REGULATION OF HEPATIC P450S BY ANTICHOLESTEROL DRUGS

新出现的证据表明，类固醇的复杂过程 细胞色素P450的生物合成和异源代谢 超级家庭密不可分地交织在一起。这种相互关系产生了 对生长的安全性和有效性的重要影响 阿森纳的降胆固醇药物正在开发中以降低 患者的血浆胆固醇水平，从而治疗或预防 冠状动脉疾病。这项提议的假设有三个方面： (1)抑制类固醇生物合成的降胆固醇药物，如 3-羟基-3-甲基戊二酰辅酶A还原酶抑制剂 或角鲨烯合成酶，通过以下途径诱导大鼠肝脏细胞色素P450 2 B1基因的表达 导致抑制CYP2B1的关键细胞甾醇的枯竭 在基础稳定状态下的表达，这导致激活 固醇调节元件结合蛋白(SREBP)，其次是 通过特异性5‘-亚基激活细胞色素P450-2B1基因 包含在苯巴比妥反应单元内的侧翼序列。 (2)降胆固醇药物，如酰辅酶A抑制剂：胆固醇 促进积累的酰基转移酶(ACAT)或角鲨烯环酶 特定的细胞甾醇，如24(S)，25-环氧胆固醇，诱导 CYP3A23基因表达通过一种机制积聚 甾醇激活LXRpha核受体，导致 CYP3A23基因通过一种特异的基因转录激活 甾醇反应的5‘侧翼序列。(3)HMG-CoA还原酶 抑制剂通过一种机制诱导细胞色素P4A基因表达 需要增加脂肪酸的生物合成，激活过氧化物酶 增殖相关受体α(PPARpha)及其转录 通过过氧化物酶体增殖物激活细胞色素P4A1基因 响应元素。这项建议的具体目的是：(1) 确定化学抑制剂对生物多样性的关键步骤的影响 胆固醇生物合成和酯化途径对P450表达的影响 在原代培养的大鼠肝细胞中的表达及相关基因模式的研究 对特定细胞类固醇水平变化的表达，(2) 鉴定与HMG-CoA还原酶有关的5‘侧翼序列(S) 抑制物和角鲨烯合成酶抑制物可诱导转录 对CYP2B1基因的激活，并确定这种调节是否 是通过SREBP转录因子介导的，(3)鉴定5‘- 提供甾醇、ACAT抑制剂和角鲨烯的侧翼序列(S) 环化酶抑制因子对细胞色素P3A23的转录激活作用 基因，并确定这一调节是否通过 LXRpha核受体和(4)确定HMG-CoA还原酶 抑制物诱导的CYP4A1诱导是通过一种机制发生的 需要增加脂肪酸的生物合成和PPARα的激活。 这些研究将为以下方面提供具有实际意义的信息 改良降胆固醇药物的发展，并将照亮 细胞识别、反应和代谢的机制 外国化学品。

Emerging evidence suggests that the complex processes of sterol biosynthesis and xenobiotic metabolism by enzymes of the cytochrome P450 superfamily are inextricably intertwined. Such an interrelationship has important implications for the safety and efficacy of the growing arsenal of "anti-cholesterol" drugs that is being developed to lower patients' plasma cholesterol levels and thereby treat or prevent coronary artery disease. The hypothesis of this proposal is three-fold: (1) Anti-cholesterol drugs that inhibit sterol biosynthesis, such as inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase or squalene synthase, induce rat hepatic CYP2B1 gene expression by causing depletion of the critical cellular sterols that suppress CYP2B1 expression in the basal steady state, which results in activation of sterol regulatory element binding proteins (SREBP), followed by transcriptional activation of the CYP2B1 gene through specific 5'- flanking sequences contained within the phenobarbital responsive unit. (2) Anti-cholesterol drugs, such as inhibitors of acyl-CoA:cholesterol acyltransferase (ACAT) or squalene cyclase, that promote accumulation of specific cellular sterols, such as 24(S),25-epoxycholesterol, induce CYP3A23 gene expression through a mechanism whereby the accumulated sterols activate the LXRalpha nuclear receptor, resulting in transcriptional activation of the CYP3A23 gene through a specific sterol-responsive 5'-flanking sequence. (3) HMG-CoA reductase inhibitors induce CYP4A gene expression through a mechanism that requires increased fatty acid biosynthesis, activation of the peroxisome proliferation associated receptor alpha (PPARalpha) and transcriptional activation of the CYP4A1 gene through a peroxisome proliferator responsive element. The specific aims of this proposal are to (1) define the effects of chemical inhibitors of key steps of the cholesterol biosynthesis and esterification pathways on P450 expression in primary cultured rat hepatocytes, and to relate patterns of gene expression to changes in levels of specific cellular sterols, (2) identify the 5'-flanking sequence(s) that confer HMG-CoA reductase inhibitor-and squalene synthase inhibitor-inducible transcriptional activation to the CYP2B1 gene, and to determine whether this regulation is mediated through an SREBP transcription factor, (3) identify the 5'- flanking sequence(s) that confer sterol-, ACAT inhibitor-and squalene cyclase inhibitor-inducible transcriptional activation to the CYP3A23 gene, and to determine whether this regulation is mediated through the LXRalpha nuclear receptor and (4) determine whether HMG-CoA reductase inhibitor-inducible CYP4A1 induction occurs through a mechanism that requires elevated fatty acid biosynthesis and activation of PPARalpha. These studies will provide information with practical implications for the development of improved anti-cholesterol drugs, and will illuminate mechanisms whereby a cell recognizes, responds to, and metabolizes foreign chemicals.