Reciprocal chromosome translocation between c-myc and immunoglobulin gamma 2b genes

Specific chromosome translocations have been observed in transformed cell lines of both man and mouse and may be implicated in the origin or maintenance of malignancy. In mouse plasmacytomas, translocations have been identified that bring the immunoglobulin alpha heavy-chain gene (C alpha, normally located on chromosome 12) into proximity with c-myc (normally located on chromosome 15), c-myc being the mouse cellular homologue of the avian myelocytomatosis virus transforming gene (v-myc). Here we identify a DNA rearrangement in a mouse hybridoma that has brought c-myc close to C gamma 2b and show that this rearrangement occurred by reciprocal chromosome translocation, as recombinant clones were isolated from the same cell line in which a rearranged variable-region (VH) gene has been brought close to 5' c-myc sequences. The translocation has resulted in the net loss of 7 base pairs (bp) of chromosome 15 sequence as well as in the presence of an additional base of unknown provenance. This reciprocal translocation was analysed in DNA from a mouse hybridoma cell line but is shown to be characteristic of the X63Ag8 myeloma parent.     

c-Ha-ras1 is not deleted in aniridia-Wilms' tumour association

Non-random tumour-specific chromosomal abnormalities have been observed in cells of many different human tumours. In Wilms' tumour (WT) and retinoblastoma, a chromosomal deletion occurs germinally or somatically and has been considered an important step in tumour development. One class of potential cellular transforming genes comprises the cellular homologues of the transforming genes of highly oncogenic retroviruses. A remarkable concordance between the chromosomal location of human cellular oncogenes and the breakpoints involved in acquired chromosomal translocations is becoming apparent in various cancers: the oncogenes c-mos, c-myc and c-abl are located at the breakpoints that occur in acute myeloblastic leukaemia, Burkitt's lymphoma and chronic myelocytic leukaemia respectively. Thus when the oncogene c-Ha-ras1 was localized to the short arm of human chromosome 11 (refs 6-8; region 11p11 leads to p15 and not 11p13 as stated in ref. 5), it was proposed as a possible aetiological agent in the aniridia-WT association (AWTA) that results from a deletion of 11p13 (although a transforming gene recently isolated from a WT cell line (G401) was shown not to be homologous to either c-Ha-ras or c-Ki-ras9). We have now looked for deletion or rearrangement of c-Ha-ras1 in the DNA from four subjects with del(11p13)-associated predisposition to Wilms' tumour, aniridia, genitourinary abnormalities and mental retardation. We report here that in no case is c-Ha-ras1 deleted, and we have further refined its location to 11p15.1 leads to 11p15.5. On the basis of enzyme studies and direct gene dosage determination for c-Ha-ras1 and beta-globin in neoplastic and non-neoplastic tissues from one patient, we conclude that deletion of the normal counterpart of 11p cannot account for the development of the tumour.     

A cellular oncogene (c-Ki-ras) is amplified, overexpressed, and located within karyotypic abnormalities in mouse adrenocortical tumour cells

The cellular oncogene c-Ki-ras is amplified 30- to 60-fold in cells of the mouse adrenocortical tumour Y1. The amplified oncogene is located in double minute chromosomes and in a homogeneously staining chromosomal region, common karyotypical anomalies of tumour cells. The amounts of c-Ki-ras specific mRNA and of the protein (p21) encoded by the amplified gene are correspondingly elevated. Amplification and enhanced expression of cellular oncogenes may contribute to the genesis and/or maintenance of at least some naturally occurring tumours.     

Viral transduction of c-myc gene in naturally occurring feline leukaemias

Feline leukaemia virus (FeLV) is epidemiologically associated with induction of the majority of lymphoid tumours of the domestic cat. However, about one-third of these tumours are devoid of exogenous virus or show evidence of virus integration only after tumour outgrowth. To help define the genetic mechanisms of feline lymphomagenesis we have explored here the possibility that cellular oncogenes (c-onc genes) are rearranged in tumour cell DNA. Of 16 FeLV-positive T-cell tumours among 31 naturally occurring lymphomas, 2 showed evidence of recombinant FeLV proviruses containing myc oncogene sequences. One of the two produced a transmissible myc-containing FeLV. In both cases c-myc and its surrounding DNA appeared unaltered. We believe that the association of myc with FeLV may result in its activation and play a part in the development of a significant fraction of cat T-cell lymphomas. Our findings contrast with studies of experimental induction of chicken lymphoma, in which myc activation occurs by retrovirus promoter insertion near c-myc (refs 3-5), rather than by incorporation into virus.     

Amplified DNA with limited homology to myc cellular oncogene is shared by human neuroblastoma cell lines and a neuroblastoma tumour

Amplified cellular genes in mammalian cells frequently manifest themselves as double minute chromosomes (DMs) and homogeneously staining regions of chromosomes (HSRs). With few exceptions both karyotypic abnormalities appear to be confined to tumour cells. All vertebrates possess a set of cellular genes homologous to the transforming genes of RNA tumour viruses, and there is circumstantial evidence that these cellular oncogenes are involved in tumorigenesis. We have recently shown that DMs and HSRs in cells of the mouse adrenocortical tumour Y1 and an HSR in the human colon carcinoma COLO320 contain amplified copies of the cellular oncogenes c-Ki-ras and c-myc, respectively. Both DMs and HSRs are found with remarkable frequency in cells of human neuroblastomas. We show here that a DNA domain detectable by partial homology to the myc oncogene is amplified up to 140-fold in cell lines derived from different human neuroblastomas and in a neuroblastoma tumour, but not in other tumour cells showing cytological evidence for gene amplification. By in situ hybridization we found that HSRs are the chromosomal sites of the amplified DNA. The frequency with which this amplification appears in cells from neuroblastomas and its apparent specificity raise the possibility that one or more of the genes contained within the amplified domain contribute to tumorigenesis.     

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.     

Localization of the c-ab1 oncogene adjacent to a translocation break point in chronic myelocytic leukaemia

The human c-ab1 oncogene maps within the region (q34-qter) of chromosome 9 which is translocated to chromosome 22, the Philadelphia (Ph') chromosome, in chronic myelocytic leukaemia (CML). The position of the Ph' chromosomal break point is shown to be variable and, in one CML patient, has been localized immediately 5' of, or within, the c-ab1 oncogene. A DNA restriction fragment corresponding to this site has been molecularly cloned and shown to represent a chimaeric fragment of DNA from chromosomes 9 and 22.     

129小鼠CgA基因cDNA 5′端部分片段及CgA基因的克隆

通过RT-PCR方法,从129小鼠脑组织中克隆到CgA基因cDNA 5′端部分片段,序列分析结果表明,所克隆到的片段序列与文献中完全一致。以此片段为探针,从129小鼠基因组库中筛选获得阳性噬菌体1-1,克隆了CgA基因,并与文献中的小鼠CgA基因限制性内切酶图谱进行了比较分析。     

Isolation by molecular cloning of a fragment in the split ovalbumin gene

An EcoRI fragment of chicken DNA (fragment 'a') containing a sequence complementary to the 3' half of ovalbumin mRNA has been isolated by molecular cloning. Analysis of the cloned fragment proves conclusively that the chicken ovalbumin gene is split. Fragment 'a' contains no extensive sequence repeated elsewhere in the genome and represents the only type of organisation of this part of the split ovalbumin gene in chicken genome.     

Isolation of an excision product of T-cell receptor alpha-chain gene rearrangements

The genes for the T-cell receptor, like the immunoglobulin genes, are rearranged as DNA. The mechanism of this rearrangement is not clear; unequal crossover between chromosomes and the looping-out and excision of the excess DNA have both been suggested. We isolated small polydisperse circular (spc) DNAs from mouse thymocytes and cloned them into a phage vector. Of the 56 clones we analysed, nine contained sequences homologous to T-cell receptor alpha-chain joining (J alpha) segments. We have characterized one of these clones; it contains one J alpha segment, and the product out of the recombination of a variable region of the alpha-chain gene (V alpha) with a J alpha gene segment. This is the first demonstration of the presence in extrachromosomal DNA of a reciprocal recombination product of any rearranging immunoglobulin or T-cell receptor gene. The finding verifies that V alpha-J alpha joining can occur by the looping-out and excision of chromosomal DNA.     

Mouse skin carcinomas induced in vivo by chemical carcinogens have a transforming Harvey-ras oncogene

Several groups have shown that the malignant phenotype can be transferred to NIH/3T3 fibroblasts by incorporation of DNA isolated from tumour cell lines. These studies have demonstrated that the transforming activity of DNA isolated from human bladder, lung and colon carcinoma cell lines is related to an alteration of the cellular homologues of the ras genes of Harvey or Kirsten murine sarcoma viruses. It is, however, unclear what relevance these observations have to the multi-stage nature of tumorigenesis in vivo, in which several independent events are required in both humans and experimental animals. The activation of a cellular oncogene in a defined experimental system for the progressive induction of solid tumours has not yet been demonstrated. We report here that high molecular weight DNA from transplanted squamous cell carcinomas induced by sequential treatment of mouse skin with initiators and promoters of carcinogenesis causes morphological transformation of NIH/3T3 fibroblasts at high frequency. The transforming properties are due to the transfer of an activated cellular homologue of the Harvey-ras (rasH) oncogene.     

Tumorigenic conversion of primary embryo fibroblasts requires at least two cooperating oncogenes

Transfection of embryo fibroblasts by a human ras oncogene does not convert them into tumour cells unless the fibroblasts are established and immortalized before transfection. The embryo fibroblasts become tumorigenic if a second oncogene such as a viral or cellular myc gene or the gene for the polyoma large-T antigen is introduced together with the ras gene.     

Translocation of the p53 gene in t(15;17) in acute promyelocytic leukaemia

Recent studies have demonstrated that the cellular tumour antigen p53 (ref. 1) can complement activated ras genes in the transformation of rat fibroblasts, suggesting that the gene encoding p53 may act as an oncogene. Here, by using in situ chromosomal hybridization, we have mapped the p53 gene to human chromosome 17, at bands 17q21-q22, the region containing one of the breakpoints in the translocation t(15;17) (q22;q21) associated with acute promyelocytic leukaemia (APL). Hybridization of p53 and erb-A (17q11-q12) probes to malignant cells from three APL patients indicated that the p53 gene is translocated to chromosome 15 (15q+), whereas erb-A remains on chromosome 17. Analysis of variant translocations demonstrates that the 15q+ chromosome contains the conserved junction, suggesting a role for p53 in the pathogenesis of APL. However, rearrangements of the p53 gene were not detected on Southern blotting of DNA from leukaemic cells of four APL patients with t(15;17).     

Identification of reciprocal translocation sites within the c-myc oncogene and immunoglobulin mu locus in a Burkitt lymphoma

The association between certain human tumours and characteristic chromosomal abnormalities has led to the hypothesis that specific cellular oncogenes may be involved and consequently 'activated' in these genetic recombinations. This hypothesis has found strong support in the recent findings that some cellular homologues of retroviral onc genes are located in chromosomal segments which are affected by specific tumour-related abnormalities (see ref. 4 for review). In the case of human undifferentiated B-cell lymphoma (UBL) and mouse plasmacytomas, cytogenetic and chromosomal mapping data have identified characteristic chromosomal recombinations directly involving different immunoglobulin genes and the c-myc oncogene (for review see refs 5, 6). In UBLs carrying the t(8:14) translocation it has been shown that the human c-myc gene is located on the region of chromosome 8 (8q24) which is translocated to the immunoglobulin heavy-chain locus (IHC) on chromosome 14. Although it is known that the chromosomal breakpoints can be variably located within or outside the c-myc locus and within the IHC mu (refs 9, 11) or IHC gamma locus, the recombination sites have not been exactly identified and mapped in relation to the functional domains of these loci. We report here the identification and characterization of two reciprocal recombination sites between c-myc and IHC mu in a Burkitt lymphoma. Nucleotide sequencing of the cross-over point joining chromosomes 8 and 14 on chromosome 14q--shows that the onc gene is interrupted within its first intron and joined to the heavy-chain mu switch region. This recombination predicts that the translocated onc gene would code for a rearranged mRNA but a normal c-myc polypeptide.