Site-specific integration of H-ras in transformed rat embryo cells

Karyotype evolution of the clonal rat liver cell line CL 52 during progression in vitro and in vivo

Liver cell line CL 52, derived from a diethylnitrosamine-treated rat at the stage of preneoplasia/early neoplasia, had an inconspicuous 2n karyotype when analyzed 6 months after in vitro propagation. Malignant progression was accompanied by cytogenetic alterations of chromosomes 1, 3, and 11. In addition, trisomy of chromosomes 4, 6, and 7 led to a significant reduction of the tumor latency period after retransplantation. During 4 years of cytogenetic observation, the once clonal 2n population showed a characteristic karyotype evolution: loss of diploidy, occurrence of polyploid sidelines, deletions followed by unbalanced rearrangements, clonal diversification, and selection of the in vitro most rapidly growing or in vivo most malignant cell type. The karyotype alterations in the four sublines of CL 52 are discussed with special reference to oncogenesis-related genes assigned to the involved rat chromosomes 1, 3, 11, 12, 4, 6, 7, 10. The observed karyotype evolution of this cell line exemplifies genetic/ chromosome instability of carcinogen-induced preneoplastic/early neoplastic liver cells and provides a tool for analyzing, under controlled conditions, stage-dependent sequences of molecular genetic alterations in liver carcinogenesis.

Direct evidence linking expression of matrix metalloproteinase 9 (92-kDa gelatinase/collagenase) to the metastatic phenotype in transformed rat embryo cells

Members of the matrix metalloproteinase (MMP) family have been implicated in the metastasis of tumor cells, but no direct evidence linking any given member of the MMP family to metastatic behavior has been presented. Rat embryo cells transformed by the Ha-ras and v-myc oncogenes or by Ha-ras alone are metastatic in nude mice and release the 92-kDa gelatinase/collagenase (MMP-9), whereas those transformed by Ha-ras plus the adenovirus E1A gene are not metastatic and do not release MMP-9. Here we demonstrate that MMP-9 expression can be induced in these tumorigenic but nonmetastatic rat cells by transfection with an MMP-9 expression vector. Transfection of a MMP-9 expression vector, but not control DNAs, conferred metastatic capacity on the nonmetastatic cells. The majority of colonies isolated after continued passage either in vivo or in vitro had lost the MMP-9 expression vector. However, occasional cells were isolated from metastases which retained MMP-9 expression after passage. These cells retained metastatic capacity. In contrast, cells isolated after losing MMP-9 expression also lost the ability to metastasize. These results provide direct evidence that MMP-9 has a role in tumor metastasis.

Transfected c-Ha-ras oncogene enhances karyotypic instability and integrates predominantly in aberrant chromosomes

A human colon tumor cell line, SW480, was transfected with the c-Ha-ras oncogene, the wild type c-Ha-ras gene, or the pSV2neo plasmid. Cytogenetic analysis and localization of chromosome integration sites were combined in an attempt to analyze the effects of transfection with the c-Ha-ras oncogene on the karyotype. All transfected cell lines showed new clonal chromosome abnormalities present in all cells, ranging from three new aberrations in pSV2neo-transfected SW480 cell lines to eight in c-Ha-ras oncogene-transfected SW480 cell lines. The level of expression of c-Ha-ras mRNA after transfection with the c-Ha-ras oncogene was positively correlated with increased genetic instability, reflected in enhanced karyotypic instability. A combination of banding and fluorescence in situ hybridization (FISH) was used to identify chromosome integration sites. Plasmids containing ras integrated predominantly in new structurally rearranged chromosomes (five of eight). Three of five integration sites in new structurally rearranged chromosomes were localized at or near translocation breakpoints situated in telomeric regions. Specific chromosomes were not involved in the chromosome rearrangements. The results indicate that 1) enhanced expression of c-Ha-ras mRNA correlates with an increase in genetic instability in c-Ha-ras oncogene-transfected SW480 cell lines, and 2) that no specific integration site was observed but ras-containing plasmids were located predominantly in aberrant chromosomes near or at translocation breakpoints involving telomeric bands.

The biology of radioresistance: similarities, differences and interactions with drug resistance

Cells and tissues have developed a variety of ways of responding to a hostile environment, be it from drugs (toxins) or radiation (summarized in Fig. 1). Three categories of radiation damage limitation are: (i) DNA repair (ii) changes in cellular metabolism (iii) changes in cell interaction (cell contact or tissue-based resistance; whole organism based resistance). DNA repair has been evaluated predominantly by the study of repair-deficient mutants. The function of the repair genes they lack is not fully understood, but some of their important interactions are now characterized. For example, the interaction of transcription factors with nucleotide excision repair is made clear by the genetic syndromes of xeroderma-pigmentosum groups B, D and G. These diseases demonstrate ultraviolet light sensitivity and general impairment of transcription: they are linked by impaired unwinding of the DNA required for both transcription and repair. The transfer of DNA into cells is sometimes accompanied by a change in sensitivity to radiation, and this is of special interest when this is the same genetic change seen in tumors. DNA repair has a close relationship with the cell cycle and cell cycle arrest in response to damage may determine sensitivity to that damage. DNA repair mechanisms in response to a variety of drugs and types of radiation can be difficult to study because of the inability to target the damage to defined sequences in vivo and the lack of a satisfactory substrate for in vitro studies. Changes in cellular metabolism as a result of ionizing radiation can impart radiation resistance, which is usually transient in vitro, but may be more significant in vivo for tissues or tumors. The mechanisms by which damage is sensed by cells is unknown. The detection of free radicals is thought likely, but distortion to DNA structure or strand breakage and a direct effect on membranes are other possibilities for which there is evidence. Changes in extracellular ATP occur in response to damage, and this could be a direct membrane effect. External purinergic receptors can then be involved in signal transduction pathways resulting in altered levels of thiol protection or triggering apoptosis. Changes in the functional level of proteins as a consequence of ionizing radiation include transcription factors, for example c-jun and c-fos; cell cycle arrest proteins such as GADD (growth arrest and DNA damage inducible proteins) and p53; growth factors such as FGF, PDGF; and other proteins leading to radioresistance.(ABSTRACT TRUNCATED AT 400 WORDS)

Specific chromosome change associated with acquisition in vivo of tumorigenicity in carcinogen-induced rat urinary bladder carcinoma cells

The correlation between chromosomal changes and tumorigenic potential of rat bladder epithelial cells was investigated. Seven cell lines were established from neoplastic urothelial cells derived from heterotopically transplanted rat bladders treated with topical application of one of two carcinogens, N-methyl-N-nitrosourea (MNU) or N-hydroxy-N-glucuronosyl-2-aminofluorene. Loss of the short arm of chromosome 3 was demonstrated in three of four lines tumorigenic in the nude mouse, but in none of three nontumorigenic lines. One of the three nontumorigenic cell lines (D44c) was treated further in vitro with MNU. All six tumorigenic, but none of the four nontumorigenic, morphologically altered cell lines derived from D44c demonstrated loss of the short arm of chromosome 3. These results suggest that chromosome 3 alterations may be associated with the tumorigenicity of carcinogen-induced rat bladder epithelial cells.

Vascularity, perfusion rate and local tissue oxygenation of tumors derived from ras-transformed fibroblasts

Tumors derived from ras-transformed rat fibroblasts were investigated in order to gain insight into possible interrelationships between oncogenic transformations and therapeutically relevant parameters of the metabolic micromilieu of solid tumors in vivo. Tumors grew in nude mice after injection of in vitro-passaged cells. Growth rates, early stages of angiogenesis, perfusion and tissue oxygenation were assessed. Compared with the parental cell line, both ras transformants grew very rapidly and exhibited an early onset of angiogenesis. Perfusion rates of one ras-transformed tumor line were similar to those of the parental tumors whereas reduced flow values were detected in tumors of the other ras line. The better perfused tumors exhibited more adequate tissue oxygen levels whereas reduced oxygen levels were obvious in the poorly perfused ras line. These results indicate that ras transformation alters therapeutically relevant parameters of the tumor micromilieu. However, the tumor phenotype cannot be predicted even if the transforming oncogene is known.

The role of the H-ras oncogene in radiation resistance and metastasis

The sensitivity of tumor cells to the killing effects of ionizing radiation is thought to be one of the major determinants of curability of tumors in patients treated with radiation therapy. This paper reviews the evidence from our laboratory and other groups which supports a role for oncogenes in the induction of radioresistance in cultured mammalian cells. Primary rat embryo cells (REC) were chosen as a model system in which the effects on radiation resistance of the H-ras oncogene could be studied on a uniform genetic background. These cells offered several useful advantages. The cells prior to transformation are diploid and because they have been in culture only for a few passages prior to transformation with the oncogene it is unlikely that any preexisting mutation affecting radiation response could be present. Additionally, the use of REC permitted the study of the effects of synergism between oncogenes on the induction of the radioresistant phenotype. The results show that the activated H-ras oncogene induces radiation resistance in primary rat cells after transformation, but that the effect of the oncogene itself is small. However, the myc oncogene, which has no effect on radiation resistance by itself, appears to have a synergistic effect on the induction of radiation resistance by H-ras. Radiation resistance induced by H-ras plus myc is characterized by an increase in the slope of the curve at high doses but there is also a large effect within the shoulder region of the radiation survival curve. The AdenoE1A oncogene which will also act synergistically with ras in transformation assays plays a less clear-cut role in assays of radiation resistance. The H-ras oncogene is also known not only to transform cells but also to induce metastatic behavior in the tumors which form after these transformed cells are injected into syngeneic animals or nude mice. We have also shown in our primary rat embryo cell system that the induction of metastatic behavior in transformed cells, like the induction of radioresistance depends on a complex interaction between oncogenes and the cellular background. This evidence will be reviewed to demonstrate some of the analogies between radiation resistance and metastasis as examples of the complex alterations in cellular phenotype which occur after oncogene transfection.(ABSTRACT TRUNCATED AT 400 WORDS)