MiR-106b~25 cluster regulates multidrug resistance in an ABC transporter-independent manner via downregulation of EP300

Area of Science:

• Oncology
• Molecular Biology
• Gene Regulation

Background:

• MicroRNA (miR)-106b~25 cluster is implicated in regulating cellular responses to chemotherapy.
• EP300, an E-cadherin transcriptional activator, is a known target of the miR-106b~25 cluster.
• Multidrug resistance (MDR) in cancer is a significant clinical challenge.

Purpose of the Study:

• To investigate if upregulation of the miR-106b~25 cluster induces a multidrug resistant (MDR) phenotype.
• To determine if this MDR phenotype is mediated by P-glycoprotein or other ATP-binding cassette (ABC) transporters.
• To elucidate the role of EP300 and E-cadherin downregulation in MDR.

Main Methods:

• Experimental upregulation of the miR-106b~25 cluster in minimally transformed mammary epithelial breast cancer cells (MTMECs) using lentiviral transfection.
• Expression of hairpins targeting EP300 or E-cadherin mRNAs via lentiviruses.
• Assessment of drug resistance (etoposide, colchicine, paclitaxel), P-glycoprotein expression, drug efflux, apoptosis markers (Annexin V), caspase activation, and cell cycle progression.

Main Results:

• Overexpression of the miR-106b~25 cluster generated MDR MTMECs resistant to etoposide, colchicine, and paclitaxel.
• The MDR phenotype was drug-transporter independent, as P-glycoprotein was not overexpressed, and paclitaxel efflux was not enhanced.
• MTMECs with upregulated miR-106b~25 cluster or downregulated EP300/E-cadherin exhibited reduced apoptosis activation and caspase activity.

Conclusions:

• The miR-106b~25 cluster confers transporter-independent MDR by promoting apoptosis evasion.
• Downregulation of EP300 by the miR-106b~25 cluster is a key mechanism driving this MDR phenotype.
• Targeting the miR-106b~25 cluster or its downstream effectors may offer novel therapeutic strategies for overcoming MDR in breast cancer.