NR4A1 (Nur77) Mediates Thyrotropin-Releasing Hormone-Induced Stimulation of Transcription of the Thyrotropin beta Gene: Analysis of TRH Knockout Mice

作者：Nakajima Yasuyo^*; Yamada Masanobu; Taguchi Ryo; Shibusawa Nobuyuki; Ozawa Atsushi; Tomaru Takuya; Hashimoto Koshi; Saito Tsugumichi; Tsuchiya Takafumi; Okada Shuichi; Satoh Tetsurou; Mori Masatomo

来源：PLos One, 2012, 7(7): e40437.

DOI：10.1371/journal.pone.0040437

Thyrotropin-releasing hormone (TRH) is a major stimulator of thyrotropin-stimulating hormone (TSH) synthesis in the anterior pituitary, though precisely how TRH stimulates the TSH beta gene remains unclear. Analysis of TRH-deficient mice differing in thyroid hormone status demonstrated that TRH was critical for the basal activity and responsiveness to thyroid hormone of the TSH beta gene. cDNA microarray and K-means cluster analyses with pituitaries from wild-type mice, TRH-deficient mice and TRH-deficient mice with thyroid hormone replacement revealed that the largest and most consistent decrease in expression in the absence of TRH and on supplementation with thyroid hormone was shown by the TSH beta gene, and the NR4A1 gene belonged to the same cluster as and showed a similar expression profile to the TSH beta gene. Immunohistochemical analysis demonstrated that NR4A1 was expressed not only in ACTH-and FSH-producing cells but also in thyrotrophs and the expression was remarkably reduced in TRH-deficient pituitary. Furthermore, experiments in vitro demonstrated that incubation with TRH in GH4C1 cells increased the endogenous NR4A1 mRNA level by approximately 50-fold within one hour, and this stimulation was inhibited by inhibitors for PKC and ERK1/2. Western blot analysis confirmed that TRH increased NR4A1 expression within 2 h. A series of deletions of the promoter demonstrated that the region between bp -138 and +37 of the TSH beta gene was responsible for the TRH-induced stimulation, and Chip analysis revealed that NR4A1 was recruited to this region. Conversely, knockdown of NR4A1 by siRNA led to a significant reduction in TRH-induced TSH beta promoter activity. Furthermore, TRH stimulated NR4A1 promoter activity through the TRH receptor. These findings demonstrated that 1) TRH is a highly specific regulator of the TSH beta gene, and 2) TRH mediated induction of the TSH beta gene, at least in part by sequential stimulation of the NR4A1-TSH beta genes through a PKC and ERK1/2 pathway.

• 出版日期2012-7-9