PROLACTIN AND BILE SECRETORY FUNCTION

本研究的目的是描述维持肝脏胆汁分泌功能所必需的两种关键转运蛋白的激素调节机制。这项研究是建立在我们新的和令人兴奋的发现的基础上的，即在产后，垂体前叶激素催乳素(PRL)增加了肝细胞基底外侧区的Na+/牛磺胆酸(TC)共转运体(NTCP)和最近被发现为肝细胞管状区P-糖蛋白(SPGP)姊妹的依赖于ATP的TC转运体的活性。PRL诱导的ntcp转录增加是由长形式的PRL受体介导的，并由JAK2-Stat5信号转导通路和ntcp启动子中的两个Stat5识别序列(GLE)转导。目的1确定其他Stat蛋白(1、3、5a、5b)和该激素家族的其他成员(即生长激素和胎盘催乳素)在调节HepG2细胞培养和/或哺乳母鼠体内ntcp和SPgp表达方面的作用。目的2确定雌二醇抑制催乳素介导的ntcp表达增加的机制(S)，并确定SPgp的表达是否也受到类似的调控。具体地说，我们将测试雌激素通过雌激素受体发挥作用的假设，以及1)结合ntcp启动子中的一半雌激素反应元件以阻止PRL介导的信号转导，或2)竞争有限的核共激活子池，例如CBP/P300，这是启动转录所必需的。目的3确定产后PRL分泌、输注或PRL或生长激素是否通过增加基因转录而增加ntcp和SPgp的mRNA和蛋白表达。用于实现这些目标的方法包括在HepG2细胞培养模型系统中进行的转基因研究，非妊娠对照组和产后大鼠的体内研究，用绵羊催乳素和/或雌二醇治疗的去卵巢大鼠和用生长激素治疗的去卵巢大鼠的体内研究。催乳素是唯一已知的增加胆汁酸转运蛋白表达的生理机制。这些催乳素作用机制的表征为开发选择性治疗措施治疗人类胆汁淤积性肝病提供了机会，例如由雌激素和早产儿引起的肝病。

The objectives of the present proposal are to characterize the mechanisms of hormonal regulation of two key transporters essential for the maintenance of hepatic bile secretory function. The research proposed builds on our novel and exciting finding that in the postpartum period, the anterior pituitary hormone prolactin (PRL) increases the activity of both the Na+/taurocholate (TC) cotransporter (ntcp) in the basolateral domain, and the ATP-dependent TC transporter, recently identified as the sister of P-glycoprotein (spgp) in the canalicular domain of the hepatocyte. The PRL-induced increase in ntcp transcription is mediated by the long form of the PRL receptor and is transduced by the Jak2-Stat5 signal transduction pathway and two Stat5 recognition sequences (GLEs) in the ntcp promoter. Aim 1 will determine the role of other Stat proteins (1, 3, 5a, 5b) and other members of this hormone family (i.e., growth hormone and placental lactogen) in regulating ntcp and spgp expression in HepG2 cell culture and/or in vivo in lactating dams. Aim 2 will identify the mechanism(s) by which estradiol inhibits the PRL-mediated increase in ntcp expression, and determine if spgp expression is similarly regulated. Specifically, we will test the hypotheses that estradiol acts via the estrogen receptor and 1) binds the half-estrogen response elements in the ntcp promoter to prevent PRL-mediated signal transduction, or 2) competes for a limited pool of nuclear coactivators, e.g., CBP/P300, which are essential for initiation of transcription. Aim 3 will determine if PRL secretion in the postpartum period or infusion or PRL or growth hormone increase expression of ntcp and spgp mRNA and protein by increasing gene transcription. Approaches used to achieve these goals include transfection studies in a HepG2 cell culture model system, studies in vivo in nonpregnant control and postpartum rats, in ovariectomized rats treated with ovine PRL and/or estradiol and hyphophysectomized rats treated with growth hormone. PRL is the only physiological mechanism identified which increases expression of bile acid transporters. Characterization of the mechanism of these PRL actions presents the opportunity for development of selective therapeutic interventions for the treatment of human cholestatic liver disease, such as that induced by estrogens and in prematurity.