Transcriptional control of the expression of mouse globin genes in myeloma x erythroleukemia cell hybrids

Transcriptional enhancement of the human gene encoding for a melanoma-associated antigen (ME491) in association with malignant transformation

A cloned DNA fragment (lambda R31) containing the human gene for melanoma-associated ME491 antigen was transfected into mouse fibroblast cell lines and the antigen expression was studied. Our preliminary observation of higher expression of the antigen in more malignant Ltk- cells and weaker expression in less malignant NIH3T3 cells tempted us to investigate the antigen expression in Harvey(H)-ras-transformed NIH3T3 cells. It was observed that malignant transformation of the lambda R31-transfected NIH3T3 cells by H-ras oncogene enhanced the antigen expression to some extent. Northern blot analysis suggested that the enhancement occurred at the transcriptional level. Nucleotide sequence analysis of the 5'-regulatory region of the ME491 antigen gene in lambda R31 identified a number of consensus sequence motifs for binding of transcription factors such as Sp1, AP-2 and polyomavirus enhancer binding proteins 2 and 3. A consensus sequence motif for binding of AP-1, known as a ras-responsive element, was not found in that region. The significance and possible involvement of the transcription factors in the enhancement of ME491 antigen expression are discussed.

Cloning and characterization of the human PIM-1 gene: a putative oncogene related to the protein kinases

The mouse PIM-1 gene has been implicated in the evolution of retrovirus-associated mouse lymphomas. We have initiated a study of the human PIM-1 gene because of its potential importance as a human oncogene. We have isolated genomic and cDNA clones for this gene and characterized this locus in detail. The predicted PIM-1 protein is 313 amino acids in length. It has homology to a number of the protein kinases but does not have a transmembrane region. The amino acid corresponding to tyrosine-416 of pp60v-src is a tyrosine (position 198), which is consistent with the hypothesis that PIM-1 is a tyrosine kinase rather than a serine-threonine kinase. The PIM-1 gene was found to have six exons and five introns derived from 5 kb of genomic DNA. The site of transcription initiation was localized by S1 nuclease protection studies which indicated that the mature PIM-1 mRNA was approximately 2.7 kb in length. The promotor of this gene had no TATA or CAAT box but did have multiple GC boxes (CCGCCC) that might bind the Sp1 protein. The PIM-1 gene was expressed in myeloid and B lymphoid cell lines, but not in T lymphoid and nonhemopoietic lines. This initial characterization of PIM-1 will allow us to define its role in normal and malignant hematolymphoid differentiation.

Analysis of the structure, transcripts, and protein products of bcl-2, the gene involved in human follicular lymphoma

We have determined that the bcl-2 (B-cell leukemia/lymphoma 2) gene is transcribed into three overlapping mRNAs, and we have cloned bcl-2 cDNA sequences. Sequence analysis of the bcl-2 cDNA clones and comparison of their sequences to their genomic counterparts indicate that the bcl-2 gene contains at least two exons. The three bcl-2 transcripts, which are 8.5, 5.5, and 3.5 kilobases (kb) long, overlap within the first exon, but only the 8.5-kb and 5.5-kb transcripts contain sequences of the second exon. The 8.5-kb and 5.5-kb transcripts seem to use different polyadenylylation sites. Sequence analysis of the cDNA clones corresponding to the 5.5-kb and 3.5-kb mRNAs indicates that the two bcl-2 transcripts carry two overlapping open reading frames, one of which is 717 nucleotides long and codes for a protein (bcl-2 alpha) of 239 amino acids and a molecular mass of 26 kDa, while the other codes for a protein of 205 amino acids (bcl-2 beta, molecular mass 22 kDa) that is identical to bcl-2 alpha except at the carboxyl terminus. The bcl-2 protein products in follicular lymphomas with or without bcl-2 rearrangements are identical to the normal bcl-2 products.

Actively transcribed genes in the raf oncogene group, located on the X chromosome in mouse and human

Murine and human cDNAs, related to but distinct from c-raf-1, have been isolated and designated mA-raf and hA-raf, respectively. The mA-raf and hA-raf cDNAs detect the same murine and human fragments in Southern blots of restriction enzyme-cleaved murine and human cellular DNA. The murine restriction enzyme fragments homologous to mA-raf cDNA cosegregate with mouse chromosome X in a panel of Chinese hamster-mouse hybrid cells, thus localizing the mA-raf locus to mouse chromosome X. Two independently segregating loci, detected by the hA-raf cDNA (or mA-raf cDNA), hA-raf-1 and hA-raf-2, are located on human chromosomes X and 7, respectively. The mA-raf locus and the hA-raf-1 locus are actively transcribed in several mouse and human cell lines.

Localization of the human pim oncogene (PIM) to a region of chromosome 6 involved in translocations in acute leukemias

The human homolog, hpim, of the murine pim-1 gene, which is activated in murine T-cell lymphomas by insertion of retrovirus proviral genomes in the pim-1 region, has been molecularly cloned; the cloned probe has been used to map the hpim locus to human chromosome region 6p21 by somatic cell hybrid analysis and chromosomal in situ hybridization. The hpim gene is expressed as a 3.2-kilobase mRNA in various human cell lines of hematopoietic lineage, most dramatically in the K562 erythroleukemia cell line, which contains a cytogenetically demonstrable rearrangement in the 6p21 region. A characteristic chromosome anomaly, a reciprocal translocation t(6;9)(p21;q33), has been described in myeloid leukemias and could involve the hpim gene.

Heterogeneity of chromosome 22 breakpoint in Philadelphia-positive (Ph+) acute lymphocytic leukemia

In chronic myelogenous leukemias (CML) with the t(9;22)(q34;q11) chromosome translocation the breakpoints on chromosome 22 occur within a 5.8-kilobase segment of DNA referred to as "breakpoint cluster region" (bcr). The same cytogenetically indistinguishable translocation occurs in approximately 10% of patients with acute lymphocytic leukemias (ALL). In this study we have investigated the chromosome breakpoints in several cases of ALL carrying the t(9;22) translocation. In three of five cases of ALL we found that the bcr region was not involved in the chromosome rearrangement and that the 22q11 chromosome breakpoints were proximal (5') to the bcr region at band 22q11. In addition, we observed normal size bcr and c-abl transcripts in an ALL cell line carrying the t(9;22) translocation. We conclude, therefore, that if c-abl is inappropriately expressed in ALL cells without bcr rearrangements, the genetic mechanism of activation must be different from that reported for CML.

Time course of arrest of immunoglobulin expression in heterokaryons and early hybrids of human lymphoma cells and mouse fibroblasts. A study of transcriptional and translational events

Early events in arrest of immunoglobulin expression were investigated at the levels of both translation and transcription in heterokaryons and early hybrids between human Daudi lymphoma cells and mouse cl. 1D cells. Large populations of 1s: 1s hybrids, isolated by fluorescence-activated cell sorting (FACS) a few hours after fusion, were grown for up to 5 days. A survey at the light-microscopical level of peroxidase-antiperoxidase-immunostained cell populations showed that arrest of expression of IgM heavy chain (mu) occurred in up to 98% of the cells. Furthermore, quantitation of mu chain contents, by using an ELISA technique, suggested that synthesis of IgM was blocked shortly after fusion. The levels of cytoplasmic mRNA specific for mu and kappa chains, respectively, decreased at rates similar to those induced in unfused Daudi cells by treatment with actinomycin D. It is concluded that arrest of immunoglobulin expression in these hybrids occurs immediately or very shortly after fusion by mechanisms that affect the levels of their cytoplasmic mRNAs.

Coexpression of translocated and normal c-myc oncogenes in hybrids between Daudi and lymphoblastoid cells

Mechanisms that affect the transcription of the c-myc oncogene take part in the development of B-cell neoplasias such as Burkitt's lymphoma. Daudi Burkitt lymphoma cells, which express only the translocated c-myc oncogene, were hybridized with human lymphoblastoid cells, which express the normal c-myc gene; the hybrids were phenotypically lymphoblastoid and expressed both the translocated and the normal c-myc gene. This result contrasts with the findings that the decapitated c-myc gene, translocated to an immunoglobulin switch mu or alpha region, is transcriptionally silent in lymphoblastoid hybrids. Thus, there may be at least two distinct enhancer-like elements capable of deregulating c-myc transcription in lymphomas and leukemias with t(8;14) chromosome translocations. In addition, since the Daudi X lymphoblastoid hybrids express both the translocated and the normal c-myc gene, the c-myc gene product does not autoregulate c-myc transcription.

Molecular cloning of a human immunoglobulin lambda chain variable sequence

We have cloned a human V lambda cDNA sequence from an Ig lambda-producing human Burkitt lymphoma cell line (BL2) by taking advantage of a cloned constant region gene as a primer for cDNA synthesis instead of an oligo(dT) primer. The amino acid sequence deduced from the nucleotide sequence of V lambda clones is highly related to that of the NEW V lambda protein of subgroup I. Southern blot hybridization of human DNAs with the V lambda I probe showed at least 12 hybridizing V lambda fragments. These fragments are amplified in K562 cells which derive from a case of chronic myelogenous leukemia and contain an amplified c-abl oncogene and amplified C lambda sequences.

Translocated c-myc oncogene of Burkitt lymphoma is transcribed in plasma cells and repressed in lymphoblastoid cells

We examined somatic cell hybrids between Burkitt lymphoma cells and either human lymphoblastoid cells or mouse plasmacytoma cells for the expression of the translocated c-myc oncogene. The results of this study indicate that the translocated c-myc oncogene is transcribed in plasma cells but is repressed in lymphoblastoid cells. Thus, the factors necessary for translocated c-myc transcription are present in plasma cells and Burkitt lymphoma cells but are absent or inactive in lymphoblastoid cells. Since the distance between the rearranged immunoglobulin loci and the c-myc oncogene can even exceed 30-50 kilobases, we speculate that the translocated c-myc oncogene is under the transcriptional control of enhancer-like elements capable of acting over long distances. The activity of this long-range enhancer may depend on the interaction with transacting factors that are active in plasma cells and in Burkitt lymphoma cells but are not active in lymphoblastoid cells. We also examined the transcription of the first exon of the c-myc oncogene, which becomes separated from the second and third exon because of the chromosomal break involving the first intron. This exon is transcribed at high levels in ST486 Burkitt lymphoma cells with the t(8;14) chromosome translocation. Hybrids between lymphoblastoid and ST486 cells expressed high levels of transcripts of the first exon, whereas hybrids between plasma cells and ST486 cells did not. Thus, transcription of the separated first exon can be enhanced in lymphoblastoid and Burkitt lymphoma cells because of its close proximity to the heavy chain enhancer that is normally located between the joining and the switch region of the C mu gene. Such enhancement, however, does not occur in plasma cells, possibly because these cells are able to suppress completely the c-myc oncogene, unless it has been placed in the proximity of a rearranged immunoglobulin constant region gene.

Repression of rearranged mu gene and translocated c-myc in mouse 3T3 cells X Burkitt lymphoma cell hybrids

The productively rearranged immunoglobulin mu chain gene and the translocated cellular oncogene c-myc are transcribed at high levels both in human Burkitt lymphoma cells carrying the t(8;14) chromosome translocation and in mouse plasmacytoma X Burkitt lymphoma cell hybrids. In the experiments reported here these genes were found to be repressed in mouse 3T3 fibroblast X Burkitt lymphoma cell hybrids. Such repression probably occurs at the transcriptional level since no human mu- and c-myc messenger RNA's are detectable in hybrid clones carrying the corresponding genes. It is therefore concluded that the ability to express these genes requires a differential B cell environment. The results suggest that the 3T3 cell assay may not be suitable to detect oncogenes directly involved in human B cell oncogenesis, since 3T3 cells apparently are incapable of transcribing an oncogene that is highly active in malignant B cells with specific chromosomal translocations.

Association of amplified oncogene c-myc with an abnormally banded chromosome 8 in a human leukaemia cell line

Several unusual chromosome structures have been described in drug-resistant cell lines and in certain tumours. These structures include elongated homogeneously staining regions (HSRs), small extrachromosomal paired chromatin bodies (double minutes, DMs) and abnormally banded regions (ABRs) with strong but anomalous band patterns. There is evidence that these are alternative forms of gene amplification, with HSRs breaking down to form DMs, and DMs integrating into the chromosome to generate HSRs and ABRs. Recently, it was demonstrated that, compared with several normal and leukaemia human cells, DNA sequences representing the human homologue of the onc gene of the avian myelocytomatosis virus (MC29), the so-called c-myc gene, were amplified in HL-60 cells. This is a human promyelocytic leukaemia cell line established in the laboratory of one of us (R.C.G.) at the National Cancer Institute (Bethesda, Maryland) in 1977, and widely used for studies on myeloid and monocytic differentiation. Amplification of the gene was present in primary leukaemic cells of the patient, and DMs were noted in some of these cells as well as in early passages of the HL-60 line. No structure resembling HSRs or ABRs were noted in karyotypic studies at this early stage and there were no alterations involving the long arm of chromosome 8 (8q), to which the c-myc gene has recently been mapped. We have now re-examined the karyotype of the HL-60 line, using cells frozen at various times during its continuous passage at the Wistar Institute (Philadelphia, Pennsylvania) to look for chromosomal abnormalities that might be associated with the amplification of c-myc. We find that, beginning in 1979, HL-60 cells at the Wistar Institute no longer had DMs, but did show an abnormal 8q+ chromosome, replacing a normal chromosome 8, and representing an ABR reflecting the site of myc gene amplification.

Translocation of an immunoglobulin kappa locus to a region 3' of an unrearranged c-myc oncogene enhances c-myc transcription

We have studied somatic cell hybrids between mouse myeloma and JI Burkitt lymphoma cells carrying a t(2;8) chromosome translocation for the expression of human kappa chains. and for the presence and rearrangements of the human c-myc oncogene and kappa chain genes. Our results indicate that the c-myc oncogene is unrearranged and remains on the 8q+ chromosome of JI cells. Two rearranged C kappa genes were detected: the expressed allele on normal chromosome 2 and the excluded kappa allele that was translocated from chromosome 2 to the involved chromosome 8 (8q+). The distribution of V kappa and C kappa genes in hybrid clones retaining different human chromosomes indicated that C kappa is distal to V kappa on 2p and that the breakpoint in this Burkitt lymphoma is within the region carrying V kappa genes. High levels of transcripts of the c-myc gene were found when it resided on the 8q+ chromosome but not on the normal chromosome 8, demonstrating that translocation of a kappa locus to region distal to the c-myc oncogene enhances c-myc transcription.

Transcriptional activation of an unrearranged and untranslocated c-myc oncogene by translocation of a C lambda locus in Burkitt

We have studied somatic cell hybrids between mouse myeloma cells and IARC-BL2 Burkitt lymphoma human cells carrying a t(8;22) chromosome translocation for the presence and expression of human immunoglobin lambda chains and for the c-myc oncogene. The results indicate that the c-myc oncogene remains on the 8q+ chromosome and that the excluded and rearranged C lambda allele translocates from chromosome 22 to this chromosome 8. As a result of the translocation, transcriptional activation of the c-myc oncogene on the rearranged chromosome 8 (8q+) occurs, while the c-myc oncogene in the normal chromosome 8 is transcriptionally silent. These findings suggest that the translocation of a rearranged immunoglobulin locus to the 3' side of an unrearranged c-myc oncogene may enhance its transcription and contribute to malignant transformation.

The structure and nucleotide sequence of the 5' end of the human c-myc oncogene

We have established the structure and nucleotide sequence of the 5' end of the human c-myc oncogene, using a cloned genomic fragment isolated from a fetal liver library (clone lambda MC41) and cloned cDNA from the human leukemic cell line K562. The human c-myc oncogene consists of three exons and two introns. Primer extension of the human c-myc mRNA of three different cell lines and S1 nuclease protection experiments served to establish the position of two transcription initiation sites. The splicing site of the first exon-intron boundary was determined by comparative analysis of the sequences of the genomic and cDNA clones. The first exon contains termination codons in all three reading frames and no translation initiation signals, confirming our previous observation that the c-myc mRNA has a long 5' noncoding sequence. This first exon also was found to be utilized in the formation of c-myc mRNAs in a variety of human cell lines.

Transfer of a cloned immunoglobulin light-chain gene to mutant hybridoma cells restores specific antibody production

The expression of immunoglobulin (Ig) genes is regulated at several levels. For example, although kappa-chain production requires a DNA rearrangement that juxtaposes variable and joining segments, this rearrangement is not sufficient for kappa-chain gene expression; that is, some cell types do not permit immunoglobulin production. The mechanisms responsible for the regulation of the expression of rearranged immunoglobulin genes are poorly understood. The technique of modifying cloned genes in vitro and transferring the modified genes to cells in culture provides a tool for identifying the structural features required for gene expression. To analyse immunoglobulin genes in this manner, however, it is first necessary to use, as recipients, cells that normally permit immunoglobulin production. We report here that a cloned kappa-chain gene is expressed in immunoglobulin-producing hybridoma cells. Furthermore, the product of the transferred kappa-chain gene is capable of restoring specific antibody production to the transformed cells.

Transcriptional activation of the translocated c-myc oncogene in burkitt lymphoma

We have previously demonstrated that translocations of V(H) genes from chromosome 14 to chromosome 8 and of the c-myc oncogene from chromosome 8 to chromosome 14 occur in Burkitt lymphomas with the t(8;14) chromosome translocation. An association of the c-myc gene with the C(mu) immunoglobulin gene has been observed in some but not all Burkitt lymphomas studied previously. In the present study, we have investigated the organization of the human heavy chain locus and of the c-myc gene in the P3HR-1 Burkitt lymphoma cell line. Becuase mouse/P3HR-1 somatic cell hybrids that retain only the 14q+ chromosome and no other human chromosome contain the human C(mu) and C(gamma) genes but not V(H) genes, we have concluded that the breakpoint on chromosome 14 in P3HR-1 cells is distal to C(mu) and between C(mu) and V(H). Thus, the breakpoint of human chromosome 14 differs in different Burkitt lymphoma cell lines. We also found that the human c-myc oncogene translocated to chromosome 14 in the P3HR-1 cell line is not recombined with the C(mu) gene. The breakpoint on human chromosome 8 may therefore also differ in different Burkitt lymphoma cell lines, because we have observed DNA rearrangement of the c-myc gene with the C(mu) gene in only some of the Burkitt lymphoma cell lines studied elsewhere. Interestingly, high levels of transcripts of the c-myc oncogene were observed in Burkitt lymphomas with translocated c-myc oncogenes both rearranged and unrearranged. Therefore, the translocation of a c-myc oncogene to the heavy chain locus on human chromosome 14 is apparently sufficient for its transcriptional activation and may be an essential step in the pathway leading to neoplasia.