A putative second cell-derived oncogene of the avian leukaemia retrovirus E26

The acute avian leukaemia retroviruses AMV and E26 both induce myeloblastosis in vivo and transform myeloblasts in vitro. Both viruses contain the oncogene v-myb first described for AMV. Unlike AMV, E26 has the additional capacity to induce erythroblastosis in vivo and to transform erythroblasts. Previous analyses indicated that the genome of E26 also contained nucleotide sequences distinct from v-myb and unrelated to viral replicative genes. Using a molecularly cloned E26 provirus, we have now identified a novel nucleotide sequence designated v-ets (for E-twenty-six specific) of approximately 1.5 kilobase pairs (kbp) located next to v-myb. v-ets possesses all the structural characteristics of a putative new oncogene: it has a conserved cellular counterpart c-ets which is transcribed in some normal chicken cells as a major 7.5-kb polyadenylated RNA. Although our results now await elucidation of their biological significance, we propose that v-ets could be a new oncogene accounting for the additional transforming properties of E26, or potentiating the transforming properties of the v-myb oncogene.     

Nucleotide sequence of chicken c-myb complementary DNA and implications for myb oncogene activation

Avian myeloblastosis virus (AMV), like other acute transforming viruses, arose by recombination between its helper virus and host cellular sequences. The latter sequences, termed v-myb, are responsible for the oncogenic properties of the virus. AMV causes acute myeloblastic leukaemia in chickens and transforms a specific class of haematopoietic cells in vitro, but does not induce morphological transformation of cultured fibroblasts, suggesting that only a restricted target-cell population is responsive to its transforming gene product. The normal cellular counterpart of v-myb, c-myb, is highly conserved and is present in all vertebrate and some invertebrate species examined. DNA rearrangements and altered expression of the myb oncogene have been reported in mouse lymphoid tumours and human myeloid and colon tumours. The mechanism of activation of the cellular proto-oncogenes is thought to involve the structural alteration of the coding regions that result in either the synthesis of an altered gene product or the enhanced expression of a proto-oncogene caused by alterations in its regulatory elements. To distinguish between these two mechanisms, we have cloned and sequenced the chicken c-myb complementary DNA and compared it with that of v-myb sequences. We demonstrate that during the transduction of the cellular sequences and/or viral passage a substantial portion of the coding region of the c-myb gene has been lost from both the 5' and 3' ends, resulting in the generation of a truncated gene product that mediates the transforming function of the virus.     

植物MYB转录因子研究

转录因子是通过转录水平或转录后水平上调控目的基因的表达来调控植物生长发育及生理代谢的.MYB(v-myb avian myeloblastosis viral oncogene homolog)转录因子是最大的植物转录因子家族成员之一,参与了细胞分化、细胞周期的调节,激素和环境因子应答,并对植物次生代谢以及叶片等器官形态建成具有重要的调节作用.文章对MYB的发现及其结构特征和功能研究进展进行综述,为进一步开展MYB基因的克隆、功能研究和利用提供参考.     

Inhibition of retroviral protease activity by an aspartyl proteinase inhibitor

Retrovirus protease is an enzyme that cleaves gag and gag-pol precursor polyproteins into the functional proteins of mature virus particles. The correct processing of precursor polyproteins is necessary for the infectivity of virus particles: in vitro mutagenesis which introduces deletions into the murine leukaemia virus genome produces a protease-defective virus of immature core form and lacking infectivity. A therapeutic drug effective against disease caused by retrovirus proliferation could likewise interfere with virus maturation. The primary structure has so far been determined for the protease of avian myeloblastosis virus, and of murine, feline and bovine leukaemia viruses. Amino acid sequencing of the retrovirus proteases, either after their purification or from prediction from the nucleotide sequence, shows that they possess the Asp-Thr-Gly sequence characteristic of the aspartyl proteinases. In this report we show that retrovirus proteases belong to the aspartyl proteinase group and demonstrate an inhibition by the aspartyl proteinase-specific inhibitor, pepstatin A, on the activity of bovine leukaemia, Moloney murine leukaemia and human T-cell leukaemia virus proteases.     

Nonspecific integration of the HTLV provirus genome into adult T-cell leukaemia cells

Human T-cell leukaemia virus (HTLV), previously also reported as ATLV, is a recently identified retrovirus which is closely associated with adult T-cell leukaemia (ATL) endemic in southwestern Japan and the Caribbean. Determination of the total nucleotide sequence of the HTLV genome has revealed no typical onc gene acquired from the cellular sequence. Screening of the HTLV provirus genome in tumour cells has shown that in all cases of ATL examined, the primary tumour cells contained the provirus genome and were monoclonal with respect to the integration site of the provirus. These findings suggest that ATL leukaemogenesis may be due to insertional mutagenesis in which the provirus genome is integrated into a specific locus on the chromosomal DNA and then activates an adjacent cellular onc gene, a mechanism already demonstrated in avian lymphoma and erythroblastosis induced by avian leukosis viruses. A common site of HTLV provirus integration in leukaemic cells among some ATL patients was reported by Hahn et al. but subsequently retracted. However, this retraction does not imply the random integration of the proviruses. Independently, we have been testing this insertional mutagenesis model in ATL and report here that the provirus did not have a common locus of integration in 35 ATL patients and did not integrate on the same chromosome in 2 ATL patients.     

The Hardy-Zuckerman 2-FeSV, a new feline retrovirus with oncogene homology to Abelson-MuLV

There is substantial evidence that oncogenes (v-onc) of acute transforming retroviruses have been acquired by transduction of cellular genes (c-onc) with retroviruses. Feline leukaemia virus (FeLV)-associated feline fibrosarcomas have proven to be extremely useful for the isolation of acute transforming retroviruses of a mammalian species. Three different v-onc genes have been identified in five acute transforming feline retroviruses. The Susan McDonough feline sarcoma virus (SMFeSV) contains the oncogene fms (ref. 4). The Snyder-Theilen (ST) and Gardner-Arnstein (GA) FeSVs contain the oncogene fes (ref. 4), which is homologous to the oncogene fps of the avian sarcoma viruses FSV, RRCII, PRCIV and 16L (refs 7, 8). The v-onc sequences of the Parodi-Irgens (PI) FeSV have recently been found to be homologous with the v-sis sequences of the simian sarcoma virus. We report here the isolation of another acute transforming feline retrovirus from a naturally occurring feline fibrosarcoma, designated the Hardy-Zuckerman 2 feline sarcoma virus (HZ2-FeSV) and demonstrate that the HZ2-FeSV and Abelson murine leukaemia virus (A-MuLV) have homologous oncogenes.     

Identification and nucleotide sequence of a human locus homologous to the v-myc oncogene of avian myelocytomatosis virus MC29

Avian myelocytomatosis virus MC29 is a replication-defective acute leukaemia virus which induces a variety of tumours in chickens including sarcomas, renal and hepatic carcinomas, and myelocytomatosis. The oncogenic potential of the virus is mediated by the gene v-myc, acquired from sequences (c-myc) present in normal uninfected chicken DNA. Sequences closely related to chicken c-myc have been highly conserved throughout evolution, from Drosophila to vertebrates. The hypothesis that c-myc may be involved in neoplastic transformation has been strengthened by the finding that B-cell lymphomas induced in chickens by avian leukosis virus (ALV) are often associated with increased expression of c-myc resulting from integration of the ALV provirus adjacent to the c-myc gene. More recently, it has been demonstrated that the malignant human cell line HL-60, derived from the peripheral blood leukocytes of a patient with acute promyelocytic leukaemia, expresses elevated levels of myc-related mRNA associated with an amplification of the c-myc gene. To explore the relationship of the human cellular myc gene with the corresponding viral oncogene from MC29, and to provide a framework for the analysis of the mechanism and significance of c-myc amplification in human tumours, we have isolated and determined the nucleotide sequence of a genomic clone prepared from a normal human library which contains all domains sharing homology with v-myc.     

The deubiquitinylation and localization of PTEN are regulated by a HAUSP-PML network

Nuclear exclusion of the PTEN (phosphatase and tensin homologue deleted in chromosome 10) tumour suppressor has been associated with cancer progression. However, the mechanisms leading to this aberrant PTEN localization in human cancers are currently unknown. We have previously reported that ubiquitinylation of PTEN at specific lysine residues regulates its nuclear-cytoplasmic partitioning. Here we show that functional promyelocytic leukaemia protein (PML) nuclear bodies co-ordinate PTEN localization by opposing the action of a previously unknown PTEN-deubiquitinylating enzyme, herpesvirus-associated ubiquitin-specific protease (HAUSP, also known as USP7), and that the integrity of this molecular framework is required for PTEN to be able to enter the nucleus. We find that PTEN is aberrantly localized in acute promyelocytic leukaemia, in which PML function is disrupted by the PML-RARalpha fusion oncoprotein. Remarkably, treatment with drugs that trigger PML-RARalpha degradation, such as all-trans retinoic acid or arsenic trioxide, restore nuclear PTEN. We demonstrate that PML opposes the activity of HAUSP towards PTEN through a mechanism involving the adaptor protein DAXX (death domain-associated protein). In support of this paradigm, we show that HAUSP is overexpressed in human prostate cancer and is associated with PTEN nuclear exclusion. Thus, our results delineate a previously unknown PML-DAXX-HAUSP molecular network controlling PTEN deubiquitinylation and trafficking, which is perturbed by oncogenic cues in human cancer, in turn defining a new deubiquitinylation-dependent model for PTEN subcellular compartmentalization.     

Chemical modification of DNA polymerase phosphoprotein from avian myeloblastosis virus.

Fractionation of purified avian myeloblastosis virus DNA polymerase, after phosphorylation in vitro, revealed the presence of a small acidic proten, a phosphate acceptor polypeptide with high specific activity. Its presence in the phosphorylated form with the polymerase resulted in as much as a 10-fold increase in the rate of DNA synthesis. Its presence in the dephosphorylated form with the polymerase had no effect in the rate of DNA synthesis.     

Reiteration frequency of the gene for tissue-specific histone H5 in the chicken genome.

Chicken erythroid cells contain a tissue specific histone known as H5 in addition to the five major histone species found in other organisms. The mRNA coding for this histone has been isolated by indirect immunoprecipitation from immature, non-dividing reticulocytes in which this is the only histone synthesised. The mRNA has been modified by the enzymatic addition of a 3' polyadenylic acid tract, and transcribed into complementary DNA (cDNA) using the RNA-dependent DNA-polymerase from avian myeloblastosis virus. Studies on the hybridisation of this cDNA indicate that the gene coding for the H5 histone is reiterated 10 times in the chicken genome.     

Spi-1 is a putative oncogene in virally induced murine erythroleukaemias

Retroviral insertional mutagenesis has been proposed as an efficient mechanism to turn on or to increase the expression of oncogenes in several avian or mammal models. Integration site studies of avian leukosis virus, murine leukaemia and murine mammary tumour viruses led to the coleutification of highly conserved genes whose expression is induced or increased during leukaemogenesis, probably through enhancer elements present in the retroviral long terminal repeats. This is reminiscent of the activation of cellular proto-oncogenes or putative oncogenes in numerous human tumours and leukaemias as a result of chromosomal translocations or DNA rearrangements. Here we report the characterization of a new putative oncogene isolated from a murine erythroleukaemia induced by the acute leukaemogenic retrovirus spleen focus forming virus (SFFV). An important and unusual feature of this genomic locus Spi-1 (for SFFV proviral integration) is that rearrangements due to SFFV integration were found in 95% of the erythroid tumours studied. A 4.0-kilobase messenger RNA was detected in rearranged tumours. No Spi-1 rearrangement was detected in other virally induced myeloid, lymphoid or erythroid tumours tested.     

Nucleotide sequence of cloned cDNA of human c-myc oncogene

Like other transforming genes of retroviruses, the v-myc gene of the avian virus, MC29, has a homologue in the genome of normal eukaryotic cells. The human cellular homologue, c-myc, located on human chromosome 8, region q24 leads to qter (refs 1, 2), is translocated into the immunoglobulin heavy-chain locus on human chromosome 14 (ref. 3) in Burkitt's lymphoma, suggesting that c-myc has a primary role in transformation of some human haematopoietic cells. In addition, c-myc is amplified in the human promyelocytic leukaemia cell line, HL60 (refs 6, 7) which also contains high levels of c-myc mRNA. Recently, Colby et al. reported the nucleotide sequence of the human c-myc DNA isolated from a genomic recombinant DNA library derived from human fetal liver. This 4,053-base pair (bp) sequence includes two exons and one intron of the myc gene, and the authors have suggested the existence of a human c-myc mRNA of 2,291 nucleotides that has a coding capacity for a protein of molecular weight (Mr) 48,812. We have approached the problem of accurately defining the characteristics of the human c-myc mRNA and c-myc protein by determining the sequence of the c-myc cDNA isolated from a cDNA library prepared from mRNA of a clone of the K562 human leukaemic cell line. K562 cells are known to contain c-myc mRNA which is similar in size to the c-myc mRNA of other human cell types. We report here the sequence of 2,121 nucleotides of a human c-myc mRNA and demonstrate that its 5' noncoding sequence does not correspond to the sequence of the reported genomic human sequence. However, our data confirm that the intact human c-myc mRNA can encode a 48,812-Mr protein with a sequence identical to that reported by Colby et al.     

亚砷酸制剂研究进展

针对近年来世界上许多国家或地区相继报道长期暴露于含砷饮用水中的个体出现不同程度的砷中毒症状,或因砷而引起的多种疾病等状况;而我国中医却应用砷剂治疗多种血液肿瘤和实体瘤,特别是治疗急性早幼粒白血病(APL)已取得了较好疗效.从治病性和致病性两个角度分别讨论了主要包括亚砷酸在内的多种含砷化物的生物学毒性,对人体各系统的损害和抗肿瘤作用,为临床应用含砷制剂治疗癌症提供借鉴,同时展望了砷制剂的临床应用前景.     

A novel c-abl protein product in Philadelphia-positive acute lymphoblastic leukaemia

Activation of cellular proto-oncogenes as a result of chromosomal abnormalities has been implicated in the development of some human malignancies. Perhaps one of the most striking examples of this association occurs in chronic myelogenous leukaemia, where the Philadelphia (Ph) translocation results in substitution of the 5' end of the c-abl proto-oncogene with bcr gene sequences. A unique hybrid bcr-abl message is produced. As the Ph translocation is also present in some patients with acute lymphoblastic leukaemia, we initiated studies to determine if similar genomic events occur in these two different forms of Ph-positive leukaemia. Here we report that the Ph translocation in acute lymphoblastic leukaemia can result in production of a novel aberrant c-abl protein that is distinct from the bcr-abl protein found in Ph-positive chronic myelogenous leukaemia. Our observations suggest that alternative mechanisms of activation of c-abl exist, and may be important in the development of human acute lymphoid rather than chronic myeloid malignancies.     

Inhibitory receptors bind ANGPTLs and support blood stem cells and leukaemia development

How environmental cues regulate adult stem cell and cancer cell activity through surface receptors is poorly understood. Angiopoietin-like proteins (ANGPTLs), a family of seven secreted glycoproteins, are known to support the activity of haematopoietic stem cells (HSCs) in vitro and in vivo. ANGPTLs also have important roles in lipid metabolism, angiogenesis and inflammation, but were considered 'orphan ligands' because no receptors were identified. Here we show that the immune-inhibitory receptor human leukocyte immunoglobulin-like receptor B2 (LILRB2) and its mouse orthologue paired immunoglobulin-like receptor (PIRB) are receptors for several ANGPTLs. LILRB2 and PIRB are expressed on human and mouse HSCs, respectively, and the binding of ANGPTLs to these receptors supported ex vivo expansion of HSCs. In mouse transplantation acute myeloid leukaemia models, a deficiency in intracellular signalling of PIRB resulted in increased differentiation of leukaemia cells, revealing that PIRB supports leukaemia development. Our study indicates an unexpected functional significance of classical immune-inhibitory receptors in maintenance of stemness of normal adult stem cells and in support of cancer development.     

Continuous in vitro generation of multipotential stem cell clones from src-infected cultures

A molecular recombinant of Rous sarcoma virus and murine amphotropic leukaemia virus, src(MoMuLV), where the avian src oncogene has been placed under the influence of a murine virus promoter sequence, has been reported. Infection of long-term marrow cultures with this virus led to a dramatic change in the relative numbers of stem cells, granulocyte-macrophage progenitor cells and mature cells found in normal haematopoietic cell development. However, although the balance between self-renewal, differentiation and development was disturbed, injection of the cultured cells into irradiated syngeneic recipients did not lead to the development of leukaemia. Thus, although the control had been 'loosened', the host regulatory mechanisms were sufficient to impose a restraint on unlimited growth of the cells. We now show that the stem cells from the src-infected cultures show a remarkably increased capacity for self-renewal in vitro in situations which are inimical to the maintenance of self-renewal in normal uninfected stem cells and that self-renewal/differentiation can be modified by the culture conditions.     

onc sequences (v-fes) of Snyder-Theilen feline sarcoma virus are derived from noncontiguous regions of a cat cellular gene (c-fes)

Type C sarcoma viruses are genetic recombinants containing portions of replication-competent helper viruses linked to sarcoma virus-specific sequences (generically designated onc genes) which are thought to be required for acute fibroblast transformation. The onc elements of different avian and mammalian sarcoma viral isolates are each homologous to subsets of cellular DNA sequences which have no well-defined role in normal cells. Because of the lack of significant homology between helper viral genes and cellular onc sequences, the recombinational mechanisms which facilitate the formation of sarcoma viral genomes remain unclear. In Moloney murine sarcoma virus, viral onc (or v-mos) and cellular onc (or c-mos) sequences exhibit complete and uninterrupted homology as determined by heteroduplex and restriction enzyme analyses of molecularly cloned DNA. By contrast, the cellular counterparts of the onc elements of Rous sarcoma virus (G. Cooper and R. Parker, personal communication), avian erythroblastosis virus (B. Vennstrom, personal communication), Abelson leukaemia virus (D. Baltimore, personal communication), Harvey sarcoma virus (E. Scolnick, personal communication) and simian sarcoma virus (R. Gallo, personal communication) are now known to contain intervening sequences which do not appear in the respective viral genomes. Here we report the use of the Southern blot technique to examine cat cellular DNA sequences (c-fes) homologous to the onc gene (v-fes) of Snyder-Theilen feline sarcoma virus (ST-FeSV). We used cloned DNA 'probes' containing defined portions of the ST-FeSV genome to show that v-fes sequences originate from at least four noncontiguous sequences in cat cellular DNA, separated from each other by intervening sequences.     

Identification of the human analogue of a regulator that induces differentiation in murine leukaemic cells

We have recently purified murine granulocyte colony-stimulating factor (G-CSF), a regulatory glycoprotein which stimulates granulocyte colony formation from committed murine precursor cells in semi-solid agar cultures. G-CSF is one of a family of colony-stimulating factors that regulate the growth and differentiation of granulocytes and macrophages. While the other murine CSFs (granulocyte-macrophage (GM)-CSF, macrophage (M)-CSF and multi-CSF) show little or no differentiation-inducing activity on murine myelomonocytic leukaemia cell lines, G-CSF (or MGI-2(6)) is able to induce the production of terminally differentiated cells from WEHI-3B and other myeloid leukaemia cell lines. More importantly, G-CSF-containing materials suppress the self-renewal of myeloid leukaemia stem cells in vitro and the leukaemogenicity of treated myeloid leukaemic cells in vivo. It is important to identify the human analogue of murine G-CSF so that its effectiveness on human myeloid leukaemia cells can be assessed. Here we show that an analogue of G-CSF does exist among the CSFs produced by human cells and that the murine and human molecules show almost complete biological and receptor-binding cross-reactivities to normal and leukaemic murine or human cells. The human G-CSF analogue is identified as a species of CSF that we have previously described as CSF-beta.     

Human T-cell lymphotropic virus type-I antibodies in Falashas and other ethnic groups in Israel

Epidemiological studies of the human T-cell leukaemia/lymphoma virus type I (HTLV-I), a type-C retrovirus of the human T-lymphotropic virus family, have used serological surveys to identify population subgroups possessing a high prevalence of naturally occurring HTLV-I-specific antibodies. Studies carried out to delineate the global distribution of the virus have demonstrated natural antibodies to HTLV-I in the serum of healthy donors from specific geographical areas, and have defined viral endemic areas in Japan, the Caribbean basin, Africa and the southeastern United States. Such studies have suggested that the prevalence of HTLV-I antibodies is directly correlated with age, is associated with the clinical syndrome of adult T-cell lymphoma, and is associated with transmission from mother to child. A separate subtype of the human retrovirus, HTLV-II (refs 21, 22), has also been identified. The population of Israel in part comprises groups of immigrants of various ethnic and geographical origins. Because of this, and the fact that Israel has a highly developed public health system, we surmised that the ethnic groups in Israel could be used in a seroepidemiological survey of HTLV infection. The serological survey reported here demonstrates a high prevalence of HTLV-I antibodies in new immigrants from Ethiopia. This previously ethnically and geographically isolated group, the 'Black Jews' or 'Falashas', from the Gondar region in the northern rural highlands of Ethiopia, has the highest endemic rate of HTLV-I yet reported outside Japan.