Modulation of p53 expression and its role in the conversion to a fully immortalized chicken embryo fibroblast line

Non-thermal plasma activates human keratinocytes by stimulation of antioxidant and phase II pathways

Non-thermal atmospheric pressure plasma provides a novel therapeutic opportunity to control redox-based processes, e.g. wound healing, cancer, and inflammatory diseases. By spatial and time-resolved delivery of reactive oxygen and nitrogen species, it allows stimulation or inhibition of cellular processes in biological systems. Our data show that both gene and protein expression is highly affected by non-thermal plasma. Nuclear factor erythroid-related factor 2 (NRF2) and phase II enzyme pathway components were found to act as key controllers orchestrating the cellular response in keratinocytes. Additionally, glutathione metabolism, which is a marker for NRF2-related signaling events, was affected. Among the most robustly increased genes and proteins, heme oxygenase 1, NADPH-quinone oxidoreductase 1, and growth factors were found. The roles of NRF2 targets, investigated by siRNA silencing, revealed that NRF2 acts as an important switch for sensing oxidative stress events. Moreover, the influence of non-thermal plasma on the NRF2 pathway prepares cells against exogenic noxae and increases their resilience against oxidative species. Via paracrine mechanisms, distant cells benefit from cell-cell communication. The finding that non-thermal plasma triggers hormesis-like processes in keratinocytes facilitates the understanding of plasma-tissue interaction and its clinical application.

Microarray analysis of early and late passage chicken embryo fibroblast cells

Primary cultured cells derived from normal tissue have a limited lifespan due to replicative senescence and show distinct phenotypes such as irreversible cell cycle arrest and enlarged morphology. Studying senescence-associated genetic alterations in chicken cells will provide valuable knowledge of cellular growth characteristics, when compared with normal and rapidly growing cell lines. Microarray analysis of early- and late-passage (passage 4 and 18, respectively) primary chicken embryo fibroblast (CEF) cells was performed with a 4X44K chicken oligo microarray. A total of 1,888 differentially expressed genes were identified with a 2-fold level cutoff that included 272 upregulated and 1,616 downregulated genes in late-passage senescent CEF cells. Bioinformatic analyses were performed using Ingenuity Pathway Analysis (IPA, http://www.ingenuity.com). Of the 1,888 differentially expressed genes in senescent CEF cells, 458 were identified as functionally known genes and only 61 genes showed upregulation. Because senescent cells generally showed the deactivated states of most cellular mechanisms for proliferation and energy metabolism, intensified analysis on upregulated genes revealed that the molecular mechanisms in senescent CEF cells are characterized by the suppression of cell cycle and proliferation, progression of cell death including apoptosis, and increased expression of various secreting factors. These regulatory pathways may be opposite to those found in the immortal CEF cell line, such as the DF-1 immortal line. Further comparison of differentially expressed genes between senescent and immortal DF-1 CEF cells showed that 35 genes overlapped and were oppositely regulated. The global gene expression profiles may provide insight into the cellular mechanisms that regulate cellular senescence and immortalization of CEF cells.

Molecular and cellular evidence for the alternative lengthening of telomeres (ALT) mechanism in chicken

Telomere maintenance is an important genetic mechanism controlling cellular proliferation. Normally, telomeres are maintained by telomerase which is downregulated upon cellular differentiation in most somatic cell lineages. Telomerase activity is upregulated in immortalized cells and cancers to support an infinite lifespan and uncontrolled cell growth; however, some immortalized and transformed cells lack telomerase activity. Telomerase-negative tumors and immortalized cells utilize an alternative mechanism for maintaining telomeres termed alternative lengthening of telomeres (ALT). This research explored evidence for the ALT pathway in chicken cell lines by studying nontransformed immortalized cell lines (DF-1 and OU2) and comparing them to a normal (mortal) cell line and a transformed cell line (DT40). The research consisted of molecular and cellular analyses including profiling of telomeric DNA (array sizing and total content), telomerase activity, and expression of genes involved in the telomerase, recombination, and ALT pathways. In addition, an immunofluorescence analysis for an ALT marker, i.e. ALT-associated promyelocytic leukemia bodies (APBs), was conducted. Evidence for ALT was observed in the telomerase-negative immortalized cell lines. Additionally, the APB marker was also found in the other cell systems. The attributes of the chicken provide an additional vertebrate model for investigation of the ALT pathway.

Genetic variation exists for telomeric array organization within and among the genomes of normal, immortalized, and transformed chicken systems

This study investigated telomeric array organization of diverse chicken genotypes utilizing in vivo and in vitro cells having phenotypes with different proliferation potencies. Our experimental objective was to characterize the extent and nature of array variation present to explore the hypothesis that mega-telomeres are a universal and fixed feature of chicken genotypes. Four different genotypes were studied including normal (UCD 001, USDA-ADOL Line 0), immortalized (DF-1), and transformed (DT40) cells. Both cytogenetic and molecular approaches were utilized to develop an integrated view of telomeric array organization. It was determined that significant variation exists within and among chicken genotypes for chromosome-specific telomeric array organization and total genomic-telomeric sequence content. Although there was variation for mega-telomere number and distribution, two mega-telomere loci were in common among chicken genetic lines (GGA 9 and GGA W). The DF-1 cell line was discovered to maintain a complex derivative karyotype involving chromosome fusions in the homozygous and heterozygous condition. Also, the DF-1 cell line was found to contain the greatest amount of telomeric sequence per genome (17%) as compared to UCD 001 (5%) and DT40 (1.2%). The chicken is an excellent model for studying unique and universal features of vertebrate telomere biology, and characterization of the telomere length variation among genotypes will be useful in the exploration of mechanisms controlling telomere length maintenance in different cell types having unique phenotypes.

Transcriptional profile of Rous Sarcoma Virus transformed chicken embryo fibroblasts reveals new signaling targets of viral-src

Transformation of chicken fibroblasts in vitro by Rous Sarcoma Virus represents a model of cancer in which a single oncogene, viral src, uniformly and rapidly transforms primary cells in culture. We experimentally surveyed the transcriptional program affected by Rous Sarcoma Virus (RSV) in primary culture of chicken embryo fibroblasts. As a control, we used cells infected with non-transforming RSV mutant td106, in which the src gene was deleted. Using Affymetrix GeneChip Chicken Genome Arrays, we report 811 genes that were modulated more than 2.5 fold in the virus transformed cells. Among these, 409 genes were induced and 402 genes were repressed by viral src. From the repertoire of modulated genes, we selected 20 genes that were robustly changed. We then validated and quantified the transcriptional changes of most of the 20 selected genes by real-time PCR. The set of strongly induced genes contains vasoactive intestinal polypeptide, MAP kinase phosphatase 2 and follistatin, among others. The set of strongly repressed genes contains TGF beta 3, TGF beta-induced gene, and deiodinase. The function of several robustly modulated genes sheds new light on the molecular mechanism of oncogenic transformation.

Loss of heterozygosity of the p53 gene and deregulated expression of its mRNA and protein in human brain tumors

Tumor-specific alterations at the p53 gene locus were analyzed in 40 human brain tumor samples. Gliomas were more prevalent in young males and meningiomas in old females. Structural changes at the intron 1 region of the p53 gene were analyzed in these tumors by Southern blotting. Among the 40 tumors, 33 were informative and 21 of these (63.6%) informative cases showed loss of heterozygosity (LOH). This is the first report showing LOH at the intron 1 region of p53 gene in human brain tumors. The level of p53 mRNA, p53 protein and Ser 392 phosphorylated p53 protein were also analyzed in all tumor samples. Normal sized p53 mRNA and protein were present in all the tumor samples; however, their levels were 1.5- to 4-fold higher compared to the control suggesting deregulated p53 pathway in these tumors. No correlation was found between LOH status and the levels of p53 mRNA and protein. In all high-grade glioblastomas majority of the p53 protein existed as Ser 392 phosphorylated form as compared to low-grade gliomas. In addition, the percentage of Ser 392 phosphorylated form of p53 protein was lower in meningiomas and other brain tumor types irrespective of tumor grade. These results suggest involvement of Ser 392 phosphorylated form of p53 protein during the later stages of glioma development. These results also indicate that deregulation of p53 gene could occur at various steps in p53 pathway and suggest an overall deregulation of p53 gene in most brain tumor types.

Contributions of differential p53 expression in the spontaneous immortalization of a chicken embryo fibroblast cell line

Background

The present study was carried out to determine whether the p53 pathway played a role in the spontaneous immortalization of the SC-2 chicken embryo fibroblast (CEF) cell line that has been in continuous culture for over three years.

Results

The SC-2 cell line emerged from an extended crisis period with a considerably slower growth rate than primary CEF cells. The phenotype of the SC-2 cells changed dramatically at about passage 80, appearing smaller than at earlier passages (e.g., passage 43) and possessing a small, compact morphology. This morphological change coincided with an increase in growth rate. Passage 43 SC-2 cells expressed undetectable levels of p53 mRNA, but by passage 95, the levels were elevated compared to primary passage 6 CEF cells and similar to levels in senescent CEF cells. However, the high level of p53 mRNA detected in passage 95 SC-2 cells did not correlate to functional protein activity. The expression levels of the p53-regulated p21^WAF1 gene were significantly decreased in all SC-2 passages that were analyzed. Examination of the Rb pathway revealed that E2F-1 and p15^INK4b expression fluctuated with increasing passages, with levels higher in passage 95 SC-2 cells compared to primary passage 6 CEF cells.

Conclusion

The present study suggests that altered expression of genes involved in the p53 and Rb pathways, specifically, p53 and p21^WAF1, may have contributed to the immortalization of the SC-2 CEF cell line.

Upregulation of chicken p15INK4b at senescence and in the developing brain

In mammalian cells, products of the INK4a-ARF locus play major roles in senescence and tumour suppression in different contexts, whereas the adjacent INK4b gene is more generally associated with transforming growth factor β (TGF-β)-mediated growth arrest. As the chicken genome does not encode an equivalent of INK4a, we asked whether INK4b and/or ARF contribute to replicative senescence in chicken cells. In chicken embryo fibroblasts (CEFs), INK4b levels increase substantially at senescence and the gene is transcriptionally silenced in two spontaneously immortalised chicken cell lines. By contrast, ARF levels are unaffected by prolonged culture or immortalisation. These expression patterns resemble the behaviour of INK4a and ARF in human fibroblasts. However, short-hairpin RNA (shRNA)-mediated knockdown of chicken INK4b or ARF provides only modest lifespan extension, suggesting that other factors contribute to senescence in CEFs. As well as underscoring the importance of the INK4b-ARF-INK4a locus in senescence, these findings imply that the encoded products have assumed different roles in different evolutionary niches. Although ARF RNA is not detectable in early chicken embryos, the INK4b transcript is expressed in the roof-plate of the developing hind-brain, consistent with a role in limiting cell proliferation.