由分子觀點來探討dexamethasone及testosterone調控細胞色素P450 3A1及3A2之機制

Molecular Aspect of Cytochrome P450 3A1 and 3A2 regulated by Dexamethasone and Testosterone

李寶松(Pao-Sung Li)

指導教授 ： 彭福佐

國立臺灣大學/醫學院/毒理學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.03298

摘要

細胞色素P450超級家族為重要Phase I代謝酵素，其中細胞色素次家族3A參與許多外來物質及藥物的代謝且可被許多廣泛的物質所誘導。大鼠肝臟中主要的細胞色素P450 3A次家族為CYP3A1與CYP3A2，CYP3A1可被dexamethasone強烈誘導表現但是CYP3A2只能被微弱地誘導。許多報導指出dexamethasone誘導CYP3A表現應該不是經由傳統的glucocorticoid receptor路徑，反而是一些孤兒受體(orphan nuclear receptor)來參與。最近認為PXR (Pregnane X receptor)應為誘導CYP3A重要的調控因子，PXR與其ligand結合進入核中與CYP3A的promoter結合而活化此基因的轉錄活性。
CYP3A2為雄性特異性的酵素，在成熟雄性大鼠中表現而雌性大鼠則幾乎不表現，此性別差異性是由於雄性荷爾蒙可誘導調控CYP3A2表現，有許多報導指出雄性荷爾蒙透過調控生長荷爾蒙分泌的間接機制來調控CYP3A2，但其詳細的分子機制仍不十分清楚。
為了探討CYP3A的誘導作用主要由哪些核受體參與，本實驗室給予大鼠dexamethasone腹腔注射偵測肝臟微粒體中各種核受體蛋白表現。在in vitro實驗大鼠肝癌細胞培養給予dexamethasone後偵測各種核受體蛋白表現。為了探討雄性荷爾蒙是否經過androgen receptor調控CYP3A2表現，雄性大鼠經性腺切除再給予雄性荷爾蒙及androgen receptor拮抗劑flutamide觀察其是否對雄性荷爾蒙調控CYP3A2造成影響。為了探討雄性荷爾蒙是經由間接或直接的方式調控CYP3A2，以大鼠肝癌細胞處理DHT偵測CYP3A2在體外表現情形。
結果顯示: (1).Dxamethasone調控CYP3A1表現中PXR、與HNF-4α等核受體應佔重要角色，而核受體COUP-TF1並明顯表現變化。 (2)在動物實驗及細胞實驗中皆可發現dexamethasone對AR蛋白表現有強烈抑制的現象，有報導指出dexamethasone或許是透過GR影響AR的基因表現。 (3)細胞處理DHT並無法誘導CYP3A2的表現，因此雄性荷爾蒙調控CYP3A2應該是經由間接的機制來執行。

關鍵字

CYP3A1 ； CYP3A2 ； dexamethasone ； 雄性荷爾蒙 ； 核受體

並列摘要

Cytochrome P450s are important Phase I enzymes. CYP3A subfamily enzymes are involved in metabolism of many xenobiotics and drugs and induced by substances of large structural diversity. In rat liver, CYP3A1 and CYP3A2 are major CYP3A enzymes. The former is induced intensely by dexamethasone but the latter is just induced slightly. It was reported that induction of CYP3A by dexamethasone is not through classical glucocorticoid receptor pathway but some orphan nuclear receptors. Recently it was regarded that pregnane X receptor (PXR) should play an important role in CYP3A induction. PXR binds to its ligand and then enter nucleus to interact with CYP3A gene promoter to activate transcription.
CYP3A2 is belong to the male specicic enzyme, so it expresses in adult male rat liver but hardly in adult rat liver. The sexual dimorphism is due to involvement of androgen in regulating CYP3A2 expression. It was reported that androgen regulate CYP3A2 expression by influencing growth hormone secretion profiles but the molecular mechanism is not yet so clear.
To explore which nuclear receptors are involved in CYP3A induction, rats were treated dexamethasone and the nuclear receptors were detected. To explore whether androgen receptor is involved in CYP3A2 regulation by testosterone, castrated male rats were treated tesetosterone and androgen receptor antagonist flutamide and CYP3A2 expression was detected. To explore whether testosterone regulate CYP3A2 directly, cultured rat hepatoma cells were treated DHT and CYP3A2 expression was detected.
The results indicated: (1)nuclear receptors such as PXR and HNF-4α should play an important role in CYP3A induction by dexamethasone. (2)In vitro and in vivo study indicated that AR protein had strongly down-regulation effect by dexamethasone. It was reported that dexamethasone could interact with AR gene through GR. (3)In vitro cell culture study indicated DHT did not have induction effects on CYP3A2 expression and it is suggested that CYP3A2 expression regulation by androgen should be direct mechanism.

並列關鍵字

CYP3A1 ； CYP3A2 ； dexamethasone ； androgen ； nuclear receptor

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