REGULATION OF HORMONE RESPONSIVENESS DURING CELLULAR DIFFERENTIATION

在狗肾细胞系中，胰高血糖素反应性选择性丧失， 经Harvey小鼠肉瘤病毒转化后的MDCK细胞 通过将转化的细胞培养在 前列腺素E2的存在。前列腺素E_2的诱导作用似乎是由 通过环状AMP。我们目前正在研究cAMP依赖的作用 蛋白激酶在诱导过程中的作用。为了界定……的性质 这种环状AMP依赖的过程，我们研究了几种分化 抑制PGE2诱导的胰升糖素反应性的抑制剂。 一定浓度的表皮生长因子抑制前列腺素E_2的诱导作用 依赖方式，但对能力没有可检测的影响 PGE2激活环磷酸腺苷的产生。我们还发现EGF 感受器在诱导过程中变得不敏感。事实证明， EGF受体不仅可以通过EGF诱导的过程磷酸化，而且可以通过EGF诱导的过程 也通过环状AMP依赖的途径。我们现在已经确定了EGF ~(35)S-蛋氨酸对转化MDCK细胞受体的影响 标记后免疫沉淀。我们目前正在研究 诱导条件下EGF受体的磷酸化 诱导分化受到抑制。

Glucagon responsiveness was selectively lost in a dog kidney cell line, MDCK cells, after transformation by Harvey murine sarcoma virus and this loss can be restored to the transformed cells by culturing the cells in the presence of prostaglandin E2. The induction by PGE2 seems to be mediated by cyclic AMP. We are currently examining the role of cyclic AMP-dependent protein kinase in the induction process. In order to define the nature of this cyclic AMP-dependent process, we have studied several differentiation inhibitors which inhibit the induction of glucagon responsiveness by PGE2. Epidermal growth factor inhibits the induction by PGE2 in a concentration dependent manner, but does not have detectable effect on the ability of PGE2 to activate cyclic AMP production. We have also found that EGF receptors become desensitized during the induction. It has been shown that EGF receptors can be phosphorylated not only by a EGF-induced process but also by a cyclic AMP-dependent pathway. We have now identified the EGF receptors in the transformed MDCK cells on SDS-PAGE by 35S-methionine labeling followed by immunoprecipitation. We are currently examining the phosphorylation of EGF receptors under the induction condition and when the induction of differentiation is inhibited.