miR-137 regulates the constitutive androstane receptor and modulates doxorubicin sensitivity in parental and doxorubicin-resistant neuroblastoma cells

Abstract

Chemotherapy is the most common treatment for cancer. However, multidrug resistance (MDR) remains a major obstacle to effective chemotherapy, limiting the efficacy of both conventional chemotherapeutic and novel biologic agents. The constitutive androstane receptor (CAR), a xenosensor, is a key regulator of MDR. It functions in xenobiotic detoxification by regulating the expression of phase I drug metabolizing enzymes and ATP-binding cassette (ABC) transporters, whose overexpression in cancers and whose role in drug resistance make them potential therapeutic targets for reducing MDR. MicroRNAs (miRNAs) are endogenous negative regulators of gene expression and have been implicated in most cellular processes, including drug resistance. Here we report the inversely related expression of miR-137 and CAR in parental and doxorubicin-resistant neuroblastoma cells, wherein miR-137 is down-regulated in resistant cells. miR-137 over-expression resulted in down-regulation of CAR protein and mRNA (via mRNA degradation); it sensitized doxorubicin-resistant cells to doxorubicin (as shown by reduced proliferation, increased apoptosis, and increased G2-phase cell cycle arrest) and reduced the in vivo growth rate of neuroblastoma xenografts. We observed similar results in cellular models of hepatocellular and colon cancers, indicating that the doxorubicin-sensitizing effect of miR-137 is not tumor type-specific. Finally, we show for the first time a negative feedback loop whereby miR-137 down-regulates CAR expression and CAR down-regulates miR-137 expression. Hypermethylation of the miR-137 promoter and negative regulation of miR-137 by CAR contribute in part to reduced miR-137 expression and increased CAR and MDR1 expression in doxorubicin-resistant neuroblastoma cells. These findings demonstrate that miR-137 is a crucial regulator of cancer response to doxorubicin treatment, and they identify miR-137 as a highly promising target to reduce CAR-driven doxorubicin resistance.

MicroRNA Pharmacoepigenetics: Posttranscriptional Regulation Mechanisms behind Variable Drug Disposition and Strategy to Develop More Effective Therapy

“…NR1I3 was found to be directly targeted by miR-137, which not only suppressed the protein expression of ABCB1 and CYP2B6 in drug-resistant cells but also sensitized the cells to doxorubicin in vitro as well as neuroblastoma xenografts to doxorubicin in vivo (Takwi et al, 2014). A separate study also demonstrated the actions of miR-137 in the regulation of murine Car/Nr1i3 .…”

Deciphering the roles of the constitutive androstane receptor in energy metabolism

“…Whether the circadian expression of CAR is mediated by RORs and/or Rev-erbs would be interesting to determine. Last but not least, miR-137 negatively regulates CAR mRNA, www.chinaphar.com Yan J et al Acta Pharmacologica Sinica npg suggesting that microRNA-mediated gene silencing is another mechanism governing CAR expression [49] .…”

CINPA1 Is an Inhibitor of Constitutive Androstane Receptor That Does Not Activate Pregnane X Receptor

“…Downstream target genes of CAR are involved in various important physiologic processes such as energy homeostasis, cell cycle regulation, and cell-cell communication (Maglich et al, 2004;Molnar et al, 2013). Dysregulation of these genes often results in pathologic conditions like insulin resistance, fatty liver disease, chemical carcinogenesis, and tumor promotion (Huang et al, 2005;Breuker et al, 2010;Takwi et al, 2014). There is a need to develop potent and specific chemical tools to uncover the molecular mechanisms governing CAR activation and its regulation of target gene expression.…”

“…CAR is the molecular target of phenobarbital (PB)-induced hepatocellular carcinoma, and activation of this receptor is an essential requirement for liver tumor development (Yamamoto et al, 2004;Huang et al, 2005). CAR overexpression in neuroblastoma drives doxorubicin resistance by increasing MDR1 levels (Takwi et al, 2014) in ovarian cancer cells, whereas pharmacologic activation of CAR leads to upregulation of MDR1 and decreased effectiveness of anticancer drugs; downregulation of CAR by RNA interference enhances the cell growth inhibition and apoptosis mediated by these anticancer drugs . CAR activation also causes hepatic lipogenesis and insulin insensitivity by upregulating the thyroid hormone-responsive spot 14 gene, which might promote fatty liver diseases and insulin resistance (Breuker et al, 2010).…”