Multidrug resistance Mediated by P-glycoprotein

P-糖蛋白介导的多药耐药性

• 批准号: 7331398
• 负责人: Antonio Fojo
• 金额: --
• 依托单位: DIVISION OF CLINICAL SCIENCES - NCI
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/7331398
• 关键词: Multidrug; resistance; Mediated; glycoprotein

Background: In the field of multidrug resistance mediated by the multidrug transporter, P glycoprotein, which is encoded by the MDR-1 gene, our efforts continue to have a major focus on translational research, while trying to pursue basic investigations that have the potential for future clinical correlations.Since its original description nearly 20 years ago, increased expression of P-glycoprotein (Pgp) has been frequently observed in cell culture models of multidrug resistance and in clinical samples obtained from refractory patients. But while progress has been made, the regulation of Pgp expression is not fully understood. Is MDR-1/Pgp expression in drug selected cells and refractory tumors under similar regulatory control as that in normal tissues, or drug sensitive cells? Our results suggest the answer is no. In all drug resistant cell lines derived from parental cells that do not normally express MDR-1 or express MDR-1 at low levels, the mechanisms regulating MDR-1 expression are acquired and abnormal. Expression from an unrelated, active promoter, proceeding in a normal or an aberrant direction, can control transcription. This occurs principally as a result of a gene rearrangement that leads to capture of MDR-1 by an unrelated promoter. Alternately, aberrant transcription can begin in a region 112 kb 5 prime of MDR-1. Following drug selection this region functions as a promoter. Evidence suggests that an HERV LTR is involved in this aberrant transcription and that acetylation of a nearby sequence may be an important epigenetic event in the activation of this aberrant promoter. Our research goals are to (1) understand the molecular basis of acquired MDR-1 expression; (2) comprehend how/why these changes occur; (3) search for them in clinical samples and (4) devise strategies to reduce or prevent their occurrence. In the clinic, in collaborative studies with Susan Bates, M.D. we continue to conduct trials examining the use of Pgp antagonists as modulators of drug sensitivity.Project Description and Plans: We have identified gene rearrangements as the mechanism responsible for the activation of MDR-1 in a large number of cell lines, and in patient samples. These rearrangements occur randomly and are characterized by the juxtaposition of a transcriptionally active gene 5 prime to MDR-1, thus avoiding disruption of MDR-1 structure. These gene rearrangements leading to activation of MDR-1 represent a mechanism of resistance with the following characteristics: (i) the rearrangement is an acquired phenotype, not detected in parental cells, and (ii) the rearrangement provides a mechanism for activation of MDR-1 in cells that do not express MDR-1 or express MDR-1 at very low levels; this is not a mechanism for over-expression of MDR-1 in a cell that expresses MDR-1 endogenously at significant levels. Additional characteristics include the following: (1) The majority of MDR-1 transcripts in these cells are hybrid mRNAs. (2) Activation occurs by juxtaposing an active promoter 5 prime to MDR-1, and initiating transcription at this promoter. Expression of the non-MDR-1 gene can be readily detected in a variety of cells suggesting the non-MDR-1 gene is constitutively active and has widespread expression. Furthermore, where information has been available for the non-MDR-1 sequences, the residues fused to MDR-1 have been from the 5 prime UTR of the respective genes (3) The rearrangements appear to occur randomly and involve genes found in chromosome 7 and in chromosomes other than 7. The sequences within 7 are found either centromeric or telomeric of MDR-1 (i.e. inversions occur). The breakpoints have been characterized in eight drug resistant cell lines. Rearrangements occurred as a result of either homologous recombination or non-homologous end joining.

背景：在由多药转运蛋白 P 糖蛋白（由 MDR-1 基因编码）介导的多药耐药领域，我们的工作继续主要集中在转化研究上，同时努力开展有潜力的基础研究。未来的临床相关性。自从近 20 年前首次描述以来，在多药耐药细胞培养模型和从难治性患者获得的临床样本中经常观察到 P-糖蛋白 (Pgp) 表达增加。尽管已经取得了进展，但 Pgp 表达的调控尚未完全了解。药物选择细胞和难治性肿瘤中的 MDR-1/Pgp 表达是否受到与正常组织或药物敏感细胞类似的调控控制？我们的结果表明答案是否定的。在所有源自正常不表达MDR-1或低水平表达MDR-1的亲本细胞的耐药细胞系中，调节MDR-1表达的机制是获得性的且异常的。来自不相关的活性启动子的表达，以正常或异常方向进行，可以控制转录。这主要是由于基因重排导致 MDR-1 被不相关的启动子捕获的结果。或者，异常转录可以从 MDR-1 的 112 kb 5 引物区域开始。在药物选择之后，该区域充当启动子。有证据表明，HERV LTR 参与了这种异常转录，并且附近序列的乙酰化可能是该异常启动子激活过程中的重要表观遗传事件。我们的研究目标是（1）了解获得性MDR-1表达的分子基础； (2) 理解这些变化如何/为何发生； (3) 在临床样本中寻找它们，(4) 制定策略来减少或预防它们的发生。在临床上，在与医学博士 Susan Bates 的合作研究中，我们继续进行试验，检查 Pgp 拮抗剂作为药物敏感性调节剂的用途。项目描述和计划：我们已确定基因重排是导致 MDR-1 激活的机制在大量细胞系和患者样本中。这些重排是随机发生的，其特点是转录活性基因 5 prime 与 MDR-1 并置，从而避免了 MDR-1 结构的破坏。这些导致 MDR-1 激活的基因重排代表了具有以下特征的耐药机制：（i）重排是一种获得性表型，在亲代细胞中未检测到；（ii）重排提供了 MDR-1 激活的机制。 1 在不表达 MDR-1 或表达水平非常低的 MDR-1 的细胞中；这不是在显着水平内源性表达 MDR-1 的细胞中过度表达 MDR-1 的机制。其他特征包括以下内容： (1) 这些细胞中的大多数 MDR-1 转录物是混合 mRNA。 (2) 通过将活性启动子 5 与 MDR-1 并置并在该启动子处启动转录来发生激活。可以在多种细胞中容易地检测到非MDR-1基因的表达，这表明非MDR-1基因具有组成型活性并且具有广泛表达。此外，在非 MDR-1 序列的信息可用的情况下，与 MDR-1 融合的残基来自相应基因的 5 素 UTR (3) 重排似乎是随机发生的，涉及在 7 号染色体中发现的基因7号染色体以外的染色体中。7号内的序列被发现是MDR-1的着丝粒或端粒（即发生倒位）。断点已在八种耐药细胞系中得到表征。重排是由于同源重组或非同源末端连接而发生的。