Deregulation of MUM1/IRF4 by chromosomal translocation in multiple myeloma.

The pathogenesis of multiple myeloma (MM), an incurable tumour causing the deregulated proliferation of terminally differentiated B cells, is unknown. Chromosomal translocations (14q1) affecting band 14q32 and unidentified partner chromosomes are common in this tumour, suggesting that they may cause the activation of novel oncogenes. By cloning the chromosomal breakpoints in an MM cell line, we show that the 14q+ translocation represents a t(6;14)x(p25;q32) and that this aberration is recurrent in MM, as it was found in two of eleven MM cell lines. The translocation juxtaposes the immunoglobulin heavy-chain (IgH) locus to MUM1 (multiple myeloma oncogene 1)/IRF4 gene, a member of the interferon regulatory factor (IRF) family known to be active in the control of B-cell proliferation and differentiation. As a result, the MUM1/IRF4 gene is overexpressed--an event that may contribute to tumorigenesis, a MUM1/IRF4 has oncogenic activity in vitro. These findings identify a novel genetic alteration associated with MM, with implications for the pathogenesis and diagnostics of this tumour.

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.

The BCL-6 proto-oncogene controls germinal-centre formation and Th2-type inflammation.

Structural alterations of the promoter region of the BCL-6 proto-oncogene represent the most frequent genetic alteration associated with non-Hodgkin lymphoma, a malignancy often deriving from germinal-centre B cells. The BCL-6 gene encodes a zinc-finger transcriptional repressor normally expressed in both B cells and CD4+ T cells within germinal centres, but its precise function is unknown. We show that mice deficient in BCL-6 displayed normal B-cell, T-cell and lymphoid-organ development but have a selective defect in T-cell-dependent antibody responses. This defect included a complete lack of affinity maturation and was due to the inability of follicular B cells to proliferate and form germinal centres. In addition, BCL-6-deficient mice developed an inflammatory response in multiple organs characterized by infiltrations of eosinophils and IgE-bearing B lymphocytes typical of a Th2-mediated hyperimmune response. Thus, BCL-6 functions as a transcriptional switch that controls germinal centre formation and may also modulate specific T-cell-mediated responses. Altered expression of BCL-6 in lymphoma represents a deregulation of the pathway normally leading to B cell proliferation and germinal centre formation.

T cell receptor beta chain gene rearrangements in lymphoproliferative disorders of large granular lymphocytes/natural killer cells.

Twelve cases of T gamma LPD (lymphoproliferative disorders of Fc gamma receptor-bearing T cells) involving an expansion of large granular lymphocyte/natural killer (LGL/NK) cells were investigated for the expression of LGL/NK-associated markers and for T beta gene rearrangement. All the cases selected were classified as T gamma LPD on the basis of morphology, function, and phenotype of the circulating cells. 10 to 12 cases displayed clonal rearrangements of the T beta locus and expression of the T3 antigen, whereas the 2 remaining cases displayed the germline configuration of the T beta gene and no expression of the T3 antigen. T8, Mol, B73.1, and N901 antigens were variably expressed among both T beta+T3+ and T beta-T3- T gamma LPD cases. We suggest that individual T gamma LPD cases represent the clonal expansion of cells frozen at different stages of differentiation/activation within an individual hematopoietic LGL/NK lineage.

Ras oncogene mutation in multiple myeloma.

The frequency of ras (H-, K-, and N-ras) and c-myc oncogenes was investigated in multiple myeloma (MM). By means of the polymerase chain reaction (PCR)/oligonucleotide hybridization method, DNA from 56 tumor biopsies was analyzed for the presence of activating mutations involving codons 12 and 61 of the H-, K-, and N-ras genes and codon 13 of the N-ras gene. Mutations, involving the N- or K-ras genes, were detected in 18 of 56 (32%) cases of which 12/43 (27%) were at diagnosis and 6/13 (46%) were after treatment. In some cases, multiple mutations affecting different ras alleles were detected. Direct nucleotide sequence analysis of PCR products indicated that a more heterogeneous nature of the base pair changes than previously shown for other tumors along with a preferential involvement of N-ras codon 61. The heterogeneity of MM cases with respect to the presence of ras oncogenes prompted an analysis of possible correlations with different clinico-pathologic characteristics of MM from which a correlation between the presence of ras oncogenes and a partial or complete lack of response to therapy emerged. The frequency of activating rearrangements or mutations of the c-myc gene were studied by Southern blot analysis and PCR sequencing, respectively. However, contrary to previous reports involving mostly MM cell lines, no structural alterations of the c-myc gene were found. These results indicate that ras, but not c-myc, oncogenes are activated in vivo in MM cells, representing the first oncogene alteration that has been associated at appreciable frequency with this type of malignancy. While the mechanism of occurrence and biological role of ras activation in MM remains to be elucidated, the preliminary correlations observed in this study between the presence of ras oncogenes and poor therapeutic response suggest that further investigations of the possible prognostic significance of these alterations are necessary.

Multiple monoclonal B cell expansions and c-myc oncogene rearrangements in acquired immune deficiency syndrome-related lymphoproliferative disorders. Implications for lymphomagenesis.

AIDS (acquired immune deficiency syndrome) and ARC (AIDS-related complex) are associated with a spectrum of lymphoproliferative disorders ranging from lymphadenopathy syndrome (LAS), an apparently benign polyclonal lymphoid hyperplasia, to B cell non-Hodgkin's lymphoma (B-NHL), i.e., malignant, presumably monoclonal B cell proliferations. To gain insight into the process of lymphomagenesis in AIDS and to investigate a possible pathogenetic relationship between LAS and NHL, we investigated the clonality of the B or T lymphoid populations by Ig or T beta gene rearrangement analysis, the presence of rearrangements involving the c-myc oncogene locus, and the presence of human immunodeficiency virus (HIV) sequences in both LAS and B-NHL biopsies. Our data indicate that multiple clonal B cell expansions are present in a significant percentage of LAS (approximately 20%) and B-NHL (60%) biopsies. c-myc rearrangements/translocations are detectable in 9 of our 10 NHLs, but not in any of the LAS cases. However, only one of the B cell clones, identified by Ig gene rearrangements carries a c-myc gene rearrangement, suggesting that only one clone carries the genetic abnormality associated with malignant B cell lymphoma. Furthermore, the frequency of detection of c-myc rearrangements in AIDS-associated NHLs of both Burkitt and non-Burkitt type suggest that the biological alterations present in AIDS favor the development of lymphomas carrying activated c-myc oncogenes. Finally, our data show that HIV DNA sequences are not detectable in LAS nor in NHL B cell clones, suggesting that HIV does not play a direct role in NHL development. Taken together, these observations suggest a model of multistep lymphomagenesis in AIDS in which LAS would represent a predisposing condition to NHL. Immunosuppression and EBV infection present in LAS can favor the expansion of B cell clones, which in turn may increase the probability of occurrence of c-myc rearrangements leading to malignant transformation.

Lymphoid tumors displaying rearrangements of both immunoglobulin and T cell receptor genes.

Ig and T beta gene rearrangements can be used as genetic markers of lineage and clonality in the study of B and T cell populations. We have addressed the issue of the respective B and T lineage specificity of these rearrangements by analyzing a panel of 63 lymphoid tumors representative of the various clinicopathologic categories of both B and T neoplasias. We report that approximately 10% of the cases tested displayed rearrangements of both Ig and T beta genes. Despite their dual genotypic pattern, these tumors retain a pure immunophenotype, i.e. they display either B or T cell lineage-restricted cell surface antigens. The implications of these findings for both normal and neoplastic lymphoid differentiation are discussed.

High frequency of clonal immunoglobulin or T cell receptor gene rearrangements in acute myelogenous leukemia expressing terminal deoxyribonucleotidyltransferase.

Ig and T cell receptor rearrangements have been used as irreversible markers of lineage and clonality in the study of B- and T-lymphoid populations. We have addressed the issue of lymphoid lineage specificity of these rearrangements by analyzing a panel of 25 TdT- acute myelogenous leukemias, 13 TdT+ AMLs, and 4 TdT+ undifferentiated leukemias. We report that while gene rearrangements represent extremely rare events in classical TdT- AML (less than 8%), rearrangements of either the Ig or T beta locus or both were detectable in the majority of the TdT+ AMLs (greater than 60%), and rearrangements of both loci were detectable in all of the TdT+ undifferentiated leukemias. These data demonstrate a significant association between TdT expression and Ig or T beta gene rearrangements even outside the lymphoid lineage, further supporting a role for TdT in Ig and T cell receptor gene assembly. These data also indicate that a coordinated program of lymphoid gene expression involving TdT-CD7-expression and Ig/T beta rearrangements can be activated before myeloid commitment. Whether the activation of this program represents a normal, albeit rare, event in early myelopoiesis or a transformation-related event present only in leukemic cells remains to be determined.

Gene expression profiling of B cell chronic lymphocytic leukemia reveals a homogeneous phenotype related to memory B cells.

B cell-derived chronic lymphocytic leukemia (B-CLL) represents a common malignancy whose cell derivation and pathogenesis are unknown. Recent studies have shown that >50% of CLLs display hypermutated immunoglobulin variable region (IgV) sequences and a more favorable prognosis, suggesting that they may represent a distinct subset of CLLs which have transited through germinal centers (GCs), the physiologic site of IgV hypermutation. To further investigate the phenotype of CLLs, their cellular derivation and their relationship to normal B cells, we have analyzed their gene expression profiles using oligonucleotide-based DNA chip microarrays representative of approximately 12,000 genes. The results show that CLLs display a common and characteristic gene expression profile that is largely independent of their IgV genotype. Nevertheless, a restricted number of genes (<30) have been identified whose differential expression can distinguish IgV mutated versus unmutated cases and identify them in independent panels of cases. Comparison of CLL profiles with those of purified normal B cell subpopulations indicates that the common CLL profile is more related to memory B cells than to those derived from naive B cells, CD5(+) B cells, and GC centroblasts and centrocytes. Finally, this analysis has identified a subset of genes specifically expressed by CLL cells of potential pathogenetic and clinical relevance.

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.

Mutations in the first exon are associated with altered transcription of c-myc in Burkitt lymphoma.

The c-myc proto-oncogene is involved in chromosomal translocations that are specifically and consistently found in Burkitt lymphoma. Although these translocations are thought to lead to a deregulation of c-myc expression, the structural and functional basis of this phenomenon has not been identified. Mutations in a specific region spanning approximately 70 base pairs and located at the 3' border of the first exon of translocated c-myc alleles were consistently detected in Burkitt lymphoma cells carrying classic (8:14) as well as variant (8:22 and 2:8) translocations. These structural alterations were accompanied by an altered pattern of c-myc transcription, namely, the removal of a block to transcriptional elongation that has been mapped to the same region. Thus, specific c-myc mutations leading to the alleviation of this block to transcriptional elongation may represent a general mechanism causing c-myc activation in Burkitt lymphoma.

Down-regulation of LFA-1 adhesion receptors by C-myc oncogene in human B lymphoblastoid cells.

The function of the c-myc gene and its role in tumorigenesis are poorly understood. In order to elucidate the role of c-myc oncogene activation in B cell malignancy, the phenotypic changes caused by the expression of c-myc oncogenes in human B lymphoblastoid cells immortalized by Epstein-Barr virus were analyzed. C-myc oncogenes caused the down-regulation of lymphocyte function-associated antigen-1 (LFA-1) adhesion molecules (alpha L/beta 2 integrin) and loss of homotypic B cell adhesion in vitro. Down-regulation of LFA-1 occurred by (i) posttranscriptional modulation of LFA-1 alpha L-chain RNA soon after acute c-myc induction, and (ii) transcriptional modulation in cells that chronically express c-myc oncogenes. Analogous reductions in LFA-1 expression were detectable in Burkitt lymphoma cells carrying activated c-myc oncogenes. Since LFA-1 is involved in B cell adhesion to cytotoxic T cells, natural killer cells, and vascular endothelium, these results imply functions for c-myc in normal B cell development and lymphomagenesis.

Binding and suppression of the Myc transcriptional activation domain by p107.

An amino-terminal transactivation domain is required for Myc to function as a transcription factor controlling cell proliferation, differentiation, and apoptosis. A complementary DNA expression library was screened with a Myc fusion protein to identify proteins interacting with this domain, and a clone encoding the Rb-related p107 protein was isolated. The p107 protein was shown to associate with Myc in vivo and to suppress the activity of the Myc transactivation domain. However, mutant forms of Myc from Burkitt lymphoma cells, which contain sequence alterations in the transactivation domain, were resistant to p107-mediated suppression. Thus, disruption of a regulatory interaction between Myc and p107 may be important in tumorigenesis.

Relationship between the c-myb locus and the 6q-chromosomal aberration in leukemias and lymphomas.

Deletions of the long arm of chromosome 6 (6q-) are frequently found in hematopoietic neoplasms, including acute lymphoblastic leukemias, non-Hodgkin lymphomas and (less frequently) myeloid leukemias. The c-myb proto-oncogene has been mapped to region 6q21-24, which suggests that it could be involved in the 6q- aberrations. By means of in situ chromosomal hybridization on cells from six hematopoietic malignancies, it was demonstrated that the c-myb locus is not deleted, but is retained on band q22, which is consistently bordered by the chromosomal breakpoints in both interstitial and terminal 6q- deletions. The deletion breakpoints were located at some distance from the myb locus since no rearrangement of c-myb sequences was found. In one case, however, amplification of the entire c-myb locus was detectable. Furthermore, in all cases tested that carry 6q- deletions, myb messenger RNA levels were significantly higher than in normal cells or in malignant cells matched for lineage and stage of differentiation but lacking the 6q- marker. These results indicate that 6q- deletions are accompanied by structural and functional alterations of the c-myb locus and that these alterations may be involved in the pathogenesis of leukemias and lymphomas.

Molecular diversity of the human T-gamma constant region genes.

The human T cell antigen-receptor gamma chain, which is expressed on the surface of a subpopulation of CD3+ T lymphocytes, exhibits size polymorphism and varies in its ability to form disulfide bonds with a second polypeptide. Analysis of both genomic and complementary DNA clones encoding the human gamma polypeptide shows differences in lengths of the coding portions of the two constant region genes, C gamma 1 and C gamma 2. A single second-exon segment is always present in the C gamma 1 gene. C gamma 2 alleles containing either duplicated or triplicated second-exon segments are present in the normal human population and are expressed as messenger RNAs. Furthermore, a cysteine residue, encoded by the second exon of C gamma 1 and probably involved in interchain disulfide bridging, is absent in all C gamma 2 second-exon segments. These differences between C gamma 1 and the two alleles of C gamma 2 may explain the variability in molecular weight and disulfide bonding of gamma molecules expressed in different cells.

Translocation and rearrangements of the c-myc oncogene locus in human undifferentiated B-cell lymphomas.

The locus for the cellular myc (c-myc) oncogene in humans is located on the region of chromosome 8 that is translocated to chromosome 14 in cells from most undifferentiated B-cell lymphomas. It is shown in this study that the c-myc locus is rearranged in 5 out of 15 cell lines from patients with undifferentiated B-cell lymphomas, and that the rearrangement involves a region at the 5' side of an apparently intact c-myc gene. In at least three patients, this rearranged region appears to contain immunoglobulin heavy chain mu sequences that are located on chromosome 14. The data indicate that this region contains the crossover point between chromosomes 8 and 14. The break point can occur at different positions on both chromosomes among individual cell lines.

Chromosomal localization of the human homolog (c-sis) of the simian sarcoma virus onc gene.

Nonrandom chromosome rearrangements of chromosome 22 have been identified in different human malignancies. As a result of Southern blot hybridization of a c-sis probe to DNA's from mouse-human somatic cell hybrids, the human homolog (c-sis) of the transforming gene of simian sarcoma virus was assigned to chromosome 22. Hybrids between thymidine kinase-deficient mouse cells and human fibroblasts carrying a translocation of the region q11-qter of chromosome 22 to chromosome 17 were also analyzed. These studies demonstrate that the human c-sis gene is on region 22q11 greater than qter.

Three distinct genes in human DNA related to the transforming genes of mammalian sarcoma retroviruses.

Southern blot hybridization was used to identify human and other vertebrate DNA sequences that were homologous to cloned DNA fragments containing the oncogenic nucleic acid sequences of three different type C mammalian retroviruses (simian sarcoma virus, the Snyder-Theilen strain of feline sarcoma virus, and the Harvey strain of murine sarcoma virus). Each onc gene counterpart has a single genetic locus, which probably contains non-onc intervening sequences. The human DNA sequences may represent genes important to cell growth or cell differentiation, or both. Their identification and isolation may allow elucidation of their role in these processes and in neoplasias.

Amplification of the c-myb oncogene in a case of human acute myelogenous leukemia.

Amplification is one of the mechanisms by which cellular oncogenes may be altered in their function, possibly leading to neoplastic transformation. The oncogenes c-myc, c- abl , and c-Ki-ras are amplified in several different human neoplasias. The oncogene c-myb, which is specifically expressed and regulated in hematopoietic cells, was found to be amplified in cell lines ML-1, ML-2, and ML-3, which were separately cultured from cells of a patient with acute myelogenous leukemia (AML). A five- to tenfold amplification was correlated with high levels of expression of normal size c-myb messenger RNA and with chromosomal abnormalities in the region 6q22 -24, where the c-myb locus is normally located. Amplification and cytogenetic abnormalities were detected in DNA's from primary and secondary cultures of ML cells, suggesting that they may have contributed to leukemogenesis. The similar AML cell lines HL-60 and ML's contain different amplified oncogenes: c-myc and c-myb, respectively. Alternative activation of structurally and possibly functionally similar oncogenes may distinguish--at the pathogenetic level--phenotypically similar tumors.