Jacob K K, Stanley F M
Department of Medicine, New York University Medical Center, NY 10016, USA.
Mol Cell Endocrinol. 1995 Apr 1;109(2):175-81. doi: 10.1016/0303-7207(95)03500-7.
Insulin and cAMP stimulate prolactin gene transcription and prolactin-CAT expression in rat pituitary tumor GH cells. Expression of prolactin-CAT construct, pPrl(-173/+75)CAT, is stimulated 10- to 30-fold by either insulin or cAMP. Addition of both insulin and cAMP resulted in an additive 20- to 60-fold stimulation. Although the regulatory sequences have not been defined precisely, both insulin and cAMP appear to stimulate transcription of prolactin-CAT expression through possibly identical sequences in the -106/-87 region of the promoter. Insulin mediated increases in prolactin-CAT expression are not ras-dependent in GH4 cells. Thus, a number of experiments were performed to determine that the effects of insulin and cAMP are independent. First, insulin does not stimulate cAMP levels in GH4 cells. Second, cAMP action was inhibited by expression of a mutant regulatory subunit of cAMP-dependent protein kinase A that does not bind cAMP and by expression of an inhibitor of cAMP-dependent protein kinase A, while insulin action was not affected by expression of these proteins. Thus, although the regulatory sequences for insulin and cAMP may be identical, the effects of insulin and cAMP on the prolactin gene are clearly mediated through distinct response pathway.
胰岛素和环磷酸腺苷（cAMP）可刺激大鼠垂体肿瘤GH细胞中催乳素基因的转录及催乳素 - 氯霉素乙酰转移酶（CAT）的表达。催乳素 - CAT构建体pPrl(-173/+75)CAT的表达可被胰岛素或cAMP刺激10至30倍。同时添加胰岛素和cAMP会产生20至60倍的叠加刺激。尽管调控序列尚未被精确界定，但胰岛素和cAMP似乎都通过启动子-106 / -87区域中可能相同的序列来刺激催乳素 - CAT的转录。在GH4细胞中，胰岛素介导的催乳素 - CAT表达增加不依赖于ras。因此，进行了多项实验以确定胰岛素和cAMP的作用是相互独立的。首先，胰岛素不会刺激GH4细胞中的cAMP水平。其次，cAMP依赖性蛋白激酶A的一种不结合cAMP的突变调节亚基的表达以及cAMP依赖性蛋白激酶A抑制剂的表达可抑制cAMP的作用，而胰岛素的作用不受这些蛋白表达的影响。因此，尽管胰岛素和cAMP的调控序列可能相同，但胰岛素和cAMP对催乳素基因的作用显然是通过不同的反应途径介导的。
