The tumor suppressor microRNA let-7 inhibits human LINE-1 retrotransposition

Area of Science:

• Genomics
• Molecular Biology
• Cancer Research

Background:

• Transposable elements (TEs), particularly Long INterspersed Element class 1 (LINE-1 or L1), comprise a significant portion of the human genome and are active in cancer.
• MicroRNAs (miRNAs) are key regulators of gene expression, and their tumor-suppressive functions are often lost in cancer.
• The role of miRNAs in controlling the mobilization of active TEs like L1 in cancer remains largely unexplored.

Purpose of the Study:

• To investigate the influence of tumor suppressor microRNAs on the mobilization of Long INterspersed Element class 1 (L1) in human lung cancer.
• To elucidate the molecular mechanism by which let-7, a crucial miRNA, affects L1 retrotransposition.

Main Methods:

• Correlation analysis between let-7 downregulation and L1 insertion accumulation in human lung cancer samples.
• Experimental validation of let-7 binding to L1 mRNA.
• Assessment of let-7's impact on the translation of the L1 ORF2 protein (ORF2p) and subsequent L1 mobilization.

Main Results:

• A significant correlation was observed between the downregulation of let-7 and the increased presence of L1 insertions in human lung cancer.
• Direct binding of let-7 to the L1 mRNA was demonstrated.
• let-7 was shown to inhibit the translation of L1 ORF2p, thereby reducing L1 retrotransposition.

Conclusions:

• let-7 plays a critical role in maintaining somatic genome integrity by suppressing L1 retrotransposition.
• The downregulation of let-7 in lung cancer contributes to genomic instability through increased L1 activity.
• let-7 represents a potential therapeutic target for mitigating L1-driven mutagenesis in cancer.