Integration and loss of a single v-Ki-ras gene affects tumorigenic potential of human osteosarcoma cells

p53 mutation and absence of mdm2 amplification and Ki-ras mutation in 4-hydroxyamino quinoline 1-oxide induced transplantable osteosarcomas in rats

Previously, we reported the establishment of two transplantable osteosarcomas, one induced by local application of a carcinogen, 4-hydroxyamino quinoline 1-oxide(4-HAQO), and another which developed spontaneously in rats, and their subdivision into four lines with high and low metastatic potential to the lung. In the present study, mutations of p53 and Ki-ras genes were investigated by PCR and SSCP followed by direct sequencing, and the amplification of the mdm2 gene was assessed by Southern blot analysis. Mutations of p53 in exon 7 were detected in 4-HAQO-induced transplantable osteosarcomas, but not their spontaneous counterparts, irrespective of the metastatic potentials. Direct sequencing revealed a CGC to CAC transition with an amino acid change of Arg to His, at codon 246. Neither Ki-ras mutations nor mdm2 amplification were detected in any of the transplantable tumors. The results suggest that while p53 mutations occurred during osteosarcoma development by 4-HAQO without mdm2 amplification and Ki-ras mutation does not contribute to osteosarcoma development in rats.

Clonal dominance of select subsets of viral Kirsten ras(+)-transformed 3T3 cells during tumor progression

Long-term culturing of viral Kirsten-ras-oncogene (v-Ki-ras)-transformed BALB/c 3T3 cells (KiMSV) selectively enriches for cells which have deleted the viral oncogene. In contrast, v-Ki-ras in vivo is amplified and expression increased in all late-stage tumors and lung metastases relative to late-passage KiMSV cells being injected. The nature and significance of these selection processes, in terms of the v-Ki-ras gene, have been explored using genetically-tagged cells, as have the properties of v-Ki-ras- revertant subclones. Inoculation of KiMSV late-passage cells (containing less than 5% v-Ki-ras+ cells) into nude mice, generated primary and lung metastatic tumors with the v-Ki-ras gene at increased dosage in all tumors and their single-cell clones, isolated at both early and late stages of tumor development; this demonstrates early and specific in vivo selection for v-Ki-ras+ cells in both induction and progression of tumors in this system. v-Ki-ras- revertant subclones, isolated from late-passage KiMSV cells and inoculated individually into athymic nude mice, yielded tumors for only 1 of the 4 revertants, with no evidence for v-Ki-ras sequences in these tumor cells, thereby revealing a v-Ki-ras-independent mechanism for tumor formation in a small subset of revertant cells. Mixtures of the 4 subclones yielded tumors in all animals, although at a much longer latent period than observed with v-Ki-ras+ cells. Experiments with mixtures of v-Ki-ras- revertant cells and pSV2neo0tagged/v-Ki-ras+ cells (both complex NeoR cell mixtures and individual NeoR clones tested) at various cell ratios revealed clonal variability among v-Ki-ras+ cells for dominance during tumor formation. Moreover, the complex NeoR cell mixtures yielded both primary and metastatic tumors with simplified patterns of pSV2neo integration sites, suggesting that secondary genetic or epigenetic events, in addition to v-Ki-ras, contribute to the tumor-progressing phenotype. These experiments taken together demonstrate (a) clone-specific early selection of distinct v-Ki-ras+ cells amongst themselves and over v-Ki-ras- cells in both induction and progression of tumors, (b) reduced tumorigenic competence of v-Ki-ras- revertant cells, with a small subset displaying a v-Ki-ras-independent mechanism for tumor formation in this BALB/c 3T3 system, and (c) the significance of additional genetic or epigenetic events for tumor-progressing competence in unique subsets of v-Ki-ras+ cells.

The molecular biology of radiation-induced carcinogenesis: thymic lymphoma, myeloid leukaemia and osteosarcoma

In mice, external X- or gamma-irradiation may induce thymic lymphomas or myeloid leukaemias, while bone-seeking alpha-emitters may induce osteosarcomas and, to a lesser extent, acute myeloid leukaemia. The present paper aims to review briefly some of the experimental data with respect to the molecular mechanisms underlying these radiation-induced carcinogenic processes. Thymic lymphomagenesis proceeds through an indirect mechanism. Recombinant proviruses often occur in the tumour cell DNA, favouring the idea that they might be involved. However, there are indications that they might mediate tumour growth rather than induction. It is plausible that activation of ras oncogenes by somatic point mutations might play a role in the carcinogenic process, although at a yet undetermined stage. Myeloid leukaemogenesis is characterized by a very early, putative initiating event, consisting of non-random rearrangements and/or deletions of chromosome 2. These may be related to deletions in the developmentally important homeobox gene clusters and to rearrangements of the sequences flanking the IL-1 beta gene. Either a gene of the homeobox family or IL-1 beta might be considered as potentially involved in the induction process. Osteosarcomagenesis in mice is often associated with the expression of proviruses, and the tumours often contain somatically acquired proviruses. These viruses may contribute to tumour development by affecting various growth-suppressor genes. Viruses isolated from bone tumours, although non-sarcomagenic, induce osteopetrosis, osteomas and lymphomas upon infection of newborn mice. Osteogenic tumours frequently display amplification of a region on mouse chromosome 15, which encompasses c-myc and Mlvi-1 sequences. Enhanced transcription of various oncogenes is found in individual tumours, but no specificity for osteosarcomas has been identified. In vitro systems of skeletoblast differentiation are being developed to study tumour induction in vitro.