Differential expression of N-myc and c-src proto-oncogenes during neuronal and schwannian differentiation of human neuroblastoma cells

Neuroblastoma (NB) cells can be induced to differentiate bidirectionally into either neuronal or schwannian cells by different inducers. However, the underlying mechanisms are poorly understood. We examined the expression of N-myc and c-src genes in 3 human NB-cell lines during either neuronal or schwannian differentiation in vitro, since proto-oncogenes are considered to play a pivotal role in regulating cell proliferation and differentiation. Decreased N-myc expression and increased c-src expression were observed during neuronal differentiation by retinoic acid, polyprenoic acid (E5166) and dibutyryl cyclic AMP, whereas the expression of N-myc and c-src genes was considerably reduced during schwannian differentiation by bromodeoxyuridine, demonstrating that the expression of N-myc and c-src genes was regulated independently in the bipolar differentiation processes of NB cells. Our results suggest that enhanced N-myc expression might be closely linked to the undifferentiated phenotypes of NB cells, that c-src expression might be related to the neuronal differentiation of NB cells, and that N-myc and c-src genes might be regulated independently in the determination of the bipolar differentiation of NB cells.     

Interleukin 4 alone and with gamma-interferon or alpha-tumor necrosis factor inhibits cell growth and modulates cell surface antigens on human renal cell carcinomas

Immune cytokines have been shown to play important roles in regulating immune cell functions as well as neoplastic cells. Interleukin-4 (IL4), primarily known as a B-cell growth factor, can also activate and differentiate other immune cells. This cytokine has recently been shown to have immunotherapeutic benefit in tumor-bearing hosts. The present study assessed the effect on human renal cell carcinoma cell lines of recombinant IL4 alone and in combination with recombinant gamma-interferon (IFN) or recombinant alpha-tumor necrosis factor (TNF). IL4 inhibited cell growth of all lines at 250-500 units/ml in a differential manner. Expression of IL4 receptors was demonstrated on renal cell carcinomas. Overall, IFN (500 units/ml) alone inhibited cell growth; however, TNF (500 units/ml) was not as strong an inhibitor. When IL4 was combined with IFN or TNF there was a significant augmentation of cell growth inhibition and modulation of cell morphology of the cell lines. Tumor-associated ganglioside antigens (NeuAc alpha 2-3Gal beta 1-4Glc beta 1-1'Cer, NeuAc alpha 2-8NeuAc alpha 2-3Gal beta 1-4Glc beta 1-1'Cer, GalNAc beta 1-4 (NeuAc alpha 2-3)Gal beta 1-4Glc beta 1-1'Cer, and GalNAc beta 1-4(NeuAc alpha 2-8NeuAc alpha 2-3)Gal beta 1-4Glc beta 1-1'Cer) HLA class I, HLA-DR, and beta 2-microglobulin on the cell surface of renal cancer lines were assessed by flow cytometry and radiometric binding assay. IL4 alone or in combination with other cytokines modulated HLA class I and HLA-DR expression. IL4 and IFN consistently enhanced NeuAc alpha 2-8NeuAc alpha 2-3Gal beta 1-4Glc beta 1-1'Cer and GalNAc beta 1-4(NeuAc alpha 2-8NeuAc alpha 2-3)Gal beta 1-4Glc beta 1-1'Cer expression on individual cell lines. The study demonstrated that IL4 alone or in combination with other cytokines can significantly inhibit growth, and modulate the expression of surface major histocompatibility and tumor-associated antigens of renal cell carcinomas.     

Prolonged N-myc protein half-life in a neuroblastoma cell line lacking N-myc amplification

Genomic amplification of the oncogene N-myc is associated with rapid tumor progression and poor prognosis in patients with neuroblastoma (NB). However, 40% of NBs which lack N-myc amplification are also clinically aggressive. Factors other than N-myc copy number must therefore play a role in determining tumor progression in these NBs. We have established an unusual human NB cell line (NBL-S) from the primary tumor of a patient with rapidly progressive disease which lacks N-myc amplification. The doubling time in vitro (48 h) and the time from injection of 2 x 10(7) cells to detectable tumors in nude mice (46 days) in similar to NB cell lines with amplified N-myc. However, karyotype analysis reveals no evidence of double minutes (DMs), homogeneously staining regions (HSRs), or chromosome 1p deletions, features commonly seen in NB cell lines. The cells have the cell surface phenotype typical of N-myc amplified NB (HLA-A,B,C negative and HSAN 1.2 positive), and similar to other NB cell lines, N-myc RNA and protein are expressed. Interestingly, the half-life of the N-myc protein in NBL-S is prolonged (approximately 100 min) compared to the short N-myc protein half-life previously described in N-myc amplified NB cell lines (approximately 30 min). Because N-myc protein is thought to have a regulatory role, prolongation of the half-life of this protein may be an important factor in the regulation of growth in NBs which lack N-myc amplification and rapidly progress.     

Relationship between Rous sarcoma virus-induced expression of membrane antigen and phenotypic transformation.

Rous sarcoma virus-transformed hamster BHK fibroblasts express a virus-induced cell surface antigen undetectable in cells either transformed by unrelated viruses or infected by transformation-defective strains of Rous sarcoma virus. To clarify whether this antigen plays any role in the process of malignant transformation or is expressed at the cell surface only as a consequence of the acquisition of the transformed phenotype, we have investigated its expression at the cell surface of Rous sarcoma virus-transformed BHK cells treated with dibutyryl cyclic adenosine 3':5'-monophosphate and at the surface of parental BHK cells transiently transformed by the tumor promoter phorbol myristate acetate. In the dibutyryl cyclic adenosine 3':5'-monophosphate-treated cells, in which most of the parameters of the transformed phenotype are reverted to normality, but the product of the transforming gene is still present, virus-induced cell surface antigen is expressed. In the mirror experiment, this antigen is not expressed by phenotypically transformed but genetically normal phorbol myristate acetate-treated cells. It is concluded that the tumor membrane antigen studied is intimately associated with the expression of the function(s) controlled by the transforming gene.     

Diverse responses to retinoid in morphological differentiation, tumorigenesis and N-myc expression in human neuroblastoma sublines

We established the subline RT-BMV-C6 from the parent human neuroblastoma cell line RT-BM by a process that required repeated subculture of cells, which were prone to disaggregation. RT-BMV-C6 and the parent cloned line, RT-BM-1, had an identical marker chromosome, confirming that both lines were derived from a common progenitor. In the analysis of surface antigen expression, RT-BMV-C6 did not react with UJ-127-11, Leu7 or KP-NAC2 MAbs to which RT-BM-1 showed positive binding. The levels of both N-myc amplification and expression in RT-BMV-C6 were twice as high as the level obtained in RT-BM-1. Colony-forming efficiency in soft agar was 2.0 +/- 0.8% for RT-BMV-C6 and 3 times greater than that for RT-BM-1 (0.6 +/- 0.1%). When 100 x 10(6) cells of RT-BM-1 and RT-BMV-C6 were inoculated into nude mice, tumor incidence was significantly higher for RT-BMV-C6 (6/6; 100%) than for RT-BM-1 (0/6; 0%). Our data show that N-myc is closely related to tumorigenicity in NB. When RT-BM-1 and RT-BMV-C6 were co-cultured with a new synthetic retinoid, polyprenoic acid (E5166), and dibutyryl cyclic AMP, RT-BM-1 was induced to neuronal differentiation, defined by the formation of neuronal processes and expression of neurofilaments, whereas RT-BMV-C6 was not. However, when exposed to E5166, N-myc expression of RT-BMV-C6 was more strongly reduced than that of RT-BM-1, and colony formation of RT-BMV-C6 was significantly inhibited as compared to RT-BM-1. These findings suggest that the reduction of N-myc expression might closely correlate with growth inhibition accompanying neuronal differentiation of neuroblastoma cells.     

Interferon-gamma cooperates with retinoic acid and phorbol ester to induce differentiation and growth inhibition of human neuroblastoma cells.

The prognosis of patients with advanced stages of neuroblastoma with N-myc amplification remains poor despite escalated therapy, a situation that has called for alternative therapeutic approaches. Neuroblastoma cells, which represent immature peripheral neuronal cells, treated with certain physiologic and nonphysiologic agents such as retinoic acid (RA), phorbol esters and interferons (IFN) in vitro undergo cellular differentiation and stop to divide, a process that mimics normal neuronal development. Such "differentiation therapy" using RA after autologous bone marrow transplantation has recently given encouraging results in neuroblastoma patients with advanced disease. Considering approaches for improved differentiation therapy, we investigated possible synergistic effects of combining agents known to influence neuroblastoma growth and differentiation in vitro. Our results show that combined treatment with IFN-gamma and RA or the phorbol ester 12-O-tetradecanoyl-phorbol acetate (TPA) had synergistic or enhancing effects on morphologic differentiation and neurite outgrowth in 5 of 5 neuroblastoma cell lines, 3 of which expressed very high levels of N-myc mRNA due to N-myc amplification. The combinations RA+IFN-gamma or TPA+IFN-gamma also enhanced induced growth inhibition in all 5 cell lines, in several cases resulting in complete growth arrest under conditions where cells stimulated with either agent alone continued to grow. The phenotypic effects of the combined RA+IFN-gamma or TPA+IFN-gamma treatments were in most, but not all, investigated cases accompanied by moderate reductions in N-myc expression, suggesting that the cooperative signals may counteract N-Myc activity at several levels. The cooperativity between IFN-gamma and other differentiation signals may be relevant for approaches to improve the therapy for high-risk neuroblastoma with N-myc-amplification.     

N-myc is a novel regulator of PI3K-mediated VEGF expression in neuroblastoma

Angiogenesis in neuroblastoma (NB) correlates with increased expression of vascular endothelial growth factor (VEGF) and a worse clinical outcome. Other cellular markers, such as Akt activation and MYCN amplification, are also associated with poor prognosis in NB; therefore, we sought to determine the role of N-myc in the regulation of the phosphatidylinositol 3-kinase (PI3K)/Akt/VEGF pathway. PI3K inhibition, using small-molecule inhibitors or phosphatase and tensin homolog adenovirus, led to decreased levels of VEGF mRNA and/or protein by reducing phosphorylation of Akt and mammalian target of rapamycin (mTOR), and attenuating hypoxia-inducible factor 1alpha expression. Moreover, PI3K inhibition decreased levels of N-myc expression in MYCN-amplified cells. To further clarify the importance of N-myc as a target of PI3K in VEGF regulation, we inhibited N-myc expression by siRNA transfection. MYCN siRNA significantly blocked VEGF secretion, irrespective of serum conditions, in MYCN-amplified NB cells; this effect was enhanced when combined with rapamycin, an mTOR inhibitor. Interestingly, in cells with low-N-myc expression, MYCN siRNA reduction of VEGF secretion was only effective with MYCN overexpression or insulin-like growth factor-1 stimulation. Our results show that N-myc plays an important role in the PI3K-mediated VEGF regulation in NB cells. Targeting MYCN, as a novel effector of PI3K-mediated angiogenesis, has significant potential for the treatment of highly vascularized, malignant NB.     

The combination of gamma-interferon and tumor necrosis factor causes a rapid and extensive differentiation of human neuroblastoma cells.

Neuroblastoma (NB), a tumor originating from the sympathetic nervous system, is the most common extracranial neurological tumor of childhood. Human NB cells may differentiate in vitro under treatment with biological agents, as gamma-interferon (IFN-gamma) and tumor necrosis factor (TNF). Unfortunately, NB cell lines resistant to the differentiation-inducing effects of both drugs have been observed. Here we demonstrate that a combination of IFN-gamma plus TNF causes extensive and generalized differentiation of NB cells toward a neuronal phenotype. Both IFN-gamma and TNF, given alone, moderately reduced cell growth and induced partial morphological maturation. Their combination further reduced cell proliferation. The combined treatment gave a synergistic rather than additive cytostatic effect, documented also by a dramatically enhanced differentiation toward a neuronal morphology. Membrane immunofluorescence showed a homologous and heterologous up-regulation of IFN-gamma receptor, as well as a marked induction of HLA Class I antigens and, to a lesser extent, of Class II antigens on NB cells induced to differentiate. Treatment of NB cell lines with IFN-gamma/TNF results in the induction of a differentiated phenotype, as indicated by the increased expression of the Mr 160,000 and 200,000 neurofilament proteins and that of microtubule-associated proteins. Evaluation of biochemical markers of neuronal differentiation confirmed the ability of the combined treatment to induce neuroblast maturation. These results suggest that the combination of IFN-gamma and TNF should be considered for experimental clinical trials in neuroblastoma.     

Cyclic AMP induces differentiation in vitro of human melanoma cells

Treating human melanoma lines with dibutyryl adenosine 3':5'-cyclic monophosphate (dbc AMP) resulted in morphologic changes associated with the altered expression of cell surface antigens. After treatment, cells developed long cellular projections characteristic of mature melanocytes and showed the presence of an increased number of Stage II premelanosomes. In addition, induction of melanin synthesis, detected as brown perinuclear pigmentation, was observed. The AMP further drastically reduced the growth rate of the five melanoma cell lines that were tested. The influence of dbc AMP was completely reversible 3 days after the agent was removed from the culture medium. The antigenic phenotype of the melanoma lines was compared before and after dbc AMP treatment. This was done with four monoclonal antibodies directed against major histocompatibility complex (MHC) Class I and II antigens and 11 monoclonal antibodies defining eight different melanoma-associated antigenic systems. Treatment with dbc AMP reduced the expression of human leukocyte antigen (HLA)-ABC antigens and beta-2-microglobulin in five of five melanoma lines. In the two HLA-DR-positive cell lines dbc AMP reduced the expression of this antigen in one line and enhanced it in the other. No induction of HLA-DR or HLA-DC antigens was observed in the Class II negative cell lines. Furthermore, dbc-AMP modulated the expression of the majority of the melanoma antigenic systems tested. The expression of a 90-kilodalton (KD) antigen, which has been found to be upregulated by interferon-gamma, was markedly decreased in all the five cell lines. A similar decrease in the expression of the high molecular weight proteoglycan-associated antigen (220-240 KD) was observed. The reduced expression of Class I and II MHC antigens as well as the altered expression of the melanoma-associated antigens studied were shown to be reversible after dbc AMP was removed. Our results collectively show that the monoclonal antibody-defined melanoma-associated molecules are linked to differentiation. They could provide useful tools for monitoring the maturation of melanomas in vivo induced by chemical agents or natural components favoring differentiation.     

Expression of myeloid and major histocompatibility antigens on small cell carcinoma of the lung cell lines analyzed by cytofluorography: modulation by gamma-interferon

Recent reports have described the expression of myeloid cell surface antigens on cells of small cell carcinoma of the lung (SCCL). In order to confirm and extend these findings, we have examined by cytofluorography a large panel of well-characterized cell lines derived from SCCL tumors for the expression of several myeloid cell-associated antigens, some of which were not examined in previous reports. In addition, we have studied the expression of Classes I and II HLA antigens on these SCCL cell lines. Finally, we examined the effect of gamma-interferon on the expression of several cell surface markers and on proliferation of SCCL cells. We have found that several SCCL cell lines expressed a Mr 55,000 polypeptide antigen, My23, previously found only on monocytes and monocytic leukemia cells. In addition, the cell lines studied expressed another antigen, defined by monoclonal antibody AML-1-99, which is associated with monocytes and hematopoietic stem cells. We confirmed previous studies that the Leu-7 antigenic determinant is expressed on SCCL cells but observed only minimal or absent binding of monoclonal antibody OKM1 to most cell lines. Class I HLA antigens were present on eight of nine lines examined while Class II HLA was expressed on three of nine lines. Gamma-Interferon decreased the proliferative rate of all lines examined. However, this lymphokine was capable of inducing Class I HLA on several lines. The effect of gamma-interferon on other cell surface antigens was variable. These studies confirm that some myeloid cell-associated antigens are expressed on cultured SCCL lines and, additionally, show that their expression can be modulated by immune interferon. Determining the significance of finding myeloid cell-associated antigens on SCCL cells will require further study.     

Modulation of human melanoma cells by interleukin-4 and in combination with gamma-interferon or alpha-tumor necrosis factor

Immune cytokines have been shown to play important roles in regulating immune cell functions. Interleukin-4 (IL4), originally described as a B-cell growth factor, is known to activate and differentiate other immune cells. IL4 has been given as an immunotherapeutic to tumor-bearing hosts. In this report, we set out to determine whether IL4 can directly modulate growth and expression of surface antigens on human melanoma cells. The effect of recombinant IL4 alone and in combination with recombinant gamma-interferon (IFN) or recombinant alpha-tumor necrosis factor (TNF) on melanoma cell lines was examined. IL4 significantly inhibited cell growth of all cell lines examined at 100-500 units/ml; but a dose-dependent differential response to individual cell lines occurred. The effect of IL4 was augmented by combination with IFN or TNF. Melanoma-associated ganglioside antigens (GM3, GD3, GM2, GD2) and human leukocyte antigen class I and DR on the cell surface of melanoma cells were assessed by flow cytometry and/or a radiometric binding assay. IL4, IFN, or TNF alone enhanced human leukocyte antigen class I, DR, and beta 2-microglobulin antigen expression. IL4 alone and in combination with IFN or TNF increased the GM3/GD3 ratio expression. GD2 was enhanced significantly by IL4, IFN, and TNF. Pretreatment of melanoma with IL4 or with other cytokines prior to stimulation with peripheral blood lymphocytes significantly enhanced mixed lymphocyte tumor reaction activity as compared with non-treated melanoma used as stimulators. These studies demonstrate that IL4 alone or in combination with IFN and TNF can modulate melanoma growth activity and surface antigen expression to a more differentiated and immunogenic phenotype.     

N-myc gene amplification in neuroblastoma is associated with altered phosphorylation of a proliferation related polypeptide (Op18)

We have recently identified and cloned the gene for a cytosolic polypeptide, designated oncoprotein 18 (Op18), which is expressed in acute lymphocytic leukemia and some solid tumors including neuroblastoma. Op18 is phosphorylated upon treatment of lymphoid cells with phorbol myristate acetate. We have proposed that unphosphorylated Op18 plays a role in cellular proliferation, and that its phosphorylated forms, namely Op18a and Op18b, are associated with diminished cell proliferation. In this study, we report that in neuroblastoma tumors, the phosphorylation of Op18 was substantially diminished with increasing N-myc gene copy number. Treatment of the neuroblastoma cell line SMS-KCNR, which contains 75 copies of the N-myc gene, with retinoic acid for ten days resulted in an increase in Op18 phosphorylation. Our findings provide evidence for distinct patterns of Op18 phosphorylation in neuroblastoma tumors with and without N-myc gene amplification.     

Loss of one HuD allele on chromosome #1p selects for amplification of the N-myc proto-oncogene in human neuroblastoma cells

In human neuroblastoma tumors, amplification of the N-myc proto-oncogene and loss of all or part of the short arm of chromosome #1 are both associated with a poor prognosis. Accruing evidence indicates that it is the absence of one allele of the HuD (ELAVL4) gene, encoding the neuronal-specific RNA-binding protein HuD and localized to 1p34, that is linked to amplification. In 12 human neuroblastoma cell lines, N-myc amplification correlates with loss of one HuD allele and decreased HuD expression. Transfection experiments demonstrate that modulating HuD expression affects N-myc gene copy number as well as expression. Introduction of a sense HuD construct into two N-myc amplified cell lines considerably increases N-myc expression whereas gene copy number decreases. Conversely, expression of antisense HuD in N-myc nonamplified SH-SY5Y cells reduces HuD and N-myc mRNA levels even as cells show amplification of the N-myc gene. Thus, N-myc gene copy number is modulated by alteration of HuD expression. We propose that haploinsufficiency of HuD due to chromosome #1p deletion in neuroblastoma selects for cells that amplify N-myc genes. Application of these findings could lead to more effective therapies in the treatment of those patients with the worst prognosis.     

Association of expression between N-myc gene and major histocompatibility complex class I gene in surgically resected human neuroblastoma

Amplification of the N-myc gene in neuroblastoma correlates with advanced stage and poor prognosis. Association of the expression between N-myc and major histocompatibility complex (MHC) class I genes in 33 neuroblastomas obtained from Japanese children was investigated. Amplification of the N-myc gene was observed in two of five cases in Stage III, six of 11 cases in Stage IV, and one of five cases in Stage IV-S. In each case, the expression of N-myc gene was significantly increased. The expression was also increased in cases without amplification of the N-myc gene, the origin being from the suprarenal region. Expression of the MHC class I gene was significantly decreased in five of these nine with a high level of N-myc expression with amplification. These results suggest that the down-modulation of the MHC class I expression may be associated with the high level of expression and amplification of N-myc gene in the advanced stage of neuroblastoma.     

HLA-class-I and -class-II expression on renal tumor xenografts and the relation to sensitivity for alpha-IFN, gamma-IFN and TNF

In this study we evaluated the usefulness of the histocompatibility leucocyte antigen (HLA) class-I and class-II expression on renal-cell carcinoma (RCC) xenografts as predictive markers for response to cytokine therapy. Eight different RCC xenografts growing in BALBC nu/nu mice were treated with 0.5 or 5.0 ng/g recombinant human alpha- or gamma-interferon (IFN), or 500 ng/g recombinant human tumor necrosis factor (TNF). Modulation of HLA class-I, -II expression was evaluated immunohistochemically using the monoclonal antibodies (MAbs) W6.32 and B8.11.2 and at the mRNA level using the plasmids pDP001 and DR alpha 120. HLA class-I expression in all lines was upregulated by alpha- and gamma-IFN and was highest in the high-IFN-dose-treated tumors. TNF also stimulated HLA-class-I expression and up-regulated class-I expression still further when combined with IFN. Highest up-regulation of HLA-class-I in all tumors was measured in the alpha-IFN-5.0/TNF-500-ng/g-treated mice, although this was not necessarily the treatment regimen resulting in the most pronounced effect on tumor growth. Hence, maximum upregulation of class-I antigens at a given regimen was not always indicative for the highest achievable anti-tumor effect. HLA-class-II expression which was present on only 3 of the untreated tumors was up-regulated by both alpha and gamma-IFN. TNF itself did not up-regulate class-II expression but enhanced the class-II expression on the alpha-IFN-treated tumors but not on the gamma-IFN-treated tumors. Irrespective of the basic expression level, inducibility of both HLA-class-I and -class-II antigens appear to be correlated to the direct effects on growth of renal-tumor xenografts towards alpha-IFN, gamma-IFN and TNF. Modulation of HLA antigens was studied in the nude mouse, hence T-cell-mediated effector mechanisms cannot explain the good correlation between inducibility and response. Nonetheless, our studies indicate that the extent of modulation of HLA-class-I and -II can serve as predictive marker for response to cytokine therapy, which may serve as a valuable criterion for inclusion of patients in cytokine treatment regimens.