrease in inositol 1,4,5-trisphosphate and of 1,2-diacylglycerol levels. No changes in inositol phospholipid metabolism were observed in gamma-IFN- or ARA-C-treated cells. 4. We conclude that RA-induced decrease in phosphatidylinositol (PI) hydrolysis is not likely to be a consequence of the acquisition of a different phenotype, as its changes precede the acquisition of neuronal markers. In addition, gamma-IFN and ARA-C, both inducing a mature phenotype, did not affect PI hydrolysis. 5. Decreased PI hydrolysis seems to be sufficient, although not necessary, to commit NB cells to neuronal differentiation. Analysis of molecular mechanisms associated with NB cell differentiation may be helpful to clarify the potential of various biological agents in affecting the development of the neural cell.