Cloning and characterization of different human sequences related to the onc gene (v-myc) of avian myelocytomatosis virus (MC29)

Identification of the novel Np17 oncogene in human leukemia

We previously defined the HERV-K Np9 as a viral oncogene. Here we report the discovery of a novel oncogene, Np17, which is homologous to the viral Np9 gene and predominantly present in Hominoidea. Np17 is located on chromosome 8, consists of 7 exons, and encodes a 16.8kDa nuclear protein with149 amino-acid residue. Functionally, knockdown of Np17 induced growth inhibition of leukemia cells, whereas enforced expression of Np17 promoted growth of leukemia cells in vitro and in vivo. In human leukemia, Np17 was detected in 59.65% (34/57) of acute myeloid leukemia (AML) patients examined and associated with refractory/relapsed AML. Mechanistically, Np17 decreased p53 levels and its mechanism might be involved in recruiting nuclear MDM2 to p53 for ubiquitin-mediated degradation. These findings reveal that Np17 is a novel oncogene associated with refractory/relapsed leukemia.

Association of MYC gene polymorphisms with neuroblastoma risk in Chinese children: A four-center case-control study

BACKGROUND

Neuroblastoma is one of the most common malignant tumors in childhood. Polymorphisms in proto-oncogene MYC are implicated in many cancers, although their role in neuroblastoma remains unclear. In the present study, we attempted to investigate the association between MYC gene polymorphisms and neuroblastoma susceptibility in Chinese children.

METHODS

We included two MYC polymorphisms (rs4645943 and rs2070583) and assessed their effects on neuroblastoma risk in 505 cases and 1070 controls via the Taqman method.

RESULTS

In single and combined locus analysis, no significant association was found between the two selected polymorphisms and neuroblastoma susceptibility. In stratification analysis, the rs4645943 CT/TT genotypes were significantly associated with a decreased neuroblastoma risk in subjects with tumors originating from other sites [adjusted odds ratio (OR) = 0.42, 95% confidence interval (CI) = 0.21-0.84, p = 0.013]. Meanwhile, the presence of one or two protective genotypes was significantly associated with a decreased neuroblastoma risk in subjects with tumors arising from other sites (adjusted OR = 0.50, 95% CI = 0.26-0.96, p = 0.036).

CONCLUSIONS

The present study indicates that MYC gene polymorphisms may have a weak effect on the neuroblastoma risk, which neeeds to be verified further.

Destruction of a Microtubule-Bound MYC Reservoir during Mitosis Contributes to Vincristine's Anticancer Activity

Tightly regulated activity of the transcription factor MYC is essential for orderly cell proliferation. Upon deregulation, MYC elicits and promotes cancer progression. Proteasomal degradation is an essential element of MYC regulation, initiated by phosphorylation at Serine62 (Ser62) of the MB1 region. Here, we found that Ser62 phosphorylation peaks in mitosis, but that a fraction of nonphosphorylated MYC binds to the microtubules of the mitotic spindle. Consequently, the microtubule-destabilizing drug vincristine decreases wild-type MYC stability, whereas phosphorylation-deficient MYC is more stable, contributing to vincristine resistance and induction of polyploidy. PI3K inhibition attenuates postmitotic MYC formation and augments the cytotoxic effect of vincristine. IMPLICATIONS: The spindle's function as a docking site for MYC during mitosis may constitute a window of specific vulnerability to be exploited for cancer treatment.

The Role of MYC and PP2A in the Initiation and Progression of Myeloid Leukemias

The MYC transcription factor is one of the best characterized PP2A substrates. Deregulation of the MYC oncogene, along with inactivation of PP2A, are two frequent events in cancer. Both proteins are essential regulators of cell proliferation, apoptosis, and differentiation, and they, directly and indirectly, regulate each other’s activity. Studies in cancer suggest that targeting the MYC/PP2A network is an achievable strategy for the clinic. Here, we focus on and discuss the role of MYC and PP2A in myeloid leukemias.

Exploring MYC relevance to cancer biology from the perspective of cell competition

Cancer has long been regarded and treated as a foreign body appearing by mistake inside a living organism. However, now we know that cancer cells communicate with neighbours, thereby creating modified environments able to support their unusual need for nutrients and space. Understanding the molecular basis of these bi-directional interactions is thus mandatory to approach the complex nature of cancer. Since their discovery, MYC proteins have been showing to regulate a steadily increasing number of processes impacting cell fitness, and are consistently found upregulated in almost all human tumours. Of interest, MYC takes part in cell competition, an evolutionarily conserved fitness comparison strategy aimed at detecting weakened cells, which are then committed to death, removed from the tissue and replaced by fitter neighbours. During physiological development, MYC-mediated cell competition is engaged to eliminate cells with suboptimal MYC levels, so as to guarantee selective growth of the fittest and proper homeostasis, while transformed cells expressing high levels of MYC coopt cell competition to subvert tissue constraints, ultimately disrupting homeostasis. Therefore, the interplay between cells with different MYC levels may result in opposite functional outcomes, depending on the nature of the players. In the present review, we describe the most recent findings on the role of MYC-mediated cell competition in different contexts, with a special emphasis on its impact on cancer initiation and progression. We also discuss the relevance of competition-associated cell death to cancer disease.

Role of genomic instability in human carcinogenesis

IMPACT STATEMENT

This review provides various genetic and cell line data previously published in a way to explain how cellular stress can lead into genetic instability.

miR-522-3p Promotes Tumorigenesis in Human Colorectal Cancer via Targeting Bloom Syndrome Protein

miR-522-3p is known to degrade bloom syndrome protein (BLM) and enhance expression of other proto-oncogenes, leading to tumorigenesis. This study aimed to investigate the molecular mechanisms of miR-522-3p in human colorectal cancer (CRC) cells. Expressions of miR-522-3p in CRC and adjacent tissues, as well as in normal human colon epithelial cell line (FHC) and five CRC cell lines, were detected. Human CRC cell lines, HCT-116 and HT29, were transfected with miR-522-3p mimic, inhibitor, or scrambled controls. Then cell viability, apoptosis, cell cycle progression, and the expressions of c-myc, cyclin E, CDK2, and BLM were assessed. It was found that miR-522-3p was highly expressed in CRC tissues when compared to adjacent nontumor tissues and was highly expressed in CRC cell lines when compared to FHC cells. miR-522-3p overexpression promoted cell viability, reduced apoptotic cell rate, arrested more cells in the S phase, and upregulated c-myc, cyclin E, and CDK2 expression. BLM was a target gene of miR-522-3p, and miR-522-3p suppression did not exert antiproliferative and proapoptotic activities when BLM was silenced. These findings demonstrate that miR-522-3p upregulation negatively regulates the expression of BLM, with upregulation of c-myc, CDK2, and cyclin E, and thereby promoting the proliferation of human CRC cells.

c-Myc-regulated long non-coding RNA H19 indicates a poor prognosis and affects cell proliferation in non-small-cell lung cancer

Recently, long non-coding RNAs (lncRNAs) have been shown to play important roles in human cancer biology. The purpose of this study was to assess the biological role of lncRNA H19 in non-small-cell lung cancer (NSCLC). Quantitative reverse transcription PCR (qRT-PCR) was used to detect the expression of H19 in tumor tissues and corresponding non-tumor NSCLC tissues from 70 patients. The higher expression of H19 was positively correlated with advanced tumor-node-metastasis (TNM) stage and tumor size. Multivariate analyses found that H19 expression could serve as an independent prognostic factor for overall survival of NSCLC. Moreover, chromatin immunoprecipitation (ChIP) assays revealed that H19 was a direct transcriptional target of c-Myc. And, knockdown of H19 significantly inhibited NSCLC cell proliferation both in vitro and in vivo. In conclusion, our study demonstrated that H19 is involved in the oncogenesis of NSCLC, and H19 may be a potential diagnostic and target for new therapies in patients with NSCLC.

Tumour immunogenicity, antigen presentation and immunological barriers in cancer immunotherapy

Since the beginning of the 20^th century, scientists have tried to stimulate the anti-tumour activities of the immune system to fight against cancer. However, the scientific effort devoted on the development of cancer immunotherapy has not been translated into the expected clinical success. On the contrary, classical anti-neoplastic treatments such as surgery, radiotherapy and chemotherapy are the first line of treatment. Nevertheless, there is compelling evidence on the immunogenicity of cancer cells, and the capacity of the immune system to expand cancer-specific effector cytotoxic T cells. However, the effective activation of anti-cancer T cell responses strongly depends on efficient tumour antigen presentation from professional antigen presenting cells such as dendritic cells (DCs). Several strategies have been used to boost DC antigen presenting functions, but at the end cancer immunotherapy is not as effective as would be expected according to preclinical models. In this review we comment on these discrepancies, focusing our attention on the contribution of regulatory T cells and myeloid-derived suppressor cells to the lack of therapeutic success of DC-based cancer immunotherapy.

MYC expression and distribution in normal mature lymphoid cells

The distribution of the product of the proto-oncogene MYC in lymphoid tissue has not been established in three decades, due to a combination of factors including low abundance, short half-life, and antibody sensitivity and specificity. We sought to validate antibodies in order to define the expression and distribution of MYC in mature normal lymphoid cells by multiparametric immunophenotyping. Having validated two antibodies for flow cytometry and for immunohistochemistry, we analysed normal tonsil tissue. MYC is expressed predominantly in B cells, some of which are interfollicular large, activated, and cycling CD30+, IRF4+, AID± blasts. Follicular mantle, isotype-switched memory B cells and FcRH4/IRTA1+ B cells express MYC in a wide range of levels and are small non-proliferating CDKN1B/p27-positive or -negative resting B lymphocytes. Germinal centre founder cells, CD30+ BCL6± AID± germinal centre blasts, and a population of GC cells in the apical light zone express MYC. MYC is expressed in all phases of the cell cycle in activated and mature B cells, but rarely in other lymphoid types and only partially fulfils the predictions derived from extractive and ex vivo experiments of the past 30 years.

Retroviral oncogenes: a historical primer

Retroviruses are the original source of oncogenes. The discovery and characterization of these genes was made possible by the introduction of quantitative cell biological and molecular techniques for the study of tumour viruses. Key features of all retroviral oncogenes were first identified in src, the oncogene of Rous sarcoma virus. These include non-involvement in viral replication, coding for a single protein and cellular origin. The MYC, RAS and ERBB oncogenes quickly followed SRC, and these together with PI3K are now recognized as crucial driving forces in human cancer.

Identification of testis-relevant genes using in silico analysis from testis ESTs and cDNA microarray in the black tiger shrimp (Penaeus monodon)

Background

Poor reproductive maturation of the black tiger shrimp (Penaeus monodon) in captivity is one of the serious threats to sustainability of the shrimp farming industry. Understanding molecular mechanisms governing reproductive maturation processes requires the fundamental knowledge of integrated expression profiles in gonads of this economically important species. In P. monodon, a non-model species for which the genome sequence is not available, expressed sequence tag (EST) and cDNA microarray analyses can help reveal important transcripts relevant to reproduction and facilitate functional characterization of transcripts with important roles in male reproductive development and maturation.

Results

In this study, a conventional testis EST library was exploited to reveal novel transcripts. A total of 4,803 ESTs were unidirectionally sequenced and analyzed in silico using a customizable data analysis package, ESTplus. After sequence assembly, 2,702 unique sequences comprised of 424 contigs and 2,278 singletons were identified; of these, 1,133 sequences are homologous to genes with known functions. The sequences were further characterized according to gene ontology categories (41% biological process, 24% molecular function, 35% cellular component). Through comparison with EST libraries of other tissues of P. monodon, 1,579 transcripts found only in the testis cDNA library were identified. A total of 621 ESTs have not been identified in penaeid shrimp. Furthermore, cDNA microarray analysis revealed several ESTs homologous to testis-relevant genes were more preferentially expressed in testis than in ovary. Representatives of these transcripts, homologs of saposin (PmSap) and Dmc1 (PmDmc1), were further characterized by RACE-PCR. The more abundant expression levels in testis than ovary of PmSap and PmDmc1 were verified by quantitative real-time PCR in juveniles and wild broodstock of P. monodon.

Conclusions

Without a genome sequence, a combination of EST analysis and high-throughput cDNA microarray technology can be a useful integrated tool as an initial step towards the identification of transcripts with important biological functions. Identification and expression analysis of saposin and Dmc1 homologs demonstrate the power of these methods for characterizing functionally important genes in P. monodon.

Colocalization of somatic and meiotic double strand breaks near the Myc oncogene on mouse chromosome 15

Both somatic and meiotic recombinations involve the repair of DNA double strand breaks (DSBs) that occur at preferred locations in the genome. Improper repair of DSBs during either mitosis or meiosis can lead to mutations, chromosomal aberration such as translocations, cancer, and/or cell death. Currently, no model exists that explains the locations of either spontaneous somatic DSBs or programmed meiotic DSBs or relates them to each other. One common class of tumorigenic translocations arising from DSBs is chromosomal rearrangements near the Myc oncogene. Myc translocations have been associated with Burkitt lymphoma in humans, plasmacytoma in mice, and immunocytoma in rats. Comparing the locations of somatic and meiotic DSBs near the mouse Myc oncogene, we demonstrated that the placement of these DSBs is not random and that both events clustered in the same short discrete region of the genome. Our work shows that both somatic and meiotic DSBs tend to occur in proximity to each other within the Myc region, suggesting that they share common originating features. It is likely that some regions of the genome are more susceptible to both somatic and meiotic DSBs, and the locations of meiotic hotspots may be an indicator of genomic regions more susceptible to DNA damage.

Hepatocyte Paraffin 1 Immunoreactivity in Early Colon Carcinogenesis

Background

This study was aimed at evaluating the correlation between Hepatocyte paraffin 1 (Hep par 1) and colorectal cancer.

Methods

To this end, 50 intestinal biopsies were analyzed including 10 colorectal polyps with low grade dysplasia, 10 with high grade dysplasia, 10 colorectal adenocarcinomas, 10 specimens of normal ileum and 10 of normal colon mucosa. Tissue sections were immunostained for Hep par 1 utilizing a commercial antibody. Normal colonic mucosa did not express Hep par 1.

Results

Immunoreactivity for Hep par 1 was detected in 20% of polyps with low grade dysplasia, 50% of polyps with high grade dysplasia and 60% of colorectal carcinomas. Hep par 1 was frequently detected in the deepest areas of adenocarcinomas mainly in infiltrating tumour cells.

Conclusions

Our data show that Hep par 1 immunoreactivity in human colon carcinogenesis is correlated with progression from low grade to high grade dysplasia and adenocarcinoma. In clinical practice, our data show that caution should be taken in utilizing Hep par 1 as the sole tool in differentiating hepatocellular carcinoma from a liver metastasis of colon adenocarcinoma. Our data encourage further investigations into the potential role played by Hep par 1 in gastrointestinal carcinogenesis.

Non-transcriptional control of DNA replication by c-Myc

The c-Myc proto-oncogene encodes a transcription factor that is essential for cell growth and proliferation and is broadly implicated in tumorigenesis. However, the biological functions required by c-Myc to induce oncogenesis remain elusive. Here we show that c-Myc has a direct role in the control of DNA replication. c-Myc interacts with the pre-replicative complex and localizes to early sites of DNA synthesis. Depletion of c-Myc from mammalian (human and mouse) cells as well as from Xenopus cell-free extracts, which are devoid of RNA transcription, demonstrates a non-transcriptional role for c-Myc in the initiation of DNA replication. Overexpression of c-Myc causes increased replication origin activity with subsequent DNA damage and checkpoint activation. These findings identify a critical function of c-Myc in DNA replication and suggest a novel mechanism for its normal and oncogenic functions.

Deregulation in trans or c-myc expression in immortalized human urothelial cells and in T24 bladder carcinoma cells

The expression of a number of cellular oncogenes was investigated in human urothelial cell lines with different in vitro growth properties. Constitutively elevated levels of expression of c-myc RNA were found in Hu609, an immortalized, nontumorigenic cell line that was derived from normal urothelium, and in the bladder carcinoma cell line T24. Potential mechanisms that might underlie deregulation of c-myc expression in these cells were investigated. It was found that the c-myc gene was apparently intact and not amplified in Hu609 and T24. No increased stability of c-myc RNA was detected. A c-myc-CAT fusion construct containing 2.5 kb of normal c-myc 5' sequences showed levels of expression that paralleled the overexpression of the endogenous gene, indicating that the high constitutive levels of c-myc expression were due, at least in part, to alterations in the activities of cellular trans-acting transcriptional regulators.

A role for p38 mitogen-activated protein kinase and c-myc in endothelin-dependent rat aortic smooth muscle cell proliferation

We have demonstrated recently that endothelin (ET) stimulates rat aortic smooth muscle cell proliferation through an extracellular signal-regulated kinase (ERK)-dependent mechanism. Approximately 70% of ET-dependent [3H]-thymidine incorporation in these cells signals through this system. In the present study, we show that the residual mitogenic activity requires an intact p38 mitogen-activated protein kinase (p38 MAPK) system and increased c-myc gene expression. ET increased [3H]-thymidine incorporation in rat aortic smooth muscle cells approximately 5-fold. p38 MAPK inhibition with SB203580 or ERK/ERK kinase inhibition with PD98059 each effected approximately 70% inhibition in ET-dependent DNA synthesis, whereas the combination led to nearly complete blockade of the ET effect. ET also increased c-myc RNA levels and c-Myc protein levels in these cells. The increment in c-Myc expression was blocked by SB203580 but not by PD98059. Use of antisense oligonucleotides directed against the translation start site of the c-myc transcript, but not scrambled oligonucleotide sequence, resulted in approximately 60% decrease in ET-dependent [3H]-thymidine incorporation. The combination of antisense c-myc and PD98059 resulted in near complete inhibition of ET-dependent DNA synthesis. Both ET and c-Myc increased expression and promoter activity of E2F, a transcription factor that has been linked to enhanced cell cycle activity. The ET-dependent increment in E2F promoter activity was suppressed after treatment with SB203580 or antisense c-myc but not by PD98059 or a scrambled oligonucleotide sequence. Collectively, these findings demonstrate that ET uses 2 complementary signal transduction cascades (ERK and p38 MAPK) to control proliferative activity of vascular smooth muscle cells.

A near-infrared Fourier transform Raman spectroscopy of epidermal keratinocytes: changes in the protein-DNA structure following malignant transformation

We report here the use of near-infrared (NIR) Fourier transform (FT) Raman spectroscopy to analyze normal human epidermal keratinocytes prior to and following malignant transformation. Our analysis indicates specific Raman spectral differences between immortalized (HPK1A) and malignant ras transformed (HPK1A-ras) cells. In addition, striking spectral differences are seen in the DNA isolated from these cells and particularly in the 843/810 cm(-1) ratio with values of 1.6 +/- 0.13 in HPK1A cells and 0.68 +/- 0.09 in HPK1A-ras cells (mean +/- S.D., n = 12, P < 0.001) indicating specific alterations in the backbone conformation markers following malignant transformation. Subsequently, we analysed the effect of a strong inhibitor of keratinocyte growth, the Vitamin D analog EB1089, on the Raman spectra of intact cells and on the 843/810 cm(-1) ratio in the DNA isolated from both cell lines. Specific changes were observed in intact cells in the 1300-750 cm(-1) region. Furthermore, the 843/810 cm(-1) ratio of isolated DNA from HPK1A cells was not affected by EB1089 but significantly increased in DNA isolated from HPK1A-ras cells so much that it became closer to the value observed for HPK1A cells (1.07 +/- 0.10). Our data suggest that Raman analysis of DNA and in particular the 843/810 cm(-1) ratio can provide useful indices of malignant transformation and efficacy of anticancer agents.

Direct Activation of HSP90A Transcription by c-Myc Contributes to c-Myc-induced Transformation

The c-myc proto-oncogene encodes a ubiquitous transcription factor involved in the control of cell growth and differentiation and implicated in inducing tumorigenesis. Understanding the function of c-Myc and its role in cancer depends upon the identification of c-Myc target genes. Heat shock protein 90 (HSP90) is involved in the folding of proteins such as signal transduction molecules (Src, Raf1, cdk4) and steroid receptors and in enhancing the activity of telomerase and nitric-oxide synthase. Here we show that c-Myc directly activates HSP90A transcription. c-Myc-mediated induction of HSP90A transcription occurs in different tissues, is independent of cell proliferation, and is mediated by a c-Myc binding site in the proximal promoter region of HSP90A gene. Overexpression of HSP90A in Rat1a cells induces transformation. Short interference RNA of HSP90A/Hsp86alpha reduces transformation activity in HeLa and RatMyc cells. These results indicate that by induction of HSP90A c-Myc may control the activity of multiple signal pathways involved in cellular transformation.

A global transcriptional regulatory role for c-Myc in Burkitt's lymphoma cells

Overexpression of c-Myc is one of the most common alterations in human cancers, yet it is not clear how this transcription factor acts to promote malignant transformation. To understand the molecular targets of c-Myc function, we have used an unbiased genome-wide location-analysis approach to examine the genomic binding sites of c-Myc in Burkitt's lymphoma cells. We find that c-Myc together with its heterodimeric partner, Max, occupy >15% of gene promoters tested in these cancer cells. The DNA binding of c-Myc and Max correlates extensively with gene expression throughout the genome, a hallmark attribute of general transcription factors. The c-Myc/Max heterodimer complexes also colocalize with transcription factor IID in these cells, further supporting a general role for overexpressed c-Myc in global gene regulation. In addition, transcription of a majority of c-Myc target genes exhibits changes correlated with levels of c-myc mRNA in a diverse set of tissues and cell lines, supporting the conclusion that c-Myc regulates them. Taken together, these results suggest a general role for overexpressed c-Myc in global transcriptional regulation in some cancer cells and point toward molecular mechanisms for c-Myc function in malignant transformation.

c-Myc directly regulates the transcription of the NBS1 gene involved in DNA double-strand break repair

The c-myc proto-oncogene encodes a ubiquitous transcription factor involved in the control of cell growth and implicated in inducing tumorigenesis. Understanding the function of c-Myc and its role in cancer depends upon the identification of c-Myc target genes. Nijmegen breakage syndrome (NBS) is a chromosomal-instability syndrome associated with cancer predisposition, radiosensitivity, and chromosomal instability. The NBS gene product, NBS1 (p95 or nibrin), is a part of the hMre11 complex, a central player associated with double-strand break (DSB) repair. NBS1 contains domains characteristic for proteins involved in DNA repair, recombination, and replication. Here we show that c-Myc directly activates NBS1. c-Myc-mediated induction of NBS1 gene transcription occurs in different tissues, is independent of cell proliferation, and is mediated by a c-Myc binding site in the intron 1 region of NBS1 gene. Overexpression of NBS1 in Rat1a cells increased cell proliferation. These results indicate that NBS1 is a direct transcriptional target of c-Myc and links the function of c-Myc to the regulation of DNA DSB repair pathway operating during DNA replication.

Molecular interactions between glucocorticoid and catecholamine signaling pathways

To study the mechanism underlying glucocorticoid regulation of the beta(1)-adrenergic receptor (beta(1)AR), we identified a 43-bp region (-1274 to -1232 from the translation start site) that contains a novel glucocorticoid regulatory unit (GRU) that confers glucocorticoid responsiveness. The sequence encompassing the GRU is (5')TAATTA(3'), which is a core-binding motif for the homeodomain proteins; an E-box ((5')CACGTG(3')) binding site for the Myc/Max family proteins, and an overlapping glucocorticoid response element half-site ((5')TGTTCT(3')). We showed that the half-site is critical for GRU-protein interactions, which also require binding of proteins to the E-box and the homeodomain region. Expression of proteins binding to the GRU was shown to be developmentally regulated, being high in embryonic hearts, reduced in newborn hearts, and undetectable in adult hearts. Overexpression of c-myc antisense significantly reduced glucocorticoid responsiveness of the beta(1)AR gene. We further demonstrated that transcriptional regulation of the beta(1)AR gene is closely related to that of the c-myc gene and that the beta(1)AR may be a potential target of c-myc. We conclude that the ovine beta(1)AR gene contains a novel, functional GRU and that the nuclear factors that transactivate through this element may have important developmental implications.

c-MYC activates protein kinase A (PKA) by direct transcriptional activation of the PKA catalytic subunit beta (PKA-Cbeta) gene

The c-MYC proto-oncogene encodes a ubiquitous transcription factor involved in the control of cell growth and differentiation and broadly implicated in tumorigenesis. Understanding the function of c-MYC and its role in cancer depends upon the identification of c-MYC target genes. Here we show that c-MYC induces the activity of Protein Kinase A (PKA), a key effector of cAMP-mediated signal transduction, by inducing the transcription of the gene encoding the PKA catalytic subunit beta (PKA-Cbeta). c-MYC-mediated induction of PKA-Cbeta gene transcription occurs in multiple tissues, is independent of cell proliferation and is mediated by direct binding of c-MYC to the PKA-Cbeta gene promoter sequences. Constitutive expression of PKA-Cbeta in Rat1A cells induces their transformation, and c-MYC-induced transformation can be reverted by pharmacological inhibition of PKA, suggesting that up-regulation of PKA is critical for c-MYC-associated tumorigenesis. These results indicate that, by activating PKA, c-MYC can provide endogenous activation of the cAMP signal transduction pathway independently of extracellular signals.

Induction or suppression of expression of cytochrome C oxidase subunit II by heregulin beta 1 in human mammary epithelial cells is dependent on the levels of ErbB2 expression

The ErbB family of receptor kinases is composed of four members: epidermal growth factor receptor (EGFR/ErbB1), ErbB2/neu, ErbB3, and ErbB4. Amplification of the ErbB2/neu is found in about 30% of breast cancer patients and is associated with a poor prognosis. Heregulin (HRG) activates the ErbB2 via induction of heterodimerization with ErbB3 and ErbB4 receptors. With suppression subtractive hybridization, we demonstrated that the expression of cytochrome c oxidase subunit II (COXII) is HRG-responsive. Two nontransformed human mammary epithelial cell lines, the HB2 and the HB2(ErbB2) (the HB2 engineered to overexpress ErbB2), displayed an opposite response to HRG-mediated regulation. HRG upregulated mRNA expression of COXII in the HB2 cells, but suppressed COXII expression in the HB2(ErbB2) cells. A human breast cancer cell line (T47D), which expresses ErbB2 at a level similar to that of the HB2 cells, also responded to HRG by increasing COXII mRNA levels. Therefore, HRG regulation of COXII expression depends on the levels of ErbB2 expression. Furthermore, the expression of COXII was inversely correlated to the levels of ErbB2, i.e., the cells overexpressing ErbB2 exhibited lower COXII levels. HRG-evoked signal transduction differed between the cells with normal ErbB expression and the cells overexpressing ErbB2. The activation of both ERK and PI3-K was essential for HRG regulation of COXII, i.e., blockage of either pathway eliminated HRG-mediated alteration. This is the first report demonstrating that the expression of mitochondria-encoded COXII is HRG-responsive. The levels of ErbB2 expression are decisive for the diverse biological activities of HRG.

The heparin-binding domain and V region of fibronectin regulate apoptosis by suppression of p53 and c-myc in human primary cells

In apoptosis the tumor suppressor p53 and the c-myc proto-oncogene are usually up-regulated. We show a novel alternative pathway of apoptosis in human primary cells that is mediated by transcriptionally dependent decreases in p53 and c-Myc and decreases in p21. This pathway is regulated by the alternatively spliced V region and high-affinity heparin-binding domain of fibronectin. Requirements for c-Myc, p53, and p21 signals in maintaining survival and for their decreases in inducing apoptosis were demonstrated by the ability of p53, c-Myc, and p21 ectopic expression to rescue this apoptotic phenotype, and the ability of p53-deficient and c-myc antisense conditions to trigger a faster rate of apoptosis.

Suppression of c-myc expression and c-Myc function in response to sustained DNA damage in MCF-7 breast tumor cells

The topoisomerase II inhibitors teniposide (VM-26), doxorubicin, and amsacrine (m-AMSA), as well as ionizing radiation, induce a transient suppression of c-myc mRNA, which correlates with growth inhibition of MCF-7 breast tumor cells. To further assess the involvement of c-mvc in the DNA damage-induced signal transduction pathways of the breast tumor cell, we determined the influence of sustained DNA damage on c-myc expression, c-Myc protein levels and c-Myc function. Continuous exposure of MCF-7 breast tumor cells to VM-26 induced DNA strand breaks that were sustained for at least 9 hr. DNA strand breakage was accompanied by a decline in c-myc transcripts and c-Myc protein levels by >90% after VM-26 exposure for 24 hr. The activity of a transcriptional target of the c-Myc protein, ornithine decarboxylase, was reduced by approximately 75% within 9 hr of DNA damage, in parallel to the declines in c-myc mRNA and protein levels. Extended exposure to VM-26 resulted in an initial loss of approximately 35% of the cell population followed by the death of additional cells such that by 72 hr only 50% of the cells were viable. Although apoptosis was evident 72 hr after initiating drug exposure [based on cell cycle analysis, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assays, and an assessment of cell morphology], the primary phase of cell killing, which occurred during the first 24 hr was non-apoptotic. These studies indicate that non-apoptotic pathways can also mediate cell death in the breast tumor cell and support the role of c-myc expression, c-Myc protein, and c-Myc function as elements of the DNA damage response pathway in the breast tumor cell.

A novel glucocorticoid regulatory unit mediates the hormone responsiveness of the beta1-adrenergic receptor gene

The effects of glucocorticoids on expression of the beta1-adrenergic receptor (beta1AR) gene have been varied. To study the mechanism underling hormonal regulation of the beta1AR, transient transfection of progressively deleted ovine beta1AR promoter fragments was used to identify a 43-bp region (-1274 to -1232 from the translation start site) that contains a novel glucocorticoid regulatory unit (GRU) and confers glucocorticoid responsiveness. Using DNase I footprinting and electrophoretic mobility shift assays (EMSA), we demonstrated the GRU was composed of a palindrome, 5'-TAATTA-3', which is a core binding motif for the homeodomain proteins, an E-box (5'-CACGTG-3'), binding site for the Myc/Max family proteins, and an overlapping glucocorticoid response element (GRE) half-site (5'-TGTTCT-3'). EMSA demonstrated that the GRE half-site is critical for GRU-protein interactions, which also require binding of proteins to the E-box and the homeodomain region. Co-transfection of a plasmid expressing a c-myc antisense construct significantly reduced glucocorticoid responsiveness of the ovine beta1AR promoter. Furthermore, expression of proteins binding to the GRU was shown to be developmentally regulated, being high in embryonic, reduced in newborn and not detectable in adult heart. We conclude that the ovine beta1AR promoter contains a novel, functional GRU and that glucocorticoid receptor (GR) and the Myc/Max family proteins are involved in the cell-specific nuclear factor binding and transactivation via this element. The results suggest an alternative pathway through which glucocorticoids may exert their effects on genes lacking a full consensus GRE.

Quantitative mRNA expression analysis from formalin-fixed, paraffin-embedded tissues using 5' nuclease quantitative reverse transcription-polymerase chain reaction

Analysis of gene expression and correlation with clinical parameters has the potential to become an important factor in therapeutic decision making. The ability to analyze gene expression in archived tissues, for which clinical followup is already available, will greatly facilitate research in this area. A major obstacle to this approach, however, has been the uncertainty about whether gene expression analyses from routinely archived tissues accurately reflect expression before fixation. In the present study we have optimized the RNA isolation and reverse transcription steps for quantitative reverse transcription-polymerase chain reaction (RT-PCR) on archival material. Using tissue taken directly from the operating room, mRNAs with half-lives from 10 minutes to >8 hours were isolated and reverse transcribed. Subsequent real-time quantitative PCR methodology (TaqMan) on these cDNAs gives a measurement of gene expression in the fixed tissues comparable to that in the fresh tissue. In addition, we simulated routine pathology handling and demonstrate that this method of mRNA quantitation is insensitive to pre-fixation times (time from excision to fixation) of up to 12 hours. Therefore, it should be feasible to analyze gene expression in archived tissues where tissue collection procedures are largely unknown.

Analysis of C-MYC function in normal cells via conditional gene-targeted mutation

Germline inactivation of c-myc in mice causes embryonic lethality. Therefore, we developed a LoxP/Cre-based conditional mutation approach to test the role of c-myc in mouse embryonic fibroblasts (MEFs) and mature B lymphocytes. Cre expression resulted in reduced proliferation of wild-type MEFs, but c-Myc-deficient MEFs showed a further reduction. In contrast to fibroblasts, Cre expression had no apparent affect on wild-type B cell proliferation. Deletion of both c-Myc genes in B cells led to severely impaired proliferation in response to anti-CD40 plus IL-4. However, treated cells did upregulate several early activation markers but not CD95 or CD95 ligand. We discuss these findings with respect to potential c-Myc functions in proliferation and apoptosis and also discuss potential limitations in the Cre-mediated gene inactivation approach.

Disruption of Myc-tubulin interaction by hyperphosphorylation of c-Myc during mitosis or by constitutive hyperphosphorylation of mutant c-Myc in Burkitt's lymphoma

Somatic mutations at Thr-58 of c-Myc have been detected in Burkitt's lymphoma (BL) tumors and have been shown to affect the transforming potential of the Myc oncoprotein. In addition, the N-terminal domain of c-Myc has been shown to interact with microtubules in vivo, and the binding of c-Myc to alpha-tubulin was localized to amino acids 48 to 135 within the c-Myc protein. We demonstrate that c-Myc proteins harboring a naturally occurring mutation at Thr-58 from BL cell lines have increased stability and are constitutively hyperphosphorylated, which disrupts the in vivo interaction of c-Myc with alpha-tubulin. In addition, we show that wild-type c-Myc-alpha-tubulin interactions are also disrupted during a transient mitosis-specific hyperphosphorylation of c-Myc, which resembles the constitutive hyperphosphorylation pattern of Thr-58 in BL cells.

Direct activation of TERT transcription by c-MYC

The MYC proto-oncogene encodes a ubiquitous transcription factor (c-MYC) involved in the control of cell proliferation and differentiation. Deregulated expression of c-MYC caused by gene amplification, retroviral insertion, or chromosomal translocation is associated with tumorigenesis. The function of c-MYC and its role in tumorigenesis are poorly understood because few c-MYC targets have been identified. Here we show that c-MYC has a direct role in induction of the activity of telomerase, the ribonucleoprotein complex expressed in proliferating and transformed cells, in which it preserves chromosome integrity by maintaining telomere length. c-MYC activates telomerase by inducing expression of its catalytic subunit, telomerase reverse transcriptase (TERT). Telomerase complex activity is dependent on TERT, a specialized type of reverse transcriptase. TERT and c-MYC are expressed in normal and transformed proliferating cells, downregulated in quiescent and terminally differentiated cells, and can both induce immortalization when constitutively expressed in transfected cells. Consistent with the recently reported association between MYC overexpression and induction of telomerase activity, we find here that the TERT promoter contains numerous c-MYC-binding sites that mediate TERT transcriptional activation. c-MYC-induced TERT expression is rapid and independent of cell proliferation and additional protein synthesis, consistent with direct transcriptional activation of TERT. Our results indicate that TERT is a target of c-MYC activity and identify a pathway linking cell proliferation and chromosome integrity in normal and neoplastic cells.

Coordinated regulation of iron-controlling genes, H-ferritin and IRP2, by c-MYC

The protein encoded by the c-MYC proto-oncogene is a transcription factor that can both activate and repress the expression of target genes, but few of its transcriptional targets have been identified. Here, c-MYC is shown to repress the expression of the heavy subunit of the protein ferritin (H-ferritin), which sequesters intracellular iron, and to stimulate the expression of the iron regulatory protein-2 (IRP2), which increases the intracellular iron pool. Down-regulation of the expression of H-ferritin gene was required for cell transformation by c-MYC. These results indicate that c-MYC coordinately regulates genes controlling intracellular iron concentrations and that this function is essential for the control of cell proliferation and transformation by c-MYC.

Mad1 expression in the absence of differentiation: effect of cAMP on the B-lymphoid cell line Reh

The protein Mad1 heterodimerizes with Max to form an E-box binding complex able to interfere with the transcriptional and transforming activities of c-Myc. Downregulation of c-Myc accompanied by induction of Mad1 upon differentiation has fueled the notion that Mad1 may play a role in the cessation of proliferation associated with the differentiation process. Since studies on Mad1 expression have so far been limited to cells undergoing differentiation, it was of interest to examine Mad1 expression in a cell system unable to differentiate. To do so, we utilized the leukemia-derived B-precursor cell line, Reh, and studied the expressions of Mad1, c-Myc, Mxil, and Max during cAMP-mediated growth inhibition of these cells. Thus, the adenylate cyclase activator forskolin induced growth inhibition of the cells in the G1 phase of the cell cycle. This growth inhibition was associated with transient increased expression of Mad1 concomitant with transient downregulation of c-Myc. The Mad1 protein levels essentially paralleled those of mRNA, with peak levels at 4 h of forskolin treatment. By coimmunoprecipitation we detected increased binding of Mad1 to Max in forskolin-treated cells, indicating that the changes in Mad1 protein levels had functional implications. By continually treating Reh cells with forskolin for 72 h, we observed a sustained elevated expression of Mad1 concomitant with downregulated c-Myc expression, still without changing the differentiation profile of the Reh cells. Interestingly, we showed that other known cell cycle regulatory proteins also were transiently regulated by forskolin. To this extent, following forskolin treatment of Reh cells, cyclin E-cdk2 activity was transiently reduced concomitant with dephosphorylation of pRB. We suggest that the early changes in Mad1 and the cell cycle regulatory proteins initiate a chain of events resulting in permanent growth arrest. Thus, the increased expression of Mad1 in the absence of differentiation indicates that Mad1 expression in Reh cells is linked to growth arrest per se.

Early captopril treatment prevents hypertrophydependent gene expression in hearts of SHR

Treatment of spontaneously hypertensive rats (SHR) with captopril (100 mg . kg-1 . day-1) throughout development and during the first 16 wk of life leads to a reduction in blood pressure and left ventricular hypertrophy. Blood pressures and hypertrophy are reduced in these animals (vs. untreated SHR) for up to 24 wk after discontinuation of the drug. We used conventional blot hybridization and Western analysis to examine hypertrophy-dependent gene expression during this period. Ventricular expression of the atrial natriuretic peptide gene was reduced by >90% at 16 wk of age in the captopril-treated SHR. Expression increased in the 24 wk after discontinuation of treatment, but remained well below that of the untreated SHR. A similar reduction in ventricular c-myc gene expression was seen with captopril treatment. Neither renal expression of the atrial natriuretic peptide gene nor ventricular expression of the c-fos gene was affected by captopril. This study demonstrates that captopril treatment during a critical period of development in the SHR leads to a sustained reduction in hypertrophy-dependent myocardial gene expression, which does not revert to levels seen in the untreated SHR after discontinuation of the drug.

The response of smooth muscle cells to alpha-thrombin depends on its arterial origin: comparison among different species

BACKGROUND

Thrombin plays a pivotal role in the pathogenesis of arterial thrombosis and exerts a wide spectrum of effects on the cells of vessel walls.

METHODS

In this paper we focus on the direct role of thrombin as a mitogen for smooth muscle cells (SMCs) derived from different vessels from the vascular tree (coronary artery, aorta, carotid artery and pulmonary artery) of different species (human and pig). All cell populations examined responded mitogenically to alpha-thrombin, however the extent of this response was dependent on both vascular origin and the species from which vessels were derived.

RESULTS

Thrombin (1-100 nmol L-1) induced DNA synthesis ranging from 1.5- to 4-fold baseline depending on cell type. Porcine coronary SMCs showed the highest response to thrombin (100 nmol L-1) in terms of protein and DNA synthesis (4.0 +/- 0.2-fold) and cell division (53.4 +/- 8.8%) among the tested cells. In these cells recombinant (r)-hirudin, a specific thrombin inhibitor, exhibited maximal effectiveness to block the mitogenic effect of thrombin. Human SMC response ([3H]-thymidine incorporation) to either sera or thrombin was lower than that of porcine cells. In contrast, c-fos mRNA levels induced by thrombin in human SMCs were higher than those induced in porcine cells. In human cells, thrombin elicited an overexpression of c-fos and a lower rate of [3H]-thymidine incorporation than in porcine cells. Insulin-like growth factor I but not insulin showed additive mitogenic effects with thrombin in human coronary SMCs. The response of these cells to thrombin from different sources was a function of thrombin specific activity.

CONCLUSION

These results suggest that the cell system chosen to check thrombin mitogenicity not only determines thrombin quantitative effects but also may affect the effectiveness of an inhibitor to block its biological activity.

cAMP increasing agents attenuate the generation of apoptosis by etoposide in promonocytic leukemia cells

Treatment of U-937 promonocytic cells with the DNA topoisomerase II inhibitor etoposide rapidly caused death by apoptosis, as determined by changes in chromatin structure, production of DNA breaks, nucleosome-sized DNA degradation, decrease in mitochondrial membrane potential and phosphatidyl serine translocation in the plasma membrane, and at the same time induced intracellular acidification. Both the execution of the apoptotic process and the intracellular acidification were reduced by the addition of forskolin plus theophylline or other cAMP increasing agents. These agents also attenuated the induction of apoptosis by camptothecin, heat-shock, cadmium chloride and X-radiation. Although etoposide slightly increased the production of reactive oxygen intermediates, this increase was not prevented by forskolin plus theophylline, and the addition of antioxidant agents failed to inhibit apoptosis. Etoposide caused a great increase in NF-(kappa)B binding activity, which was not prevented by forskolin plus theophylline, while AP-1 binding was little affected by the topoisomerase inhibitor. The treatments did not significantly alter the levels of Bcl-2 and Bax. By contrast, the expression of c-myc, which was very high in untreated U-937 cells and only partially inhibited by etoposide, was rapidly and almost totally abolished by the cAMP increasing agents. Finally, it was observed that etoposide caused a transient dephosphorylation of retinoblastoma (Rb), which was associated with cleavage of poly(ADP-ribose) polymerase (PARP). Both Rb dephosphorylation and PARP cleavage were inhibited by forskolin plus theophylline. The inhibition of Rb (type I) phosphatase and ICE/CED-3-like protease activities, and the abrogation of c-myc expression, are mechanisms which could explain the anti-apoptotic action of cAMP increasing agents in myeloid cells.

Role of Oncogenic Transcription Factor c-Myc in Cell Cycle Regulation, Apoptosis and Metabolism

The myc gene was initially discovered as a prototypical retrovirally transduced oncogene. Over the decades, abundant evidence has emerged to support a causal role for the activated cellular gene, c-myc, in animal and human tumors. The gene encodes an oncogenic helix-loop-helix leucine zipper transcription factor that acts as a heterodimer with its partner protein, Max, to activate genes regulating the cell cycle machinery as well as critical metabolic enzymes. The additional ability of c-Myc to repress transcription of differentiation-related genes suggest that c-Myc is a central and key molecular integrator of cell proliferation, differentiation and metabolism.

Combined chromosome microdissection and comparative genomic hybridization detect multiple sites of amplification DNA in a human lung carcinoma cell line

Chromosome microdissection-fluorescence in situ hybridization and comparative genomic hybridization (CGH) were performed in parallel to identify the native location of amplified DNA in a human non-small cell lung cancer (NSCLC) cell line exhibiting a homogeneously staining region (hsr) and double minutes (dmin). The native locations of microdissected DNA from the hsr and dmin were 7p12-13 and 8q24, respectively. Southern analysis revealed coamplification of EGFR (7p12) and MYC (8q24). CGH detected amplification of DNA not only from 7p12-13 and 8q24, but also from 9p24 and 10q22.

Control of vascular smooth-muscle cell growth by macrophage-colony-stimulating factor

Since in several vascular diseases abnormal vascular smooth-muscle cell (VSMC) proliferation is often associated with the presence of macrophages, we examined whether macrophage-colony-stimulating factor (M-CSF) might play a role in the control of VSMC growth. VSMCs were isolated from rat aorta and maintained in culture. Using a bioassay, a macrophage-colony-stimulating activity was detected in the serum-free supernatant of VSMCs, which could be inhibited by the addition of specific anti-M-CSF antibodies. The presence of M-CSF receptor protein and of M-CSF and M-CSF receptor gene transcripts was demonstrated by immunocytochemistry, using a specific anti-c-Fms antibody and Northern blot analysis respectively. [3H]Thymidine incorporation was measured following the addition to quiescent VSMCs of various dilutions of L929 cell supernatant (as a source of M-CSF) or of recombinant M-CSF. Both exogenous M-CSF and serum-free VSMC conditioned medium promoted DNA synthesis in a concentration-dependent manner, and this effect could be abrogated by the presence of a specific anti-M-CSF antibody. Under similar experimental conditions, L929 cell supernatant modulated proto-oncogene expression, as assessed by Northern blot analysis of c-fos, c-myc, egr-1 and junB. It was further demonstrated that M-CSF could act in synergy with thrombin, platelet-derived growth factor or basic fibroblast growth factor in promoting VSMC DNA synthesis. These results support the hypothesis that M-CSF affects the growth of cultured rat VSMCs through paracrine/autocrine mechanisms. Its effects at both the macrophage and the VSMC level confer to M-CSF a central role in the development of vascular lesions that occurs during atherosclerotic progression.

Endoglin modulates cellular responses to TGF-beta 1

Endoglin is a homodimeric membrane glycoprotein which can bind the beta 1 and beta 3 isoforms of transforming growth factor-beta (TGF-beta). We reported previously that endoglin is upregulated during monocyte differentiation. We have now observed that TGF-beta itself can stimulate the expression of endoglin in cultured human monocytes and in the U-937 monocytic line. To study the functional role of endoglin, stable transfectants of U-937 cells were generated which overexpress L- or S- endoglin isoforms, differing in their cytoplasmic domain. Inhibition of cellular proliferation and downregulation of c-myc mRNA which are normally induced by TGF-beta 1 in U-937 cells were totally abrogated in L-endoglin transfectants and much reduced in the S-endoglin transfectants. Inhibition of proliferation by TGF-beta 2 was not altered in the transfectants, in agreement with the isoform specificity of endoglin. Additional responses of U-937 cells to TGF-beta 1, including stimulation of fibronectin synthesis, cellular adhesion, platelet/endothelial cell adhesion molecule 1 (PECAM-1) phosphorylation, and homotypic aggregation were also inhibited in the endoglin transfectants. However, modulation of integrin and PECAM-1 levels and stimulation of mRNA levels for TGF-beta 1 and its receptors R-I, R-II, and betaglycan occurred normally in the endoglin transfectants. No changes in total ligand binding were observed in L-endoglin transfectants relative to mock, while a 1.5-fold increase was seen in S-endoglin transfectants. The degradation rate of the ligand was the same in all transfectants. Elucidating the mechanism by which endoglin modulates several cellular responses to TGF-beta 1 without interfering with ligand binding or degradation should increase our understanding of the complex pathways which mediate the effects of this factor.

Roles of stem cell factor in the in vitro growth of blast clonogenic cells from patients with acute myeloblastic leukemia

We investigated the effects of stem cell factor (SCF) on the growth of blast clonogenic cells from 27 patients with acute myeloblastic leukemia (AML) and 3 patients with chronic myelocytic leukemia in myeloid crisis. SCF alone showed a significant stimulatory activity in 15 of 30 patients (50%). A marked reduction in the number of blast cell colonies supported by SCF alone was noted by the addition of neutralizing antibody (Ab) against granulocyte-macrophage colony-stimulating factor (GM-CSF). Ab against interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) also moderately reduced the number of colonies, whereas Ab against granulocyte CSF (G-CSF) failed to do so. All four Ab together completely abolished the growth in 5 of 6 patients tested. c-kit antisense oligonucleotides reduced the colony formation supported by IL-3 or G-CSF or, in the absence of growth factor, in only 2 of 10 patients tested. SCF caused stimulation by acting synergistically with G-CSF, GM-CSF, IL-3, IL-6, IL-9, IL-11, and IL-12 in 20 of 27 (74%), 17 of 27 (63%), 14 of 28 (50%), 9 of 28 (32%), 1 of 15 (7%), 3 of 28 (11%), and 2 of 15 (13%) patients, respectively. Thus, SCF alone or in combination with some other factor stimulated the growth in 27 of 30 (90%) patients. Of 3 nonresponders, 2 were AML, M3 at presentation. G-CSF at the optimal concentration increased the sensitivity of blasts to SCF. Taken together, SCF acting in combination with other factors, but not alone, stimulates the growth of blast clonogenic cells. GM-CSF, IL-6, and TNF-alpha may be produced endogenously, whereas G-CSF and SCF may be supplied exogenously. Autocrine regulation of the growth of blasts seems to increase the responsiveness of the cells to any of these factors, allowing them to achieve a highly active growth state.

p53 mutations, c-myc and bcl-2 rearrangements in human non-Hodgkin's lymphoma cell lines

Fourteen Non-Hodgkin's lymphoma cell lines were generated and assessed for the presence of structural p53, c-myc and bcl-2 gene changes. Single or multiple changes were observed in 11 of the lines. Alterations of the p53 gene were most frequent and documented for 10 lines by immunoprecipitation using the antibodies PAb 240 and PAb 1801, sequencing studies and Southern blot analysis. A detailed study was performed in one of the cell lines (OCI-Ly 4) for which material of the original tumor sample was available. Two point mutations identified by sequencing cDNA derived from the cell line were also present in the original tumor specimen. In contrast, DNA prepared from fibroblasts of the same patient did not show the mutations. Six of the 14 lines demonstrated c-myc rearrangements, while bcl-2 changes were observed in 4. The presence of c-myc was associated with shorter survival of this group of patients with aggressive disease. None of the other changes present as single or composite alterations were correlated with clinical outcome measures.

cAMP increasing agents prevent the stimulation of heat-shock protein 70 (HSP70) gene expression by cadmium chloride in human myeloid cell lines

Treatment of U-937 human promonocytic cells with the cAMP increasing agents isoproterenol plus theophylline decreased the basal level of heat-shock protein 70 (HSP70) mRNA. In addition, the cAMP increasing agents attenuated the increase in HSP70 mRNA and protein levels produced by cadmium chloride in U-937 and other human myeloid cell lines, reduced the capacity of cadmium treatment to generate stress-tolerance, and attenuated the cadmium-produced stimulation of heat-shock factor (HSF) binding activity. By contrast, isoproterenol plus theophylline failed to attenuate the stimulation of HSP70 gene expression and HSF binding activity caused by heat-shock. Isoproterenol plus theophylline did not prevent the uptake of cadmium into the cells, and increased to a similar extent the intracellular cAMP levels in cadmium- and heat-treated cells. The cAMP increasing agents reduced the induction by cadmium of the HSP27 stress gene, but failed to attenuate other cadmium-elicited stress reactions such as the inhibition of total protein synthesis. It is concluded that cAMP does not inhibit the stress response as a whole, but it interferes with some step of the pathway by which cadmium specifically stimulates HSF binding activity and as a consequence HSP70 gene expression, in human myeloid cell lines.

Investigation of the cooperative effects of transforming growth factor alpha and c-myc overexpression in rat liver epithelial cells

Overexpression of both transforming growth factor (TGF)-alpha and c-myc is consistently reported in hepatic tumors. We transfected rat liver epithelial cells (RLECs) with expression vectors for TGF-alpha, c-myc, or both and analyzed the morphology, biological properties, and tumorigenicity of clones that overexpressed these genes. The transfectants were morphologically indistinguishable from the parental RLECs, but the overexpression of TGF-alpha resulted in changes in growth properties and an enhanced response to the mitogenic effects of hepatocyte growth factor. The concomitant overexpression of c-myc decreased growth factor requirements of the TGF-alpha lc-myc clones compared with RLEC and TGF-alpha clones. The TGF-alpha and TGF-alpha lc-myc clones were tumorigenic in nude mice at frequencies of 27% and 53%, respectively, indicating that the genes cooperate in malignant transformation. However, the untransformed nature and low tumorigenicity of the transfectants suggest that transformation depends on other cellular events in addition to the overexpression of TGF-alpha or c-myc. Characterization of tumor cell lines showed that in contrast to the transfectants, the tumor clones were morphologically transformed, capable of autonomous growth and anchorage-independent growth, and aggressively tumorigenic with a frequency of 100%. Clearly, the tumor cells differed from the transfectants and had undergone biological or genetic alterations (or both) as a consequence of the overexpression of TGF-alpha or c-myc. Our data suggest that the overexpression of TGF-alpha leads to enhanced responsiveness to hepatocyte growth factor, whereas the concomitant overexpression of c-myc confers growth-factor independence, providing a potential explanation of the mechanisms by which the overexpression of these genes results in transformation.