Structure of the polymorphic feline c-myc oncogene locus

Two feline c-myc DNA clones (CM-2 and CM-3), isolated from a cat DNA library, are structurally very similar. However, they differ at a SmaI site in exon III which is present only in CM-2. In the outbred feline population, cats heterozygous for this site or homozygous for the CM-3-type gene have been observed. The results provide a physical map of the feline c-myc locus, and define hitherto unidentified alleles of this gene.     

Analysis of the structure and expression of the c-myc oncogene in cervical tumor and in cervical tumor-derived cell lines

The structure of the c-myc oncogene in 17 cervical tumors and patient-matched nontumor tissues from Chinese patients residing in Taiwan was analysed. In contrast to recent reports on Mexican patients, none of the samples showed rearrangements and sequence amplification in the c-myc gene. The discrepancy may be explained by different carcinogenesis mechanisms being in operation in different geographic regions. Although no structural alterations in the c-myc gene were found in seven cervical carcinoma cell lines analysed, Northern blot analysis indicated different levels of c-myc gene expression which may be related to the presence of human papillomavirus (HPV) sequence in the cell and suggests a possible c-myc-hpv interaction in some stages of the transformation process.     

c-myc oncogene expression inhibits the initiation of myogenic differentiation

The role of c-myc oncogene expression in myogenic differentiation has been established by transfecting rat myoblasts of the L6 cell line with plasmid pMT-myc, in which the c-myc coding sequences were under the control of the metallothionein I promoter. We observed that the constitutive expression of the exogenous c-myc gene inhibits muscular differentiation. A diminution of the endogenous c-myc gene expression occurs within the first 24 h after the transfer of the cells to a differentiating medium. This early decrease of c-myc expression is required for cell differentiation to occur. We have also observed that exogenous myc gene expression has no effect on endogenous myc expression.     

Analysis of the expression of the oncogene c-myc in human breast adenocarcinoma

The c-myc oncogene was characterized and its expression analyzed in 32 mammary adenocarcinomas and in 2 benign breast tumors from 34 untreated patients. Southern blot hybridization experiments have demonstrated the amplification of the oncogene (3 to 30 fold) in 3 carcinomas. The analysis of total RNA by Northern blot revealed the presence of a 2.4 kb c-myc RNA band. In 7 out of 10 carcinomas from patients with 3 or more than 3 lymph node metastases the level of c-myc expression evaluated by dot blot analysis was 4 to 14 fold greater than that of normal human tissues. In only 5 out of 22 carcinomas from patients without lymph node metastases or less than 3 invaded nodes the level of c-myc expression was also higher (4 to 10 fold). The level of c-myc expression was not significantly enhanced in the 2 benign tumors. It is suggested that the c-myc gene activation could be associated to a higher degree of malignancy of mammary carcinomas.     

Proteins encoded by the human c-myc oncogene: differential expression in neoplastic cells.

To examine myc protein products in the wide variety of human tumor cells having alterations of the c-myc locus, we have prepared an antiserum against a synthetic peptide corresponding to the predicted C-terminal sequence of the human c-myc protein. This antiserum (anti-hu-myc 12C) specifically precipitated two proteins of 64 and 67 kilodaltons in quantities ranging from low levels in normal fibroblasts to 10-fold-higher levels in Epstein-Barr virus-immortalized and Burkitt's lymphoma cell lines, to 20- to 60-fold-higher levels in cell lines having amplified c-myc. The p64 and p67 proteins were found to be highly related by partial V8 proteolytic mapping, and both were demonstrated to be encoded by the c-myc oncogene, using hybrid-selected translation of myc-specific RNA. In addition, the p64 protein was specifically precipitated from cells transfected with a translocated c-myc gene. Both p64 and p67 were found to be nuclear phosphoproteins with extremely short half-lives. In tumor cell lines having alterations at the c-myc locus due to amplification or translocation, we observed a significant change in the expression of p64 relative to p67 when compared with normal or Epstein-Bar virus-immortalized cells.     

Amplification of the expression of the c-myc oncogene in bronchial epidermoid carcinoma in man

Squamous cell lung carcinomas from 10 untreated patients were examined for the state of the oncogene c-myc. Blot hybridization experiments have demonstrated the amplification of the oncogene of about six fold in only one tumor. The oncogene amplification was not detected in normal tissues of patients. The analysis of RNA by Northern blot revealed the presence in the seven tumors examined of a 2.4 kb c-myc RNA band. The level of c-myc expression evaluated by dot blot analysis was 5 to 14 fold greater in tumors than that of histologically normal lung of the same patients.     

Amplification and expression of a cellular oncogene (c-myc) in human gastric adenocarcinoma cells.

Three of 16 human gastric adenocarcinoma samples, maintained as solid tumors in nude mice, were found to carry amplified c-myc genes. In two samples with a high degree of c-myc DNA amplification (15- to 30-fold), double minute chromosomes were observed in karyotype analysis. The level of c-myc RNA was markedly elevated in a rapidly growing and poorly differentiated tumor, whereas it was only slightly elevated in a slowly growing and more differentiated tumor.     

Requirement of lipocalin 2 for hematopoietic and solid tumor malignancies

Our published studies indicate that lipocalin 2 is a critical factor for invasion of hematopoietic tissues by chronic myelogenous leukemia cells. Lipocalin 2 is secreted by Bcr-Abl+ chronic myeloid leukemia cells causing apoptosis in normal hematopoietic cells but not in Bcr-Abl+ cells. Secreted lipocalin 2 forms a complex with metalloproteinase MMP-9, and is reported to stabilize its activity, which implies that lipocalin 2 may have a role in solid tumor formation. Our studies indicate that Bcr-Abl+ mouse marrow cells lacking the lipocalin 2 gene are not only defective for leukemia induction but also are defective in forming solid tumors compared to Bcr-Abl marrow cells that express lipocalin 2. Thus, our findings indicate that lipocalin 2 has two functions in tumor malignancies: one involving induction of apoptosis in normal hematopoietic cells and the other to facilitate solid tumor formation.     

Analysis of polyadenylation site usage of the c-myc oncogene.

The c-myc gene contains 2 well conserved polyadenylation (pA) sites. In all human and rat cell lines from various differentiation stages and tissue types the amount of mRNA terminating at the second pA site is 6-fold higher than the amount ending at the upstream site. This is not due to a difference in stability of the two mRNA types and therefore must be due to preferential usage of the downstream site. The usage of the pA sites is not altered during growth factor induction of quiescent cells. We have not been able to detect differences in behavior between mRNAs ending at either pA site. Both types of mRNA are induced upon treatment of cells with cycloheximide. Furthermore, we have shown that the poly(A) tail of c-myc mRNA is lost during degradation of the messenger, as was described previously for c-myc mRNA in an in vitro system. The time required for the loss of the poly(A) tail is similar to the half-life of c-myc mRNA.     

恶性血液病患者医院侵袭性真菌感染的危险因素分析

目的了解恶性血液病患者袭性真菌感染的发生率及危险因素,为重症患者的真菌感染防治提供依据。方法回顾性调查2013年1月至12月期间的495例恶性血液病住院患者资料,用卡方检验及多因素Logistic回归分析等统计方法分析侵袭性真菌感染的危险因素。结果 16.4%(81/495)的患者发生侵袭性真菌感染,其中急性白血病、慢性白血病、骨髓增生异常综合征、淋巴瘤和多发性骨髓瘤患者的真菌感染发生率分别为31.1%(66/212)、0.0%(0/19)、31.2%(5/16)、4.8%(10/207)和0.0%(0/41)。外周血白细胞计数低值≤1.0E+9/L、粒细胞缺少时间≥8天、使用糖皮质激素及抗生素使用种类≥3种是恶性血液病患者侵袭性真菌感染的独立危险因素,预防性使用抗真菌药物是独立保护因素(OR值分别为15.830、41.667、3.745、8.264及39.085,P值分别为0.000、0.011、0.035、0.007及0.000)。结论合理使用抗生素和糖皮质激素、在粒细胞缺少时间较长病例中及时使用集落刺激因子、抗真菌药或重建微生态是防治恶性血液病患者真菌感染的必要措施。     

A hemodynamic load in vivo induces cardiac expression of the cellular oncogene, c-myc

To establish whether a hemodynamic load that causes cardiac hypertrophy in the intact animal might interact with cellular pathways that are thought to transduce growth signals in model systems, we have analyzed expression of the cellular oncogene, c-myc, after a systolic pressure load. Aortic constriction increased c-myc mRNA abundance in both the atria and left ventricle of 28-day rats, but did not activate a second "competence" gene, r-fos, whose expression by cardiac cells ceases upon termination of mitotic growth. In 80-day rats, c-myc was induced in the atria alone. Induction of c-myc by aortic constriction in vivo may correlate with the respective capacity of atrial and ventricular myocytes to replicate DNA during cardiac hypertrophy. Activation of c-myc was not sufficient to account for inhibition of muscle creatine kinase (mck) mRNA, which was decreased only in 28-day rats.     

Targeted expression of a conditional oncogene in hematopoietic cells of transgenic mice

We have produced two lines of transgenic mice in which the expression of temperature-sensitive SV-40 large T antigen is targeted to bone marrow megakaryocytes via the platelet factor 4 (PF4) tissue-specific promoter. The progeny of these transgenic mice were observed for about 3 mo, and no malignancies were detected over this period of time. The offspring of these transgenic mice, 6- to 12-wk of age, served as a source of bone marrow cells, which upon in vitro cultivation at the permissive temperature yielded immortalized cell lines (MegT). At the permissive temperature, MegT cells exhibit the characteristics of early 2N and 4N megakaryocytes which include the presence of specific gene products such as PF4, glycoprotein IIb, acetylcholinesterase, and CD45 as well as the absence of molecular markers of other cell lineages such as the macrophage marker Mac-1, the T helper cell marker CD4, the mast cell marker IgE, the T cell marker CD2 or the erythroid cell marker alpha-globin. The inactivation of the oncogene by a shift of temperature from 34 degrees to 39.5 degrees C produces a reduction in the frequency of the 2N cells, in conjunction with the appearance of 8N and 16N cells, consisting of 27 and 3% of total cells, respectively. Thus, we have generated hematopoietic cell lines that are trapped in the early stages of megakaryocyte commitment, but able to undergo part of the normal program of terminal differentiation.     

Suppression of c-myc oncogene expression by a polyamine-complexed triplex forming oligonucleotide in MCF-7 breast cancer cells.

Polyamines are excellent stabilizers of triplex DNA. Recent studies in our laboratory revealed a remarkable structural specificity of polyamines in the induction and stabilization of triplex DNA. 1,3-Diaminopropane (DAP) showed optimum efficacy amongst a series of synthetic diamines in stabilizing triplex DNA. To utilize the potential of this finding in developing an anti-gene strategy for breast cancer, we treated MCF-7 cells with a 37mer oligonucleotide to form triplex DNA in the up-stream regulatory region of the c-myc oncogene in the presence of DAP. As individual agents, the oligonucleotide and DAP did not downregulate c-myc mRNA in the presence of estradiol. Complexation of the oligonucleotide with 2 mM DAP reduced c-myc mRNA signal by 65% at 10 microM oligonucleotide concentration. In contrast, a control oligonucleotide had no significant effect on c-myc mRNA. The expression of c-fos oncogene was not significantly altered by the triplex forming oligonucleotide (TFO). DAP was internalized within 1 h of treatment; however, it had no significant effect on the level of natural polyamines. These data indicate that selective utilization of synthetic polyamines and TFOs might be an important strategy to develop anti-gene-based therapeutic modalities for breast cancer.     

UV damage and repair in the domain of the human c-myc oncogene

We have used a modification of the Southern hybridization method to analyze the removal of UV-induced pyrimidine cyclobutane dimers from the domain of the c-myc oncogene. The study was performed in human COLO320HSR cells, which exhibit a 30- to 40-fold amplification of c-myc that is maintained in a marker chromosome as a homogeneously staining region. Intron 2 and the region upstream from the gene showed better dimer removal than intron 1 or the region downstream from the c-myc gene. Regions showing less repair coincide with regions that are hotspots for mutations and chromosome translocations. Therefore, it is proposed that the inefficiency of DNA repair may play an important role in the origin of c-myc rearrangements.