Study on the gene abnormalities that cause glucocorticoid-resistant POMC gene expression in corticotroph adenoma cells Cushing's disease

为阐明促肾上腺皮质激素(ACTH)高分泌及ACTH分泌对糖皮质激素抵抗的机制，对促肾上腺皮质激素(ACTH)腺瘤细胞c-fos基因表达、CRF-R1基因表达、ACTH对DDAVP的反应及Vi b基因特征进行了研究，结果表明：(1)促肾上腺皮质激素腺瘤细胞c-fos基因表达高于非腺瘤细胞；C-fos基因5‘端非编码区有2个点突变(体细胞突变)。FOS似乎与OR结合，并抑制OR对POMG基因表达的抑制。此外，Fos还可刺激POMO基因的表达。(2)CRF可下调促肾上腺皮质激素细胞CRF-R1mRNA的表达，但上调促肾上腺皮质激素腺瘤细胞CRF-R1mRNA的表达。这些CRF诱导的CRF-R1mRNA水平的下调和上调是通过cAMP.VP和糖皮质激素下调两种类型的ACTH细胞的CRF-RI mRNA水平所介导的。(3)V2激动剂DDAVP刺激促肾上腺皮质激素腺瘤细胞分泌ACTH，但不刺激正常ACTH细胞分泌。VP和CRF刺激后，促肾上腺皮质激素腺瘤细胞VIB基因表达增加，其大小与V1b基因的大小相近。(4)柴胡皂甙和5-羟色胺刺激大鼠下丘脑室旁核GRF基因表达。

To clarity the mechanism of hypersecretion of ACTH and the resistance of ACTH secretion to glucocorticoid, (1) gene expression of c-fos, (2) gene expression of CRF-R1, (3) response of ACTH to DDAVP and characterization of Vi b mRNA were studied in ACTH-producing pituitary adenoma cells.(1) c-f os Gene expression of c-fos in corticotroph adenoma cells was greater than that in non-adenoma cells. There were 2 point mutations (somatic mutation) at 5'-UTR in c-fos gene. Fos seems to bind to OR and inhibit OR-induced suppression of POMG gene expression. In addition, Fos may stimulate POMO gene expression.(2) CRF-R1 mRNA levels were down-regulated by CRF in corticotrophs, but were up-regulated by CRF in corticotroph adenoma cells. These CRF-induced down- and up-regulation of CRF-R1 mRNA levels were mediated by cAMP.VP and glucocorticoid down-regulated CRF-RI mRNA levels in both types of ACTH cells.(3) DDAVP, V2-agonist, stimulated ACTH secretion from corticotroph adenoma cells, but did not stimulate it in normal ACTH cells. Vib mRNA levels in corticotroph adenoma cells increased after stimulation of VP and CRF.The size of Vib mRNA in adenoma cells was similar to that of authentic V1 b mRNA.(4) Saikosaponin and serotonin stimulated GRF gene expression in the paraventricular nucleus of the hypothalamus in rats.