IgH enhancer-mediated deregulation of N-myc gene expression in transgenic mice: generation of lymphoid neoplasias that lack c-myc expression

A comparative analysis of N-myc and c-myc expression and cellular proliferation in mouse organogenesis

The distribution of c-myc and N-myc transcripts during mouse organogenesis was investigated by in situ hybridization and compared to proliferation in several tissues. Only c-myc expression was found during the formation of cartilage, brown adipose tissue, glandula submandibularis, thymus and liver. There was a temporally and spatially ordered expression of N-myc only during the organogenesis of brain, retina and eye lens. In some organs (e.g., in lung and tooth bud), c-myc and N-myc were expressed in a striking complementary pattern that reflected the ontogenic origins of different tissue components. Transcripts of both genes were found in the early gut epithelium, but as formation of villi began, the spatial expression pattern of N-myc and c-myc diverged. The results suggest a link between the proliferative state of cell types and the differential expression of N-myc vs. c-myc. Specifically, c-myc is only expressed in rapidly proliferating tissues, while N-myc expression often persists through cytodifferentiation, e.g., during development of eye lens, retina, telencephalon and gut epithelium. Thus, in spite of the structural similarities of N-myc and c-myc genes and proteins their developmental expression patterns suggest different functional roles.

Enhanced expression of the cellular oncogene MYCN and progression of human neuroblastoma

A central issue in cancer research is how tumors evolve and acquire a more aggressive phenotype. It is a widely discussed hypothesis that tumor cell populations progress by evolutionary change as a result of the generation of a variant cell through genomic instability followed by selection of particular variant clones having a growth advantage within the particular tissue environment. Genetic instability appears to be characteristic of neoplastic cells, but no consistent increase in instability seems to accompany progression of the malignant phenotype of the tumor. It is reasonable to assume that quantitative or qualitative changes of cellular oncogenes contribute to the emergence of more malignant phenotypes. Although any one of the molecular changes of cellular oncogenes identified over the past years is a good candidate as an element in progression, amplification appears particularly frequently as a correlate to advanced tumor stage. The fact that amplification does not show up in all progressing tumors of a particular type, for instance in only 50% of advanced-stage neuroblastomas, is often construed as speaking against a role in progression. One should be aware, however, that it is the enhanced expression of a gene consequent to amplification and not amplification per se that affects the cellular phenotype. There are alternative molecular pathways by which expression of a particular gene may become deregulated. During the past decade much information has accrued about genetic alterations in tumor cells. The activation of the oncogenic potential of cellular genes can take different routes among which mutational alteration, translocation and amplification predominate. In particular, amplification has found its way to practical use due to its association with more aggressively growing types of human cancer. MYCN amplification in neuroblastoma is a paradigm for the prognostic significance of oncogene alteration, and at the same time has represented the clinical debut of oncogene research. The full significance of oncogene amplification as a predictor for poor prognosis became clear with the more recent identification of amplified ERBB2 in aggressively growing breast cancers. The state of the art is that amplified cellular oncogenes define cancer patients who have a poor prognosis and require a specific therapeutic regimen.

Amplification of the MYCN oncogene and deletion of putative tumour suppressor gene in human neuroblastomas

Human neuroblastoma cells often carry non-random chromosomal abnormalities signalling genetic alterations. Quite frequent are 'double minutes' (DMs) and homogeneously staining regions (HSRs), both cytogenetic manifestations of amplified DNA, and chromosome 1p-deletions indicating loss of genetic information. With the identification of amplified MYCN and the demonstration of a consensus deletion spanning the chromosome 1p36.1-2 region it appears now likely that both amplification of a cellular oncogene and loss of a tumour-suppressor gene play an important role in neuroblastoma. Amplification of MYCN is an indicator for poor prognosis, even when classical morphological criteria would suggest a better outcome. Consequently, patients with amplification are subjected to more intensive therapeutic regimens. Amplification of MYCN is a paradigm for the clinical use of an oncogene alteration.

Heterogeneous expression of proto-oncogenes in Hodgkin's disease derived cell lines

The expression of 20 proto-oncogenes was analysed by Northern blotting in four cell lines derived from patients with Hodgkin's disease (L428, L540, CO and DEV) and compared to lymphoid and myeloid leukemia cell lines and normal hematopoietic cells. Expression of the proto-oncogenes c-myc, p53, c-jun, pim-1, lck, c-syn, c-raf and N-ras were detected in Hodgkin's disease derived cell lines and in normal hematopoietic cells. Transcripts of the proto-oncogene c-met were detected in the Hodgkin's derived cell lines L428 and L540 but not in the lymphoid or myeloid leukemia cell lines or in tonsil cells, peripheral blood mononuclear cells and granulocytes. Expression of the proto-oncogenes N-myc and lck were observed in the Hodgkin's derived cell line CO which express T cell receptor genes and in the T cell lines JM and CEM. L428 cells and CO cells expressed aberrant transcripts of the c-fes proto-oncogene. Thus Hodgkin's disease derived cell lines are heterogeneous in their expression pattern of proto-oncogenes, expressing normal and aberrant transcripts of proto-oncogenes which are not found in untransformed hematopoietic cells.

Amplification of cellular oncogenes: a predictor of clinical outcome in human cancer

Increased dosage of cellular oncogenes resulting from amplification of DNA is a frequent genetic abnormality of tumor cells and the study of oncogene amplification has been paradigmatic for the usefulness of molecular genetic research in clinical oncology. Certain types of human tumors carry an amplified cellular oncogene at frequencies of up to 50-60%. Human neuroblastoma has been prototypic for the importance of oncogene amplification in tumorigenesis, and evidence is emerging that amplification may be an early event involved in a more malignant form of this cancer. It is unclear at which stage amplification plays a role in other cancers. Amplification of cellular oncogenes is a good predictor of clinical outcome in some human malignancies.