REGULATION OF HORMONE RESPONSIVENESS DURING CELLULAR DIFFERENTIATION

胰高血糖素反应性在狗肾细胞系中选择性丧失， MDCK细胞，经哈维鼠肉瘤病毒转化后， 通过在培养皿中培养细胞，可以恢复转化细胞的损失。 前列腺素E2的存在。 PGE 2的诱导作用似乎是通过 环AMP。 我们目前正在研究环腺苷酸依赖的作用， 蛋白激酶在诱导过程中。 为了定义 这个循环AMP依赖的过程，我们已经研究了几个分化 抑制PGE 2诱导胰高血糖素反应性的抑制剂。 表皮生长因子在一定浓度下抑制PGE 2的诱导作用 依赖的方式，但对能力没有可检测的影响 PGE 2激活cAMP的产生。 我们还发现，EGF 受体在诱导过程中变得不敏感。 已经显示 EGF受体不仅可以通过EGF诱导的过程磷酸化， 也通过环腺苷酸依赖性途径。 EGF的功效 通过35 S-甲硫氨酸在SDS-PAGE上观察转化MDCK细胞中的受体 标记后进行免疫沉淀。 我们目前正在研究 EGF受体在诱导条件下的磷酸化， 分化的诱导被抑制。

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.