Ziober B L, Willson J K, Hymphrey L E, Childress-Fields K, Brattain M G
Department of Pharmacology, Baylor College of Medicine, Houston, Texas 77030.
J Biol Chem. 1993 Jan 5;268(1):691-8.
The GEO colon carcinoma cell line is weakly tumorigenic in athymic mice and shows differentiated properties both in tissue culture and in xenografts. Proliferating monolayer cultures of GEO cells which normally require exogenous epidermal growth factor (EGF) for optimal growth displayed a marked inhibition in growth upon addition of antibodies that block binding to the EGF receptor or neutralize TGF-alpha. These results indicated that GEO cells utilize TGF-alpha in a weak autocrine loop. The availability of a weakly malignant model system in which TGF-alpha had demonstrable, but low level autocrine activity, permitted the investigation of the role of TGF-alpha in tumorigenesis by generating a stronger autocrine loop through the overexpression of the polypeptide. GEO cells were electroporated with an expression vector containing the human TGF-alpha cDNA, and stable clones were isolated that constitutively expressed the TGF-alpha cDNA in a strong autocrine loop. However, the growth rate of the parental cells in EGF-supplemented medium was the same as that of transfected cells with or without growth factor-supplemented medium. Thus, any biological changes generated by the overexpression of TGF-alpha were due to the autocrine nature of the growth mechanism rather than due to any decrease in doubling time leading to a faster growth rate. Transfected GEO cells showed an increase in anchorage-independent growth and formed tumors more readily in athymic nude mice indicating that TGF-alpha plays a role in progression of transformed properties.
GEO结肠癌细胞系在无胸腺小鼠中致瘤性较弱，在组织培养和异种移植中均表现出分化特性。GEO细胞的增殖单层培养物通常需要外源性表皮生长因子（EGF）才能实现最佳生长，在添加能阻断与EGF受体结合或中和转化生长因子-α（TGF-α）的抗体后，其生长受到显著抑制。这些结果表明，GEO细胞在一个微弱的自分泌环中利用TGF-α。有一个弱恶性模型系统，其中TGF-α具有可证明但低水平的自分泌活性，通过过表达该多肽产生更强的自分泌环，从而能够研究TGF-α在肿瘤发生中的作用。用含有人类TGF-α cDNA的表达载体对GEO细胞进行电穿孔，并分离出稳定克隆，这些克隆在一个强大的自分泌环中组成性表达TGF-α cDNA。然而，在补充EGF的培养基中，亲代细胞的生长速率与在补充或不补充生长因子的培养基中转染细胞的生长速率相同。因此，TGF-α过表达产生的任何生物学变化是由于生长机制的自分泌性质，而不是由于倍增时间的任何减少导致更快的生长速率。转染的GEO细胞在非锚定依赖性生长方面有所增加，并且在无胸腺裸鼠中更容易形成肿瘤，这表明TGF-α在转化特性的进展中发挥作用。
