A Synthetic Sponge System Against miRNAs of the miR-17/92 Cluster Targets Transcriptional MYC Dosage Compensation in Aneuploid Cancer.

BACKGROUND

Genomic instability, a hallmark of cancer, leads to copy number variations disrupting gene dosage balance and contributing to tumor progression. One of the most affected oncogenes is MYC, whose overexpression is tightly regulated to avoid cytotoxicity. In aneuploid cancer cells, gene dosage compensation mechanisms involving microRNAs (miRNAs) from the miR-17/92 cluster contribute in regulating MYC expression. Targeting this miRNA-mediated compensation system represents a promising therapeutic strategy leading to an uncontrolled and lethal MYC overexpression.

RESULTS

Synthetic miRNA sponges targeting miR-17, miR-19a, and miR-20a, key regulators of MYC dosage compensation, were designed and validated. Breast cancer cells (MCF7) with stable exogenous MYC overexpression were used to assess the impact of sponge constructs on MYC regulation. Quantitative RT-PCR revealed a significant reduction in miRNA expression and a corresponding increase in endogenous MYC levels upon sponge treatment. Functional assays in multiple colorectal cancer cell lines with varying MYC copy numbers demonstrated a time-dependent increase in cell death following sponge transfection. Cytotoxic effects increased with MYC copy number, confirming a correlation between gene dosage sensitivity and therapeutic response.

CONCLUSIONS

Our findings demonstrate that miRNA sponges targeting the miR-17/92 cluster can effectively disrupt MYC dosage compensation, leading to selective cytotoxicity in MYC-amplified cancer cells.