Sublocalization of c-myb to 6q21----q23 by in situ hybridization and c-myb expression in a human teratocarcinoma with 6q rearrangements

c-MYB and DMTF1 in Cancer

The c-Myb gene encodes a transcription factor that regulates cell proliferation, differentiation, and apoptosis through protein-protein interaction and transcriptional regulation of signaling pathways. The protein is frequently overexpressed in human leukemias, breast cancers, and other solid tumors suggesting that it is a bona fide oncogene. c-MYB is often overexpressed by translocation in human tumors with t(6;7)(q23;q34) resulting in c-MYB-TCRβ in T cell ALL, t(X;6)(p11;q23) with c-MYB-GATA1 in acute basophilic leukemia, and t(6;9)(q22-23;p23-24) with c-MYB-NF1B in adenoid cystic carcinoma. Antisense oligonucleotides to c-MYB were developed to purge bone marrow cells to eliminate tumor cells in leukemias. Recently, small molecules that inhibit c-MYB activity have been developed to disrupt its interaction with p300. The Dmp1 (cyclin D binding myb-like protein 1; Dmtf1) gene was isolated through its virtue for binding to cyclin D2. It is a transcription factor that has a Myb-like repeat for DNA binding. The Dmtf1 protein directly binds to the Arf promoter for transactivation and physically interacts with p53 to activate the p53 pathway. The gene is hemizygously deleted in 35-42% of human cancers and is associated with longer survival. The significances of aberrant expression of c-MYB and DMTF1 proteins in human cancers and their clinical significances are discussed.

[Antisense therapy in oncology: present situation]

The purpose of antisense therapy is to control the regulation of genes contributing to cancer progression while sparing normal cell growth, which represents a novel alternative with fewer side effects when compared to conventional chemotherapy. Antisense oligonucleotides control cell proliferation by specifically blocking the expression of selected genes, and hence they are being developed as molecular drugs with potential activity for cancer treatment. Extensive clinical information and a number of clinical trials show encouraging results. This review discusses the most significant aspects of this new therapeutic alternative in oncology. Clinical trials performed thus far have demonstrated their short- to mid-term efficacy and safety; however, long-term studies are needed to definitely define their clinical effectiveness and true toxic profile.

The future of antisense therapy: combination with anticancer treatments

The current direction in cancer research is rational drug design, which is based on the evidence that transformed cells are characterized by alterations of genes devoted to the regulation of both cell proliferation and apoptosis. A variety of approaches have been carried out to develop new agents selective for cancer cells. Among these, antisense oligonucleotides (ASOs) are one of such class of new agents able to inhibit specifically the synthesis of a particular cancer-associated protein by binding to protein-encoding RNA, thereby preventing RNA function. In the past decade, several ASOs have been developed and tested in preclinical and clinical studies. Many have shown convincing in vitro reduction in target gene expression and promising activity against a wide variety of tumors. However, because of the multigenic alterations of tumors, the use of ASOs as single agents does not seem to be effective in the treatment of malignancies. Antisense therapy that interferes with signaling pathways involved in cell proliferation and apoptosis are particularly promising in combination with conventional anticancer treatment. An overview of the progress of ASOs used in combination therapy is provided.

Chromosomal anomalies in a case of proliferative myositis

Proliferative myositis, a reactive lesion similar to proliferative fasciitis and nodular fasciitis, has only been cytogenetically described in one other report to date. This previously described case showed trisomy 2. Cytogenetic analysis and fluorescence in situ hybridization (FISH) of a proliferative myositis lesion in the present study did not reveal trisomy 2 but the following clonal translocation was observed: 46,XX,t(6;14)(q23;q32).

Characterization of a rearrangement in the c-MYB promoter in the acute lymphoblastic leukemia cell line CCRF-CEM

Despite the frequent description of 6q- structural abnormalities in human leukemias and lymphomas, rearrangements of the c-MYB locus have not been detected. We have detected a rearrangement in the c-MYB proto-oncogene in the cell line CCRF-CEM, an immature T-cell leukemia cell line which is not 6q-. Due to this rearrangement, a large portion of the c-MYB promoter conserved between the human and murine c-MYB genes is lost. The rearranged locus, which we have designated MRR (MYB rearranged region), has been cloned and mapped to chromosome 6. Field inversion gel electrophoresis (FIGE) studies reveal that the MRR sequence is linked to the c-MYB locus, suggesting that the rearrangement is due to a submicroscopic deletion. The rearrangement appears to have no effect on c-MYB promoter activity as analyzed in CCRF-CEM cells. The normal locus of the MRR sequence has been cloned from a human placental genomic library. Partial sequence analysis of this clone reveals that a portion of the DNA lost in the rearrangement shows a high degree of homology to a member of the myc family of oncogenes. Thus the characterization of this rearrangement has yielded a new set of probes for the study of chromosome 6q abnormalities in human leukemias and lymphomas and provides the first evidence for potential involvement of the c-MYB locus itself in submicroscopic deletions within chromosome 6.

Chromosomal localization of a sequence with in vivo activity for initiation of DNA replication

The genomic fragment containing the sequence of human cDNA clone 343, previously characterized as capable of autonomous replication upon transfection into mammalians cells and occupying a genomic region inclusive of an initiation zone for DNA replication, was mapped on human chromosome 6q22-qter by a combination of in situ hybridization and G-banding. Southern blot hybridization with a panel of human-hamster somatic cells confirmed the location of the 343 gene on chromosome 6. Fragile sites have been mapped to the region at 6q21 and 6q26. Several neoplastic disorders, including melanoma, acute nonlymphocytic leukemia, acute lymphocytic leukemia, and malignant lymphoma, have also exhibited translocations and deletions involving the region 6q21-6q27.

t(6;12)(q23;q13) and t(10;16)(q22;p11) in a phyllodes tumor of breast

Cytogenetic analysis of short-term cultures from a phyllodes tumor showed clonal chromosome changes including t(6;12)(q23;q13) and t(10;16)(q22;p11). This is the first reported karyotype in this tumor type. We discuss the breakpoints of these translocations in relation to the involvement of possible candidate genes.

Chromosomal reallocation of the chicken c-myb locus and organization of 3'-proximal coding exons

In the course of our studies concerning the tissue-specific expression of the c-myb proto-oncogene, we have established the nucleotide sequence of the chicken c-myb 3'-proximal coding exons. In situ hybridization performed with different genomic DNA probes corresponding to nearly all the c-myb gene allowed us to localize the corresponding locus on the large acrocentric chromosome 3 in chicken. Our sequencing data also indicate that the 3'-proximal noncoding sequences represented in c-myb mRNA species are derived from non-contiguous exons.

Human interferon gamma receptor 1 (IFNGR1) gene maps to chromosome region 6q23-6q24

The human interferon gamma receptor (IFNGR1) gene has been localized by in situ hybridization to chromosome 6 at q23-q24. This chromosomal region is often deleted in lymphoid cell malignancies.

Expression of c-myb in embryonal carcinoma cells and embryonal stem cells

Mouse c-myb has been implicated in the regulation of differentiation and proliferation of haematopoietic cells. Analysis of the chromatin structure of the promoter region of c-myb in embryonal carcinoma (EC) cells and embryonal stem (ES) cells reveals a DNAse I-hypersensitive site coincident with a site found in c-myb-expressing haematopoietic cells, but absent in murine fibroblasts (which do not express c-myb). EC and ES cells were found to express c-myb mRNA, albeit at a level lower than found in haematopoietic cells. Differentiation of ES cells into embryoid bodies resulted in an elevated level of c-myb expression.

Human teratocarcinomas

Teratocarcinomas are one of the commonest forms of cancer in young adult men. Cell lines derived from these tumors, and particularly the cell lines composed of their embryonal carcinoma (EC) stem cells, may provide useful information concerning the development and subsequent pathology of teratocarcinomas in humans. In addition, it is likely that human EC cells resemble early embryonic cells and can be used as an in vitro counterpart of such cells from the human embryo. Several common properties of human EC cells have been identified, and a human EC cell line, TERA-2, that is capable of extensive somatic differentiation has been cloned. In nude mice, TERA-2 EC cells form tumors containing neural elements and glandular structures that resemble primitive gut. In culture, these EC cells can be induced to differentiate by exposure to retinoic acid and hexamethylenebisacetamide (HMBA). Differentiation is marked by the disappearance of several cell surface antigens characteristic of human EC cells, and the appearance of other antigens on the various subsets of differentiated derivatives. In retinoic acid-induced cultures, these differentiated derivatives include neurons and cells permissive for the replication of cytomegalovirus, a virus that can cause birth defects in humans. On the other hand, HMBA appears to activate an alternative pathway of differentiation for TERA-2 EC cells, although the identity of the resulting cells remains to be elucidated. In addition to providing a tool for analyzing the evolution of teratocarcinomas in human patients, the TERA-2 EC cells may provide us with insights into the mechanisms of cellular differentiation in the human embryo and a model in which to investigate how teratogenic agents such as HCMV can disrupt these processes.

Expression of chromosome 21 specific sequences in normal and Down's syndrome tissues

Using RNA isolated from age and sex matched normal and Down's Syndrome foetal liver and brain tissues, Northern blots were prepared and probed with 4 chromosome 21 specific sequences. The results show that no consistent pattern of expression emerges when Down's Syndrome tissue is compared with normal tissue but the results are very different from the 3/2 ratio of expression which may be expected. Two sequences 21.3 and 26C show only minor differences in expression in trisomy 21 liver samples but significant changes in their expression pattern when normal and Down's Syndrome brain samples are compared. The other sequences, JG77 and JG90 show a 5 fold higher degree of expression in Down's brain but when liver samples are compared one of these sequences shows equal levels of expression in normal and Down's Syndrome samples and the other shows a decrease in expression level in Down's Syndrome samples.

The human c-ros gene (ROS) is located at chromosome region 6q16----6q22

The human homolog, c-ros, of the transforming gene, v-ros, of the avian sarcoma virus, UR2, has been isolated from a human genomic library. A single-copy fragment from the human c-ros genomic clone has been used to map the human c-ros homolog (ROS) to human chromosome region 6q16----6q22 by somatic cell hybrid analysis and chromosomal in situ hybridization. Thus, the c-ros gene joins the c-myb oncogene, which is distal to the c-ros gene on the long arm of human chromosome 6, as a candidate for involvement in chromosome 6q deletions and rearrangements seen in various malignancies.