Establishment Of Teratocarcinoma Stem Cell Lines Derived From Embryonic Stem Cells

Cancer has been the top killer of human all over the world. Nowadays, the maincancer treatments are chemotherapy and radiation therapy. Although the fastdevelopment of early diagnosis and cancer treatment has greatly increased thesurvival rates for victims of this lethal disease, the survivors still face the threat ofrecurrence. Now, the most important issue in cancer treatment is that there is no curecan eradicate cancer.There are many hypothesizes for the origin of cancer. Among those, the stem celltheory of cancer received increasing attention, which originated from the investigationof teratocarcinomas. Stem cells derived from teratocarcinomas are named embryonalcarcinoma cells and now considered to be a useful model for researching cancer stemcells at the embryonic stage. Moreover, more and more evidences suggest that cancercells may originate from normal stem cells, such as from cancerization of embryonicstem cells. The mechanisms involved are the focus of research. Several researchesshow that, sequential transplantation of embryonic carcinoma cells in vivo canaccelerate the growth and malignancy of teratocarcinomas, which is similar to theprocess of tumorigenesis. However, the possible molecular mechanisms involved inthis process are still unknown.In order to identify which genes are involved in the malignancy ofteratocarcinoma, we established a tumorigenesis model. Firstly, teratocarcinomaswere induced via subcutaneously injecting mouse embryonic stem cells intoimmune-deficiency mice. Secondly, teratocarcinoma stem cells were isolated from theformed teratocarcinoma in serum-free culture medium. Thirdly, the derivedteratocarcinoma stem cells were injected into immune-deficiency mice again. Afterfive times of transplantations, we obtained several teratocarcinoma stem cell lines andone of them could proliferate stably in feeder-free and growth factors-free culturemedium contained10%FBS. Identification of these teratocarcinoma stem cellsconfirmed the process of malignancy. By using high-throughput deep sequence technology, we identified a series of genes that might relate to the malignancy ofteratocarcinoma stem cell. According to these results, we focused on two signalingpathways: LIF/JAK/STAT3and Wnt/β-catenin signaling, both of which have beenproved to be involved in the regulation of embryonic stem cell self-renewal,pluripotency and tumorigenesis. Among the many signaling events downstream of theLIF receptor, activation of STAT3by JAK phosphorylation plays a central role inmediating LIF’s functions. Since Wnt/β-catenin signaling tightly regulatedself-renewal of stem cells, it has raised the possibility that dysregulated activation ofthis pathway results in the malignant proliferation of cancer cells. We found that,LIF/JAK/STAT3signaling might be unnecessary in maintaining self-renewal andpluripotency of this cell line, and up-regulation of Wnt/β-catenin signaling mightclosely related to the occurrence of tumors.We established a teratocarcinoma stem cell line with high malignance derivedfrom normal embryonic stem cells for the first time, the cell state of which is betweennormal stem cells and cancer cells. Compared to ECCs, this cell line is much closer toordinary cancer cells from the perspective of growth demand. Our studies not onlyprovide powerful evidences for cancer stem cell theory, but also establish a usefulmodel of tumorigenesis, which are meaningful for understanding the mechanisms oftumorigenesis and developing more effective cancer treatment methods.