Tumorigenic potential is restored during differentiation in fusion-reprogrammed cancer cells

Detailed understanding of the mechanistic steps underlying tumor initiation and malignant progression is critical for insights of potentially novel therapeutic modalities. Cellular reprogramming is an approach of particular interest because it can provide a means to reset the differentiation state of the cancer cells and to revert these cells to a state of non-malignancy. Here, we investigated the relationship between cellular differentiation and malignant progression by the fusion of four independent mouse cancer cell lines from different tissues, each with differing developmental potentials, to pluripotent mouse embryonic stem (ES) cells. Fusion was accompanied by loss of differentiated properties of the four parental cancer cell lines and concomitant emergence of pluripotency, demonstrating the feasibility to reprogram the malignant and differentiative properties of cancer cells. However, the original malignant and differentiative phenotypes re-emerge upon withdrawal of the fused cells from the embryonic environment in which they were maintained. cDNA array analysis of the malignant hepatoma progression implicated a role for Foxa1, and silencing Foxa1 prevented the re-emergence of malignant and differentiation-associated gene expression. Our findings support the hypothesis that tumor progression results from deregulation of stem cells, and our approach provides a strategy to analyze possible mechanisms in the cancer initiation.

Non-viral FoxM1 gene delivery to hepatocytes enhances liver repopulation

Hepatocyte transplantation as a substitute strategy of orthotopic liver transplantation is being studied for treating end-stage liver diseases. Several technical hurdles must be overcome in order to achieve the therapeutic liver repopulation, such as the problem of insufficient expansion of the transplanted hepatocytes in recipient livers. In this study, we analyzed the application of FoxM1, a cell-cycle regulator, to enhance the proliferation capacity of hepatocytes. The non-viral sleeping beauty (SB) transposon vector carrying FoxM1 gene was constructed for delivering FoxM1 into the hepatocytes. The proliferation capacities of hepatocytes with FoxM1 expression were examined both in vivo and in vitro. Results indicated that the hepatocytes with FoxM1 expression had a higher proliferation rate than wild-type (WT) hepatocytes in vitro. In comparison with WT hepatocytes, the hepatocytes with FoxM1 expression had an enhanced level of liver repopulation in the recipient livers at both sub-acute injury (fumaryl acetoacetate hydrolase (Fah)^–/– mice model) and acute injury (2/3 partial hepatectomy mice model). Importantly, there was no increased risk of tumorigenicity with FoxM1 expression in recipients even after serial transplantation. In conclusion, expression of FoxM1 in hepatocytes enhanced the capacity of liver repopulation without inducing tumorigenesis. FoxM1 gene delivered by non-viral SB vector into hepatocytes may be a viable approach to promote therapeutic repopulation after hepatocyte transplantation.

438. PLZF is a spermatogonia stem cell-specific marker in the sheep testis: application to enrichment of ovine spermatogonial stem cell

Identification and isolation of spermatogonial stem cells (SSCs) are prerequisite for long-term culture, genetic manipulation, and transplantation research. The promyelocytic leukemia zinc-finger (PLZF) has been identified as a spermatogonia stem cell marker in rodent and other species, however its expression in sheep testis has not been reported yet. In this study, we validated an antibody that specifically binds to spermatogonia stem cell in sheep testis, thus demonstrated that PLZF is a spermatogonia stem cell marker and can be used for its identification. Testes from 12 Merino rams were selected to represent four stages of testis development at testis weights of 3–5 g (neonatal), 30 g (peripubertal), 50 g (prepubertal) and 100 g (mature). Three testes sections from 4 different developmental stage were stained with PLZF antibody and 25 individual tubules in each section were counted. In the sections, the percentage of PLZF positive cells/per tubule was increased nearly 2-fold from neonatal (6. 4 ± 0. 4%) to peripubertal (1 2.2 ± 2.8%), and then the percentage begin to decline in prepubertal (4.6 ± 0. 7%) and mature testes (3.1 ± 0.6%). A single cell suspension of testicular cells was generated by a two step enzymic digestion (n = 4) and spermatogonia stem cells were enriched by overnight differential plating with 0.2% gelatine coated flask. The percentages of spermatogonia stem cells in the single cell suspensions were assessed by PLZF antibody staining of smears. Compared with the initial isolation (3.1 ± 0.6%), spermatogonia were enriched 11-fold in overnight differential plating (34.0 ± 5.7,%) (P < 0.05). These data provide the basis for future studies aimed at refining conditions of spermatogonial stem cell culture and manipulation before male germ stem cell transplantation in sheep.