Embryonic Stem (ES) Cell Reprogramming Cancer Cells After Cell Fusion

ES cells are pluripotent stem cells, which are derived from inner cell mass of blastocyst. The capacity of ES cell in reprogramming the epigenetic property of several adult cells has been known recently. After mouse ES cells fused with mouse embryonic fibroblasts, mouse adult neuronal cells and mouse adult B-lymphocytes, the fusion hybrid cells (4N) acted as pluripotent stem cells, which carried the similar characters of ES cells. These included the characters of having the capacity of self-renewal and induced differentiation in vitro, to become teratomas after transplantation into adult mouse and to normally become the differentiated after blastcyte injection. Further researches confirmed that the somatic genomes of hybrid cells exhibited hyperacetylation of histones H3 and H4, global di- and tri-methylation of lysine 4 of H3, and hyperacetylation of lysine 4 of H3 within the Oct4 promoter.Recently several groups tried to reprogram tumor cells into normal embryonic stem cells by nuclear transfer. Nuclear of mouse melanoma, embryonic carcinoma, and medulloblastoma were enucleated and transferred to mouse oocytes to investigate whether aberrant epigenetic status would be altered. While although the reprogrammed NT cell regained pluripotent potential, the malignant tumor properties remained. The results were not unequivocally because of the internal defects of nuclear transfer, such as inadequate reprogramming both in reproductive and therapeutic cloning, though the latter one is more efficient than the former, mice generated from the cumulus cells or ES cells exhibited aberrant gene expression as judged by microarray analysis of liver and placenta RNA. Compared to nuclear transfer, cell fusion with embryonic stem cells seems like to be a more reliable and simple method to perform reprogramming. However, up to now, it has not been known yet that whether ES cells can also reprogram the epigenetic property of malignant tumor cells after cell fusion.We have investigated how to fuse ES cells with several types of tumor cells and analyzed the fusion cells that are derived from ES cells and tumor cells. Two tumor cell lines with varied differentiation degrees were adopted: mouse teratocarcimona P19 and mouse adult tumor cell Hepal-6, in which the DNA hypermethylation and histone modulation status on the tumor suppressors were distinct according to their differentiation status respectively. By means of fusion with ES cells, both of the tumor cell lines can be reprogrammed in that 1) although ES×P19 owned homogenous clone like phenotype, and the ES×Hepa1-6 owned three ones, the phenotype and the proliferation rate of the survival ES×tumor hybrids under selection were similar with the ES cells, while established great difference with the fusion parent tumor cells. 2) After fused with ES cells, pluripotent gene expression of the ES×tumor were similar with ES cells, and the tissue specific gene expression TTR and ALB in ES×Hepa1-6 were obviously decreased compared to that of Hepa1-6. 3) Tumor associated gene expression were changed after fusion in which tumor supressors expressions were obviously increased in ES-adult cell hybrids. ES-EC cell hybrids also had increased P19 and P16 expression, though the genes originally were expressed in the embryonic carcinomas. Also some oncogenes expressions were decreased via fusion with ES cells. 4) Reprogrammed tumor cells regained differentiation ability as examined by both in vivo and in vitro experiments. 5) Reprogrammed tumor cells did not lose the tumorigenic characters that the percent areas of undifferentiated cells in teratoma were much higher than that of ES cells derived ones and cancer nests were obvious in the ES×tumor hybrids.In our experiments, the fused cells (4N) derived from ES cells and tumor cells have been found to be different from those derived from ES cells and ES×normal non-tumor cells. Significant differences were found from hybrids derived teratomas. We conclude that ES cells cannot completely reprogram tumor cells to become the hybrid cells (4N) that are similar to ES cells (2N). What we have got were some kind of ES cell like teratoma with infinite self-renew and differentiation ability. The results of partial reprogramming in the hybrid of ES cells×tumor cells suggested a special epigenetic regulation in tumor cells. We hypothesize that, in the fusion hybrids (4N) derived from ES cells and tumor cells, some unique epigenetic control factors from tumor cells such as H3K9me3 and H3K27me2, which compact the chromosome structure into heterochromatin, would block the reprogramming process introduced from ES cells. These potential epigenetic control factors may be the potential key targets to correct tumors in future.