Chromosomal aberrations as markers of oncogene amplification

Karyotypic evolution of cells in culture: a new concept

The Chapter summarizes peculiarities of karyotypic variability during establishment and long-term cultivation of permanent cell lines. A new concept on pathways of karyotypic evolution of cells in culture is put forward. A detailed description is presented of the author's original approach of cytogenetic analysis of cell lines provided for a principally new characteristic of the cell line: its generalized reconstructed karyotype (GRK). Its use as a criterion to evaluate authenticity, purity, and stability of cell lines is discussed. Based on analysis of the GRK, two stages of karyotype evolution of cell lines are revealed: establishment and stabilization, different in karyotypic variability of the cell population and in peculiarities of clone selection. Comparison of peculiarities of karyotypic variability of leukemic and tumor cells both in vitro and in vivo was made, and general regularities of their karyotypic evolution have been established, such as nonrandom changes in the number and structure of chromosomes and deletion of one of the sex chromosomes, as well as regularities characteristic only of cells in culture in most human and animal cell lines (at least 85%) of disomy on all autosomes. The rest of the cell lines, 15%, are characterized by either partial or total monosomies on certain autosomes during long-term cultivation. Three main compensatory mechanisms of maintaining viability of cell lines that have lost genetic material are discussed: polyploidization of the initial cell clone, amplification of oncogenes (predominantly of mys family), and extracopying of whole autosomes or of their fragments.

Specific cytogenetic aberrations in two novel human prostatic cell lines immortalized by human papillomavirus type 18 DNA

Using chromosome banding and fluorescence in situ hybridization (FISH) with painting probes, sequential cytogenetic analysis was performed of two novel prostate cell lines, PZ-HPV-7 and CA-HPV-10, established by human papillomavirus (HPV) 18 DNA transformation. PZ-HPV-7 originates from a normal diploid prostate epithelial cell strain. PZ-HPV-7 progressed from an initial diploid to a hypertetraploid chromosome number with a relative gain of chromosomes 5 and 20 (7 to 8 copies each). Structural changes were limited; 3p- (2 copies), 3q- (1 copy), and possibly a der(16p;12q). CA-HPV-10 originates from an epithelial cell strain derived from a high-grade human prostate cancer specimen, which showed several karyotypic abnormalities including an extra Y chromosome and double minutes (dmin). In early passage the karyotype of CA-HPV-10 appeared unstable with a decreasing number of cells exhibiting dmin. In late passage the dmin were replaced by a large homogeneously staining region (hsr) on 9p+ marker. The hsr was shown by FISH to be of chromosome 1 origin. The modal number was mainly hypertriploid (72, range 69 to 75). Loss of Y was remarkable (0 to 1 copy). Consistent markers included two copies each of del(1)(q12q31) and der(9)t(1;9)(?;p22), and one der(11)t(4;11) (?;q21). HPV type 18 genomic integration sites were identified on 1p for PZ-HPV-7 and on the 9p+ marker for CA-HPV-10. In conclusion, both PZ-HPV-7 and CA-HPV-10 showed clonal cytogenetic changes. These two cell lines constitute a novel in vitro model to study the mechanisms involved in human prostate carcino-genesis.

Cell senescence and a mechanism of clonal evolution leading to continuous cell proliferation, loss of heterozygosity, and tumor heterogeneity: studies on two immortal colon cancer cell lines

Extensive karyotypic analysis was performed on early and late passages of two continuous human cell lines, SW480 and SW620, that were derived from the same colon cancer patient. We cultivated these two cell lines in vitro for a period of 24 months and periodically examined their chromosome constitution. SW480 cells, from passage 138, were injected subcutaneously into 20 nude mice. The tumors that grew in nude mice were then cultivated in vitro for several passages to compare histopathologic findings and tumor growth patterns with clonal chromosomal profiles. Despite some karyotypic diversity, the two cell lines exhibited common marker chromosomes and followed similar patterns of evolution. During subsequent passages, acquisition of new chromosomal abnormalities gave rise to sidelines with a near-diploid genome that frequently underwent endoreduplication. Genomic instability seemed to play an important role in the emergence, growth, and subsequent elimination of the heterogenous sidelines by selection, clonal expansion, and cell death by senescence. Despite continuous growth, both the cell lines occasionally showed telomeric associations and random dicentric and multicentric formations. These lesions were considered evidence of cell senescence and were related to the disappearance of particular sidelines through evolution. Successful evolutionary steps were characterized by elimination of pre-existing marker chromosomes that were subsequently replaced in the karyotype by their cytologically intact homologous chromosomes possibly after selective endoreduplication. Frequent loss of heterozygosity for the chromosomes taking part in this process is postulated. We suggest that one of the mechanisms by which cancer cells bypass senescence may be related to their potential for continuous clonal diversification.

Extrachromosomal gene amplification in acute myeloid leukemia; characterization by metaphase analysis, comparative genomic hybridization, and semi-quantitative PCR

A case of acute myeloid leukemia (M-3) with complex karyotypic aberrations and double minute (dmin) chromosomes is presented. The patient had no history of prior exposure to mutagenic or carcinogenic agents or of other malignancies. She died from CNS involvement six weeks after the initial diagnosis. We used comparative genomic hybridization to identify the amplified sequences presumed to represent the dmin of the leukemic cells; the tumor/normal ratios indicated increased signal intensity at 8q24. This localization prompted investigation by semi-quantitative PCR that revealed amplification of the MYC oncogene. The extent of chromosome aberrations and the oncogene amplification, both linked with poor prognosis, may relate to the rapid course of this patient's disease.

Dinitropyrene metabolism, DNA adduct formation, and DNA amplification in an SV40-transformed Chinese hamster embryo cell line

The environmental pollutants 1,6-dinitropyrene (1,6-DNP) and 1,8-dinitropyrene (1,8-DNP) are strongly carcinogenic in a number of animal models. These DNPs are metabolized by nitroreduction to N-hydroxy arylamine derivatives that either directly or after acetylation bind to cellular DNA. In the experiments reported here, we examined whether DNA adduct formation by 1,6-DNP and 1,8-DNP was associated with amplification of specific DNA sequences, a process that may be causally related to tumorigenesis. CO60 cells, an SV40-transformed Chinese hamster embryo cell line, were incubated with 2.5 or 50 ng/mL [4,5,9,10(-3)H]1,6-DNP for 5 h. High-pressure liquid chromatographic analysis of organic extracts of the medium indicated the presence of 1-acetylamino-6-nitropyrene, suggesting that these cells are capable of nitroreduction and acetylation. 32P-Postlabeling analysis of DNA isolated from cells exposed to 1.0 or 2.5 ng/mL 1,6-DNP revealed dose-related formation of N-(deoxyguanosin-8-yl)-1-amino-6-nitropyrene. A similar adduct, presumably N-(deoxyguanosin-8-yl)-1-amino-8-nitropyrene, was detected after incubations with 1,8-DNP. DNA isolated from analogous experiments was slot-blotted onto nylon membranes and hybridized with 32P-labeled SV40, c-fos, or beta-actin DNA probes. beta-Actin was not amplified and c-fos was amplified only a small amount; however, there was dose-related amplification of SV40 sequences, whose levels were in some instances approximately 20 times that observed in solvent-treated controls. These data indicate that DNA adduct formation by 1,6-DNP and 1,8-DNP is associated with the amplification of certain DNA sequences, a response that may be related to the tumorigenic potential of these compounds.

Cytogenetic study of breast cancer: clinicopathologic significance of homogeneously staining regions in 84 patients

A cytogenetic study performed on 84 primary breast cancers was conducted to detect the presence of chromosomes with homogeneously staining regions (HSRs) which are assumed to correspond to gene amplification. Homogeneously staining regions were found in 60% of the cases. To assess the prognostic significance of HSRs, clinical and pathologic data were correlated with the cytogenetic findings. Median follow-up for the 84 patients was 40 months. Differences in overall survival and disease-free survival rates between patients with HSRs (50 cases) and patients without HSRs (34 cases) were not significant. Although an excess of HSRs was found in patients considered to have poor prognostic factors (eg, young age, high histologic grade, metastatic axillary nodes, loss of hormonal receptors), no statistically significant correlation between variables could be demonstrated. The high percentage of cases with HSRs strongly suggests that they have an important biologic role, but more cases should be studied with a longer follow-up to assess their significance.

Karyotypic and phenotypic changes during in vitro aging of human endothelial cells

Karyotypic and phenotypic changes were found in human adult endothelial cells (EC) during aging in vitro. A trisomy of chromosome 11 was found in 11 out of 12 EC cultures examined, derived from 9 cell lines from 8 donors. The incidence of this trisomy in some cell lines increased over time from 0% to as much as 100% near the end of their in vitro life span. A number of oncogenes and other important genes are on chromosome 11. These genes might play a role in the changes observed. An increase in the percentage of polyploid cells was also found near the end of the in vitro life span in 6 lines. The cellular levels of two gene products characteristic of the EC, von Willebrand factor (vWF) or Factor VIII, and angiotensin converting enzyme (ACE) were also monitored. vWf was studied in 2 lines and was decreased in both with serial passage. ACE decreased in three out of the four lines examined. These chromosomal and phenotypic changes which occur with increasing age in vitro make the endothelial cell a suitable model to study in vitro culture-related changes, senescence, cardiovascular disease, and tumorigenesis.

The future anatomic pathology laboratory for molecular diagnosis and prognosis: circa 1990-95

Molecular biology provides analytical tools for the study of human disease. These clinical assays can help make a diagnosis, predict a prognosis, or elucidate the pathogenesis of poorly understood diseases. The detection and/or quantitation of specific genes, messenger RNA's, and their protein products provide diagnostic and prognostic information for physicians. Illustrative applications of some of these techniques in human virus infection and breast cancer will suggest the future direction that an anatomic pathology laboratory should consider if it is to provide optimal and competitive service to physicians.

Evaluation of the genotoxicity of gentian violet in bacterial and mammalian cell systems

Previous studies indicate that gentian violet (GV), a triphenylmethane dye used in agriculture and human medicine, is a clastogen in vitro and a carcinogen in chronically exposed mice and rats. Data on its genotoxic activity, however, have been incomplete and partly contradictory. Mutagenesis and DNA damage experiments were conducted to re-evaluate the genotoxic potential of GV in both bacterial and mammalian cell systems. GV was mutagenic in Salmonella typhimurium tester strains TA97 and TA104, but there was little mutagenic activity detected in strains TA98 and TA100. A rat liver homogenate fraction (S9) tended to increase mutagenicity. The major microsomal metabolites of GV, pentamethylpararosaniline and N,N,N',N'-tetramethylpararosaniline were less mutagenic in TA97 and TA104, while N,N,N',N"-tetramethylpararosaniline was a weak mutagen in Salmonella. GV was not mutagenic in Chinese hamster ovary (CHO) cell strain CHO-K1-BH4, and was a questionable mutagen in CHO-AS52 cells. While GV produced DNA damage as measured by sedimentation of nucleotids derived from B6C3F1 mouse lymphocytes treated in vitro, no damage was found in lymphocytes isolated from mice dosed with GV. GV was also a weak producer of gene amplification in an SV40-transformed Chinese hamster cell line. The results indicate that GV is a point mutagen in bacteria; however, since similar exposure conditions produced weak mutagenic activity in mammalian cells, GV may be carcinogenic by virtue of its clastogenic activity.