Conversion of premalignant human cells to tumorigenic cells by methylmethane sulfonate and methylnitronitrosoguanidine

Do you know the sex of your cells?

Do you know the sex of your cells? Not a question that is frequently heard around the lab bench, yet thanks to recent research is probably one that should be asked. It is self-evident that cervical epithelial cells would be derived from female tissue and prostate cells from a male subject (exemplified by HeLa and LnCaP, respectively), yet beyond these obvious examples, it would be true to say that the sex of cell lines derived from non-reproductive tissue, such as lung, intestine, kidney, for example, is given minimal if any thought. After all, what possible impact could the presence of a Y chromosome have on the biochemistry and cell biology of tissues such as the exocrine pancreatic acini? Intriguingly, recent evidence has suggested that far from being irrelevant, genes expressed on the sex chromosomes can have a marked impact on the biology of such diverse tissues as neurons and renal cells. It is also policy of AJP-Cell Physiology that the source of all cells utilized (species, sex, etc.) should be clearly indicated when submitting an article for publication, an instruction that is rarely followed (http://www.the-aps.org/mm/Publications/Info-For-Authors/Composition). In this review we discuss recent data arguing that the sex of cells being used in experiments can impact the cell's biology, and we provide a table outlining the sex of cell lines that have appeared in AJP-Cell Physiology over the past decade.

A new insect cell line from pupal ovary of Spodoptera exigua established by stimulation with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)

A continuous cell line derived from the pupal ovary of Spodoptera exigua was established by treating primary cells with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Three days after treating cells with 3.0 μg/ml of MNNG, the cells formed a monolayer and were initially subcultured 60 d after the MNNG was removed, followed by subculturing for 30 passages. The established cell line, designated IOZCAS-Spex 12, consisted of a mixture of three types of cells, including spherical, spindle-shaped, and oval cells. The population doubling time of the cell line during its logarithmic growth phase was found to be 71 h. DNA amplification fingerprinting polymerase chain reaction analysis confirmed that the new cell line originated from S. exigua. Susceptibility of IOZCAS-Spex 12 cells to infection by certain nucleopolyhedroviruses was investigated. The results showed that the cell line was highly susceptible to infection by S. exigua nucleopolyhedrovirus and Autographa californica multiple nucleopolyhedrovirus, slightly susceptible to infection by Spodoptera litura nucleopolyhedrovirus, and not susceptible to infection by Helicoverpa armigera nucleopolyhedroviruses or Hyphantria cunea nucleopolyhedroviruses. The results of this study suggest that MNNG treatment may overcome existing limitations to obtaining continually proliferating cells and may open up the possibilities for immortalizing isolated insect cells.

Chemoprotective effects of curcumin in esophageal epithelial cells exposed to bile acids

AIM: To investigate the ability of curcumin to counteract the impact of bile acids on gene expression of esophageal epithelial cells.

METHODS: An esophageal epithelial cell line (HET-1A) was treated with curcumin in the presence of deoxycholic acid. Cell proliferation and viability assays were used to establish an appropriate dose range for curcumin. The combined and individual effects of curcumin and bile acid on cyclooxygenase-2 (COX-2) and superoxide dismutase (SOD-1 and SOD-2) gene expression were also assessed.

RESULTS: Curcumin in a dose range of 10-100 μmol/L displayed minimal inhibition of HET-1A cell viability. Deoxycholic acid at a concentration of 200 μmol/L caused a 2.4-fold increase in COX-2 gene expression compared to vehicle control. The increased expression of COX-2 induced by deoxycholic acid was partially reversed by the addition of curcumin, and curcumin reduced COX-2 expression 3.3- to 1.3-fold. HET-1A cells exposed to bile acid yielded reduced expression of SOD-1 and SOD-2 genes with the exception that high dose deoxycholic acid at 200 μmol/L led to a 3-fold increase in SOD-2 expression. The addition of curcumin treatment partially reversed the bile acid-induced reduction in SOD-1 expression at all concentrations of curcumin tested.

CONCLUSION: Curcumin reverses bile acid suppression of gene expression of SOD-1. Curcumin is also able to inhibit bile acid induction of COX-2 gene expression.

Epstein-Barr virus growth-transformed cells are converted to malignancy following transfection of a 1.3-kb CATR1 antisense construct independent of a change in the level of c-myc expression followed by a 8;14 chromosomal translocation

The AGLCL Epstein-Barr virus (EBV) growth-transformed cell line is incapable of inducing tumors in nude mice. When the cells were transfected with a 1.3-kb CATR1 antisense cDNA construct, progressively growing lymphomas could be induced in nude mice. Chromosome analysis of the parental, transfected, and tumor cells revealed that a chromosomal translocation t(8;14)(q24.1;q32) had occurred in the transfected cells and was retained in cells derived from tumors. Moreover, enhanced c-myc expression, usually associated with this translocation, was either unchanged or under-expressed. These data suggest that the malignant transformation of the EBV growth-transformed cells was independent of c-myc expression and suggest that the CATR1 gene may act synergistically with the chromosomal translocation facilitating the conversion of AGLCL cells from a growth-transformed state to a malignant phenotype.

Karyotypic changes associated with spontaneous acquisition and loss of tumorigenicity in a human transformed bronchial epithelial cell line: evidence for in vivo selection of transformed clones

In this study, we describe the karyotypic changes associated with the spontaneous acquisition of tumorigenicity in an immortalized tumor bronchial cell line. Neoplastic transformation of the NL20 human bronchial epithelial cell line occurred after 3 yr in culture, and was associated with loss of chromosome 18 together with acquisition of multiple copies of 9q21.2-->34. The nontumorigenic NL20 cell line had been established by transfection of human bronchial epithelial cells with the SV40 T antigen, and had retained a relatively stable karyotype after the first 32 passages in vitro. However, when cells from p184 were inoculated into nude mice, a transplantable tumor was obtained that was derived from a minor clone present in this otherwise stable line. Subsequent passaging of the NL20 cells in vitro did not yield further tumors, and the minor clone from which the tumorigenic NL20T cell line derived was no longer evident in NL20 cells by Passage 205. Furthermore, the original tumorigenic NL20T cells lost the neoplastic phenotype after 25 passages in vitro and reverted to the nontumorigenic karyotype observed at p189. In contrast to the loss of the tumorigenic phenotype and karyotype, which occurred with in vitro passaging of the original tumor, when the NL20T cells were passaged in other nude mice, they continued to give rise to tumors with sevenfold amplifications of 9q sequences and loss of chromosome 18, and cells from the secondary tumors (NL20T-A cells) have maintained a stable karyotype and remain tumorigenic even after 64 passages in vitro. A mixture of 10% tumorigenic NL20T-A and 90% nontumorigenic NL20 cells formed tumors in athymic nude mice when cultured in vitro on fibronectin, but not on plastic; cytogenetic analysis demonstrated that the tumors and cell cultures were composed of tumorigenic NL20T-A cells, whereas cytogenetic analysis of cells cultured on plastic were identical to the nontumorigenic NL20 cells. These data support the hypothesis that neoplastic transformation in our original cell line arose from in vivo selection of a small mutant clone, which had arisen in culture and was subsequently selected in vivo but was lost with in vitro culture.

Malignant conversion of chemically transformed normal human cells

Two structurally unrelated chemicals, aflatoxin B1 and propane sultone, transformed human foreskin cells to a stage of anchorage-independent growth. Isolation from agar and repopulation in monolayer culture of these transformed cells was followed by transfection with a cDNA library, which resulted in cells that exhibited an altered epithelioid morphology. Chemically transformed/nontransfected cells and transfected normal cells did not undergo a significant morphological change. These epithelioid-appearing, transfected cells, when inoculated into nude mice, form progressively growing tumors. The tumors are histopathologically interpreted as carcinomas. All of the first generation tumors in the surrogate hosts exhibited characteristic rates of growth similar to those of transplants of spontaneous human tumors. In the second generation of tumor xenografts, the progressively growing tumors derived from the transfected cells exhibited a more rapid rate of growth. Southern analysis and reverse transcription PCR confirmed that a 1.3-kb genetic element was integrated into the genome and was actively being transcribed. Examination of the metaphase chromosomes in normal human cells revealed that the genetic element responsible for this conversion was located at site 31-32 of the q arm of chromosome 7. The DNA sequence of this 1.3-kb genetic element contains a coding region for 79 amino acids and a long 3'-untranslated region and appears to be identical to CATR1.3 isolated from tumors produced by methyl methanesulfonate-converted, nontransplantable human tumor cells.

A conundrum in molecular toxicology: molecular and biological changes during neoplastic transformation of human cells

The process of multistage carcinogenesis lends itself to the concept that the effects of carcinogens are mediated through dose-related, multi-hit, linear changes. Multiple in vitro model systems have been developed that are designed to examine the cellular changes associated with the progression of cells through the different stages in the process; however, these systems may have inherent limitations due to the cell lines used for these studies, the manner of assessing the effects of the carcinogens, and the subsequent growth and differentiation of the exposed cells. Each of these variables results in increasing levels of uncertainty relative to the correlation of the events with the actual process of human tumor development. Therefore, the prediction of the ultimate effect of any carcinogen is difficult. Moreover, relationships between individual biological endpoints resulting from carcinogen treatment appear at best to be approximations. The presence of an activated carcinogen inside the cell can give rise to multiple outcomes, only some of which may be critical events. For example, site-specific modification of the 12th and 13th codons of H-ras is different than that in the adjacent 14th and 15th codons. It is interesting to speculate what effect these differences might have on a biological outcome, e.g., transformation to anchorage-independent growth. The use of different model systems to examine the effects of activated carcinogens also creates additional problems. Comparisons of in vitro transformed cells with similar cells isolated from human tumors indicate that the culture environment appears to influence the expression of a particular phenotype, in that human tumor cells in culture express many of the same parameters as those found in cells transformed with carcinogens in vitro. If the process of transformation is linear, then less aggressive phenotypes should progress to a more aggressive transformed stage. However, in carcinogen-transformed human cells, the populations exhibit phenotypic diversity in that many of the transformed cells differentiate and fail to continue to divide in culture. Historically, we have assumed only a limited role for epigenetic modulation of molecular changes that occur during progression; however, our data suggest quite strongly that nonmalignant tumor populations can be converted to a more malignant phenotype without additional mutations taking place and, conversely, malignant populations can be downregulated to a nontumorigenic phenotype. Tumor cell plasticity is not only a fundamental characteristic of diverse types of human tumors, but also appears as an integral characteristic of carcinogen-transformed cells in vitro.