Bypass of senescence, immortalization, and transformation of human hematopoietic progenitor cells

Immortalized erythroid cells as a novel frontier for in vitro blood production: current approaches and potential clinical application

BACKGROUND

Blood transfusions represent common medical procedures, which provide essential supportive therapy. However, these procedures are notoriously expensive for healthcare services and not without risk. The potential threat of transfusion-related complications, such as the development of pathogenic infections and the occurring of alloimmunization events, alongside the donor's dependence, strongly limits the availability of transfusion units and represents significant concerns in transfusion medicine. Moreover, a further increase in the demand for donated blood and blood transfusion, combined with a reduction in blood donors, is expected as a consequence of the decrease in birth rates and increase in life expectancy in industrialized countries.

MAIN BODY

An emerging and alternative strategy preferred over blood transfusion is the in vitro production of blood cells from immortalized erythroid cells. The high survival capacity alongside the stable and longest proliferation time of immortalized erythroid cells could allow the generation of a large number of cells over time, which are able to differentiate into blood cells. However, a large-scale, cost-effective production of blood cells is not yet a routine clinical procedure, as being dependent on the optimization of culture conditions of immortalized erythroid cells.

CONCLUSION

In our review, we provide an overview of the most recent erythroid cell immortalization approaches, while also describing and discussing related advancements of establishing immortalized erythroid cell lines.

Immortalized striatal precursor neurons from Huntington's disease patient-derived iPS cells as a platform for target identification and screening for experimental therapeutics

We have previously established induced pluripotent stem cell (iPSC) models of Huntington's disease (HD), demonstrating CAG-repeat-expansion-dependent cell biological changes and toxicity. However, the current differentiation protocols are cumbersome and time consuming, making preparation of large quantities of cells for biochemical or screening assays difficult. Here, we report the generation of immortalized striatal precursor neurons (ISPNs) with normal (33) and expanded (180) CAG repeats from HD iPSCs, differentiated to a phenotype resembling medium spiny neurons (MSN), as a proof of principle for a more tractable patient-derived cell model. For immortalization, we used co-expression of the enzymatic component of telomerase hTERT and conditional expression of c-Myc. ISPNs can be propagated as stable adherent cell lines, and rapidly differentiated into highly homogeneous MSN-like cultures within 2 weeks, as demonstrated by immunocytochemical criteria. Differentiated ISPNs recapitulate major HD-related phenotypes of the parental iPSC model, including brain-derived neurotrophic factor (BDNF)-withdrawal-induced cell death that can be rescued by small molecules previously validated in the parental iPSC model. Proteome and RNA-seq analyses demonstrate separation of HD versus control samples by principal component analysis. We identified several networks, pathways, and upstream regulators, also found altered in HD iPSCs, other HD models, and HD patient samples. HD ISPN lines may be useful for studying HD-related cellular pathogenesis, and for use as a platform for HD target identification and screening experimental therapeutics. The described approach for generation of ISPNs from differentiated patient-derived iPSCs could be applied to a larger allelic series of HD cell lines, and to comparable modeling of other genetic disorders.

Direct reprogramming of human Sertoli cells into male germline stem cells with the self-renewal and differentiation potentials via overexpressing DAZL/DAZ2/BOULE genes

We propose a new concept that human somatic cells can be converted to become male germline stem cells by the defined factors. Here, we demonstrated that the overexpression of DAZL, DAZ2, and BOULE could directly reprogram human Sertoli cells into cells with the characteristics of human spermatogonial stem cells (SSCs), as shown by their similar transcriptomes and proteomics with human SSCs. Significantly, human SSCs derived from human Sertoli cells colonized and proliferated in vivo, and they could differentiate into spermatocytes and haploid spermatids in vitro. Human Sertoli cell-derived SSCs excluded Y chromosome microdeletions and assumed normal chromosomes. Collectively, human somatic cells could be converted directly to human SSCs with the self-renewal and differentiation potentials and high safety. This study is of unusual significance, because it provides an effective approach for reprogramming human somatic cells into male germ cells and offers invaluable male gametes for treating male infertility.

Transcriptome analysis to elucidate the toxicity mechanisms of fenvalerate, sulfide gatifloxacin, and ridomil on the hepatopancreas of Procambarus clarkii

Most antibiotics, insecticides, and other chemicals used in agricultural and fishery production tend to persist in the environment. Fenvalerate, sulfide gatifloxacin, and ridomil are widely used in aquaculture as antibacterial, antifungal, and antiparasitic drugs; however, their toxicity mechanism remains unclear. Thus, we herein analyzed the effects of these three drugs on the hepatopancreas of Procambarus clarkii at the transcriptome level. Twelve normalized cDNA libraries were constructed using RNA extracted from P. clarkii after treatment with fenvalerate, sulfide gatifloxacin, or ridomil and from an untreated control group, followed by Kyoto Encyclopedia of Genes and Genomes pathway analysis. In the control vs fenvalerate and control vs sulfide gatifloxacin groups, 14 and seven pathways were significantly enriched, respectively. Further, the effects of fenvalerate and sulfide gatifloxacin were similar on the hepatopancreas of P. clarkii. We also found that the expression level of genes encoding senescence marker protein-30 and arylsulfatase A was downregulated in the sulfide gatifloxacin group, indicating that sulfide gatifloxacin accelerated the apoptosis of hepatopancreatocytes. The expression level of major facilitator superfamily domain containing 10 was downregulated, implying that it interferes with the ability of the hepatopancreas to metabolize drugs. Interestingly, we found that Niemann pick type C1 and glucosylceramidase-β potentially interact with each other, consequently decreasing the antioxidant capacity of P. clarkii hepatopancreas. In the fenvalerate group, the downregulation of the expression level of xanthine dehydrogenase indicated that fenvalerate affected the immune system of P. clarkii; moreover, the upregulation of the expression level of pancreatitis-associated protein-2 and cathepsin C indicated that fenvalerate caused possible inflammatory pathological injury to P. clarkii hepatopancreas. In the ridomil group, no pathway was significantly enriched. In total, 21 genes showed significant differences in all three groups. To conclude, although there appears to be some overlap in the toxicity mechanisms of fenvalerate, sulfide gatifloxacin, and ridomil, further studies are warranted.

A prospect of cell immortalization combined with matrix microenvironmental optimization strategy for tissue engineering and regeneration

Cellular senescence is a major hurdle for primary cell-based tissue engineering and regenerative medicine. Telomere erosion, oxidative stress, the expression of oncogenes and the loss of tumor suppressor genes all may account for the cellular senescence process with the involvement of various signaling pathways. To establish immortalized cell lines for research and clinical use, strategies have been applied including internal genomic or external matrix microenvironment modification. Considering the potential risks of malignant transformation and tumorigenesis of genetic manipulation, environmental modification methods, especially the decellularized cell-deposited extracellular matrix (dECM)-based preconditioning strategy, appear to be promising for tissue engineering-aimed cell immortalization. Due to few review articles focusing on this topic, this review provides a summary of cell senescence and immortalization and discusses advantages and limitations of tissue engineering and regeneration with the use of immortalized cells as well as a potential rejuvenation strategy through combination with the dECM approach.

Non-invasive in vivo molecular imaging of intra-articularly transplanted immortalized bone marrow stem cells for osteoarthritis treatment

Pathophysiology of osteoarthritis (OA) is characterized by progressive loss of articular cartilage in the knee-joints. To impart regenerative ability in lowly metabolizing chondrocytes, the bone marrow stem cells (BMSCs) has recently been recognized as a superior alternative treatment for OA. However, study of primary BMSCs-mediated chondrogenesis is difficult due to progressive cellular aging and replicative senescence. To obtain a therapeutic cell population for OA, BMSCs were immortalized by human papilloma virus (HPV)-16 E6/E7 along with mCherry luciferase (mCL), a gene marker for non-invasive imaging, and designated as iBMSCs-mCL. Next, their cell morphology, population doubling time (PDT) and colony forming ability (CFU) were evaluated. Furthermore, pluripotency and immunophenotypic markers were investigated. To deduce therapeutic ability, iBMSCs-mCL were intra-articularly injected into right knee of anterior cruciate ligament transaction (ACLT)-OA mice model and tracked through non-invasive bioluminescence imaging. Cell morphology of iBMSCs-mCL was similar to parental BMSCs. PDT and CFU ability of iBMSCs-mCLs were significantly increased. Pluripotency and immunophenotypic markers were highly expressed in iBMSC-mCL. Long-term survival and tri-lineage differentiation particularly chondrogenic potential of iBMSCs-mCL were also demonstrated in vitro and then in vivo which was monitored through non-invasive imaging. Intensive bioluminescent signals in iBMSCs-mCL administered knee-joint indicated a marked in vivo survival and proliferation of iBMSCs-mCL. Immunohistochemical staining for type II collagen (IHC of Col II) and alcian blue & safranin o staining of proteoglycans also corroborated cartilage regeneration by iBMSCs-mCL. Conclusively, iBMSCs-mCL maintains stemness and in vivo cartilage regeneration potential suggesting a promising avenue for development of OA therapeutics.

Generation and characteristics of human Sertoli cell line immortalized by overexpression of human telomerase

Sertoli cells are required for normal spermatogenesis and they can be reprogrammed to other types of functional cells. However, the number of primary Sertoli cells is rare and human Sertoli cell line is unavailable. In this study, we have for the first time reported a stable human Sertoli cell line, namely hS1 cells, by overexpression of human telomerase. The hS1 cells expressed a number of hallmarks for human Sertoli cells, including SOX9, WT1, GDNF, SCF, BMP4, BMP6, GATA4, and VIM, and they were negative for 3β-HSD, SMA, and VASA. Higher levels of AR and FSHR were observed in hS1 cells compared to primary human Sertoli cells. Microarray analysis showed that 70.4% of global gene profiles of hS1 cells were similar to primary human Sertoli cells. Proliferation assay demonstrated that hS1 cells proliferated rapidly and they could be passaged for more than 30 times in 6 months. Neither Y chromosome microdeletion nor tumorgenesis was detected in this cell line and 90% normal karyotypes existed in hS1 cells. Collectively, we have established the first human Sertoli cell line with phenotype of primary human Sertoli cells, an unlimited proliferation potential and high safety, which could offer sufficient human Sertoli cells for basic research as well as reproductive and regenerative medicine.

Fluorescent Proteins for Flow Cytometry

Fluorescent proteins have become standard tools for cell and molecular biologists. The color palette of fluorescent proteins spans the ultraviolet, visible, and near-infrared spectrum. Utility of fluorescent proteins has been greatly facilitated by the availability of compact and affordable solid state lasers capable of providing various excitation wavelengths. In theory, the plethora of fluorescent proteins and lasers make it easy to detect multiple fluorescent proteins simultaneously. However, in practice, heavy spectral overlap due to broad excitation and emission spectra presents a challenge. In conventional flow cytometry, careful selection of excitation wavelengths and detection filters is necessary. Spectral flow cytometry, an emerging methodology that is not confined by the "one color, one detector" paradigm, shows promise in the facile detection of multiple fluorescent proteins. This chapter provides a synopsis of fluorescent protein development, a list of commonly used fluorescent proteins, some practical considerations and strategies for detection, and examples of applications. © 2017 by John Wiley & Sons, Inc.

Evolution of malignant plasmacytoma cell lines from K14E7 Fancd2-/- mouse long-term bone marrow cultures

We tested the effect of expression of the Human Papilloma Virus (HPV E7) oncogene on hematopoiesis in long-term bone marrow cultures (LTBMCs) derived from K14E7 (FVB) Fancd2-/- (129/Sv), K14E7 Fancd2+/+, Fancd2-/-, and control (FVB X 129/Sv) Fl mice. K14E7 Fancd2-/- and Fancd2-/- LTBMCs showed decreased duration of production of total nonadherent hematopoietic cells and progenitors forming day 7 and day 14 multilineage CFU-GEMM colonies in secondary cultures (7 wks and 8 wks respectively) compared to cultures from K14E7 Fancd2+/+ (17 wks) or control mice (18 wks) p < 0.0001. Marrow stromal cell lines derived from both K14E7 Fancd2-/- and Fancd2-/- cultures were radiosensitive, as were IL-3 dependent hematopoietic progenitor cell lines derived from K14E7 Fancd2-/- cultures. In contrast, Fancd2-/- mouse hematopoietic progenitor cell lines and fresh marrow were radioresistant. K14E7 Fancd2-/- mouse freshly explanted bone marrow expressed no detectable K14 or E7; however, LTBMCs produced K14 positive factor-independent (FI) clonal malignant plasmacytoma forming cell lines in which E7 was detected in the nucleus with p53 and Rb. Transfection of an E6/E7 plasmid into Fancd2-/-, but not control Fancd2+/+ IL-3 dependent hematopoietic progenitor cell lines, increased cloning efficiency, cell growth, and induced malignant cell lines. Therefore, the altered radiobiology of hematopoietic progenitor cells and malignant transformation in vitro by K14E7 expression in cells of the Fancd2-/- genotype suggests a potential role of HPV in hematopoietic malignancies in FA patients.

Cardiac Stem Cell Secretome Protects Cardiomyocytes from Hypoxic Injury Partly via Monocyte Chemotactic Protein-1-Dependent Mechanism

Cardiac stem cells (CSCs) were known to secrete diverse paracrine factors leading to functional improvement and beneficial left ventricular remodeling via activation of the endogenous pro-survival signaling pathway. However, little is known about the paracrine factors secreted by CSCs and their roles in cardiomyocyte survival during hypoxic condition mimicking the post-myocardial infarction environment. We established Sca-1+/CD31- human telomerase reverse transcriptase-immortalized CSCs (Sca-1+/CD31- CSCs(hTERT)), evaluated their stem cell properties, and paracrine potential in cardiomyocyte survival during hypoxia-induced injury. Sca-1+/CD31- CSCs(hTERT) sustained proliferation ability even after long-term culture exceeding 100 population doublings, and represented multi-differentiation potential into cardiomyogenic, endothelial, adipogenic, and osteogenic lineages. Dominant factors secreted from Sca-1+/CD31- CSCs(hTERT) were EGF, TGF-β1, IGF-1, IGF-2, MCP-1, HGF R, and IL-6. Among these, MCP-1 was the most predominant factor in Sca-1+/CD31- CSCs(hTERT) conditioned medium (CM). Sca-1+/CD31- CSCs(hTERT) CM increased survival and reduced apoptosis of HL-1 cardiomyocytes during hypoxic injury. MCP-1 silencing in Sca-1+/CD31- CSCs(hTERT) CM resulted in a significant reduction in cardiomyocyte apoptosis. We demonstrated that Sca-1+/CD31- CSCs(hTERT) exhibited long-term proliferation capacity and multi-differentiation potential. Sca-1+/CD31- CSCs(hTERT) CM protected cardiomyocytes from hypoxic injury partly via MCP-1-dependent mechanism. Thus, they are valuable sources for in vitro and in vivo studies in the cardiovascular field.

Establishment and Characterization of Human Germline Stem Cell Line with Unlimited Proliferation Potentials and no Tumor Formation

Spermatogonial stem cells (SSCs) have significant applications in both reproductive and regenerative medicine. However, primary human SSCs are very rare, and a human SSC line has not yet been available. In this study, we have for the first time reported a stable human SSC line by stably expressing human SV40 large T antigen. RT-PCR, immunocytochemistry, and Western blots revealed that this cell line was positive for a number of human spermatogonial and SSC hallmarks, including VASA, DAZL, MAGEA4, GFRA1, RET, UCHL1, GPR125, PLZF and THY1, suggesting that these cells are human SSCs phenotypically. Proliferation analysis showed that the cell line could be expanded with significant increases of cells for 1.5 years, and high levels of PCNA, UCHL1 and SV40 were maintained for long-term culture. Transplantation assay indicated that human SSC line was able to colonize and proliferate in vivo in the recipient mice. Neither Y chromosome microdeletions of numerous genes nor tumor formation was observed in human SSC line although there was abnormal karyotype in this cell line. Collectively, we have established a human SSC line with unlimited proliferation potentials and no tumorgenesis, which could provide an abundant source of human SSCs for their mechanistic studies and translational medicine.

Age-Related Increase of EED Expression in Early Hematopoietic Progenitor Cells is Associated with Global Increase of the Histone Modification H3K27me3

Human hematopoietic stem and progenitor cells (HSPCs) from umbilical cord blood exhibit higher differentiation potential and repopulation capacity compared to adult HSPCs. The molecular basis for these functional differences is currently unknown. Upon screening for epigenetic effector genes being differentially expressed in neonatal and adult HSPC subpopulations, the Polycomb Repressive Complex 2 (PRC2) member EED was identified. Even though EED is expressed at comparable amounts in neonatal and adult multipotent HSPCs, early adult lineage committed progenitors of the lymphomyeloid (LM) and erythromyeloid lineages expressed higher EED amounts than neonatal HPCs. We demonstrate that EED overexpression directly leads to higher H3K27me3 levels, a repressive histone modification that is mediated by the PRC2 complex. Quantitative analysis of H3K27me3 levels by FPLC-based ELISA revealed elevated levels in primary blood cells from adults. Besides quantitative changes, gene ontology analysis of the genome-wide H3K27me3 distribution revealed qualitative changes in adult HSPCs with elevated levels in genes associated with nonhematopoietic development pathways. In contrast, H3K4me3 which labels active chromatin was enriched on hematopoietic genes. In vitro differentiation of EED-transfected neonatal HSPCs revealed aberrant expression of the myelopoietic marker CD14, suggesting that EED affects the lymphoid versus myeloid decision processes within the lymphomyeloid lineage. This is in line with LM progenitors having the most pronounced differences in EED expression. Highlighting the dynamic roles of epigenetic modifications in human hematopoiesis, the present data demonstrate shifts in the PRC2-associated histone modification H3K27me3 from birth to adulthood.

SIRT1 inhibition affects angiogenic properties of human MSCs

Human mesenchymal stem cells (hMSCs) are attractive for clinical and experimental purposes due to their capability of self-renewal and of differentiating into several cell types. Autologous hMSCs transplantation has been proven to induce therapeutic angiogenesis in ischemic disorders. However, the molecular mechanisms underlying these effects remain unclear. A recent report has connected MSCs multipotency to sirtuin families, showing that SIRT1 can regulate MSCs function. Furthermore, SIRT1 is a critical modulator of endothelial angiogenic functions. Here, we described the generation of an immortalized human mesenchymal bone marrow-derived cell line and we investigated the angiogenic phenotype of our cellular model by inhibiting SIRT1 by both the genetic and pharmacological level. We first assessed the expression of SIRT1 in hMSCs under basal and hypoxic conditions at both RNA and protein level. Inhibition of SIRT1 by sirtinol, a cell-permeable inhibitor, or by specific sh-RNA resulted in an increase of premature-senescence phenotype, a reduction of proliferation rate with increased apoptosis. Furthermore, we observed a consistent reduction of tubule-like formation and migration and we found that SIRT1 inhibition reduced the hypoxia induced accumulation of HIF-1α protein and its transcriptional activity in hMSCs. Our findings identify SIRT1 as regulator of hypoxia-induced response in hMSCs and may contribute to the development of new therapeutic strategies to improve regenerative properties of mesenchymal stem cells in ischemic disorders through SIRT1 modulation.

MePR: a novel human mesenchymal progenitor model with characteristics of pluripotency

Human embryo stem cells or adult tissues are excellent models for discovery and characterization of differentiation processes. The aims of regenerative medicine are to define the molecular and physiological mechanisms that govern stem cells and differentiation. Human mesenchymal stem cells (hMSCs) are multipotent adult stem cells that are able to differentiate into a variety of cell types under controlled conditions both in vivo and in vitro, and they have the remarkable ability of self-renewal. hMSCs derived from amniotic fluid and characterized by the expression of Oct-4 and Nanog, typical markers of pluripotent cells, represent an excellent model for studies on stemness. Unfortunately, the limited amount of cells available from each donation and, above all, the limited number of replications do not allow for detailed studies. Here, we report on the immortalization and characterization of novel mesenchymal progenitor (MePR) cell lines from amniotic fluid-derived hMSCs, whose biological properties are similar to primary amniocytes. Our data indicate that MePR cells display the multipotency potential and differentiation rates of hMSCs, thus representing a useful model to study both mechanisms of differentiation and pharmacological approaches to induce selective differentiation. In particular, MePR-2B cells, which carry a bona fide normal karyotype, might be used in basic stem cell research, leading to the development of new approaches for stem cell therapy and tissue engineering.

Role of microRNAs in lung cancer: microRNA signatures in cancer prognosis

Lung cancer-related mortality is the most common cause of cancer death worldwide. Detecting lung cancer at an earlier stage and, ideally, predicting who will develop the disease and particularly the most aggressive forms of cancer are the biggest challenge. MicroRNAs (miRNAs) are short, noncoding RNA molecules with regulatory function on protein-coding genes. Because of their fundamental role in development and differentiation, their involvement in the biological mechanisms underlying tumorigenesis, as well as their low complexity, stability, and easy detection, they represent a promising class of tissue- and blood-based biomarkers of cancer. We summarize the current literature on the use of microRNAs as diagnostic and prognostic tools in lung cancer and discuss the relevant clinical implications of these findings.

Targeting telomerase in hematologic malignancy

Over the past two decades, it has become increasingly apparent that telomerase-mediated telomere maintenance plays a crucial role in hematopoiesis. Supporting evidence is underscored by recent findings of mutations in genes involved in telomerase-mediated telomere maintenance that contribute to the pathogenesis of bone marrow failure syndromes. More recently described telomere-independent functions of telomerase are also likely to contribute to both normal hematopoiesis and hematologic diseases. The high levels of telomerase detected in aggressive leukemias have fueled fervent investigation into diverse approaches to targeting telomerase in hematologic malignancies. Successful preclinical investigations that employed genetic strategies, oligonucleotides, small-molecule inhibitors and immunotherapy have resulted in a rapid translation to clinical trials. Further investigation of telomere-independent functions of telomerase and detailed preclinical studies of telomerase inhibition in both normal and malignant hematopoiesis will be invaluable for refining treatments to effectively and safely exploit telomerase as a therapeutic target in hematologic malignancies.

Establishment of an erythroid cell line from primary CD36+ erythroid progenitor cells

OBJECTIVE

Most continuous cell lines with erythroid characteristics are derived from patients with myelogenous leukemia or erythroleukemia. Among them, a few cell lines have been reported to be positive for CD36. We tried to establish a continuous erythroid cell line from the primary CD36(+) erythroid progenitor cells (EPCs) by the lentivirus-mediated gene transduction system.

MATERIALS AND METHODS

A lentiviral vector carrying SV40T, hTERT, or the human papillomavirus type 16 (HPV16) E6 and E7 (E6/E7) viral oncogenes, was introduced into CD36(+) EPCs, singularly or combined. Transformed cells were characterized in terms of histology, phenotype, karyotype, and gene expression profile.

RESULTS

The lentiviral vector carrying HPV16 E6/E7 genes successfully transformed CD36(+) EPCs, creating a continuous cell line, CD36E. Immunophenotype analysis revealed that the CD36E cells had characteristics of erythroid progenitors, among which about 27% of the cell population produced hemoglobin. Colony-forming cell assay demonstrated that the CD36E cells were capable of forming erythroid colonies. Using cytokines or chemical agents, attempts were made to induce differentiation of the CD36E cells but were ineffective, indicating the irreversible erythroid lineage commitment of the cells. The gene expression profile of the CD36E cells displayed a marked difference from that of the CD36(+) EPCs.

CONCLUSIONS

The continuous CD36E cell line is an erythroid progenitor cell line possessing the ability to produce hemoglobin. The CD36E cell line would be an excellent tool for applied research involving erythroid lineage cells and comparative studies with primary CD36(+) EPCs.

TLX1 and NOTCH coregulate transcription in T cell acute lymphoblastic leukemia cells

BACKGROUND

The homeobox gene TLX1 (for T-cell leukemia homeobox 1, previously known as HOX11) is inappropriately expressed in a major subgroup of T cell acute lymphoblastic leukemia (T-ALL) where it is strongly associated with activating NOTCH1 mutations. Despite the recognition that these genetic lesions cooperate in leukemogenesis, there have been no mechanistic studies addressing how TLX1 and NOTCH1 functionally interact to promote the leukemic phenotype.

RESULTS

Global gene expression profiling after downregulation of TLX1 and inhibition of the NOTCH pathway in ALL-SIL cells revealed that TLX1 synergistically regulated more than 60% of the NOTCH-responsive genes. Structure-function analysis demonstrated that TLX1 binding to Groucho-related TLE corepressors was necessary for maximal transcriptional regulation of the NOTCH-responsive genes tested, implicating TLX1 modulation of the NOTCH-TLE regulatory network. Comparison of the dataset to publicly available biological databases indicated that the TLX1/NOTCH-coregulated genes are frequently targeted by MYC. Gain- and loss-of-function experiments confirmed that MYC was an essential mediator of TLX1/NOTCH transcriptional output and growth promotion in ALL-SIL cells, with TLX1 contributing to the NOTCH-MYC regulatory axis by posttranscriptional enhancement of MYC protein levels. Functional classification of the TLX1/NOTCH-coregulated targets also showed enrichment for genes associated with other human cancers as well as those involved in developmental processes. In particular, we found that TLX1, NOTCH and MYC coregulate CD1B and RAG1, characteristic markers of early cortical thymocytes, and that concerted downregulation of the TLX1 and NOTCH pathways resulted in their irreversible repression.

CONCLUSIONS

We found that TLX1 and NOTCH synergistically regulate transcription in T-ALL, at least in part via the sharing of a TLE corepressor and by augmenting expression of MYC. We conclude that the TLX1/NOTCH/MYC network is a central determinant promoting the growth and survival of TLX1+ T-ALL cells. In addition, the TLX1/NOTCH/MYC transcriptional network coregulates genes involved in T cell development, such as CD1 and RAG family members, and therefore may prescribe the early cortical stage of differentiation arrest characteristic of the TLX1 subgroup of T-ALL.

Hematopoietic immortalizing function of the NKL-subclass homeobox gene TLX1

Translocations resulting in ectopic expression of the TLX1 homeobox gene (previously known as HOX11) are recurrent events in human T-cell acute lymphoblastic leukemia (T-ALL). Transduction of primary murine hematopoietic stem/progenitor cells with retroviral vectors expressing TLX1 readily yields immortalized hematopoietic progenitor cell lines. Understanding the processes involved in TLX1-mediated cellular immortalization should yield insights into the growth and differentiation pathways altered by TLX1 during the development of T-ALL. In recent clinical gene therapy trials, hematopoietic clonal dominance or T-ALL-like diseases have occurred as a direct consequence of insertional activation of the EVI1, PRDM16 or LMO2 proto-oncogenes by the retroviral vectors used to deliver the therapeutic genes. Additionally, the generation of murine hematopoietic progenitor cell lines due to retroviral integrations into Evi1 or Prdm16 has also been recently reported. Here, we determined by linker-mediated nested polymerase chain reaction the integration sites in eight TLX1-immortalized hematopoietic cell lines. Notably, no common integration site was observed among the cell lines. Moreover, no insertions into the Evi1 or Prdm16 genes were identified although insertion near Lmo2 was observed in one instance. However, neither Lmo2 nor any of the other genes examined surrounding the integration sites showed differential vector-influenced expression compared to the cell lines lacking such insertions. While we cannot exclude the possibility that insertional side effects transiently provided a selective growth/survival advantage to the hematopoietic progenitor populations, our results unequivocally rule out insertions into Evi1 and Prdm16 as being integral to the TLX1-initiated immortalization process.

Transforming growth factor beta1 promotes chromosomal instability in human papillomavirus 16 E6E7-infected cervical epithelial cells

Uterine cervical cancer, the second most frequently occurring cancer in women worldwide, is tightly associated with the expression of high-risk human papillomavirus [mainly human papillomavirus (HPV)-16 and HPV18] oncogenes E6 and E7 and characteristically exhibits chromosomal instability. However, the mechanisms underlying chromosomal instability in cervical cancer are still not fully understood. In this study, we observed that two of three human cervical epithelial cell lines expressing HPV16 E6E7 became immortalized without extensive chromosomal instability and crisis. The introduction of transforming growth factor (TGF)-beta1, a multiple functional cytokine/growth factor, in the culture medium induced crisis, which was associated with massive chromosomal end-to-end fusions and other structural aberrations. The distributions of structural aberrations on individual chromosomes were significantly correlated with the profiles of telomere signal-free ends. The immortalized cells that emerged from the TGF-beta1-induced crisis showed multiple clonal structural aberrations that were not observed in cells without TGF-beta1 treatment. Overexpression of the catalytic subunit of telomerase (hTERT) abolished the effects of TGF-beta1 on chromosomal instability. Interestingly, another HPV16 E6E7-expressing cervical cell line that experienced crisis and telomere dysfunction under ordinary culture condition had a higher level of autocrine TGF-beta1 production than the other two crisis-free immortalized cell lines. Blocking the TGF-beta1 pathway by an inhibitor of TGF-beta1 receptor type I prevented the crisis and telomere-mediated chromosomal instability. In addition, more dramatic telomere shortening was observed in cervical intraepithelial neoplasias having higher expression of TGF-beta1 in vivo. These results together suggest an important role of TGF-beta1 in the early process of cervical carcinogenesis.

Transfection of adult canine Schwann cells and olfactory ensheathing cells at early and late passage with human TERT differentially affects growth factor responsiveness and in vitro growth

Adult canine Schwann cells and olfactory ensheathing cells (OECs) are closely related cell types that are considered attractive candidates for translational studies of neural repair. To establish a reliable cell source by comparing the in vitro properties of immortalized Schwann cells and OECs for transplantation purposes, we transfected both cell types with human telomerase reverse transcriptase (hTERT). Ectopic hTERT expression has been shown to induce immortalization of various cell types without substantial alterations of their phenotypes. Schwann cells and OECs were isolated from adult dogs, transfected with hTERT at early (P4) and late passage (P26), characterized regarding in vitro proliferation, antigenic expression and senescence-associated genes in the presence and absence of fibroblast growth factor-2 (FGF-2). Ectopic hTERT expression in late passage glia treated with but not without FGF-2 prevented the decline in proliferation observed in non-transfected cells. Immortalization did not alter p75(NTR) and GFAP but O4 and A2B5 expression. Contrary to this, early passage hTERT transfection significantly reduced proliferation independent of FGF-2 and lowered expression of O4 and GFAP in both cell types. Transfection did not alter mRNA expression of senescence-associated genes such as p53 and p16. No substantial differences were found between Schwann cells and OECs underscoring the close relationship of both cell types. Taken together, we established a stable source of adult canine Schwann cells and OECs and demonstrated that the effects of hTERT expression on in vitro growth and growth factor responsiveness depend on the replicative age.

Establishment of Immortalized Human Hepatocytes by Introduction of HPV16 E6/E7 and hTERT as Cell Sources for Liver Cell-Based Therapy

For future cell-based therapies for liver diseases, the shortage of cell sources must be resolved. Immortalized human hepatocytes are expected to be among the new sources. In addition to telomerase activation by the introduction of human telomerase reverse transcriptase (hTERT), inactivation of the p16/RB pathway and/or p53 by E6/E7 of human papillomavirus type 16 (HPV16) has been shown to be useful for efficient immortalization of several human cell types. Here we report the immortalization of human hepatocytes by the introduction of HPV16 E6/E7 and hTERT. Human adult hepatocytes were lentivirally transduced with HPV16 E6/E7 and hTERT. Two human immortalized hepatocyte cell lines were established and were named HHE6E7T-1 and HHE6E7T-2. Those cells proliferated in culture beyond 200 population doublings (PDs). Albumin synthesis and expression of liver-enriched genes were confirmed, but gradually decreased as passages progressed. Karyotype analysis showed that HHE6E7T-1 cells remained near diploid but that HHE6E7T-2 cells showed severe aneuploidy at 150 PDs. Subcutaneous injection of these cells into severe combined immunodeficiency (SCID) mice did not induce tumor development. Intrasplenic transplantation of dedifferentiated HHE6E7T-1 cells over 200 PDs significantly improved the survival of acetaminophen-induced acute liver failure SCID mice. In conclusion, we successfully established immortalized human hepatocytes that retain the characteristics of differentiated hepatocytes. We also showed the reduction of hepatocyte-specific functions in long-term culture. However, the results of intrasplenic transplantation to SCID mice with acetaminophen-induced acute liver failure showed the possibility of HHE6E7T-1 serving as a cell source for hepatocyte transplantation.

Telomeres, senescence, and hematopoietic stem cells

The replicative lifespan of normal somatic cells is restricted by the erosion of telomeres, which are protective caps at the ends of linear chromosomes. The loss of telomeres induces antiproliferative signals that eventually lead to cellular senescence. The enzyme complex telomerase can maintain telomeres, but its expression is confined to highly proliferative cells such as stem cells and tumor cells. The immense regenerative capacity of the hematopoietic system is provided by a distinct type of adult stem cell: hematopoietic stem cells (HSCs). Although blood cells have to be produced continuously throughout life, the HSC pool seems not to be spared by aging processes. Indeed, limited expression of telomerase is not sufficient to prevent telomere shortening in these cells, which is thought ultimately to limit their proliferative capacity. In this review, we discuss the relevance of telomere maintenance for the hematopoietic stem cell compartment and consider potential functions of telomerase in this context. We also present possible clinical applications of telomere manipulation in HSCs and new insights affecting the aging of the hematopoietic stem cell pool and replicative exhaustion.

Evidence for a stem cell hierarchy in the adult human breast

Cellular pathways that contribute to adult human mammary gland architecture and lineages have not been previously described. In this study, we identify a candidate stem cell niche in ducts and zones containing progenitor cells in lobules. Putative stem cells residing in ducts were essentially quiescent, whereas the progenitor cells in the lobules were more likely to be actively dividing. Cells from ducts and lobules collected under the microscope were functionally characterized by colony formation on tissue culture plastic, mammosphere formation in suspension culture, and morphogenesis in laminin-rich extracellular matrix gels. Staining for the lineage markers keratins K14 and K19 further revealed multipotent cells in the stem cell zone and three lineage-restricted cell types outside this zone. Multiparameter cell sorting and functional characterization with reference to anatomical sites in situ confirmed this pattern. The proposal that the four cell types are indeed constituents of an as of yet undescribed stem cell hierarchy was assessed in long-term cultures in which senescence was bypassed. These findings identify an adult human breast ductal stem cell activity and its earliest descendants.

Identification of putative stem cell markers, CD133 and CXCR4, in hTERT-immortalized primary nonmalignant and malignant tumor-derived human prostate epithelial cell lines and in prostate cancer specimens

Understanding normal and cancer stem cells may provide insight into the origin of and new therapeutics for prostate cancer. Normal and cancer stem cells in prostate have recently been identified with a CD44(+)/alpha(2)beta(1)(high)/CD133(+) phenotype. Stromal cell-derived factor-1 (SDF-1) and its receptor, CXCR4, have multiple essential functions, including homing of stem cells and metastasis of cancer cells. We show here that human telomerase reverse transcriptase (hTERT)-immortalized primary nonmalignant (RC-165N/hTERT) and malignant (RC-92a/hTERT) tumor-derived human prostate epithelial cell lines retain stem cell properties with a CD133(+)/CD44(+)/alpha(2)beta(1)(+)/34betaE12(+)/CK18(+)/p63(-)/androgen receptor (AR)(-)/PSA(-) phenotype. Higher CD133 expression was detected in the hTERT-immortalized cells than in primary prostate cells. These immortalized cells exhibited "prostaspheres" in nonadherent culture systems and also maintained higher CD133 expression. The CD133(+) cells from these immortalized cell lines had high proliferative potential and were able to differentiate into AR(+) phenotype. In three-dimensional culture, the CD133(+) cells from RC-165N/hTERT cells produced branched structures, whereas the CD133(+) cells from RC-92a/hTERT cells produced large irregular spheroids with less branched structures. SDF-1 induced, but anti-CXCR4 antibody inhibited, migration of CD133(+) cells from RC-92a/hTERT cells, which coexpressed CXCR4. CXCR4/SDF-1 may sustain tumor chemotaxis in cancer stem cells. Furthermore, immunostaining of clinical prostate specimens showed that CD133 expression was detected in a subpopulation of prostate cancer cells and corresponded to the loss of AR. Expression of CXCR4 was also detected in CD133(+) cancer cells. These novel in vitro models may offer useful tools for the study of the biological features and functional integration of normal and cancer stem cells in prostate.

Telomere length of cord blood-derived CD34(+) progenitors predicts erythroid proliferative potential

Excessive telomere shortening has been demonstrated in inherited and acquired blood disorders, including aplastic anemia and myelodysplastic syndromes. It is possible that replicative exhaustion, owing to critical telomere shortening in hematopoietic progenitor cells (HPCs), contributes to the development of cytopenias in these disorders. However to date, a direct link between the telomere length (TL) of human HPCs and their proliferative potential has not been demonstrated. In the present investigation, the TL and level of telomerase enzyme activity (TA) detected in cord blood (CB)-derived HPCs was found to predict erythroid expansion (P<0.01 and P=0.01 respectively). These results were corroborated by a correlation between proliferation of erythroid cells and telomere loss (P=0.01). In contrast, no correlations were found between initial TL, telomere loss or TA and the expansion of other myeloid lineage-committed cells. There was also no correlation between TL or TA and the number of clonogenic progenitors, including primitive progenitors derived from long-term culture. Our investigations revealed upregulation of telomerase to tumor cell levels in CD34- cells undergoing erythroid differentiation. Together, these results provide new insight into the regulation of TL and TA during myeloid cell expansion and demonstrate that TL is an important determinant of CB-derived erythroid cell proliferation.

TLX1/HOX11-induced hematopoietic differentiation blockade

Aberrant expression of the human homeobox-containing proto-oncogene TLX1/HOX11 inhibits hematopoietic differentiation programs in a number of murine model systems. Here, we report the establishment of a murine erythroid progenitor cell line, iEBHX1S-4, developmentally arrested by regulatable TLX1 expression. Extinction of TLX1 expression released the iEBHX1S-4 differentiation block, allowing erythropoietin-dependent acquisition of erythroid markers and hemoglobin synthesis. Coordinated activation of erythroid transcriptional networks integrated by the acetyltransferase co-activator CREB-binding protein (CBP) was suggested by bioinformatic analysis of the upstream regulatory regions of several conditionally induced iEBHX1S-4 gene sets. In accord with this notion, CBP-associated acetylation of GATA-1, an essential regulator of erythroid differentiation, increased concomitantly with TLX1 downregulation. Coimmunoprecipitation experiments and glutathione-S-transferase pull-down assays revealed that TLX1 directly binds to CBP, and confocal laser microscopy demonstrated that the two proteins partially colocalize at intranuclear sites in iEBHX1S-4 cells. Notably, the distribution of CBP in conditionally blocked iEBHX1S-4 cells partially overlapped with chromatin marked by a repressive histone methylation pattern, and downregulation of TLX1 coincided with exit of CBP from these heterochromatic regions. Thus, we propose that TLX1-mediated differentiation arrest may be achieved in part through a mechanism that involves redirection of CBP and/or its sequestration in repressive chromatin domains.

Serum-derived hepatitis C virus infectivity in interferon regulatory factor-7-suppressed human primary hepatocytes

BACKGROUND/AIMS

The development of an efficient in vitro infection system for HCV is important in order to develop new anti-HCV strategy. Only Huh7 hepatocyte cell lines were shown to be infected with JFH-1 fulminant HCV-2a strain and its chimeras. Here we aimed to establish a primary hepatocyte cell line that could be infected by HCV particles from patients' sera.

METHODS

We transduced primary human hepatocytes with human telomerase reverse transcriptase together with human papilloma virus 18/E6E7 (HPV18/E6E7) genes or simian virus large T gene (SV40 T) to immortalize cells. We also established the HPV18/E6E7-immortalized hepatocytes in which interferon regulatory factor-7 was inactivated. Finally we analyzed HCV infectivity in these cells.

RESULTS

Even after prolonged culture HPV18/E6E7-immortalized hepatocytes exhibited hepatocyte functions and marker expression and were more prone to HCV infection than SV40 T-immortalized hepatocytes. The susceptibility of HPV18/E6E7-immortalized hepatocytes to HCV infection was further improved, in particular, by impairing signaling through interferon regulatory factor-7.

CONCLUSIONS

HPV18/E6E7-immortalized hepatocytes are useful for the analysis of HCV infection, anti-HCV innate immune response, and screening of antiviral agents with a variety of HCV strains.

Immortalization of Epstein-Barr virus-negative human B lymphocytes with minimal chromosomal instability

The genes required for immortalization of human B cells infected by Epstein-Barr virus are multiple, and the precise mechanism of this process remains to be elucidated. In the present study HPV16 E6 and E7 were retrovirally transduced into human primary B cells stimulated by CD40-CD40L interaction, thereby establishing an Epstein-Barr virus negative immortalized human B cell line, which continued to proliferate for more than 2 years (100 population doublings). The established cell line had a high telomerase activity from the beginning of the culture period, and no shortening of the telomere length was observed. A chromosomal analysis revealed that a large portion of the HPV16E6E7 transduced cells had retained a normal karyotype. Similar to human epithelial cells, human B lymphocytes seem to require two steps for immortalization, namely, the inactivation of the p16/Rb pathway and the activation of telomerase, the latter that can be induced by the CD40-CD40L interaction. Furthermore, using this system, it is possible to analyze the role of individual genes in human B lymphocyte immortalization without the influence of a pre-existing Epstein-Barr virus genome.

Stable gammaretroviral vector expression during embryonic stem cell-derived in vitro hematopoietic development

Unlike conventional gammaretroviral vectors, the murine stem cell virus (MSCV) can efficiently express transgenes in undifferentiated embryonic stem cells (ESCs). However, a dramatic extinction of expression is observed when ESCs are subjected to in vitro hematopoietic differentiation. Here we report the construction of a self-inactivating vector from MSCV, MSinSB, which transmits an intron embedded within the internal transgene cassette to transduced cells. The internal transgene transcriptional unit in MSinSB comprises the composite cytomegalovirus immediate early enhancer-chicken beta-actin promoter and associated 5' splice site positioned upstream of the natural 3' splice site of the gammaretroviral envelope gene, and is configured such that the transgene translational initiation sequence is coincident with the envelope ATG. MSinSB could be produced at titers approaching 10(6) transducing units/ml and directed higher levels of transgene expression in ESCs than a splicing-optimized MSCV-derived vector, MSGV1. Moreover, when transduced ESCs were differentiated into hematopoietic cells in vitro, MSinSB remained transcriptionally active in greater than 90% of the cells, whereas MSGV1 expression was almost completely shut off. Persistent high-level expression of the MSinSB gammaretroviral vector was also demonstrated in murine bone marrow transplant recipients and following in vitro myelomonocytic differentiation of human CD34(+) cord blood stem/progenitor cells.

Telomerase: not just for the elongation of telomeres

Telomerase RNA component (TERC) and telomerase reverse transcriptase (TERT) function together to elongate telomeres and to protect chromosomal ends. Recent studies have discovered that overexpression of telomerase's TERT subunit promoted epidermal stem-cell mobilization, hair growth and stem-cell proliferation without changes in length of telomeres.1,2 This telomerase functional characteristic is TERC independent and is operated through a mechanism other than telomere elongation. These findings open new doors for future explorations to understand telomerase function and its interaction with other cell components in the regulation of cell senescence and tumorigenesis.

Hematopoietic stem cells

Hematopoietic stem cells (HSCs) have the capacity to self-renew and the potential to differentiate into all of the mature blood cell types. The ability to prospectively identify and isolate HSCs has been the subject of extensive investigation since the first transplantation studies implying their existence almost 50 years ago. Despite significant advances in enrichment protocols, the continuous in vitro propagation of human HSCs has not yet been achieved. This chapter describes current procedures used to phenotypically and functionally characterize candidate human HSCs and initial efforts to derive permanent human HSC lines.

Correction of murine hemophilia A by hematopoietic stem cell gene therapy

A serious complication of current protein replacement therapy for hemophilia A patients with coagulation factor VIII (FVIII) deficiency is the frequent development of anti-FVIII inhibitor antibodies that preclude therapeutic benefit from further treatment. Induction of tolerance by persistent high-level FVIII synthesis following transplantation with hematopoietic stem cells expressing a retrovirally delivered FVIII transgene offers the possibility of permanently correcting the disease. Here, we transplanted bone marrow cells transduced with an optimized MSCV-based FVIII oncoretroviral vector into immunocompetent hemophilia A mice that had been conditioned with a potentially lethal dose of irradiation (800 cGy), a sublethal dose of irradiation (550 cGy), or a nonmyeloablative preparative regimen involving busulfan. Therapeutic levels of FVIII (42, 18, and 11% of normal, respectively) were detected in the plasma of the transplant recipients for the duration of the study (over 6 months). Moreover, subsequent challenge with recombinant FVIII elicited at most a minor anti-FVIII inhibitor antibody response in any of the experimental animals, in contrast to the vigorous neutralizing humoral reaction to FVIII that was stimulated in naive hemophilia A mice. These findings represent an encouraging advance toward potential clinical application and long-term amelioration or cure of this progressively debilitating, life-threatening bleeding disorder.