Chaudhary P M, Roninson I B
Department of Genetics, University of Illinois, Chicago 60612.
J Natl Cancer Inst. 1993 Apr 21;85(8):632-9. doi: 10.1093/jnci/85.8.632.
The MDR1 (multidrug resistance) gene (also known as PGY1), which encodes the transmembrane efflux pump P-glycoprotein (Pgp), confers resistance to Pgp-transported cytotoxic drugs in tissue culture. The increase in MDR1 expression in tumors after chemotherapy is usually attributed to selection of pre-existing multidrug-resistant cells by Pgp-transported drugs. MDR1 expression in tissue culture can be increased by several types of stress-inducing treatment, including agents that activate protein kinase C (PKC). Previous studies, however, failed to demonstrate that short-term exposure to any chemotherapeutic drug can induce the expression of the resident MDR1 gene in drug-sensitive human cells.
This study was designed to utilize highly sensitive assays to determine if transient exposure to chemotherapeutic drugs would have an effect on MDR1 expression in human cells and to assess if PKC inhibitors would influence such an effect.
We analyzed the MDR1 gene expression in several human cell lines derived from leukemias or solid tumors, after treatment with different cytotoxic drugs, in the presence or absence of PKC inhibitors. Pgp function and expression were studied by flow cytometric assays, and MDR1 messenger RNA (mRNA) was assayed by polymerase chain reaction.
Transient exposure to chemotherapeutic drugs, including agents that are not transported by Pgp, induced Pgp and MDR1 mRNA expression in subpopulations of treated cells in most of the tested cell lines. This induction was observed along with microscopically detectable cell damage. The drug-induced MDR1 expression and the associated twofold to threefold increase in resistance to vinblastine were sustained in K562 leukemia cells for at least several weeks after the removal of the drug. Drug-mediated MDR1 induction was blocked by nonspecific protein kinase inhibitors that are active against PKC, but not by a protein kinase inhibitor ineffective against PKC.
Expression of the human MDR1 mRNA and Pgp can be induced in response to cellular damage by cytotoxic drugs regardless of whether the drugs are transported by Pgp. This induction can be prevented by protein kinase inhibitors.
Induction of MDR1 expression in response to cellular damage may account for increased MDR1 expression in treated human tumors. Protein kinase inhibitors may be useful in preventing the emergence of multidrug resistance during cancer chemotherapy.
多药耐药基因1（MDR1）（也称为PGY1）编码跨膜外排泵P-糖蛋白（Pgp），在组织培养中赋予对Pgp转运的细胞毒性药物的抗性。化疗后肿瘤中MDR1表达的增加通常归因于Pgp转运药物对预先存在的多药耐药细胞的选择。在组织培养中，MDR1的表达可通过几种应激诱导处理增加，包括激活蛋白激酶C（PKC）的试剂。然而，先前的研究未能证明短期暴露于任何化疗药物可诱导药物敏感的人类细胞中固有MDR1基因的表达。
本研究旨在利用高灵敏度检测方法来确定短暂暴露于化疗药物是否会对人类细胞中的MDR1表达产生影响，并评估PKC抑制剂是否会影响这种效应。
我们分析了几种源自白血病或实体瘤的人类细胞系在使用不同细胞毒性药物处理后，在有或没有PKC抑制剂存在的情况下MDR1基因的表达。通过流式细胞术检测Pgp功能和表达，并通过聚合酶链反应检测MDR1信使核糖核酸（mRNA）。
短暂暴露于化疗药物，包括那些不由Pgp转运的药物，在大多数测试细胞系中诱导了处理后细胞亚群中Pgp和MDR1 mRNA的表达。这种诱导伴随着显微镜下可检测到的细胞损伤。在去除药物后，K562白血病细胞中药物诱导的MDR1表达以及对长春碱抗性相关的两到三倍增加至少持续了几周。药物介导的MDR1诱导被对PKC有活性的非特异性蛋白激酶抑制剂阻断，但未被对PKC无效的蛋白激酶抑制剂阻断。
无论药物是否由Pgp转运，细胞毒性药物引起的细胞损伤均可诱导人类MDR1 mRNA和Pgp的表达。这种诱导可被蛋白激酶抑制剂阻止。
响应细胞损伤而诱导MDR1表达可能解释了治疗的人类肿瘤中MDR1表达增加的原因。蛋白激酶抑制剂可能有助于预防癌症化疗期间多药耐药性的出现。
