肝癌中生殖细胞样细胞的分离及鉴定

It has been noted for a long time that embryonic/germ-cell development and tumor formation share important similarities. For instance, immortalization, invasion, independence, lack of adhesion, migratory behavior, demethylation, and immune evasion are examples of features and processes shared by cancer cells and cells undergoing germ cell/gamete/trophoblast differentiation. Janic et al. reported that germline traits are necessary for tumor growth and that inactivation of germline genes can have tumor-suppressing effects in Drosophila, which indicated that the acquisition of embryonic/ germline-cell traits contributes to tumor malignancy. However, it is still unknown what kind of cells in tumors contributes to tumors' germline/embryonic traits. Some researchers postulated that the traits attribute to "germ cell reside" or "germ cell formation" in tumors, both of them suggesting that germ cells might be present in tumors". In our previous study, we have showed that germ cell-like cells were present in transformed mouse bone marrow-derived cells and long-term cultured cancer cells. The concepts are strong attractive, howerver, the appearance of germ cell-like cells in cultured cancer cell cells might arribute to long-term culture in vitro. Therefore, it is essential to determine if cells that function as germ cells are present in human natural tumors. In present study, we try to isolate and identify germ cell-like cells from human hepatic tumors in order to answer the question. In preliminary experiments, we have obsevered that early germ cell-like cells, oocyte-like cells, and parthenogenetic embryo-like structures appear in human hepatic cells. Appearance of germ cell-like cells in human soamtic tumors will provide a way to understand the idea "why somatic cancer cells have strong features of embryonic / germ-cell development" and will be useful to better understand what kind of cells palys key roles in hapatic tumors. Germ cell-like cells in soamtic tumors might provide potential targets to hepatic tumor biology, diagnosis and therapy.

胚胎/生殖细胞发育特性是肿瘤最根本的恶性特征，如：永生化、侵袭、非整倍体、转移、快速生长、免疫逃避等。文献报道：肿瘤生殖细胞特性在肿瘤的恶性行为中具有关键性作用。然而到底何种细胞赋予了肿瘤如此强大的胚胎/生殖细胞发育特性呢？至今仍是个谜。肿瘤高度的胚胎/生殖细胞发育特性预示着：肿瘤中存在着生殖细胞。我们前期研究报道：无论是体外人为诱导的肿瘤细胞还是体外长期培养的肿瘤细胞株中都存在着生殖细胞样细胞。因此在本课题中，我们拟以人肝癌为研究模型，证实人天然肿瘤中存在着生细胞样细胞。并进一步研究"生殖细胞样细胞"在肝癌的启动、生长和转移中是否具有重要作用。"生殖细胞样细胞"的存在及其在肝癌恶性行为中具有重要作用的证实，（1）将有利于解释"肿瘤为什么具有高度胚胎/生殖细胞发育特性？"（2）将为我们认识何种细胞在肝癌中起着"干性"提供新的思路。（3）将为肝癌生物学研究、诊断、及治疗提供潜在的靶点。

肿瘤为何具有高度“胚胎/生殖细胞”特性？肿瘤的胚胎/生殖细胞假说认为是由于肿瘤中存在着“生殖细胞”。因此我们以肝癌为研究模型，拟证实肿瘤中可能存在着生殖细胞样肿瘤细胞，并且该细胞在肿瘤的恶性行为中可能具有“干性”作用。我们的实验结果证实人肝癌组织中存在着生殖细胞样肿瘤细胞，并从肝癌组织中分离出生殖细胞样肿瘤细胞，该细胞在裸鼠体内具有形成含有畸胎瘤/癌成分的肿瘤；而且生殖细胞样细胞在形成中具有重要作用。由于接种到裸鼠皮下肝癌向肝脏转移后，在肝脏组织中频繁观察到生殖细胞样细胞。因此我们进一步以小鼠为实验模型研究生殖细胞样细胞在肝脏转移中的作用。我们的实验结果显示：多种不同类型的肿瘤在肝脏转移中出现相似的原始生殖细胞样细胞。我们进一步研究证实：原始生殖细胞样肿瘤细胞在肿瘤的转移中具有关键性作用，可能是肿瘤肝脏转移的种子。而且化学致癌剂可以激活骨髓细胞的生殖细胞发育潜能。因此，我们的实验结果支持我们的实验假说：肝癌中存在着生殖细胞样细胞，而且提示生殖细胞样肿瘤细胞在肿瘤的形成及转移中可能具有“干性”作用。因此我们的实验结果提示：（1）肿瘤中的存在的生殖细胞样细胞可以解释"肿瘤为什么具有高度胚胎/生殖细胞发育特性"；（2）生殖细胞样肿瘤细胞在肝癌的形成及向肝脏转移中具有重要作用，从而为肝癌生物学研究、诊断、及治疗提供了新的靶点；（3）生殖细胞样肿瘤细胞可能在肿瘤中具有“干性作用”，从而为肿瘤的胚胎/生殖细胞发育假说提供了有力的实验支持。