Evidence for the multistep nature of in vitro human epithelial cell carcinogenesis (original) (raw)
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Neoplastic transformation of immortalized human epidermal keratinocytes by ionizing radiation
Proceedings of the National Academy of Sciences, 1990
Efforts to investigate the progression of events that cause human cells to become neoplastic in response to ionizing radiation have been aided by the development of tissue culture systems of epithelial cells. In the present study, nontumorigenic human epidermal keratinocytes immortalized by adenovirus type 12 and simian virus 40 have been transformed by exposure to x-ray irradiation. Such transformants showed morphological alterations, formed colonies in soft agar, and induced carcinomas when transplanted into nude mice, whereas primary human epidermal keratinocytes exposed to radiation in this manner failed to show any evidence of transformation. These findings demonstrate the malignant transformation of human primary epithelial cells in culture by the combined action of a DNA tumor virus and radiation, indicating a multistep process for radiation-induced neoplastic conversion. This in vitro system may be useful as a tool for dissecting the process of radiation-induced neoplastic transformation of human epithelial cells and for detecting previously unreported human oncogenes.
Cancer research, 1992
Initiation and promotion in mouse skin carcinogenesis produce multiple benign tumors, squamous papillomas, but only a few squamous cell carcinomas. The spontaneous conversion from the benign to the malignant phenotype occurs over many months and in stages, but induced malignant conversion can be accomplished more rapidly by exposure of papilloma-bearing mice to mutagens or by transfection of papilloma cell lines with specific oncogenes. The analysis of genetic targets responsible for carcinogen-induced neoplastic progression would be facilitated by the development of in vitro models where the process is rapid, focal, and quantitative. To this end, primary newborn mouse keratinocytes were initiated in vitro by the introduction of the v-rasHa oncogene via a defective retrovirus. Recipient cells produce squamous papillomas and have a high proliferation rate in culture medium with 0.05 mM Ca2+, but fail to grow in medium with 0.5 mM Ca2+ which is permissive for growth of malignant kerat...
Malignant transformation of a preneoplastic hamster epidermal cell line by the EJ c-Ha-ras-oncogene
Cancer research, 1986
We have investigated whether the activation of endogenous ras genes is associated with the immortalization or malignant transformation of primary hamster epidermal cells by chemical carcinogens. We have also asked whether transfection of a cloned c-Ha-ras oncogene (pEJ) into a nontumorigenic cell line established from hamster epidermal cells by N-methyl-N'-nitro-N-nitrosoguanidine treatment can induce conversion to a malignant phenotype. DNA from the nontumorigenic epidermal cell line (H5-MNNG) and from two neoplastic cell lines transformed by benzo(a)pyrene was not capable of transforming NIH/3T3 cells. This result suggests that these cells do not contain an activated (mutated) ras gene. However, when H5-MNNG cells were cotransfected with pEJ and pSV2-gpt, a plasmid containing the dominant selectable marker gene Ecogpt, seven of nine clones of Ecogpt transformants formed carcinomas in nude mice and colonies in soft agar. Southern blot analysis of BamHl-digested genomic DNA from...
Analysis of the multistep nature of human carcinogenesis utilizing human fibroblasts
Radiation Oncology Investigations, 1995
We have developed a human fibroblast cell lineage in which, by sequential clonal selection, we have been able to isolate cells that exhibit more and more of the characteristics of tumor-derived cells. The ultimate cells in the lineage form rapidly proliferating sarcomas in athymic mice. Analysis indicates that various "activated" oncogenes, such as ras, sis and my, can play a causal role in the transformation of human fibroblasts. The evidence suggests that some of the steps in the transformation process that we have not yet been able to associate with a specific gene involve loss of expression of suppressor genes.
Interruption of cell transformation and cancer formation
The FASEB Journal, 2006
A review of the results of X-ray and chemical carcinogen induction of transformation of mouse cells supports a two-step epigenetic model of transformation. According to this model, exposure induces an epigenetic regulatory alteration that makes the cells hypermutable so that when the cell population inheriting this alteration becomes sufficiently large, the second step, a mutation to the transformant phenotype, becomes increasingly likely. The epigenetic alteration in X-ray-exposed mouse cells has been demonstrated to be reversible by brief exposure to certain protease inhibitors. If the rodent cell experiments constitute a valid system for studying human cancer, then this two-step model may herald rich opportunities for preventing and perhaps even treating cancer in humans.-Fox, M. S., Klawansky, S. Interruption of cell transformation and cancer formation. FASEB J. 20, 2209 -2213 (2006)
In Vitro Cellular & Developmental Biology - Animal, 1993
Human fibroblasts (KMST-6) immortalized by treatment with 6°Co gamma rays were further neoplastically transformed by transfection of the c-Ha-ras oncogene from human lung cancer. The ras-transfected cells formed undifferentiated fibrosarcoma in nude mice. One of the tumors was recultured and a neoplastic human fibroblast line, KMST-6/RAS, was established. To analyze muhistep carcinogenesis of human cells, the cellular characteristics of these genetically matched immortalized (KMST-6) and neoplastic (KMST-6/RAS) cell lines were studied in detail. KMST-6/RAS cells showed an increased saturation density, colony formation on confluent monolayers of normal human fibroblasts, proliferation in neomycin-containing medium, anchorage-independent growth, and enhanced expression of the transfected c-Ha-ras oncogene, whereas the immortalized cells did not demonstrate these characteristics. Unexpectedly, growth of KMST-6/ RAS cells was serum-dependent, although the), were neoplastic. Interestingly, the neoplastic cells did not show the criss-crossing or piling up growth pattern characteristic of transformed rodent fibroblasts.