Immortalization of hepatic progenitor cells

Cre Recombinase and Other Tyrosine Recombinases

Tyrosine-type site-specific recombinases (T-SSRs) have opened new avenues for the predictable modification of genomes as they enable precise genome editing in heterologous hosts. These enzymes are ubiquitous in eubacteria, prevalent in archaea and temperate phages, present in certain yeast strains, but barely found in higher eukaryotes. As tools they find increasing use for the generation and systematic modification of genomes in a plethora of organisms. If applied in host organisms, they enable precise DNA cleavage and ligation without the gain or loss of nucleotides. Criteria directing the choice of the most appropriate T-SSR system for genetic engineering include that, whenever possible, the recombinase should act independent of cofactors and that the target sequences should be long enough to be unique in a given genome. This review is focused on recent advancements in our mechanistic understanding of simple T-SSRs and their application in developmental and synthetic biology, as well as in biomedical research.

Review of the history and current status of cell-transplant approaches for the management of neuropathic pain

Treatment of sensory neuropathies, whether inherited or caused by trauma, the progress of diabetes, or other disease states, are among the most difficult problems in modern clinical practice. Cell therapy to release antinociceptive agents near the injured spinal cord would be the logical next step in the development of treatment modalities. But few clinical trials, especially for chronic pain, have tested the transplant of cells or a cell line to treat human disease. The history of the research and development of useful cell-transplant-based approaches offers an understanding of the advantages and problems associated with these technologies, but as an adjuvant or replacement for current pharmacological treatments, cell therapy is a likely near future clinical tool for improved health care.

Human hepatocyte transplantation: state of the art

Hepatocyte transplantation is making its transition from bench to bedside for liver-based metabolic disorders and acute liver failure. Over eighty patients have now been transplanted world wide and the safety of the procedure together with medium-term success has been established. A major limiting factor in the field is the availability of good quality cells as hepatocytes are derived from grafts that are deemed unsuitable for transplantation. Alternative sources of cell, including stem cells may provide a sustainable equivalent to primary hepatocytes. There is also a need to develop techniques that will improve the engraftment, survival and function of transplanted hepatocytes. Such developments may allow hepatocyte transplantation to become an accepted and practical alternative to liver transplantation in the near future.

A novel immortalization vector for the establishment of penaeid shrimp cell lines

Cell immortalization technology based on gene transfer has been successfully used to generate cell lines from a wide variety of cell types. The inability to stably introduce and express foreign genes has hampered application of this strategy in shrimp cells. We report here the use of replication-defective pantropic retrovirus to achieve a novel immortalization vector in which simian virus 40 large T antigen (SV40T) gene is expressed from Moloney murine leukemia virus (MoMLV) promoter. Data confirmed the presence of transferred SV40T gene and its stable mRNA expression in transduced lymphoid cells of Penaeus chinensis. The transduced cells showed a higher growth rate and a longer replication life-span compared with their untransduced counterparts. These results indicate the pantropic retrovirus-based immortalization-inducing gene delivery system is a potential tool for establishing cell lines from shrimp.

Reversible transfection of human melanocytes mediated by Cre/loxP site-specific recombination system and SV40 large T antigen

OBJECTIVE

To study the reversible transfection of human melanocytes mediated by simian virus 40 large T antigen (SV40LTAg) and Cre/loxP site-specific recombination system.

METHODS

The reconstructed SV40LTAg-EGFP-neo-loxP vector was transfected into primary cultured human melanocytes with Sofast(TM) transfection reagent and the positive cells were selected using G418. After expanding culture of these positive cell clones, the expression of SV40LTAg was detected by polymerase chain reaction (PCR), reverse transcription-polymerase chain reaction (RT-PCR) and immunofluorescent method. After that, these positive cells were infected by virus supernatant of Cre-ER(T2) retrovirus vector and Cre recombinase was induced to act by tamoxifen. On the 6th and 10th day after Cre recombinase acting, the expression of SV40LTAg was detected using the same methods as above, and cell tumorigenicity was studied using soft agar assay, athymic mouse study and karyotype analysis. On 10th day after tamoxifen treatment, cell biological characters were identified with immunofluorescent staining and transmission electron microscopy. Then these cells were transplanted into vitiligo animal model to observe their melanogenesis ability in vivo.

RESULTS

The genome DNA and total RNA were isolated from the positive cells transfected by SV40LTAg (designated as MCT) and specific 288 bp fragment was amplificated using PCR and RT-PCR methods. The results of immunofluorescence confirmed the expression of SV40LTAg in cell nucleus. On the 6th day after tamoxifen treatment in infected cells by Cre-ER(T2) retrovirus vector (designated as MCT-Cre), there could be detected SV40LTAg expression, but on 10th day, there could not be detected SV40LTAg expression in cells. These results showed that the excised efficiency of Cre recombinase increased along with time prolongation, and would obtain complete recombination efficiency. The identification of MCT-Cre cell biological characters showed that these cells had normal parent-cell-like cell phenotype and no tumorigenicity in vitro. The pigmentation started in 4 weeks and formed black macula in 3 months after grafting. The pathological results showed that there had been significant melanocytes and melanin accumulation in epidermis and some hair follicle in transplanted area, which confirmed that MCT-Cre had melanogenesis function in vivo.

CONCLUSION

Human melanocytes could be mediated by reversible transfection by SV40LTAg and Cre/loxP site-specific recombination system, which had stable parent-cell-like phenotypic characters and no tumorigenicity in vitro; moreover, these cells still had melanogenesis function in vivo.

Establishment of immortalized rat Kupffer cell lines

BACKGROUND

Kupffer cells have been implicated in the pathogenesis of various liver diseases. Primary cultures of Kupffer cells have a very limited life span, tend to de-differentiate and become senescent, and therefore are not suitable for cell signaling studies.

AIM

To establish immortalized rat Kupffer cell lines that facilitate mechanistic studies of cell signaling and signal transduction.

METHODS

Rat Kupffer cells were sub-cultured with EGF to obtain rat Kupffer Cell line 1 (RKC1), and subsequently transfected with Simian Virus 40 Large T-antigen expression vector to obtain rat Kupffer Cell line 2 (RKC2).

RESULTS

RKC1 and RKC2 are similar to primary Kupffer cells as they express the molecular markers ED1, ED2, ED3, and F4/80, and upregulate TNF-alpha, IL-6, IL-1beta, Fas /FasL, and NF-kappaB, as well as TLR4 in response to LPS or pancreatic elastase. Additionally, RKC1 and RKC2 maintain phagocytic properties of latex beads and exhibit increased telomerase and stabilized p53 activity.

CONCLUSION

Immortalized RKC1 and RKC2 cells maintain properties of primary Kupffer cells and can be valuable tools in evaluating the role of Kupffer cells in immune diseases and in liver-cell based drug discovery.

New hepatocytes for toxicology?

In a recent article M.G. Sacco and co-workers described the establishment of immortalized untransformed transgenic hepatocyte (MMH-GH) cell lines, obtained from a cross between the AT/cytoMet and Hsp70/hGH transgenic mice. This strategy proved to be successful because the MMH-GH showed stability in culture and sensitivity to chemical exposure. Based on these results, the MMH-GH cell lines could prove to be a valid alternative cell-based assay for use in toxicological studies.

Maintenance of cell type diversification in the human breast

Recent genome-wide expression analysis of breast cancer has brought new life to the classical idea of tumors as caricatures of the process of tissue renewal as envisioned by Pierce and Speers (Cancer Res 1988;48:1996-2004) more than a decade ago. The search for a cancer founder cell or different cancer founder cells is only possible if a hierarchy of differentiation has been established for the particular tissue in question. In the human breast, the luminal epithelial and myoepithelial lineages have been characterized extensively in situ by increasingly elaborate panel of markers, and methods to isolate, culture, and clone different subpopulations have improved dramatically. Comparisons have been made with the mouse mammary gland in physiological three-dimensional culture assays of morphogenesis, and the plasticity of breast epithelial cells has been challenged by immortalization and transformation. As a result of these efforts, several candidate progenitor cells have been proposed independently of each other, and some of their features have been compared. This research has all been done to better understand breast tissue homeostasis, cell-type diversification in general and breast cancer evolution in particular. The present review discusses the current approaches to address these issues and the measures taken to unravel and maintain cell type diversification for further investigation.

The establishment and characterization of the first canine hepatocellular carcinoma cell line, which resembles human oncogenic expression patterns

Background

Hepatocellular carcinoma (HCC) is one of the most worldwide frequent primary carcinomas resulting in the death of many cirrhotic patients. Unfortunately, the molecular mechanisms of this cancer are not well understood; therefore, we need a good model system to study HCC. The dog is recognized as a promising model for human medical research, namely compared with rodents. The objective of this study was to establish and characterize a spontaneous canine tumor cell line as a potential model for studies on HCC.

Results

Histomorphological, biochemical, molecular biological and quantitative assays were performed to characterize the canine HCC cell line that originated from a dog with a spontaneous liver tumor. Morphological investigations provided strong evidence for the hepatocytic and neoplastic nature of the cell line, while biochemical assays showed that they produced liver-specific enzymes. PCR analysis confirmed expression of ceruloplasmin, alpha-fetoprotein and serum albumin. Quantitative RT-PCR showed that the canine HCC cell line resembles human HCC based on the measurements of expression profiles of genes involved in cell proliferation and apoptosis.

Conclusions

We have developed a novel, spontaneous tumor liver cell line of canine origin that has many characteristics of human HCC. Therefore, the canine HCC cell line might be an excellent model for comparative studies on the molecular pathogenesis of HCC.

Adenoviral-mediated efficiency expression of enhanced green fluorescence protein in adult liver stem cells of rats

AIM: To investigate the feasibility of adenoviral-mediated exogenous gene expression in adult liver stem cells of rats and to establish a cell line that stably and efficiently express enhanced green fluorescence protein (EGFP).

METHODS: A pAd-CMV-EGFP vector under the control of CMV promoter was constructed by homologous recombination in E.coilBJ 5 183, and the recombinant virus was Packaged in HEK 293 cell line. Hepatic adult stem cells cultured in vitro were infected with recombinant adenovirus. Expression of EGFP was observed by fluorescent microscopy and infection efficiency was analyzed. Adult liver stem cells were further cultured to estabilish a cell line that stably and efficiently expressed EGFP through cloning culture and the biological characteristics of the cell line were observed and analyzed by fluorescence microscopy, immunocytochemistry and differentiation-inducing experiment.

RESULTS: Adenovirus vector of pAd-CMV-EGFP was constructed and high titer recombinant virus were produced successfully. EGFP, mediated by adenovirus, could be transfected into hepatic adult stem cells with a high efficiency (about 40-70%). After cloning culture, WB-EGFP cell line was established, and it could stably express EGFP in 8-9 generations. Furthermore, biological characteristics such as marker of stem cells, proliferation speed and differentiation capability had not been affected.

CONCLUSION: Target gene can be efficiently transfected into hepatic adult stem cells through adeno-vector system. EGFP can be stably and long-term expressed in transfected cells and their offspring. It can serve as a tracker in the research of stem cells.